The equations in this study (Table 5.3) showed a higher regression

The equations in this study (Table 5.3) showed a higher regression coefficient for muscle depth when
predicting percentage lean (b = 0.1346) than Bruwer (1992) obtained (b = 0.0547). This indicates that
the muscle thickness measurement although small, may have had a bigger contribution in predicting
percentage lean in this study, than what Bruwer (1992) observed. It certainly caused a bigger variation
(Figure 6.1).
Figure 6.2 illustrates the comparison of the two lines. The predicted lean is plotted on the y – axis and
the actual dissected lean on the x – axis. Actual fat thickness and a constant eye muscle thickness were
substituted into Equations 1 and 3 (pg 64). The two lines are almost parallel, which indicates that
Equation 3 of Bruwer (1992) does predict carcass lean content sufficiently accurate on carcasses of
higher weights (exceeding 100kg) although the difference between the two studies declined at higher
weights.
Secondly, the probable difference in methodology caused the study of Bruwer (1992) to predict much
higher lean percentages, by expressing the percentage relative to a carcass without head and trotters.
The Renco lean-meater® had the lowest prediction value of the three devices (R2 = 0.577 compared to
0.620 and 0.614 of the Intrascope® and Hennessy Grading Probe® respectively) and the highest
standard error value (S.E. = 2.48), (Table 5.2 and Table 5.3). The Intrascope® and Hennessy Grading
Probe® standard error values were 2.35 and 2.37 respectively. The differences in R2 values between
the three devices were more than 1%. Therefore the Hennessy Grading Probe® is according to the
adjusted R2 value the most accurate in predicting carcass lean, when the muscle thickness is included
followed by the Intrascope® and then the Renco lean-meater ®, with the lowest value.
Findings in this trial where the Hennessy Grading Probe® had higher prediction values (R2 value)
than the Renco lean-meater® confirm the results obtained by Hulsegge and Merkus (1997), Hudson
and Payne-Crostin (1984). In their study ultrasonic measurements had lower prediction values than
devices such as the Intrascope® and Hennessy Grading Probe®. In this study, similar to Hulsegge et
al. (1999) it was found that Renco leanmeater ® fat measurements in millimetres of live animals
showed lower measuring values than carcass fat measurements did from devices such as the Hennessy
Grading Probe® and Intrascope®. Hudson and Payne-Crostin (1984) showed that the inclusion of live
weight improved the prediction equations for predicting carcass back fat thickness (P<0.05) for
different ultrasonic devices. In the present study (Table 5.2) the inclusion of slaughter weight only
showed a small improvement in the prediction equations for percentage lean. The improvement
obtained by the inclusion of the slaughter weight is too small to justify (P>0.05) the inclusion.
It is therefore speculated that a muscle depth measurement should, similar to the Hennessy Grading
Probe®, improve the prediction accuracy of the Renco lean-meater® substantially.
Greer et al. (1987) pointed out that the accuracy of the Renco lean-meater® improved when
measurements were greater than 18mm, but a lower accuracy was observed with pigs that had little
back fat. They also concluded that the Renco lean-meater® could be used to predict back fat depth on
the carcass. This can be valuable because the technique is not invasive. The observation was made in
this study that Renco lean-meater® failed to indicated fat depths exceeding 25mm and fat depths of
less than 9mm were all recorded as 9mm. Renco lean-meater® under predicted fat thickness
completely, but the prediction equation sufficiently predicted percentage lean in the carcass.
In the present study the T2/3 site mostly produced the highest R-square value between the three sites
(Figure 4.1). Bruwer (1992) found the T2/3, site 45mm from the split line to be the best measuring site
for the prediction of percentage lean, under South African conditions for both the Hennessy Grading
Probe® and Intrascope®.
Authors from other countries found other sites to be better predictors of percentage lean. Pomar et al.
(2001), Hulsegge and Merkus (1997) found the site between the 3rd and 4th of last rib to be the best
measuring site. Berg et al. (1999), found the last rib-measuring site to be the best. Hulsegge,
Sterrenburg and Merkus (1994) on the other hand, found the site between the 13th and 14th last rib
(site between the 1st and 2nd last thoracic vertebrae) to be the best predictor of lean meat. They also
observed that multiple-site measurements, although small, reduced the residual standard deviation and
likewise Cook, Chadwick and Kempster, (1989) observed an improvement in lean prediction.
Results from measurements on the warm carcasses were constantly either better or equal to the
measurements on cold carcasses. If only one variable was used for the Hennessy Grading Probe, at
some sites the cold measurements seemed to have better adjusted R2 values. When two variables for
255
the Intrascope were used in a model, the measurements on warm carcasses seemed to have better
values.
In the present trial the measurements on warm carcasses were overall better predictors, of percentage
lean than measurements on cold carcasses, in terms of adjusted R2 value (Table 5.2 and Table 5.3). In
a trial done by Berg et al. (1999) the same findings were made. Anderson et al. (1995) found in their
study that measurements on cold carcasses were just as good predictors of percentage lean meat than
measurements on warm carcasses.
For practical reasons it is better to take measurements on warm carcasses 45 minutes after slaughter
than measurements on cold carcasses.
6.3 PERCENTAGE FAT
Producers are indirectly getting penalised for the amount of fat in the carcass, as they get paid for the
percentage lean in the carcass and not the percentage fat. It can be expected that a fat measurement
would best predict percentage fat in the carcass while predicting lean, bone or skin percentage, to a
lesser extent although the correlations might be high or moderate.
The prediction values are high in terms of R2 values for percentage fat, as can be expected when linear
fat measurements are used. All three devices gave a satisfactory level of accuracy in predicting
percentage fat in the carcass. Intrascope® (R2 = 0.828) had the highest fat prediction value followed
by Hennessy Grading Probe® (R2 = 0.796) and the Renco leanmeater ® (R2 = 0.761) (Table 5.4 &
5.5).
The same findings were observed in a study done by Berg, Forrest and Fisher, (1994) who found a
high correlation between probe fat depth and actual fat depth (r = 0.919). There is a high correlation
between ultrasonic back fat thickness measurements on live pigs and Hennessy Grading Probe® fat
thickness measurements according to Hulsegge et al. (1999).
Bruwer (1992) found a R2 value of 0.700 and 0.670 for the Hennessy Grading Probe® and
Intrascope® respectively at the T2/3 site, when predicting percentage fat. In the present study the
Hennessy Grading Probe® adjusted R2 value was 0.796, while the Intrascope® had a higher value of
0.828.
At the L3/4 site the measurement on cold carcasses seemed to be a better predictor of fat and lean
percentage for the Hennessy Grading Probe® than measurements on warm carcasses in terms of
adjusted R2 value (Table 5.3 and Table 5.5). The L3/4 site is however not recommended as a
measuring site due to the poor prediction values obtained, compared to the other two sites.
The predictions at the T2/3 and the L5/6 site gave the highest R2 value, using only one fat
measurement for measurements on warm carcasses, while measurements on cold carcasses at the T2/3
used a fat and a muscle measurement to obtain the same R2 value.
6.4 PERCENTAGE BONE
Bone is not an economically important tissue, it is a relative small (± 10%) portion of the carcass and
although meat processors would rather have less bone in a carcass, bone is not discriminated against.
For the purpose of this study and for the comparison of future research, percentage bone in the carcass
was included. Overall very low prediction values were obtained for percentage bone in the carcass,
when fat measurements were used. Only the results of lean and fat percentage in the carcass are
published, due to their economical importance. Apart from Bruwer (1992) there is no literature
published on linear fat measurements used to predict percentage bone in the carcass.
For the Intrascope® bone percentage was best predicted by a fat thickness measurement at the L3/4
site. The inclusion of cold carcass weight improved the R2 value for the L5/6 and L3/4 site on cold
carcasses to predict percentage bone (Table 5.6). The Hennessy Grading Probe® had the highest
prediction value at the T2/3 site for measurements on cold carcasses with a fat and a muscle
measurement (0.505). For measurements on warm carcasses a fat thickness measurement at the L3/4
site was the best predictor of percentage bone in the carcass (Table 5.7).
The percentage bone was predicted, with a R2 value of 0.630 for the HGP at the T2/3 site and 0.390
for the Intrascope® at the L3/4 site in a study done by Bruwer (1992). In the present study the
Hennessy Grading Probe® T2/3 site had a lower value (R2 = 0.505) for measurements on cold
carcasses and the Intrascope® at the L3/4 site had a slightly higher value (R2 = 0.421) for the
measurements on warm carcasses. According to the results in this study, fat measurements are
256
relatively poor predictors of bone percentage in the carcass. Only about 50 percent of the variation in
percentage bone can be explained by the variation in back fat thickness.
6.5 PERCENTAGE SKIN
In South Africa skin is not an important carcass tissue, it is normally sold as part of the commercial
cuts or it is used in emulsion products. The prediction values for percentage skin were low, with the
highest value obtained with the Hennessy Grading Probe® for measurements on warm carcasses with
a fat and muscle thickness measurement at the L5/6 site (R2 = 0.434). With the Intrascope® a fat
thickness measurement at the L3/4 site, together with cold carcass weight, best-predicted percentage
skin (R2 = 0.380).
The Renco lean-meater® predicted percentage skin the best with two variables, a fat thickness
measurement and slaughter weight, with an adjusted R2 value of 0.333 (Table 5.8). For the other sites
cold carcass weight and a fat thickness measurement seemed to be the best predictor of percentage
skin. There is no literature available on the use of fat measurements for the prediction of skin
percentage in the carcass.
Fat measurements are poor predictors of percentage carcass bone and skin. It is not common practice
to predict bone or skin percentage and even to a lesser extent using fat measurements. Therefore these
two tissues will not be discussed further.
6.6 INTERPRETATION OF PARALLELISM
Figure 5.1 illustrates the relationship between the regression lines of Intrascope®, Hennessy Grading
Probe® and Renco lean-meater ®. The slopes differed significantly (P = 0.002). Intrascope® and
Hennessy Grading Probe® differed form Renco lean-meater ®, but not from each other.
Although the slope for the Renco lean-meater® differed from the slopes for the Hennessy Grading
Probe® and Intrascope®, any of the three models can be used to determine percentage lean. It should
be kept in mind that percentage lean meat decreases more per unit increase in fat for Renco leanmeater® than for Hennessy Grading Probe® and Intrascope®. This indicates that there is a difference
in the physical measurements taken by the different devices and not the ability to predict the
percentage lean in the carcass. It would be true to say Renco lean-meater® under predicts live animal
fat measurements, but adequately predicts percentage carcass lean.
CHAPTER 7
CONCLUSION
The accuracy of a measuring device can be expressed in different ways, which complicates the
comparison of data from different studies with one another. The comparison between devices should
be carefully analysed in order to have a clear understanding of how their specific measurements can
firstly, be interpreted and secondly, best applied.
Although there is no norm for acceptability of accuracy it was decided that in this study R2 values of
less than 0.50 were not acceptable and R2 values of more than 0.75 were accepted as very good. In
this study the variation of the independent variables was high which resulted in lower R2 values.
The results from this study indicated that the Hennessy Grading Probe® and the Intrascope®
adequately predict carcass composition with a fair degree of accuracy. The live animal measurements
proved to be less accurate than the carcass measurements. The first hypothesis that, currently applied
measuring devices, still accurately predict carcass composition on genetically improved pig carcasses,
should therefore be accepted.
Prediction values obtained from the Intrascope® measurements were acceptable (R2 value > 50%).
The Intrascope® fat measurements were adequate in predicting carcass composition. The inclusion of
warm carcass weight improved the prediction values.
The Hennessy Grading Probe® fat measurements were fairly accurate in predicting percentage carcass
fat and lean composition. The increasing level of accuracy achieved when eye muscle thickness
measurements were included, an existing practice in the industry. Taking multiple measurements with
one action, transmitting data to a computer and the electronics favours the application of the Hennessy
Grading Probe® for classification. The accuracy achieved with the Hennessy Grading Probe® from a
fat and muscle thickness measurement is sufficient for the prediction of percentage carcass lean.
Both the Intrascope® and the Hennessy Grading Probe® predicted percentage lean with a high level
of accuracy, but the inclusion of a second variable justifies the inclusion. Both the muscle thickness
257
for the Hennessy Grading Probe® and warm carcass weight for the Intrascope® are measurements that
are taken in abattoirs currently.
According to the results of the live animal Renco lean-meater® measurements, the adjusted R2 values
show that the Renco lean-meater® is accurate in predicting percentage lean in the carcass. The Renco
leanmeater ® measurements constantly gave lower actual fat thickness readings than the Hennessy
Grading Probe® and Intrascope® devices. This phenomenon definitely affects the prediction
capability and accuracy of the Renco lean-meater® measurements.
The Hennessy Grading Probe® measurements gave the best prediction values for the prediction of
carcass composition, followed by the Intrascope® and Renco lean-meater® respectively. R2 values
less than 0.5 are not adequate for the prediction of carcass composition the accuracy is too low.
It was therefore concluded that measurements from all three devices were accurate, for the prediction
of carcass composition, although different methods were used to take measurements.
The second hypotheses, namely ultrasound measurements on live animals accurately predict carcass
composition can therefore be accepted. The third hypothesis, slaughter line measurements are better
predictors of carcass composition than live animal measurements can also be accepted.
The specific measuring site used to conduct the measuring process seemed to be very important. There
was a large difference in prediction accuracy for carcass composition, between the different sites for
the different carcass tissues. The T2/3 site still yields the highest prediction accuracy for most of the
parameters. The T2/3 site is the currently applied measuring site of the industry. This is also the most
practical measuring site to take measurements. The fourth hypothesis, namely, the site between the
2nd and 3rd last thoracic vertebrae is the most accurate and practical site to take measurements for the
prediction of carcass composition can therefore be accepted.
Better overall results were obtained from measurements on warm carcasses than from cold carcasses
in predicting carcass composition. The differences in some cases were small. It is easier to conduct the
classification process on warm carcasses on-line just after the carcasses have been cleaned, than at a
later stage in the cold room. The fifth hypothesis namely warm carcass measurements are better
predictors of carcass composition than cold measurements can therefore be verified.
7.1 RECOMMENDATIONS
It is recommended to use measurements on warm carcasses rather than measurements on cold
carcasses, to conduct the classification process, as is currently the practice. Measurements on warm
carcasses are slightly better predictors of percentage lean and fat.
The further use of the T2/3 site as the standard measuring site for the Hennessy Grading Probe® and
Intrascope® is recommended. It is easy to find and practical to apply in practice and still the most
accurate site to take measurements.
The Hennessy Grading Probe® fat and muscle measurements are recommended for the prediction of
carcass composition. The fat measurements adequately predict carcass lean while the inclusion of a
muscle thickness measurement further improved the R2 value.
The Intrascope® fat measurements are also recommended for the prediction of carcass composition if
the Hennessy Grading Probe® is not available. The inclusion of warm carcass weight in the
Intrascope® equation should be considered.
The Renco lean-meater® is recommended for use on farm in predicting percentage lean and fat in the
carcass. Although the fat measurements obtained by the Renco lean-meater® were lower than the fat
thickness measurements obtained from the other two devices, it can still predict percentage lean
adequately. The Renco lean-meater® is therefore recommended to measure fat thickness on live
animals and used with its own equation to predict lean content.
The Hennessy Grading Probe®, Intrascope® and Renco lean-meater® measurements make use of
single site technologies, which have more variation in their measurements than devices which take
multiple site or whole body measurements.
It is recommended that future research should include new technologies for the prediction of carcass
composition. Devices that take whole body measurements and obtain a higher level (R2 > 0.75) of
accuracy.
7.2 FUTURE RESEARCH
258
There are many different devices and techniques available that can be used to predict carcass
composition. It would be recommended to do thorough research on new technology entering the
carcass classification and grading field.
The above-mentioned technology is unfortunately very expensive, but it has all the required features
of increased accuracy, automation and efficiency. The South African Pork industry is fairly small
compared to other countries.
The use of new technology would not necessarily be cost effective. Therefore new technology should
be selected carefully.
If the gained accuracy achieved and the number of pigs slaughtered in South Africa can justify the cost
of new equipment, considerations should be made to import or develop compatible equipment. The
development of non-invasive technology such as ultrasound equipment with the capability to measure
eye muscle diameter is one such a possibility.
The ideal solution would be a machine that can take measurements on the live animals, measuring fat
and eye muscle thickness. At the same time it should be implemented and applied in the abattoir to
take measurements on the carcasses. Measurements on live animals and carcasses can be compared
directly. This will enable producers to make better marketing decisions before marketing their pigs, by
knowing the status of the animals.
REFERENCES
ANDERSON, A., HANSSON, I., LÜNDSTROM, K. & KARLSSON, A. 1995. Influence of Sex and
Breed on the Prediction of the Official Swedish Pig Carcass Grading. Swedish J. Agric. Res. 25:51-59.
BAULAIN, U. 1997. Magnetic resonance imaging for the in vivo determination of body composition
in animal science. Computers and Electronics in Agriculture 17:189-203.
BEALE, E.M.L. & LITTLE, R.J.A. 1975. Missing values in multivariate analysis. J.R. Statist. SOC.
Vol. 37:129-145.
BERG, E.P., FORREST, J.C. & FISHER, J.E. 1994. Electromagnetic Scanning of Pork Carcasses in
an On-line Industrial Configuration. J. Anim. Sci. 72:2642-2652.
BERG, E.P., GRAMS, D.W., MILLER, R.K., WISE, F.W., FORREST, J.C., & SAVELL, J.W. 1999.
Using on-line carcass evaluation parameters to estimate boneless and bone-in pork carcass yield as
influenced by trim level. J. Anim. Sci. 77:1977-1984.
BRANDSCHEID, W., SACK, E., GRUNDL, E., & DEMPFLE, L. 1989 . Breed influence on the
validity of grading results and the effect of different systems in meat quality. In: New Techniques in
pig evaluation. EAAP Publication No: 41.
BRUWER, G.G. 1992. The evaluation of pig carcasses for the development of a classification system.
Ph.D. (Agric) Thesis, University of Pretoria.
BUSCH, D.A., DINKEL, C.A., & MINYARD, J.A. 1969. Body measurement, subjective scores and
estimates of certain carcass traits as predictors of edible portion in beef cattle. J. Anim. Sci. 29:557.
COOK, G.L., CHADWICK, J.P. & KEMPSTER, A.J. 1989. An assessment of carcass probes for use
in Great Britain for the EC pig carcass grading scheme. Anim. Prod. 48:427-434.
DAUMAS, G. 2001. Non electronic techniques to classify pig carcasses in small slaughterhouses. In:
Second International Virtual Conference on Pork Quality, November, 05 to December, 06-2001.
Via
Internet.
http://www.conferencia.uncnet.br/pork/seg/pal/anais01p2_en.pdf
(2002-02-25).
[Accessed: 03/03/2005]
DIESTRE, A., & KEMPSTER, A.J. 1985. The estimation of pig carcass composition from different
measurements with special reference to classification and grading. Anim. Prod. 41:383-391.
DRAPER, N., & SMITH, H. 1981. Applied Regression Analysis. 2nd ed. New York: John Wiley &
Sons.
FORTIN, A. 1984. Pork Carcass Grading: A Comparison of the New Zealand Hennessy Grading
Probe® and the Danish Fat-O-Meater. Meat Sci. 10:131-144.
GenStat for Windows. 2000. Release 4.2, 5th ed. VSN International Ltd., Oxford, UK.
GOLDENBERG, A.A. & LU, Z. 1997. Automation of meat pork grading process. Computers and
Electronics in Agriculture 16:125-135.
Government Gazette, 1992. Regulation No. R. 1748. Agricultural Product Standards Act, 1990 (Act
No. 119 of 1990). Regulations regarding the classification and marking of meat. Government Gazette
No. 14060, 26 June 1992. Pretoria: Government Printer. South Africa.
259
GREER, E.B., MORT, P.C., LOWE, T.W. & GILES, L.R. 1987. Accuracy of ultrasonic back fat
testers in predicting carcass P2 fat depth from live pig measurements and the effect on accuracy of
mislocating the P2 site on the live pig. Aust. J. Exp. Agric. 27:27-34.
GRESHAM, J.D., McPEAKE, S.R., BERNARD, J.K., & HENDERSON, H.H. 1992. Commercial
adaptation of ultrasonography to predict pork carcass composition from live animal and carcass
measurements. J. Anim. Sci. 70: 631-639.
GU, Y., SCHINCKEL, A.P., MARTON, T.G., FORREST, J.C., KUEI, C.H., & WATKINS, L.E.
1992. Genotype and treatment biases in estimation of carcass lean on swine. J. Anim. Sci. 70:17081718.
HENNESSY® GRADING SYSTEMS. 1989. Operator’s manual. New Zealand: Hennessy® grading
systems. Ltd.
HICKS, C., SCHINCKEL, A.P., FORREST, J.C., AKRIDGE, J.T., WAGNER, J.R., & CHEN, C.
1998. Biases associated with genotype and sex in prediction of fat-free lean mass and carcass value in
hogs. J. Anim. Sci. 76: 2221-2234.
HUDSON J.E. & PAYNE-CROSTIN A. 1984. A comparison of ultrasonic machines for the
prediction of backfat thickness in the live pig. Aust. J. Exp. Agric. Anim. Husb., 24:512-515.
HULSEGGE, B., STERRENBURG, P. & MERKUS, G.S.M. 1994. Prediction of lean proportion in
pig carcasses and in the major cuts from multiple measurements made with the Hennessy Grading
Probe®. Anim. Prod. 59: 119-123.
HULSEGGE, B., & MERKUS, G.S.M. 1997. A comparison of the optical probe HGP and the
ultrasonic devices Renco lean-meater® and Pie Medical for estimation of the lean meat proportion in
pig carcasses. Anim. Sci. 64: 379-383.
HULSEGGE, B., MATEMAN, G., MERKUS, G.S.M., & WALSTRA, P. 1999. Choice of probing
site for classification of live pigs using ultrasonic measurements. Anim. Sci. 68: 641-645.
JONES, S. D. M. 1992. The Canadian Pork Carcass Grading System and the 1992 National Carcass
Cut Out. Agriculture and Agri-Food
Canada. http://www.mark.asci.ncsu.edu/nsif/96proc/jones.htm.
KAUFFMAN, R.G., & WARNER, R.D. 1993. Evaluating pork carcasses for composition and quality.
Ch. 9:141-166. In: Growth of the Pig. Ed: Hollis. Urbana.
KEMPSTER, A. J., CHADWICK, J.P. & JONES D.W. 1985. An evaluation of the Hennessy Grading
Probe® and the SFK Fat-omeater for use in pig carcass classification and grading. Anim. Prod.
40:323-329.
KOLSTAD, K. 2001. Fat deposition and distribution measured by computer tomography in three
genetic groups of pigs. Livest. Prod. Sci. 67:281-292.
MARCHELLO, M.J., BERG, P.T., SWANTEK, P.M. & TILTON, J.E. 1999. Predicting live and
carcass lean using bioelectrical impedance technology in pigs. Livest. Prod. Sci. 58:151-157.
POMAR, C., FORTIN, A., & MARCOUX, M. 2001a. Estimation of lean yield of pork carcasses
based on different methodologies measuring fat and muscle depth. J. Rech. Porcine France 33, pp. 6369.
POMAR, C., RIVEST, J., JEAN DIT BAILLEUL, P., & MARCOUX, M. 2001b. Predicting loin-eye
area from ultrasound and grading probe measurements of fat and muscle depths in pork carcasses.
Can. J. Anim. Sci. 81:429-434.
SATHER, A.P., NEWMAN, J. A., JONES, S.D.M., TONG, A.K.W., ZAWADISKI, S.M., &
COLPITTS, G. 1991. The prediction of pork carcass composition using the Hennessy Grading Probe®
and the Aloka SSD-210DXII Echo Camera. Can. J. Anim. Sci. 71:993-1000.
SIEBRITS, F. K. 1984. Some aspects of chemical and physical development of lean and obese pigs
during growth. DSc. (Agric.) Thesis, University of Pretoria.
SMITH, C.R. (S.a.). Classification Systems for the assessment of carcass meat content and
conformation. Henessy Grading Systems Ltd, Auckland, New Zealand & Hennesy Europe B.V.,
Rijswijk, The Netherlands.
SWATLAND, H.J. 1998. Probes and robots for on-line evaluation of pork. Ch.24 In, Progress in pig
science. Eds: Wiseman, I., Varley, M.A. & Chadwick, P. Nottingham University Press: Nottingham.
SZABO, C.S., BABINSZKY, L., VERSTEGEN, M.W.A., VANGEN, O., JANSMAN, A.J.M., &
KANIS, E. 1999. The application of digital imaging techniques in the in vivo estimation of the body
composition of pigs: a review. Livest. Prod. Sci. 60:1-11.
260
WALSTRA, P. 1989. Automated grading probes for pigs currently in use in Europe, their accuracy,
costs and ease of use. Proc. EAAP In: O’Grady, J.F. New techniques in pig carcass evaluation.
Finland: Wageningen: Pudoc:16- 27.
WHITTEMORE, C. 1998. The Science and Practice of Pig Production. 2nd edition. Oxford:
Blackwell Sciences Ltd.
YOUSSAO, I., VERLEYEN, V., MICHAUX, C., & LEROY. P. L. 2002. Choice of probing site for
estimation of carcass lean percentage in Pietrain pig using the real-time ultrasound. Biotechnol. Agron.
Soc. Environ. 2002 6 (4), 195-200.
I.5.1.6. N.I.R.
La técnica de espectroscopia de reflectancia de infrarrojos cercanos es un
procedimiento que se ha desarrollado en los últimos años para el análisis químico de
los alimentos, entre ellos la carne, sustituyendo a procedimientos más laboriosos.
PREDICTION OF THE CHEMICAL COMPOSITION OF MUTTON WITH NEAR
INFRARED REFLECTANCE SPECTROSCOPY
M. Viljoena, b, L.C. Hoffmanb and T.S. Branda, b, c,
a
,
Elsenburg Agricultural Research Centre, Private Bag X1, Elsenburg 7607, South Africa
b
Department of Animal Sciences, University of Stellenbosch, Private Bag X1, Matieland 7602, South
Africa
c
Department of Anatomy & Physiology, University of Pretoria, Private Bag X04, Onderstepoort 0110,
South Africa
Small Ruminant Research Volume 69, Issues 1-3, May 2007, Pages 88-94
Abstract
Near infrared reflectance spectroscopy (NIRS) was evaluated as a tool to predict the chemical
composition of freeze-dried mutton. Samples used for the ash, dry matter (DM), crude protein (CP)
and fat calibrations consisted of M. longissimus dorsi (eye muscle) from 19-month-old Merino sheep,
while mineral calibrations were developed with M. semimembranosus from Merino crossbreed lambs
slaughtered at a live weight of 40 kg. Samples were minced, freeze-dried and analysed according to
standard laboratory procedures. Samples were scanned (1100–2500 nm) and partial least-squares
regression (PLSR) was used to predict the chemical and mineral composition. Multiple correlation
coefficients (r) and standard error of performance (SEP) for chemical composition constituents were:
ash (0.97; 0.15%), DM (0.96; 0.38%), CP (1.00; 0.92%) and fat (1.00; 0.43%), respectively. K, P, Na,
Mg, Fe and Zn showed acceptable SEP values of 600, 900, 77.89, 40, 3.15 and 3.59 mg/kg,
respectively. The r values ranged from 0.86 for Zn and K to 0.92 for Mg. Very low r values (0.26–
0.49) were obtained for Cu, B, Mn, Ca and Al. It was concluded that NIRS could be used as a rapid
tool for predicting proximate chemical composition and certain minerals in freeze-dried mutton.
Keywords: Chemical composition; Mineral composition; Mutton; Near infrared reflectance
spectroscopy
1. Introduction
Near infrared reflectance spectroscopy (NIRS) has been developed as a rapid tool for estimation of
chemical composition of foods (Osborne, 1992). It has been used for the determination of moisture
and protein content in cereal grains (Reeves, 1994, Shenk and Westerhaus, 1985 and Williams, 1975),
moisture, protein and oil contents of oilseeds (Hymowitz et al., 1974 and Krishnan et al., 1994) and
major constituents in forages (Norris et al., 1976). This spectropic technique has been developed to
replace the laborious, time-consuming and expensive conventional methods, i.e. Kjeldahl method for
protein, various solvent extraction methods for fat and oven-drying methods for moisture (Lanza,
261
1983). Ben-Gera and Norris (1968) used transmission spectroscopy in the NIR range to determine the
fat and moisture contents of meat products. Kruggel et al. (1981) estimated fat, moisture and protein
contents in fresh emulsified beef and ground lamb by NIR reflectance, while Lanza (1983) determined
moisture, protein, fat and calorie contents in raw emulsified pork and beef by NIR reflectance and
transmittance. All these studies, however, were conducted on fresh meat. The energy absorbed by
water is temperature dependent. This is due to the presence of hydrogen bonds between the molecules,
which alter the force constant for the covalent O H bond and the frequency of the O H absorption
band. The hydrogen bonds may also give a distribution of O H bond lengths, which give rise to the
broad area of absorption (Thyholt and Isaksson, 1997). An increase in temperature causes disruption
of hydrogen bonds by thermal collisions, giving a change in the absorption profile. Thus, there will be
an increase in absorption at the higher frequency area of the O H absorption region. A temperature
shift will also affect hydrophilic components such as protein and carbohydrates, which form hydrogen
bonds with the water molecules. Therefore, temperature fluctuations reduce the accuracy of NIR
analysis of several compounds if water is present (Thyholt and Isaksson, 1997). Consequently,
removing water (e.g. by freeze-drying) means removing the hydrogen bonding interference and giving
small molecules, such as sugars, amino acids and minerals, more characteristic spectra.
Minerals do not have reflectance spectra in the infrared region. If some form of correlative relationship
can be found, it would be in association with some organic constituent(s) that varies as the mineral
varies in the sample (Shenk et al., 1979). Minerals in agricultural products probably exist in both
organic and inorganic complexes. The possibility that NIRS could be used for determining mineral
concentrations would therefore seem remote (Clark et al., 1987). Clark et al., 1987 and Clark et al.,
1989, Shenk et al., 1979 and Shenk et al., 1981 and Valdes et al. (1985) however, reported the use of
NIRS for determining mineral composition in forages. Shenk et al. (1979) and Valdes et al. (1985)
reported accurate calibrations for K, Mg, Ca and P. Clark et al. (1987) reported successful calibrations
for Ca, P, K and Mg and suggested that NIRS is indirectly measuring these minerals by their
association with organic acids. They did not, however, find any similarities in wavelengths chosen for
P and those highlighted in phytate or phosphate spectra.
The aim of this study was to develop NIRS calibrations for the proximate and mineral composition of
freeze-dried mutton samples.
2. Materials and methods
Samples analysed for ash, dry matter (DM), crude protein (CP) and fat used for NIRS calibrations
were the same as those used in a study by Cloete (2002) and consisted of M. longissimus dorsi from
168 19-month-old Merino sheep. Mineral calibrations were developed with M. semimembranosus
samples from Merino crossbreed lambs slaughtered at a live weight of 40 kg. The samples were
minced, freeze-dried, ground with a Knifetec 1095 Sample Mill (Tecator, Box 70, S-263 21 Hoganäs,
Sweden) using a 1 mm sieve and analysed for chemical composition. The protein was measured by a
FP-428 Nitrogen and Protein Determinator (Leco Corporation, 3000 Lakeview Avenue, St. Joseph, MI
49085-2396). Lipid (petroleum ether extraction) was measured according to AOAC (1984) (Method
number 7.061). Moisture was determined by drying a sample (ca. 1.0 g) at 100 ºC to a constant weight
and ash content by placing the sample in a furnace at 500 ºC overnight (AOAC, 1984) (Method
numbers 7.003 and 7.009, respectively). Minerals were determined according to Watson (1994).
Element concentrations were measured on an ICP-AES (inductive coupled plasma atomic emission
spectrophotometer; Liberty Series AA Varian).
All samples were divided into two sets for each constituent: a larger set for the calibration equations
(calibration set) and a smaller set for the validation (validation set) of the calibrations (n values are
shown in Table 1, Table 2, Table 4 and Table 5, respectively). Outliers were removed according to
suggestions by the software (Bran + Luebbe SESAME Version 2.00-software, BRAN + LUEBBE
GmbH, Norderstedt, Germany). Outliers listed as ‘T’- and ‘H’-values were taken into consideration.
The ‘T’-value measures how closely the reference value matches the predicted value. The spectrum is
listed and flagged with an asterisk (*) if the ‘T’-value is greater than 2.5 times the standard error of
calibration. These values can be potential outliers, because they do not fit the calibration equation as
well as the other samples. The ‘H’-value is a measure of leverage. It puts a numerical value on the
262
influence of a particular spectrum in determining the regression line. It is a measure of
multidimensional distance of a spectrum to the regression line. If a spectrum with a large ‘H’-value
has a small ‘T’-value, it is likely to be valuable for the calibration. If both the ‘H’- and the ‘T’-values
are large, it is more likely to be a true outlier. Equations of best fit were chosen for each constituent
based on statistical analysis. After removal of the outliers, every fifth sample was selected for the
validation sets. Wet chemistry and NIRS analyses were done simultaneously for all the samples.
Table 1. Summary of chemical composition (%) of freeze-dried mutton samples used in the calibration
set, showing number of samples (n), mean, range of values, standard deviation (S.D.) and coefficient
of variation (C.V.)
Chemical component (%)
n
Mean
Min
Max
S.D.
C.V.
Ash
128
3.81
2.09
5.17
0.70
18.37
DM
131
93.41
90.55
95.92
1.07
1.15
CP
118
73.92
52.94
86.95
8.97
12.13
Fat
120
19.20
7.30
51.80
11.02
57.40
Table 2. Summary of chemical composition (%) of freeze-dried mutton used in the validation set,
showing number of samples (n), mean, range of values, standard deviation (S.D.) and coefficient of
variation (C.V.)
Chemical component (%)
n
Mean
Min
Max
S.D.
C.V.
Ash
26
3.87
2.27
4.67
0.68
17.57
DM
26
93.45
90.55
95.92
1.29
1.38
CP
23
71.74
53.49
84.33
10.48
14.61
Fat
27
19.76
7.30
51.80
12.24
61.94
NIRS analyses were done with an InfraAlyzer 500 near infrared reflectance analyser (IA-500) using
Bran + Luebbe SESAME Version 2.00-software (BRAN + LUEBBE GmbH). Approximately 6 g of
each sample was packed into an open sample cup. Spectra were measured over the wavelength range
1100–2500 nm, recorded as log 1/R at 2 nm intervals. Calibration equations were developed for each
constituent following the recommended protocol of Windham et al. (1989). Calibrations were
developed by means of partial least-squares regression (PLSR) on normalised spectra for Na, Fe, Zn
and Mn, on first derivative spectra (segment = 1; gap = 0) for Al, Cu, Mg and P, and on second
derivative spectra (segment = 1; gap = 0) for ash, DM, CP, fat, B, Ca and K content.
3. Results and discussion
The range, mean values, standard deviations (S.D.) and coefficients of variation (C.V.) of the
calibration and validation sets for the chemical composition constituents are shown in Table 1 and
Table 2, respectively. The variation in the chemical composition of the samples used seemed to cover
the whole spectrum found for mutton reported in the literature for mutton (Berg et al., 1997, Hopkins
et al., 1992 and Teixeira et al., 1996). The fat content of the mutton (Table 1) showed a large variation
(7.30–51.80%). Kruggel et al. (1981) suggested, in a study on ground lamb meat, that NIRS is not as
suitable for the determination of protein compared to the determination of fat and moisture when used
with lamb meat samples containing 17.8–26.2% fat. The study (Kruggel et al., 1981), however, was
conducted on raw meat and it was found that the fat content influenced the particle size of the samples.
This phenomenon was not observed in this investigation, possibly due to the use of freeze-dried
samples.
263
Table 3 shows the statistics, including standard errors of calibration (SEC) and multiple correlation
coefficient (r) values for the equations of best fit obtained for each of the constituents. The r values for
the validation sets and standard errors of performance (SEP) are also shown in Table 3, as well as the
standard error of laboratory (SEL) (Snedecor and Cochran, 1980) and predicted mean values. If the
SEP for the validation is within two multiplications of the SEL for the primary reference method
analysis, the final NIRS equation can be accepted for use, and the SEP for validation can be used as a
reliable indication of the accuracy of the final NIRS equation (Windham et al., 1989). All four of the
chemical constituent calibrations fitted these limitations and could be accepted for rapid predictions of
the constituents (ash = 0.15% (SEP) veraus 0.13% (SEL); DM = 0.38% (SEP) versus 0.25% (SEL);
CP = 0.92% (SEP) versus 2.18% (SEL); fat = 0.43% (SEP) versus 2.36% (SEL)). The SEC and r
values for CP (1.42% and 0.99) and fat (0.66% and 1.00) were similar to that reported by Kruggel et
al. (1981) who noted values of 0.61% and 0.77 for protein and 2.41% and 0.85 for fat in raw lamb.
The reason for the difference between values obtained in the two studies could be due to the freezedried state of the samples used in this investigation. The physical appearance of freeze-dried meat is
more homogenous than raw minced meat, due to the influence of the fat on the particle size of raw
minced meat samples (Kruggel et al., 1981). Water is extracted and cannot have any influence on
possible temperature fluctuations. The SEP values from this investigation were similar to values
obtained in studies with wet beef (DM = 0.59%; CP = 1.15%; fat = 0.27%—Lanza, 1983); (DM =
1.21%; CP = 0.45%; fat = 1.30%—Tøgersen et al., 1999) and wet pork (DM = 0.66%; CP = 0.92%;
fat = 0.28%—Lanza, 1983); (DM = 1.18%; CP = 0.57%; fat = 1.35%—Tøgersen et al., 1999).
Table 3. Statistics of the calibration equations of best fit and validation including the number of PLSR
factors used for each equation, standard error of calibration (SEC), standard error of performance
(SEP) and standard error of laboratory (SEL)
Chemical
component
Number
of Calibration
PLSR factors
set
r
SEC
(%)
Validation set
r
SEP
(%)
SEL
(%)
Predicted
Laboratory
mean values
mean values (%)
(%)
Ash
1
0.93
0.25 0.97
0.15
0.13
3.87
3.87
DM
13
0.99
0.16 0.96
0.38
0.25
93.45
93.37
CP
3
0.99
1.42 1.00
0.92
2.18
71.74
71.58
Fat
2
1.00
0.66 1.00
0.43
2.36
19.76
19.76
The correlation between the NIRS predicted values and the laboratory determined values for the
proximate composition are shown in Fig. 1.
Fig. 1. Relationship between laboratory determined and NIRS predicted values for ash, DM, CP and
fat content in freeze-dried mutton, using between 23 and 27 samples for each validation.
Some of the important wavelengths for water (1190; 1940 nm) (Osborne et al., 1993), protein (1680;
2050; 2180 nm) (Osborne et al., 1993) and fat (1200; 1734; 1765; 2310; 2345 nm) (Osborne et al.,
1993) in freeze-dried mutton corresponded with wavelengths noted for the same constituents in freezedried ostrich meat (Viljoen et al., 2005), in spite of the differences in protein and fat composition of
the different types of meat.
The range, mean values, standard deviations and coefficients of variation of the calibration and
validation sets for the minerals are shown in Table 4 and Table 5, respectively. The number of samples
used for the K, Na, B and Mn calibrations were less than the minimum number (50) of samples
suggested for a narrow-based population (Windham et al., 1989). This was, however, the only samples
available and calibrations were attempted to test the accuracy of NIRS for the particular minerals. If
the number of samples were to be increased, it would result in more robust, and probably more
accurate, calibrations.
264
Table 4. Summary of the mineral composition (mg/kg freeze-dried) of the calibration set for freezedried mutton meat showing number of samples (n), mean, range of values, standard deviation (S.D.)
and coefficient of variation (C.V.)
Mineral
n
Mean
Min
Max
S.D.
C.V.
K
49
9100.00
7400.00
11500.00
1100.00
12.08
P
51
8200.00
5000.00
10600.00
1900.00
23.17
Na
48
1154.67
831.00
1629.00
173.45
15.02
Mg
52
600.00
500.00
700.00
60.00
10.00
Cu
52
0.79
0.57
2.09
0.21
26.58
Fe
52
35.89
26.20
58.40
6.60
18.39
Zn
50
56.78
45.90
72.30
6.07
10.69
B
44
0.46
0.24
0.90
0.15
32.61
Mn
40
0.31
0.24
0.46
0.05
16.13
Ca
51
200.00
100.00
300.00
60.00
30.00
Al
51
4.62
2.72
8.31
1.41
30.52
Table 5. Summary of the mineral composition (mg/kg freeze-dried) of the validation set for freezedried lamb meat showing number of samples (n), mean, range of values, standard deviation (S.D.) and
coefficient of variation (C.V.)
Mineral
n
Mean
Min
Max
S.D.
C.V.
K
10
9300.00
8300.00
11500.00
1200.00
12.90
P
10
8800.00
5400.00
10400.00
1500.00
17.05
Na
10
1170.00
960.00
1629.00
179.44
15.34
Mg
11
600.00
500.00
700.00
80.00
13.33
Cu
10
0.75
0.58
0.94
0.12
16.00
Fe
10
35.12
26.20
47.90
6.73
19.16
Zn
10
58.93
51.50
72.30
7.05
11.96
B
10
0.45
0.30
0.67
0.14
31.11
Mn
10
0.30
0.24
0.37
0.04
13.33
Ca
10
200.00
100.00
300.00
60.00
30.00
Al
10
4.47
3.60
6.10
0.89
19.91
Table 6 shows the SEC and r values for the equations of best fit obtained for each of the constituents.
The r values for the validation sets and SEP values are also shown in Table 6, as well as the SEL and
predicted and laboratory mean values. Calibrations which were acceptable on account of their SEP
values in comparison with the SEL values were: K (600 mg/kg versus 400 mg/kg); P (900 mg/kg
versus 500 mg/kg); Na (77.89 mg/kg versus 56.75 mg/kg), Mg (40 mg/kg versus 20 mg/kg); Fe (3.15
mg/kg versus 2.13 mg/kg) and Zn (3.59 mg/kg versus 2.23 mg/kg). Clark et al. (1987) suggested that
NIRS is indirectly measuring these minerals by their association with organic constituents(s) that
varies as the mineral varies in the sample.
265
Table 6. Statistics of the calibration equations of best fit and validation including the number of PLSR
factors used for each equation, standard error of calibration (SEC), standard error of performance
(SEP) and standard error of laboratory (SEL)
Chemical
Component
Number of
Calibration
PLSR
set
factors
r
SEC
(mg/kg
Validation set
r
Laboratory
mean values
(mg/kg)
Predicted
mean values
(mg/kg)
SEP
SEL
(mg/kg) (mg/kg)
K
5
0.94 400.00 0.86 600.00
400.00
9300.00
9400.00
P
5
0.85 1100.00 0.88 900.00
500.00
8800.00
8500.00
Na
5
0.84 100.17 0.89
77.89
56.75
1170.00
1153.63
Mg
5
0.82
40.00
0.92
40.00
20.00
600.00
600.00
Cu
5
0.73
0.15
0.47
0.14
0.04
0.75
0.80
Fe
2
0.70
4.80
0.88
3.15
2.13
35.12
35.86
Zn
3
0.67
4.68
0.86
3.59
2.23
58.93
57.83
B
3
0.60
0.13
0.39
0.12
0.04
0.45
0.44
Mn
4
0.59
0.04
0.29
0.04
0.01
0.30
0.30
Ca
3
0.58
50.00
0.49
50.00
20.00
180.00
190.00
Al
1
0.32
1.35
0.26
0.86
0.28
4.47
4.58
The relative small numbers of samples, which were randomly selected for validation, could result in
samples deviating a lot form the mean of the selected samples. In the validation set for Na, most of the
samples ranged between 960 and 1237 mg/kg, except for one sample with the concentration of 1629
mg/kg. It is conceded that the leverage caused by this particular data point could influence the
outcome of the validation, but at present this is the only samples available. An increase in the number
of samples for both the calibration and validation sets would probably solve this problem. Further
research is necessary to conclude to the accuracy of NIRS for prediction of minerals in freeze-dried
mutton.
The correlation between the NIRS predicted values and the laboratory determined values for the
mineral composition are shown in Fig. 2, Fig. 3 and Fig. 4.
Fig. 2. Relationship between laboratory determined and NIRS predicted values for K and P in freezedried mutton, using 10 samples for each validation.
Fig. 3. Relationship between laboratory determined and NIRS predicted values for Na, Mg, Cu, Fe,
Zn, B, Ca and Mn in freeze-dried mutton, using 10 or 11 samples for each validation.
Fig. 4. Relationship between laboratory determined and NIRS predicted values for Al in freeze-dried
mutton, using 10 samples for the validation.
4. Conclusion
The major advantage of near infrared reflectance spectroscopy analysis is that once the instrument is
calibrated, the results for protein and fat for freeze-dried mutton can be obtained within seconds.
Freeze-dried samples led to more accurate calibrations than that noted in the literature, possibly due to
266
the homogenous nature of the samples and the lack of moisture. The latter may change the chemical
composition of the sample with fluctuations in temperature. Freeze-drying, however, can be expensive
and timely. This led to the conclusion that if NIRS is to be used in the industry for quality control
purposes, it would probably be more cost effective to have a less accurate calibration using raw meat
than a more accurate calibration using freeze-dried meat. Accurate use of NIRS to determine mineral
composition in mutton appears limited to certain minerals (K, P, Na, Mg, Fe and Zn) only.
Acknowledgements
The Elsenburg Agricultural Research Centre partly funded this study. The authors also wish to thank
the Red Meat Research and Development Trust and Technology and Human Resources for Industry
Program (THRIP) of South Africa for their financial contributions.
References
AOAC, 1984 AOAC, Official Methods of Analysis (14th ed.), Association of Official Analytical
Chemists, Inc., Arlington, Virginia, USA (1984) pp. 152–169.
Ben-Gera and Norris, 1968 I. Ben-Gera and K.H. Norris, Direct spectrophotometric determination of
fat and moisture in meat products, J. Food Sci. 33 (1968), pp. 64–67.
Berg et al., 1997 E.P. Berg, M.K. Neary, J.C. Forrest and D.L. Thomas, Evaluation of electronic
technology to assess lamb carcass composition, J. Anim. Sci. 75 (1997), pp. 2433–2440.
Clark et al., 1987 D.H. Clark, H.F. Mayland and R.C. Lamb, Mineral analysis of forages with near
infrared reflectance spectroscopy, Agron. J. 79 (1987), pp. 485–490.
Clark et al., 1989 D.H. Clark, E.E. Cary and H.F. Mayland, Analysis of trace elements in forages by
near infrared reflectance spectroscopy, Agron. J. 81 (1989), pp. 91–95.
Cloete, 2002 Cloete, J.J.E., 2002. Carcass traits in relation to genotype in sheep. MSc. Thesis.
University of Stellenbosch, pp. 11–15.
Hopkins et al., 1992 D.L. Hopkins, K.D. Gilbert, K.L. Pirlot and A.H.K. Roberts, Elliottdale and
crossbred lambs: growth rate, wool production, fat depth, saleable meat yield, carcass composition and
muscle content of selected cuts, Aust. J. Agric. Res. 32 (1992), pp. 429–434.
Hymowitz et al., 1974 T. Hymowitz, J.W. Dudley, F.I. Collins and C.M. Brown, Estimation of protein
and oil concentration in corn, soybean and oat seed by near infrared light reflectance, Crop Sci. 14
(1974), pp. 713–715.
Krishnan et al., 1994 P.G. Krishnan, W.J. Park, K.D. Kepjart, D.L. Reeves and G.L. Yarrow,
Measurement of protein and oil content of oat cultivars using near infrared reflectance spectroscopy,
Cereal Foods World 39 (1994), pp. 105–108.
Kruggel et al., 1981 W.G. Kruggel, R.A. Field, M.L. Riley, H.D. Radloff and K.M. Horton, Near
infrared reflectance determination of fat, protein and moisture in fresh meat, J. Assoc. Anal. Chem. 64
(1981), pp. 692–696.
Lanza, 1983 E. Lanza, Determination of moisture, protein, fat and calories in raw pork and beef by
near infrared spectroscopy, J. Food Sci. 48 (1983), pp. 471–474. f
Norris et al., 1976 K.H. Norris, R.F. Barnes, J.E. Moore and J.S. Shenk, Predicting forage quality by
infrared reflectance spectroscopy, J. Anim. Sci. 43 (1976), pp. 889–897.
Osborne, 1992 B.G. Osborne, NIR analysis of baked products. In: D.A. Burns and E.W. Ciurczak,
Editors, Handbook of Near Infrared Analysis (1992), pp. 527–548.
Osborne et al., 1993 B.G. Osborne, T. Fearn and P.H. Hindle, Applications of near infrared
spectroscopy in food and beverage analysis. In: D. Browning, Editor, Practical NIR Spectroscopy with
Applications in Food and Beverage Analysis, Longman Scientific & Technical/Marcel Dekker, Inc.,
London/270 Madison Avenue, New York, 10016, USA (1993), pp. 145–159.
Reeves, 1994 J.B. Reeves, Use of near infrared reflectance spectroscopy as a tool for screening treated
forages and by-products, J. Dairy Sci. 77 (1994), pp. 1030–1037.
Shenk et al., 1979 J.S. Shenk, M.O. Westerhaus and M.R. Hoover, Analysis of forages by infrared
reflectance, J. Dairy Sci. 62 (1979), pp. 807–812.
Shenk et al., 1981 J.S. Shenk, I. Landa, M.R. Hoover and M.O. Westerhaus, Description and
evaluation of a near infrared reflectance spectro-computer for forage and grain analysis, Crop Sci. 21
(1981), pp. 355–358.
267
Shenk and Westerhaus, 1985 J.S. Shenk and M.O. Westerhaus, Accuracy of NIRS instruments to
analyse forage and grain, Crop Sci. 25 (1985), pp. 1120–1122.
Snedecor and Cochran, 1980 G.W. Snedecor and W.G. Cochran, Statistical Methods (seventh ed.),
Iowa State University Press, Ames, Iowa (1980) p. 593.
Teixeira et al., 1996 A. Teixeira, R. Delfa and T. Treacher, Carcass composition and body fat depots
of Galego Bragançano and crossbred lambs by Suffolk and Merino Precoce sire breeds, J. Anim. Sci.
63 (1996), pp. 389–394.
Thyholt and Isaksson, 1997 K. Thyholt and T. Isaksson, Near infrared spectroscopy of dry extracts
from high moisture food products on solid support—a review, J. Near Infr. Spec. 5 (1997), pp. 179–
193.
Tøgersen et al., 1999 G. Tøgersen, T. Isaksson, B.N. Nilsen, E.A. Bakker and K.I. Hildrum, On-line
NIR analysis of fat, water and protein in industrial scale ground meat batches, Meat Sci. 51 (1999), pp.
97–102.
Valdes et al., 1985 E.V. Valdes, L.G. Young, I. McMillan and J.E. Winch, Analysis of hay, haylage
and corn silage samples by near infrared reflectance spectroscopy, Can. J. Anim. Sci. 65 (1985), pp.
753–760.
Viljoen et al., 2005 M. Viljoen, L.C. Hoffman and T.S. Brand, Prediction of the chemical composition
of freeze dried ostrich meat with near infrared reflectance spectroscopy, Meat Sci. 69 (2005), pp. 255–
261.
Watson, 1994 C. Watson, Official and Standardized Methods of Analysis (third ed.), The Royal
Society of Chemistry, Cambridge (1994).
Williams, 1975 P.C. Williams, Application of near infrared reflectance spectroscopy to analysis of
cereal grains and oilseeds, Cereal Chem. 52 (1975), pp. 561–576.
Windham et al., 1989 W.R. Windham, D.R. Mertens and F.E. Barton II., 1. Protocol for NIRS
calibration: sample selection and equation development and validation. In: G.C. Marten, J.S. Shenk
and F.E. Barton II., Editors, Near Infrared Reflectance Spectroscopy (NIRS): Analysis of Forage
Quality, United States Department of Agriculture, Springfield, VA, USA (1989), pp. 96–103.
METHODS OF PREDICTING LAMB CARCASS COMPOSITION: A REVIEW
K. Stanforda, S. D. M. Jonesb and M. A Pricec
a
Alberta Agriculture, Food and Rural Development, Agriculture Centre, Bag 3014, Lethbridge,
Alberta, Canada T1J 4C7. bResearch Centre, Agriculture and Agri-Food, Canada, Box 3000,
Lethbridge, Alberta, Canada T1J 4B1. c Department of Agriculture, Food and Nutritional Sciences,
310 AgForestry Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2P5.
Small Ruminant Research, 29, 3, 241-254, 1998.
Abstract
Methods presently available for the prediction of body and carcass composition in lambs were
reviewed in terms of cost, speed, precision and current usage. In vivo methods reviewed included
liveweight, linear measurements, ultrasound, X-ray computed tomography (CT) and nuclear magnetic
resonance (NMR)/magnetic resonance imaging. Methods reviewed for predicting composition of
carcasses included subjective measurements, carcass weight, specific gravity, dressing percentage,
linear measurements, optical probes, video image analysis (VIA), total body electrical conductivity
(TOBEC) and bioelectrical impedance. All methods were not directly comparable as few studies have
used multiple methods for prediction of body or carcass composition. Limited comparisons were
possible through the residual standard deviations (RSD) published for the various methods. Although
subjective methods for predicting body and carcass compositions are rapid and relatively inexpensive,
the sheep industry should adopt objective methods in order to more readily change lamb carcass
composition to meet consumer demand.
Author Keywords: Lamb; Carcass; Yield; Composition; Review.
1. Introduction
The sheep industry world-wide faces a fundamental problem. With the exception of the major lambexporting countries (New Zealand and Australia) and some areas of the Middle East, consumption of
lamb has markedly declined over the past 30 years (Lewis et al., 1993). Although consumption of
268
other red meats has also declined during this period, lamb consumption in North America has fallen to
the point where it is difficult to even assess. With a high degree of error, it is estimated on an annual
per capita retail-weight basis at 0.6 to 0.7 kg in the USA (Economic Research Service, 1994) and 0.8
kg in Canada (Statistics Canada, 1995).
In order to reverse the downward trend in lamb consumption, the needs of the modern consumer have
to be more closely addressed. As outlined by Ward et al. (1995), consumers require meat with more
lean, less fat (the minimal fat level required to maintain juiciness and flavour), consistent quality,
portions that are considered good value for money with minimal wastage, convenience/ease in cooking
and a high level of choice/flexibility in available cuts. Unfortunately, the studies of Ward et al. (1995)
and others (Harris et al., 1990; Beermann et al., 1995) have shown that lamb is currently failing to
meet these consumer demands.
Before lamb carcasses can be changed to better meet consumer demand, carcasses must be evaluated
using two equally important categories: (1) quality attributes such as tenderness, cut size, fat cover,
marbling, meat and fat colour; and (2) composition attributes such as saleable meat yield, or
proportions of fat, lean and bone (Harrington and Kempster, 1989). It is the intent of this paper to
review and evaluate methods available for prediction of body/carcass composition in sheep which
may, in some cases, also allow prediction of quality attributes.
Although prediction of carcass composition in sheep has been the subject of earlier reviews (Alliston,
1980; Kempster, 1980; Allen, 1990; Fisher, 1990; Simm, 1992), more recent reviews have either had a
narrow focus (Russel, 1995) or have excluded sheep (Forrest, 1995; Jones, 1995). A re-evaluation of
methods for predicting carcass composition in sheep is warranted due to changes in technology since
publication of the earlier reviews.
The methods of predicting carcass composition discussed in this paper are required for a variety of
purposes. Extremely rapid methods, capable of evaluating a carcass in 6 s or less would be relevant for
on-line use (Hopkins et al., 1995), provided that damage to the commercial value of the carcass is
minimal. Relatively rapid and inexpensive in vivo methods which do not harm animal performance
would be applicable for the selection of breeding stock or estimation of market-readiness. In contrast,
methods of extreme accuracy and/or precision may be useful in research applications, regardless of
cost or time/labour requirements.
2. Body composition in vivo
The keys to changing carcass composition to better meet consumer demand are methods of evaluating
body composition in vivo. It is desirable that in vivo methods be applicable in young animals, enabling
early selection of lambs with highly desirable body/carcass composition as breeding stock (Brask et
al., 1992). Generally, carcass composition traits in sheep are moderately highly heritable (Simm,
1992). Heritability estimates on a weight-adjusted basis for percentages of carcass lean and fat are
commonly found to be 0.40 for lean and 0.45 for fat (Wolf and Smith, 1983; Simm et al., 1987).
Improvement in carcass composition by genetic selection is possible for traits such as fat distribution
which show a high degree of variation in individual animals within a breed (Butterfield, 1988), but
would be limited for other traits such as muscle weight distributions which show very small variation
either within or across breeds when sheep are compared at the same stage of maturity (Kempster and
Cuthberson, 1977). Ignoring genetic factors such as selection intensity which are beyond the scope of
this paper, the rate of improvement would be largely dependent on the precision of the method used
for estimating body/carcass composition in vivo. Other factors which need to be evaluated to
determine the utility of methods for prediction of body and carcass composition include the cost/ease
of taking the predicting measurements and the stability of the prediction between animals differing in
sex, or feeding regime (Kempster et el., 1976). The suitability of a method for use within a particular
breed must also be determined. A summary of available methods for evaluation of body composition
in vivo is shown in Table 1.
2.1. Subjective measurements
Visual appraisal in combination with condition scoring (manual assessment of fatness) is the most
rapid and inexpensive method for prediction of body composition in vivo (Kempster, 1984). However,
the large variation between breeds in the proportion of fat stored subcutaneously (Fahmy et al., 1992)
limits the usefulness of this method. Within breeds, trained livestock evaluators have been able to
estimate lamb carcass composition with accuracies superior to that of ultrasound (Nicol and Parratt,
269
1984; Edwards et al., 1989). Provided breed types are relatively uniform, lamb `drafters' in New
Zealand use visual appraisal/condition scoring for prediction of carcass composition with accuracies
approaching those of ultrasound (Dodd et al., 1986). However, the small number of suitably
experienced/proficient personnel in countries other than New Zealand and difficulties in maintaining
standards across time and geographical regions would limit the usefulness of subjective estimates of
body composition.
2.2. Liveweight
In vivo techniques commonly use liveweight as the standard to which other predictors of body
composition are compared (Kempster, 1984; Simm, 1992) although live weight may be difficult to
accurately measure due to the influence of gut fill and fleece length/hydration. As outlined by
Butterfield (1988), tissues within the body follow predictable patterns of development from birth to
maturity. The proportion of muscle in sheep compared at fleece-free empty body weights has been
shown to be relatively uniform, ranging from 28% (McClelland et al., 1976) to 30% (Thoney et al.,
1987). The currently reported exceptions to this general rule are the Soay and Texel breeds, the Soay
having less fat and more bone (McClelland et al., 1976) and the Texel having less fat and more lean
than would be expected. The usefulness of liveweight as a predictor of body composition is limited by
difficulties in assessing an animal's stage of maturity which can be influenced by genotype, nutrition,
disease, physical environment, level of activity, social environment and age (Taylor, 1965). In lambs
of equal maturity (same age and breed), liveweight predicted % carcass lean with a residual standard
deviation (RSD) ranging from 1.4 (Cuthberson et al., 1984) to 2.2 (Fortin and Shrestha, 1986), with R2
values of 0.51 and 0.76, respectively. When lambs were of differing maturity (varying ages, multiple
breeds), liveweight has been less useful for predicting % carcass fat (RSD of 3.9, Purchas and Beach,
1981) and % saleable meat yield (RSD of 1.5, and R2 of only 0.14, Stanford et al., 1995a).
2.3. Linear measurements
Prior to development of technologies enabling in vivo prediction of carcass composition, a number of
linear measurements (shoulder height, heart girth, body length...) were evaluated as predictors of body
composition in sheep (Orme et al., 1962; Orme, 1963; Cunningham et al., 1967), but were found to be
of marginal utility in lambs of varying age, sex or breed type. Although the use of linear
measurements has been periodically re-investigated (Cuthberson et al., 1984; Edwards et al., 1989),
the inability of linear measurements to distinguish between lean and fat would limit their application
as primary predictors of body composition to goats and certain breeds of sheep which have limited
subcutaneous fat stores (Stanford et al., 1995b). The utility of linear measurements has also been
reduced by the accuracy to which the measurements may be recorded. Most studies have used either
callipers or measuring tapes, leading to increased error due to animal movement and variations in
fleece cover.
2.4. Ultrasound
Ultrasound equipment converts electrical pulses to high-frequency sound waves which are reflected
from the boundaries between tissues of different bioacoustic densities (Houghton and Turlington,
1992). Two types of ultrasound equipment are used: (A) mode machines, available since the 1950's,
which measure echo amplitude against time, with the distance between echoes being related to the
distance between successive tissue interfaces (Simm, 1983); (B) mode or real-time machines
developed in the early 1980's, where `grey-scales' measure echo intensity in a two-dimensional scan
(Stouffer, 1988). The velocity of ultrasound through soft tissues is also used to predict body
composition (Miles et al., 1991), offering the advantage of absolute values instead of images requiring
subjective interpretation.
Early studies reported that ultrasound was either of little (Jones et al., 1982; Hamby et al., 1986) or no
use (Leymaster et al., 1985; Fortin and Shrestha, 1986; Edwards et al., 1989) for predicting
body/carcass composition in sheep. The limited utility of ultrasound was attributed to the small size
and lack of variation in subcutaneous fat thickness and longissimus muscle area in sheep as compared
to cattle and pigs (Houghton and Turlington, 1992). Additionally, Purchas and Beach (1981) attributed
the reduced utility of ultrasound in sheep to a soft, mobile subcutaneous fat layer, with wool an added
complicating factor. However, in more recent work (Stanford et al., 1995a), ultrasound measurement
of subcutaneous fat depth taken at the first lumbar vertebra was a better predictor of saleable meat
yield (RSD=1.2, R2=0.64) than liveweight (RSD=1.5, R2=0.14). Additionally, the use of ultrasonic
measurements of backfat and longissimus muscle depth (`C' and `B' measurements, respectively of
270
Palsson, 1939) at the third lumbar vertebrae has been shown to improve genetic selection for carcass
fatness by 10.3% and carcass grade (muscling and fatness) by 14.5%, compared to selection based on
liveweight alone (Olesen and Husabo, 1994).
Regardless of the precision of ultrasound methods, sheep body composition has been significantly
improved after 3¯4 years of selection using indexes based on ultrasonically measured backfat, muscle
depth and liveweight (Cameron and Bracken, 1992; Simm et al., 1993). Additionally, the relatively
low cost and ease of portability of ultrasound equipment has led to incorporation of ultrasound
measurements into national genetic programs for lamb carcass quality improvement in many parts of
the world (Table 2).
2.5. X-ray computed tomography
Unlike ultrasound which was first used for military purposes, the equipment used in X-ray computed
tomography (CT) was first developed for human medicine (Vangen, 1989). An X-ray generator and Xray detectors are rotated around the subject, firing pulses of radiation and measuring the amount of
radiation transmitted through the subject (Simm, 1992). The rate of attenuation of the X-rays allows
computerized calculation of densities in a cross section of the subject, the densities being standard
values which vary from -1000 for air to +1000 for bone (Standal, 1984). In vivo use of CT is
applicable only for smaller livestock such as sheep, goats, chickens and pigs due to the human-scale of
the equipment (Vangen, 1989).
Although studies where CT has been used for prediction of body composition in sheep are limited,
Sehested (1984) reported that CT values with live weight could predict kg fat-free lean in lambs with
R2 values of 0.92 to 0.94, RSD 0.5 to 0.6, compared to prediction with liveweight alone (R2=0.83,
RSD=0.8). Jopson et al. (1995) reported that compared to ultrasound, CT would double the rate of
genetic improvement for lean meat traits in lambs as direct selection was possible for protein content
and proportions of lean, intermuscular and intramuscular fat. However, the 10-fold higher cost of CT
(equipment and operating expenses) as compared to ultrasound (Parratt and Simm, 1987) will likely
result in general use of ultrasound for evaluation of body composition in sheep, with CT reserved for a
select group of the most promising rams. X-ray CT has been used for evaluation of elite rams in the
UK (Simm, 1992) and Australia (Jopson et al., 1995). Recently, CT equipment was also purchased in
New Zealand for a commercial scanning service (Innervision) for high-value sheep (Davis and
Fennessy, 1996).
2.6. Nuclear magnetic resonance/magnetic resonance imaging
A nuclear magnetic resonance (NMR) machine consists of an electromagnet with a central opening
large enough for a human. The strong magnetic field tends to induce resonance of protons in the
subject (Wells, 1984). The time needed for the protons to re-establish original conditions has been
defined as spin-lattice relaxation time T1 and spin-spin relaxation time T2 (Groeneveld et al., 1984)
which differ depending on factors such as the state of hydration or fat content of a tissue (Simm,
1992). Contrary to CT, there are no standardized values in NMR due to changes in conditions and
parameters between measurements (Groeneveld et al., 1989). However, NMR has additional
capabilities compared to CT, including evaluation of muscle metabolism and prediction of carcass
quality attributes such as water holding capacity (Monin and Renou, 1989). Spectroscopy and
magnetic resonance imaging are discrete types of NMR, although both are applicable to the prediction
of body composition (Simm, 1992).
The accuracy of NMR at predicting body composition is thought to be superior to that of CT
(Groeneveld et al., 1984; Simm, 1992), although CT and NMR were found to be of equal value in
determining adipose tissue volumes of rats (Ross et al., 1991). High operating costs for NMR,
estimated to be equivalent to the wages of 20 research staff (Pedersen, 1989), have restricted access to
NMR equipment for livestock species to a larger extent than access to CT. In the sole study where
NMR has been used to evaluate body composition in sheep, Streitz et al. (1995) reported R2 values
ranging from 0.78 to 0.91 for percentage of lean in lambs at body weights from 10 to 50 kg. Presently,
programs using NMR for the genetic improvement of carcass quality in livestock are restricted to
poultry (Mitchell et al., 1991; Liu et al., 1994). Additional studies with sheep would be required before
the benefits of using NMR for prediction of body composition could be evaluated relative to costs.
271
2.7. Other methods for in vivo prediction of body composition
Other techniques for prediction of body composition presently used in human medicine include dualphoton absorptiometry (Maezess et al., 1990); dual X-ray absorptiometry (Dalsky et al., 1990) and
underwater weighing (Wang et al., 1989). However, underwater weighing would be practical only for
sheep carcasses. Additionally, radionucleotides are costly and their use in meat animals would be a
perceived human health concern. Dilution techniques for estimating body water using radionucleotides
(Robelin and Theriez, 1981) and urea (Jones et al., 1982) have been used to predict body composition
of sheep, but due to the length of time required (up to 48 h animal-1) and the amount of labour
involved, are applicable only in research studies (Robelin, 1984). Discussions of total body electrical
conductivity (TOBEC) and bioelectrical impedance analysis (BIA) are presented in Section 3.6 and
Section 3.7, respectively.
3. Carcass composition ex vivo
Carcass composition assessment serves three functions: (1) assigns carcass value; (2) allows sorting of
carcasses for further processing or fresh meat merchandising; and (3) transfers information back to the
production sector, hopefully ensuring that carcasses meet consumer demand. As with in vivo methods,
it is desirable that methods of assessing carcass composition ex vivo be precise, accurate over time and
distance and across lambs of varying breeds, sexes and ages. However, cost, ease of measurement and
speed of methods are crucial. Highly precise methods such as NMR and CT would be too slow for online use (Forrest, 1995), even if they were cost effective. Other methods, such as dissection of small
regions of the carcass (Timon and Bichard, 1965; Kempster et al., 1976), while precise and requiring
little expenditure for capital equipment, would be slow, labour-intensive and result in reduced carcass
marketability/value. A summary of currently available inexpensive manual, nondestructive methods of
carcass evaluation ex vivo is shown in Table 3, while methods requiring sophisticated equipment are
shown in Table 4.
3.1. Subjective measurements
Lamb carcass composition is commercially evaluated in many countries (Australia, USA, South
Africa, UK) by subjective assessment of fatness or conformation (Jones et al., 1992). Even in New
Zealand where a system for objective measurement is in place, body composition/fatness of lambs is
usually subjectively evaluated (Kirton et al., 1992). Conformation and fatness are related, as lamb
carcasses with good conformation are generally fatter than those with poor conformation (Kirton and
Pickering, 1967; Kempster et al., 1981; Stanford et al., 1995a). The only exceptions to this are wellmuscled individuals, breeds such as the Texel (Kempster et al., 1987; Leymaster and Jenkins, 1993) or
genetic mutations such as the Callipyge (Busboom et al., 1996).
The utility of subjective methods for evaluating carcass composition has been largely dependent on the
population of lambs evaluated. When lambs have been of varying breed types, ages or sizes, subjective
assessments have been useful predictors of carcass composition (Kirton et al., 1992; Jones et al., 1993;
Stanford et al., 1997), but have had little utility in more uniform lamb populations (Kempster et al.,
1981; Horgan et al., 1995). However, even in highly diverse lamb populations, subjective evaluations
alone have been marginal predictors of carcass composition (R2=0.61, RSD=1.71% for the best
equation including GR measurement and subjective conformation predicting saleable meat yield vs.
R2=0.55, RSD=1.84% for the same equation excluding conformation; Jones et al., 1993). A global
change to objective evaluation and more precise methods for assessing lamb carcass composition
would be the first step in identifying and rewarding production of the lean yet well-muscled lamb
needed to meet consumer demand.
3.2. Carcass weight, specific gravity and dressing percentage
Fat has a lower density than other carcass components and the determination of carcass specific
gravity [weight in air/(weight in air-weight underwater)] was the subject of early investigations
(Kirton and Barton, 1958; Timon and Bichard, 1965). In these studies, carcass specific gravity was
found to be equal to dressing percentage (hot carcass weight (HCW)/live weight) as a predictor of
carcass fat content, although specific gravity was not deemed sufficiently accurate for individual
carcass determination due to a high RSD (2.98 to 3.2 for % carcass fat) and its reduced accuracy at
lower levels of fatness. Comparing carcass weight, specific gravity and dressing percentage, Barton
and Kirton (1958) found carcass weight to be the superior predictor of carcass fat content in sheep as it
was not subject to as many errors in measurement as was specific gravity and was not influenced by
272
variations in gut fill as was dressing percentage. More recently, Kirton et al. (1985) reported that
although the New Zealand lamb grading system was based on HCW, adding HCW into a regression
after Grade Rule (GR) (Kirton and Johnson, 1979) was in the model did not increase R2 for any
measure of carcass composition by more than 0.03. Similarly, Jones et al. (1993) reported that HCW
was not a significant predictor of saleable meat yield in lambs. However, lamb carcasses are routinely
valued based on HCW and HCW is available with limited expense. Accordingly, use of carcass
composition predictors other that HCW are warranted only if they improve the accuracy of prediction
compared to use of HCW alone.
3.3. Linear measurements¯¯GR and others
Many attempts have been made to find rapid, inexpensive and accurate methods of estimating carcass
composition from carcass dimensions and fat or muscle depths at various locations on the lamb
carcass (Palsson, 1939; Timon and Bichard, 1965; Kirton and Johnson, 1979; Bennett et al., 1988;
Stanford et al., 1997). However, there is not one ideal measurement or set of measurements. Some
measurements primarily identify carcass composition differences associated with factors such as sex,
breed or weight and are useful in heterogenous populations, although the same measurements may be
less useful for discriminating among uniform populations of sheep (Bennett et al., 1988).
Palsson (1939) was first to identify a number of sheep carcass measurements, some of which remain in
use today. These include 'A', the maximum width of the longissimus muscle; 'B', the maximum depth
of the longissimus muscle measured at right angles to 'A'; 'C', the depth of backfat over 'B'; 'J' the
greatest depth of backfat over the rib. Carcasses must be cut to determine these measurements, unless
advanced imaging technologies are employed. Currently, many national ultrasound programs for lamb
carcass quality improvement utilize 'C' and/or 'B' at various locations on the carcass (Table 2). Palsson
(1939) also described numerous external carcass dimensions including carcass length 'L', length of the
leg 'T' and depth of the leg 'H'. However, Kempster (1981) concluded that carcass dimensions are poor
individual predictors of carcass composition, a finding supported by Bennett et al. (1988). In contrast,
use of a number of carcass dimension measurements, although too time-consuming for on-line use,
were good predictors of both saleable meat yield (R2=0.61, RSD=1.3%) and % of the leg primal
(R2=0.80, RSD=0.6%) in lamb carcasses (Stanford et al., 1997).
GR is a measurement of total tissue thickness between the surface of a lamb carcass and the 12th rib at
a point 11 cm from carcass mid-line (Kirton and Johnson, 1979). GR can be measured in intact
carcasses by use of a sharpened metal ruler (Kirton et al., 1984) or by a variety of optical probes
(Jones et al, 1992; Hopkins et al., 1995; Kirton et al., 1995). GR has been shown to explain 40 to 76%
and 44 to 72% of the variation in carcass fat and lean, respectively (Kirton et al., 1985; Jones et al.,
1992). Comparing GR to other carcass measurements, Kirton and Johnson (1979) reported that GR
was as accurate as 'C' for prediction of carcass fat. The superiority of GR over longissimus muscle
area and 'B' for prediction of carcass composition was confirmed by Jones et al. (1992) in accord with
Kempster (1981) who concluded that area and depth of the longissimus muscle were of limited utility
in prediction of lamb carcass composition.
3.4. Optical probes
Optical probes objectively measure fat and muscle depths and are routinely used to measure GR
according to New Zealand export lamb grading regulations (Price, 1995). Optical probes consist of a
light-emitting diode which illuminates the meat from under an optical window. Detectors respond to
an increase in reflected light when the optical window passes from muscle to fat as the probe is
withdrawn from the carcass (Swatland, 1995). As reported by Kirton et al. (1995), probes currently
available for prediction of lamb carcass composition include the Hennessy Grading Probe (Hennessy
Grading Systems, Auckland, NZ), the AUS-Meat Sheep Probe (SASTEK, Hamilton, Queensland,
Australia), the Swedish FTC lamb probe (FTC Sweden, Upplands, Väsby, Sweden) and the Ruakura
GR Lamb Probe (Hamilton, NZ). Only the AUS-Meat probe is capable of functioning at chain speeds
of nine to 10 carcasses per minute (Cabassi, 1990; Hopkins et al., 1995). On hot carcasses, optical
probes have measured GR with accuracy equivalent to a manual GR knife/ruler (Jones et al., 1992;
Hopkins et al., 1995). In a comparison of all commercially available optical probes (Kirton et al.,
1995), manual GR probes on chilled carcasses were found to account for a higher percentage of
variation in carcass fat content (59%) than optical probes on hot carcasses (49%). However, the
increased accuracy of manual as compared to optical probes in the study of Kirton et al. (1995) is
273
likely due to improvements in the accuracy of prediction of carcass composition in cold as compared
to warm carcasses as noted by Chadwick and Kempster (1983) and Jones et al. (1992).
3.5. Video image analysis
Where time and labour requirements restrict, usually to one, the number of manual or optical probe
measurements that can be made under commercial conditions, VIA allows for the automated
collection of multiple carcass dimension and colour measurements (Jones et al., 1995). Wood et al.
(1991) described VIA as a system capable of objectively measuring carcass conformation, with
equipment including a video camera, controlled lighting of the carcass and computer/software
necessary to digitize the video image. Although evaluations of VIA for prediction of carcass
composition in lambs are limited, early indications as to its utility are promising. In lambs of uniform
age and breed, Horgan et al. (1995) reported that VIA shape variables for cold carcasses, carcass
weight and sex could predict saleable meat yield with greater accuracy (R2=0.16, RSD=0.89 kg) than
carcass weight, sex and the current subjective system used in the UK (R2=0.04, RSD=0.95 kg). For
lambs of diverse ages, breeds and sexes, VIA colour and shape variables for warm carcasses with
carcass weight increased accuracy of prediction of saleable meat yield (R2=0.71, RSD=14 g kg-1)
compared to GR and subjective conformation scores (R2=0.52, RSD=18 g kg-1) used in the present
Canadian Classification System for lamb (Stanford et al., 1998). As the VIA equipment required for
evaluation of lamb carcasses is approximately equal in value to the yearly wages of a livestock grader,
VIA shows potential as an objective, accurate, yet cost-effective method of evaluation of lamb carcass
composition.
3.6. Total body electrical conductivity
Lean tissue is approximately 20 times more conductive of electricity than fat or bone because of
higher concentrations of water and electrolytes (Funk, 1991). Based on this principle, carcasses passed
through an electromagnetic coil generate a relative energy absorption curve. Areas under parts of the
curve and differences between positions on the curve are therefore related to lean mass (Swatland,
1995). Although this technology has been used on live pigs (EMME electronic meat measuring
equipment, EMME, Phoenix, AZ), movement of the pigs led to inaccurate estimates of lean content
(Forrest et al., 1991). Using TOBEC (Meat Quality, Springfield IL), electrical conductivity
measurements and carcass length were able to predict % carcass lean in lambs with a reasonable
degree of accuracy (R2=0.78, RSD=1.71%), although carcass position within the scanner, carcass
temperature and geometric orientation of the carcass were recognized as sources of error (Berg et al.,
1994). As carcass geometry and temperature cannot always be controlled, TOBEC technology is
currently most applicable to evaluation of lean content in boxed meat (Eustace and Thornton, 1991)
and in pig carcasses (Gu et al., 1992) which have less variation in inter/intramuscular fat content and
size/shape than beef or lamb carcasses.
3.7. Bioelectrical impedance analysis (BIA)
Another method dependant on transmission of electric current through a carcass, bioelectrical
impedance measures are related to conductor length, cross-sectional area and signal frequency; leading
to the hypothesis that a fat lamb should impede the transmission of electrical current to a larger extent
than a lean lamb (Berg et al., 1996). Two pairs of transmitter and detector electrodes (21 gauge
needles) are located in an anterior to posterior sequence along the full length of the animal's back
(Swatland, 1995). Impedance measurements include resistance and reactance which are calculated by
transmitting alternating current between the outer two electrodes and measuring the voltage drop
between the inner two detector electrodes (Berg and Marchello, 1994). Jenkins et al. (1988) reported
that carcass weight and resistance accounted for 93.6% of the variation in fat-free soft tissue, although
carcass weight alone accounted for 91.1% of the variability. Accordingly, Berg et al. (1996) concluded
that bioelectrical impedance measurements along with body length and live weight did not predict
proportional carcass yield with a high degree of accuracy (R2=0.296, RSD=2.53, for % boneless
closely trimmed primal cuts). An advantage to bioelectrical impedance is that measurements can be
made in live animals as well as carcasses (Berg and Marchello, 1994; Berg et al., 1996), although the
invasiveness of the procedure as well as its low precision would not favourably compare to other
relatively inexpensive in vivo methods such as ultrasound.
4. Conclusions
As part of the impetus to meet consumer demand and increase consumption of lamb, a change has to
be made from subjective to objective evaluation of body and carcass composition. Even though
274
subjective methods are the most rapid and inexpensive techniques for evaluation of body and carcass
composition, the sheep industry, if it is to survive in the long-term, can no longer afford the error
inherent in subjective predictions. Continuance of traditional, subjective methods for evaluation of
body and carcass composition, will not reverse the current decline in lamb consumption compared to
other meats.
In live sheep, the high cost/limited access of some of the more precise methods for evaluation of body
composition such as X-ray CT or NMR will make ultrasound the method of choice, despite its
relatively low precision. In countries where the size of the sheep industry warrants greater capital
expenditure by private industry, methods such as X-ray CT, NMR or others are or will likely become
available for selection of breeding stock.
Development of improved methods for carcass composition evaluation is of little utility unless these
methods are eventually adopted by the meat industry. Even in New Zealand, the global leader in lamb
merchandising, GR measurements are usually made subjectively due to high slaughter-chain speeds.
Where wholly subjective methods are currently used, adoption of an objective measurement such as
GR would be a first step towards more precise evaluation of lamb carcasses. The next step would be
use of methods with higher precision than GR such as VIA, with added advantages of use on-line on
warm carcasses, facilitating the early channelling of carcasses to their most profitable and/or
consumer-desired endpoints.
References
Allen, P., 1990. New approaches to measuring body composition in live meat animals. In: Wood, J.D.,
Fisher, A.V. (Eds.), Reducing Fat in Meat Animals. Elsevier, London, UK, pp. 201¯247.
Alliston, J.C., 1980. Evaluation of carcass quality in the live animal. In: Haresign, W. (Ed.), Sheep
Production. Butterworth, London, UK, pp. 75¯96.
Atkins, K.D., Murray, J.I., Gilmour, A.R. and Luff, A.L., 1991. Genetic variation in liveweight and
ultrasonic fat depth in Australian Poll Dorset sheep. Aust. J. Agric. Res. 42, pp. 629¯640
Barton, R.A. and Kirton, A.H., 1958. Carcass weight as an index of carcass components with
particular reference to fat. J. Agric. Sci. 50, pp. 331¯334
Beermann, D.H., Robinson, T.F. and Hogue, D.E., 1995. , Impact of composition manipulation on
lean lamb production in the United States. J. Anim. Sci. 73, pp. 2493¯2502
Bennett, G.L., Meyer, H.H. and Kirton, A.H., 1988. Effect of average carcass fat concentration on
correlations among lamb carcass measurements. Anim. Prod. 47, pp. 369¯377
Berg, E.P. and Marchello, M.J., 1994. Bioelectrical impedance analysis for the prediction of fat-free
mass in lambs and lamb carcasses. J. Anim. Sci. 72, pp. 322¯329
Berg, E.P., Forrest, J.C., Thomas, D.L., Nusbaum, N. and Kauffman, R.G., 1994. , Electromagnetic
scanning to predict lamb carcass composition. J. Anim. Sci. 72, pp. 1728¯1736
Berg, E.P., Neary, M.K., Forrest, J.C., Thomas, D.L. and Kauffman, R.G., 1996. Assessment of lamb
carcass composition from live animal measurement of bioelectrical impedance or ultrasonic tissue
depths. J. Anim. Sci. 74, pp. 2672¯2678
Brash, L.D., Forgarty, N.M., Gilmour, A.R. and Luff, A.F., 1992. Genetic parameters for live weight
and ultrasonic fat depth in Australian meat and dual purpose sheep breeds. Aust. J. Agric. Res. 43, pp.
831¯841
Busboom, J.R., Snowder, G.D., Cockett, N.E., 1996. Synopsis of the heavy muscled (Callipyge) lamb
symposium. February 15th and 16th, Salt Lake City, UT.
Butterfield, R., 1988. New Concepts of Sheep Growth. Griffin Press, Australia, 168 pp.
Cabassi, P., 1990. The prediction of lamb carcass composition from objective measurements of fatness
taken at slaughter chain speed with the Aus-Meat sheep probe. Proc. Aust. Soc. Anim. Prod. 18, pp.
164¯167
Cameron, N.D. and Bracken, J., 1992. Selection for carcass lean content in a terminal sire breed of
sheep. Anim. Prod. 54, pp. 379¯388
Cameron, N.D. and Smith, C., 1985. Estimation of carcass leanness in young rams. Anim. Prod. 40,
pp. 303¯308
Chadwick, J.P. and Kempster, A.J., 1983. The estimation of beef carcass composition from
subcutaneous fat measurements taken on the intact side using different probing instruments. J. Agric.
Sci. 101, pp. 241¯248
275
Cunningham, N.L., Carpenter, Z.L., King, G.T., Butler, O.D. and Shelton, J.M., 1967. Relationship of
linear measurements and certain carcass characteristics to retail value, quality and tenderness of ewe,
wether, and ram lambs. J. Anim. Sci. 26, pp. 683¯687
Cuthbertson, A., Croston, D., Jones, D.W., 1984. In vivo estimation of lamb carcass composition and
lean tissue growth rate. In: Lister, D. (Ed.), In Vivo Measurement of Body Composition in Meat
Animals. Elsevier, London, pp. 163¯166.
Dalsky, G.P., Kraemer, W., Zetterlund, A.E., Conroy, B., Fry, A., Judge, J.O., Smith, J., 1990. A
comparison of methods to assess body composition. Proc. Am. College of Sports Med. Salt Lake City,
UT, May 22¯25.
Davis, G.H., Fennessy, P.F., 1996. The organisation of the sheep industry in New Zealand. Proc. Int.
Symp. on the Sheep Industry, October 11¯12. Sherbrooke, Quebec, pp. 37¯46.
Dodd, C.J., Purchas, R.W., Bennett, G.L., 1986. Lean Lamb Selection, A Manual of Procedures. MAF
Advisory Services Division, Wellington, New Zealand.
Economic Research Service, 1994. Red Meats Yearbook, US Dept. Agric. Statistical Bulletin 885.
Edwards, J.W., Cannell, R.C., Garrett, R.P., Savell, J.W., Cross, H.R. and Longnecker, M.T., 1989.
Using ultrasound, linear measurements and live fat thickness estimates to determine the carcass
composition of market lambs. J. Anim. Sci. 67, pp. 3322¯3330
Eustace, I.J., Thornton, R.F., 1991. Electromagnetic scanning: evaluation of cartoned meat. Proc.
Symp. Electronic Evaluation of Meat in Support of Value-Based Marketing, March 27¯28. Purdue
Univ., West Lafayette, IN, pp. 113¯122.
Fahmy, M.H., Boucher, J.M., Poste, L.M., Gregoire, R. and Comeau, J.E., 1992. Feed efficiency,
carcass characteristics and sensory quality of lambs with or without prolific ancestry fed diets with
different protein supplements. J. Anim. Sci. 70, pp. 1365¯1374.
Fisher, A.V., 1990. New approaches to measuring fat in the carcasses of meat animals. In: Wood, J.D.,
Fisher, A.V. (Eds.), Reducing Fat in Meat Animals. Elsevier, London, UK, pp. 255¯335.
Forrest, J.C., 1995. New techniques for estimation of carcass composition. In: Morgan Jones, S.D.
(Ed.), Quality and Grading of Carcasses of Meat Animals. CRC Press, Boca Raton, pp. 157¯172
Forrest, J.C., Kuei, C.H., Chen, W., Lin, R.S., Schinckel, A.P., Walstra, P., Kooper, H., Judge, M.D.,
1991. Electromagnetic scanning: carcass evaluation. Proc. Symp. Electronic Evaluation of Meat in
Support of Value-Based Marketing, March 27¯28. Purdue Univ., West Lafayette, IN, pp. 85¯112.
Fortin, A. and Shrestha, J.N.B., 1986. In vivo estimation of carcass meat by ultrasound in ram lambs
slaughtered at average live weight of 37 kg. Anim. Prod. 43, pp. 469¯475
Funk, R., 1991. Electromagnetic scanning: basis and recent advances in technology. Proc. Symp.
Electronic Evaluation of Meat in Support of Value-Based Marketing, March 27¯28. Purdue Univ.,
West Lafayette, IN, pp. 73¯84.
Groeneveld, E., Kallweit, E., Henning, M., Pfau, A., 1984. Evaluation of body composition of live
animals by X-ray and nuclear magnetic resonance computed tomography. In: Lister, D. (Ed.), In Vivo
Measurement of Body Composition in Meat Animals. Elsevier, London, pp. 84¯89.
Groeneveld, E., Henning, M., Kallweit, E., 1989. Growth patterns and carcass evaluation in pigs NMR
measurements. In: Kallweit, E., Henning, M., Groeneveld, E. (Eds.), Application of NMR Techniques
on the Body Composition of Live Animals. Elsevier, New York, pp. 137¯148.
Gu, Y., Schinckel, A.P., Martin, T.G., Forrest, J.C., Kuei, C.H. and Watkins, L.E., 1992. Genotype
and treatment biases in estimation of carcass lean of swine. J. Anim. Sci. 70, pp. 1708¯1718
Hamby, P.L., Stouffer, J.R. and Smith, S.B., 1986. Muscle metabolism and real-time ultrasound
measurement of muscle and subcutaneous adipose tissue growth in lambs fed diets containing a betaagonist. J. Anim. Sci. 63, pp. 1410¯1417
Harrington, G., Kempster, A.J., 1989. Improving lamb carcass composition to meet modern consumer
demand. In: Dyrmundsson, O.R., Thorgeirsson, S. (Eds.), Reproduction, Growth and Nutrition in
Sheep. Agricultural Research Inst., Reykjavik, Iceland, pp. 79¯90.
Harris, J.J., Savell, J.W., Miller, R.K., Hale, D.S., Griffin, D.B., Beasley, L.C. and Cross, H.R., 1990.
A national market basket survey for lamb. J. Food Qual. 13, pp. 453¯465
Hopkins, D.L., Anderson, M.A., Morgan, J.E. and Hall, D.G., 1995. A probe to measure GR in lamb
carcasses at chain speed. Meat Sci. 39, pp. 159¯165
Horgan, G.W., Murphy, S.V. and Simm, G., 1995. Automatic assessment of sheep carcasses by image
analysis. Anim. Sci. 60, pp. 197¯202
276
Houghton, P.L. and Turlington, L.M., 1992. Application of ultrasound for feeding and finishing
animals: a review. J. Anim. Sci. 70, pp. 930¯941
Jenkins, T.G., Leymaster, K.A. and Turlington, L.M., 1988. Estimation of fat-free soft tissue in lamb
carcasses by use of carcass and resistive impedance measurements. J. Anim. Sci. 66, pp. 2174¯2179
Jensen, N.E., 1990. Performance tests of ram lambs 1990. Report 684, National Institute of Animal
Science, Denmark, p. 44.
Jones, S.D.M., 1995. Future directions for carcass assessment. In: Jones, S.D.M. (Ed.), Quality and
Grading of Carcasses of Meat Animals. CRC Press, Boca Raton, USA, pp. 215¯228.
Jones, S.D.M., Walton, J.S., Wilton, J.W. and Szkotnicki, J.E., 1982. The use of urea dilution and
ultrasonic backfat thickness to predict the carcass composition of live lambs and cattle. Can. J. Anim.
Sci. 69, pp. 641¯648
Jones, S.D.M., Jeremiah, L.E., Tong, A.K.W., Robertson, W.M. and Gibson, L.L., 1992. Estimation of
lamb carcass composition using an electronic probe, a visual scoring system and carcass
measurements. Can. J. Anim. Sci. 72, pp. 237¯244
Jones, S.D.M., Robertson, W.M., Price, M.A., 1993. The assessment of saleable meat yield in lamb
carcasses. Int. Congr. Meat Sci. Technol. Calgary, p. 190 (Abstr.).
Jones, S.D.M., Richmond, R.J. and Robertson, W.M., 1995. Instrument beef grading. Meat Focus Int.
4, pp. 59¯62
Jopson, N.B., McEwan, J.C., Dodds, K.G. and Young, M.J., 1995. Economic benefits of including
computed tomography measurements in sheep breeding programmes. Proc. Aust. Assoc. Anim. Breed.
Genet. 11, pp. 194¯197
Kempster, A.J., 1980. Carcass quality and its measurement in sheep. In: Haresign, W. (Ed.), Sheep
Production. Butterworth, London, UK, pp. 59¯74.
Kempster, A.J., 1981. The indirect evaluation of sheep carcass composition in breeding scheme
population studies and experiments. Livest. Prod. Sci. 8, pp. 263¯271
Kempster, A.J., 1984. Cost¯benefit analysis of in vivo estimates of body composition in meat animals.
In: Lister, D. (Ed.), In Vivo Measurement of Body Composition in Meat Animals. Elsevier, New
York, pp. 191¯203.
Kempster, A.J. and Cuthbertson, A., 1977. A survey of the carcass characteristics of the main types of
British lamb. Anim. Prod. 25, pp. 165¯179
Kempster, A.J., Avis, P.R., Cuthbertson, A. and Harrington, G., 1976. Prediction of lean content of
lamb carcasses of different breed types. J. Agric. Sci. Cambridge 86, pp. 23¯34
Kempster, A.J., Croston, D. and Jones, D.W., 1981. Value of conformation as an indicator of sheep
carcass lean content within and between breeds. Anim. Prod. 33, pp. 39¯49
Kempster, A.J., Jones, D.W. and Wolf, B.T., 1986. A comparison of alternative methods for predicting
the carcass composition of crossbred lambs of different breeds and crosses. Meat Sci. 18, pp. 89¯110.
Kempster, A.J., Croston, D., Guy, D.R. and Jones, D.W., 1987. Growth and carcass characteristics of
crossbred lambs by ten sire breeds compared at the same estimated carcass subcutaneous fat
proportion. Anim. Prod. 44, pp. 194¯201
Kirton, A.H. and Barton, R.A., 1958. Specific gravity as an index of the fat content of mutton
carcasses and various joints. New Zealand J. Agric. Res. 1, pp. 633¯641
Kirton, A.H. and Johnson, D.L., 1979. Interrelationship between GR and other lamb carcass fatness
measurements. Proc. New Zealand Soc. Anim. Prod. 39, pp. 194¯201
Kirton, A.H. and Pickering, P.S., 1967. Factors associated with difference in carcass conformation in
lambs. New Zealand J. Agric. Res. 1, pp. 633¯641
Kirton, A.H., Woods, E.G., Duganzich, D.M., 1984. Predicting the fatness of lamb carcasses from
carcass wall thickness measured by ruler or by a total depth indicator (TDI) probe.
Kirton, A.H., Duganzich, D.M., Feist, C.L., Bennett, G.L. and Woods, E.G., 1985. Prediction of lamb
carcass composition from GR and carcass weight. Proc. New Zealand Soc. Anim. Prod. 45, pp. 63¯65
Kirton, A.H., Mercer, G.J.K. and Duganzich, D.M., 1992. A comparison between subjective and
objective (carcass weight plus GR or the Hennessy Grading Probe) methods for classifying lamb
carcasses. Proc. New Zealand Soc. Anim. Prod. 52, pp. 41¯44
Kirton, A.H., Mercer, G.J.K., Duganzich, D.M. and Uljee, A.E., 1995. Use of electronic probes for
classifying lamb carcasses. Meat Sci. 39, pp. 167¯176.
277
Lewis, R.M., Simm, G. and Warkup, C.C., 1993. , Enjoying the taste of lamb. Meat Focus Int. 2, pp.
393¯395.
Leymaster, K.A. and Jenkins, T.G., 1993. Comparison of Texel- and Suffolk-sired crossbred lambs for
survival, growth and compositional traits. J. Anim. Sci. 71, pp. 859¯869.
Leymaster, K.A., Mersmann, H.J. and Jenkins, T.G., 1985. Prediction of the chemical composition of
sheep by use of ultrasound. J. Anim. Sci. 61, pp. 165¯172
Liu, Z., Lirette, A., Fairfull, R.W. and McBride, B.W., 1994. Embryonic adenosine triphosphate:
phosphate diesters ratios obtained with in vivo nuclear magnetic resonance spectroscopy (Phosphorus31): a new technique for selecting leaner broiler chickens. Poultry Sci. 73, pp. 1633¯1641
Mazess, R.B., Barden, H.S. and Olrich, E.R., 1990. Skeletal and body composition effects of anorexia
nervosa. Am. J. Clin. Nutr. 52, pp. 438¯441
McClelland, T.H., Bonaiti, B. and Taylor, C.S., 1976. Breed differences in body composition of
equally mature sheep. Anim. Prod. 23, pp. 281¯293
Miles, C.A., Fursey, G.A.J., Fisher, A.V. and Page, S.J., 1991. , Estimation of lamb carcass
composition from measurements of the speed of ultrasound in the soft tissues of live animals and
carcasses. Meat Sci. 30, pp. 245¯256
Mitchell, A.D., Wang, P.C., Rosebrough, R.W., Elsasser, T.H. and Schmidt, W.F., 1991. Assessment
of body composition of poultry by nuclear magnetic resonance imaging and spectroscopy. Poultry Sci.
70, pp. 2494¯2500
Monin, G., Renou, J.P., 1989. Spectroscopy and meat quality. In: Kallweit, E., Henning, M.,
Groeneveld, E. (Eds.), Application of NMR Techniques on the Body Composition of Live Animals.
Elsevier, New York, pp. 121¯133.
Nicol, A.M. and Parratt, A.C., 1984. Methods of ranking two-toothed rams for fat-free carcass growth
rate. Proc. New Zealand Soc. Anim. Prod. 44, pp. 253¯259
Olesen, I. and Husabø, J.O., 1994. Effect of using ultrasonic muscle depth and fat depth on the
accuracy of predicted phenotypic and genetic values of carcass traits on live ram lambs. Acta Agric.
Scand., Sect. A. Anim. Sci. 44, pp. 65¯72
Orme, L.E., 1963. , Estimating composition from linear measurements, live probe and body weight.
Ann. New York Acad. Sci. 110, pp. 307¯310
Orme, L.E., Christian, R.E. and Bell, T.D., 1962. Live animal and carcass indices for estimating the
carcass composition in lambs. J. Anim. Sci. 21, p. 666 Abstr.
Palsson, H., 1939. , Meat qualities in the sheep with special reference to Scottish breeds and crosses. J.
Agric. Sci. 29, pp. 544¯625
Parratt, A.C. and Simm, G., 1987. Selection indicies for terminal sires to improve lean meat
production from sheep in the United Kingdom. Anim. Prod. 45, pp. 87¯96
Pedersen, O.K., 1989. Current and future projects. In: Kallweit, E., Henning, M., Groeneveld, E.
(Eds.), Application of NMR Techniques on the Body Composition of Live Animals. Elsevier, New
York, p. 159.
Price, M.A., 1995. Development of carcass grading and classification systems. In: Morgan Jones, S.D.
(Ed.), Quality and Grading of Carcasses of Meat Animals. CRC Press, Boca Raton, pp. 173¯199.
Puntilla, M.L., 1986. Experiences using ultrasound scanner for evaluation of body composition in
young Finnsheep rams. The 37th Ann. Meeting of EEAP, Budapest.
Puntilla, M.L., Nylander, A., 1993. Possibilities to predict body composition from live animals in pure
and crossbred Finnsheep. The 43rd Ann. Meeting of the EAAP.
Purchas, R.W. and Beach, A.D., 1981. Between operator repeatability of fat depth measurements
made on live sheep and lambs with an ultrasonic probe. New Zealand J. Exp. Agric. 9, pp. 213¯220
Robelin, J., 1984. Prediction of body composition in vivo by dilution technique. In: Lister, D. (Ed.), In
Vivo Measurement of Body Composition in Meat Animals. Elsevier, New York, pp. 106¯112.
Robelin, J. and Theriez, M., 1981. Relationship between water and lipid content of empty body weight
in growing cattle and sheep. Reprod. Nutr. Dev. 21, pp. 335¯353
Ross, R., Leger, L., Guardo, R., de Guise, J., Pike, B.G. and de Guise, J., 1991. Adipose tissue volume
measured by magnetic resonance imaging and computerized tomography in rats. J. Appl. Phys. 70, pp.
2164¯2172
Russel, A.J.F. 1995. Ultrasonography and body composition in sheep. In: Goddard, P.J. (Ed.),
Veterinary Ultrasonography. CAB International, Wallingford, UK, pp. 315¯324.
278
Sehested, E., 1984. Computerized tomography of sheep. In: Lister, D. (Ed.), In Vivo Measurement of
Body Composition in Meat Animals. Elsevier, New York, pp. 69¯74.
Simm, G., 1983. The use of ultrasound to predict the carcass composition of live cattle¯¯a review.
Anim. Breed. Abstr. 51, pp. 853¯875
Simm, G. 1992. Selection for lean meat production in sheep. In: Speedy, A.W. (Ed.), Progress in
Sheep and Goat Research. CAB International, Wallingford, UK, pp. 193¯215.
Simm, G., Young, M.J. and Beatson, P.R. 1987. An economic selection index for lean meat
production in New Zealand sheep. Anim. Prod. 45, pp. 307¯316
Simm, G., Dingwall, W.S., Lewis, R.M. 1993. Genetic improvement of meat production. Proc. Third
Int. Sheep Vet. Conf. Edinburgh, June 27¯July 1.
Standal, N., 1984. Establishment of a CT facility for farm animals. In: Lister, D. (Ed.), In Vivo
Measurement of Body Composition in Meat Animals. Elsevier, New York, pp. 43¯51.
Stanford, K., Clark, I. and Jones, S.D.M. 1995. Use of ultrasound in prediction of carcass
characteristics in lambs. Can. J. Anim. Sci. 75, pp. 185¯189
Stanford, K., McAllister, T.A., MacDougall, M. and Bailey, D.R.C. 1995. Use of ultrasound for
prediction of carcass characteristics in Alpine goats. Small Rumin. Res. 15, pp. 195¯201
Stanford, K., Woloschuk, C.M., McClelland, L.A., Jones, S.D.M. and Price, M.A. 1997. Comparison
of objective external carcass measurements and subjective conformation scores for prediction of lamb
carcass quality. Can. J. Anim. Sci. 77, pp. 217¯223
Stanford, K., Richmond, R.J., Jones, S.D.M., Robertson, W.M., Price, M.A. 1998. Video image
analysis for classification of lamb carcasses. Anim. Sci., submitted.
Statistics Canada, 1995. Livestock Statistics. Publication No. 23-603E.
Stouffer, J.R. 1988. Ultrasonics for live lamb and carcass evaluation. Methods to Improve the Lean
Yield of Lamb. NC-III Technical Committee for Increased Efficiency of Sheep Production
Symposium, Denver, CO, pp. 26¯30.
Streitz, E., Baulain, U. and Kallweit, E. 1995. Investigation of body composition of growing lambs by
means of magnetic resonance imaging. Zuchtungskunde 67, pp. 392¯403
Swatland, H.J. 1995. On-Line Evaluation of Meat. Technomic, Lancaster, PA, p. 347.
Taylor, C.S., 1965. , A relation between mature body weight and time taken to mature in mammals.
Anim. Prod. 7, pp. 203¯220
Thonney, M.L., Taylor, C.S., Murray, J.I. and McClelland, T.H., 1987. Breed and sex differences in
equally mature sheep and goats: II. Body components at slaughter. Anim. Prod. 45, pp. 261¯276
Timon, V.M. and Bichard, M., 1965. Quantitative estimates of lamb carcass composition: III. Carcass
measurements and a comparison of the predictive efficiency of sample joint composition, carcass
specific gravity determinations and carcass measurements. Anim. Prod. 7, pp. 189¯201
Vangen, O., 1989. X-Ray CT for body composition. In: Kallweit, E., Henning, M., Groeneveld, E.
(Eds.), Application of NMR Techniques on the Body Composition of Live Animals. Elsevier, New
York, pp. 91¯99.
Wang, J., Heymsfield, S.B., Aulet, M., Thorton, J.C. and Pierson, R.N., 1989. Body fat from body
density: underwater weighing vs. dual-photon aborptiometry. Am. J. Phys. 256, pp. E829¯E834
Ward, C.E., Trent, A. and Hildebrand, J.L., 1995. Consumer perception of lamb compared with other
meats. Sheep Goat Res. J. 11 2, pp. 64¯70
Wells, P.N.T., 1984. Introduction to imaging technology. In: Lister, D. (Ed.), In Vivo Measurement of
Body Composition in Meat Animals. Elsevier, New York, pp. 25¯35.
Wolf, B.T., Smith, C., 1983. Selection for carcass quality. In: Haresign, W. (Ed.), Sheep Production.
Butterworth, London, pp. 493¯514.
Wood, J.D., Newman, P.B., Miles, C.A., Fisher, A.V., 1991. Video image analysis: comparisons with
other novel techniques for carcass assessment. Proceedings of the Symposium Electronic Evaluation
of Meat in Support of Value-Based Marketing, March 27-28. Purdue University, IN, pp. 145¯169.
279
I.5.1.7. COMPOSICIÓN QUIMICA DE LA CANAL
La canal se pica y mediante análisis químico se determina el contenido en proteínas,
lípidos y cenizas.
1.6. CALIDAD
Son muchos los factores que inciden en la calidad
CALIDAD DEL TEJIDO ADIPOSO
A la hora de hablar de calidad del tejido adiposo, debemos distinguir tres tipos:
nutricional, organoléptica y tecnológica.
La calidad nutricional viene determinada por su capacidad para aportar los nutrientes
necesarios al consumidor, tanto para su conservación como para la salud. El tejido
adiposo provee una serie de ácidos grasos esenciales (linoléico, C18:1, y linolénico,
C18:3) que no pueden ser sintetizados por el organismo. Igualmente, las
recomendaciones nutricionales indican un descenso en la cantidad de lípidos
ingeridos, especialmente de ácidos grasos saturados, en favor de los ácidos grasos
poli-insaturados.
La calidad organoléptica del tejido adiposo viene determinada por el color, flavor y
textura. El color normal de la grasa, blanco a cremoso, depende de la composición
en ácidos grasos, ya que un elevado porcentaje de insaturados conduce a un color
oscuro o grisáceo. Este fenómeno es corriente en animales jóvenes en los que los
lípidos de reserva son relativamente insaturados. Además puede adquirir colores
anormales (amarillento, anaranjado, grisáceo). El color anaranjado suele deberse a
la peroxidación de los ácidos grasos poli-insaturados
Generalmente, el color amarillento de la grasa subcutánea viene determinado por:
-acumulación excesiva de carotenoides: la causa es mal conocida ya que se conoce
poco del metabolismo de degradación de estas sustancias. Podemos formular varias
hipótesis:
1) un aporte excesivo puede sobrepasar la capacidad del animal para
metabolizar estas sustancias
2) una alteración del metabolismo de su degradación por ausencia o
deficiencia de enzimas intestinales o hepáticas
3) un origen genético: Baker et al (19859 han señalado que el color
amarillento de la grasa es debido en parte a la acción de un gen mayor recesivo,
causante de un déficit en las enzimas que intervienen en la oxidación de los
carotenoides.
-acumulación excesiva de bilirrubina: derivada del metabolismo de la hemoglobina,
el exceso en la grasa subcutánea puede ser debido a una ictericia consecuente a
una hemólisis importante o a problemas hepáticos.
La coloración grisácea-rojiza de la grasa subcutánea puede deberse a:
-variación en la reflexión lumínica consecuente a la menor firmeza de la grasa
-acumulación excesiva de pigmentos hemínicos
280
-formación de productos coloreados por peroxidación de grasas insaturadas.
El flavor de la grasa puede modificarse por:
-oxidación de los ácidos grasos insaturados que lleva a la producción de aldehídos y
cetonas responsables de malos olores.
-presencia de malos olores en la fracción insaponificable de los lípidos.
La textura, determinada por la cantidad de colágeno y composición y disposición de
los acúmulos grasos, puede integrarse en la calidad tecnológica.
La calidad tecnológica corresponde a la capacidad de mantener sus características
durante la transformación y conservación del producto. Las características que más
influyen en la calidad tecnológica son: consistencia, cohesión y sensibilidad a la
oxidación. La consistencia depende principalmente de la trama de colágeno,
cantidad y composición de los lípidos y contenido en agua. La escasez de trama de
colágeno, un elevado contenido en agua y/o una elevada proporción de ácidos
grasos insaturados (de menor punto de fusión) reducen la firmeza del tejido adiposo,
más cuando aumenta la temperatura.
El tiempo de conservación del tejido adiposo depende grandemente de la tasa de
oxidación, favorecida por el mayor contenido en agua e índice de insaturación de los
ácidos grasos; actividad que aumenta con la temperatura.
Factores de variación de la cantidad y composición del tejido adiposo
Las características del tejido adiposo dependen fundamentalmente de:
1.- localización anatómica: la composición y estructura del tejido adiposo varían
según el tipo de depósito (subcutáneo, intermuscular, intramuscular), así como por la
localización: en el cerdo, la grasa subcutánea tiene distinta composición en el dorso
que en la barriga, y también hay diferencias entre la capa externa y la interna (la
externa contiene mayor cantidad de agua y menos lípidos). Las características del
tejido adiposo varían tanto entre localizaciones anatómicas que podrían
considerarse como tejidos diferentes.
2.- adiposidad: conforme aumenta la cantidad de grasa en un depósito adiposo
disminuye la cantidad de agua y, por tanto, aumenta el tenor en lípidos. Así mismo,
varia el grado de insaturación de los ácidos grasos, ya que a medida que aumenta la
adiposidad siendo menor en los animales grasos que en los magros como resultado
de la dilución de los ácidos grasos poli-insaturados en el seno de lípidos de origen
endógeno o exógeno.
3.- el tipo sexual: los depósitos grasos de los machos contienen mayor cantidad de
agua y menor de lípidos que las hembras. El sexo incide en el potencial lipogénico,
más elevado en las hembras. Este hecho incide en la composición química de los
tejidos adiposos, de manera que a igualdad de peso vivo y adiposidad, el grado de
insaturación es mayor en los machos que en las hembras.
4.- Nivel de alimentación: cuando a los animales se les somete a una subnutrición
durante el periodo de engrasamiento se produce una reducción del peso vivo y del
peso de los depósitos adiposos, con una modificación de su composición química,
observándose un aumento en la cantidad de agua y del grado de insaturación,
afectando especialmente a la tasa de ácido linoléico.
281
5.- Composición del alimento: en líneas generales, una ración rica en proteínas
aumenta la tasa de crecimiento y reduce el porcentaje en grasa, efecto mas notorio
en monogástricos que en rumiantes. Por el contrario, el aumento de tenor en lípidos
de la ración conlleva un aumento del espesor de los depósitos subcutáneos o un
aumento de la adiposidad del animal, si bien reduce el potencial de actividad
lipogénica como consecuencia de una disminución del aporte de glucosa.
6.- efecto específico de algunos nutrientes: además de la cantidad y proporción de
lípidos en la ración, influye la composición de ésos lípidos, principalmente en
monogástricos. En éstos, el aumento en contenido en ácido linolénico, del grado de
insaturación y de la longitud de la cadena de los ácidos grasos, produce un aumento
de la adiposidad corporal y del potencial de síntesis de lípidos. Esto no suele ocurrir
en rumiantes ya que los ácidos grasos de la ración son hidrolizados por las bacterias
del rumen.
7.- vitaminas y minerales: en general, el tejido adiposo no posee antioxidantes, de
ahí que la inclusión de estos agentes en la dieta tenga un efecto beneficioso en las
características tecnológicas de la grasa. La carencia en biotina suele producir un
aumento de la relación monoinsaturados/saturados al limitarse la síntesis de novo
de ácidos grasos. La suplementación con cobre reduce el tenor en ácido estearico y
palmítico, del punto de fusión y aumento de ácidos grasos insaturados de cadena
larga.
8.- somatotropina: la administración exógena de este factor de crecimiento produce
una mejora espectacular de la eficiencia alimentaria, de la tasa de crecimiento y una
disminución de la tasa de deposición de ácidos grasos. Como ya hemos visto con
anterioridad, la disminución de la adiposidad influye en la composición de los
depósitos grasos (aumenta el contenido en agua y disminuye el de lípidos) al tener
un efecto negativo sobre la capacidad lipogénica de la insulina, aumentando a la vez
el grado de insaturación de los ácidos grasos.
9.- beta-agonistas: modifican las rutas metabólicas de los alimentos, orientándolas a
la producción de tejidos magros en detrimento del tejido adiposo.
10.- factores ambientales: principalmente afecta la temperatura. A medida que
disminuye la temperatura aumentan las necesidades de mantenimiento, por lo que a
igualdad de nivel nutritivo, desciende el contenido en grasa de los animales.
Las temperaturas elevadas influyen en la composición en ácidos grasos de algunos
depósitos adiposos. La temperatura disminuye el nivel de ácidos grasos insaturados,
a la vez que aumenta la tasa de saturados y poli-insaturados.
CALIDAD DEL MÚSCULO
Cuando se sacrifica el animal, los músculos sufren una transformación compleja que
los convierte en carne, mediante una serie de procesos enzimáticos (acción de las
proteasas endógenas) y físico-químicos (descenso del pH y aumento de la presión
osmótica).
El músculo tiene como principal misión la contracción, para lo cual requiere, entre
otros elementos, de energía tanto para realizar dicha contracción como para el
mantenimiento de la integridad funcional de las células musculares. Dicha energía la
obtiene a través del ATP gracias al metabolismo de los ácidos grasos (almacenados
principalmente como triglicéridos) y de la glucosa (almacenada como glucógeno);
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siendo utilizados en primera instancia los ácidos grasos y la glucosa libre,
empleándose el glucógeno cuando se requiere mayor cantidad de energía.
Mediante glicólisis, el glucógeno libera moléculas de glucosa-1fosfato, que tras
fosforilización y decarboxilación se liberan ATP y se obtiene ácido pirúvico. El
proceso de obtención de ATP requiere condiciones aeróbicas. La glicólisis acontece
en el sarcoplasma, mientras que la fosforilización y carboxilación oxidativas tienen
lugar en la mitocondria.
Bajo condiciones anaeróbicas (tras la muerte) sólo acontece la glicólisis, por lo que
el ácido pirúvico es transformado en ácido láctico. En estas condiciones, los ATP
sólo pueden ser regenerados por rotura del glucógeno, por lo que se produce una
acumulación de ácido láctico, lo que a su vez produce el descenso del pH: desde
valores próximos a 7,0-7,2 a 5,4-5,8. Este proceso de acidificación tiene una
duración de 10-15 minutos (aves) a 4-8 horas (cerdos) o 15-36 horas (bovinos). El
pH final depende del tipo de fibra muscular y es inversamente proporcional a la
cantidad inicial de glucógeno en músculo. Además, el pH afecta a la estructura de
las células musculares, produciendo la destrucción de la estructura de sus fibrillas, a
la par que detiene la glicólisis.
Debido a la disminución de los niveles de ATP, la actina y la miosina se unen
formando la actomiosina, reduciéndose considerablemente la elasticidad del
músculo. Cada fibra entra en rigor cuando el nivel de ATP en su interior se reduce
por debajo de 5 mmol/kg; ahora bien no todas las fibras entran en rigor mortis a la
vez por lo que la duración de este proceso depende de diversos factores, entre los
que se encuentran: nivel de glicógeno y creatin-fosfato al momento de la muerte y la
tasa de metabolismo post-mortem: si el animal sufrió estrés antes del sacrificio y sus
reservas de glucógeno bajaron, el rigor se produce después; si se refrigera
rápidamente, el proceso se ralentiza. En general, el rigor mortis se instaura a las 4
horas post-mortem en aves y tras 24 horas en bovinos.
Después de un determinado tiempo, el rigor mortis va desapareciendo. Las
miofibrillas se fragmentan y la carne comienza a ser más tierna. Las enzimas
proteolíticas endógenas (proteasas calcio dependientes o calpainas, proteasas
lisosomales o catepsinas) comienzan a actuar tras la liberación de iones calcio, el
descenso del pH y el aumento de la presión osmótica, variando la intensidad de esta
proteolisis con la temperatura de conservación, así como con el tipo de fibra, las
reservas de ATP. La tasa con la que este aumento de la terneza se produce difiere
con la temperatura (se retrasa a medida que aumenta la temperatura) y entre
especies (la máxima terneza se produce en 8 h en aves y tras 10 días en bovinos).
Durante la vida del animal, se produce continuamente una proteolisis enzimática de
la fibrillas musculares, que son repuestas por otras de nueva formación, fase última
que no acontece cuando el animal es sacrificado. Las enzimas implicadas en este
proceso son las catepsinas y las calpainas, de mayor importancia estas últimas en
mamíferos y las primeras en peces y en la carne que se mantiene a altas
temperaturas. Las calpainas se activan por iones calcio y tienen su mayor actividad
a pH neutro o ligeramente básico y son inhibidas por las calpastatinas. Tras el rigor
mortis se rompen las mitocondrias y el retículo sarcoplasmático con lo que aumenta
la concentración de iones calcio y por tanto se activan las calpainas, actividad que
también se favorece por las altas temperaturas y elevado pH.
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Además de estos cambios (acidificación y rigor mortis), se produce un cambio de
color y en la capacidad de retención de agua por acción de la acidificación. Con el
tiempo, el flavor y la jugosidad de la carne aumentan.
El color del músculo viene determinado principalmente por la mioglobina, presente
principalmente en las fibras rojas. Producir músculos con mayor contenido de fibras
blancas aumenta la producción de carne poco coloreada. La estabilidad del color
varía con el tipo contráctil: un elevado porcentaje de fibras βR altera la estabilidad
del color.
La terneza está ligada a la cantidad y calidad del colágeno muscular, y de otra parte
de la desnaturalización de las miofibrillas durante la fase de maduración. Dado que
los animales se sacrifican a edades muy tempranas, el efecto del colágeno sobre la
terneza es muy limitado. Por el contrario el grosor de la miofibrilla si tiene mayor
influencia en la terneza.
CALIDAD DE LA CARNE
El término "CALIDAD", tiene un sentido ambiguo, depende del punto de vista con el
que se analice. La Real Academia de la Lengua la define como: "cualidad, índole o
manera de ser de una persona o cosa".
En sentido estrictamente académico, DUMONT (1972) considera el término calidad
bajo un doble aspecto:
- Calidad "estado" o calidad natural: manera de ser más o menos característica por
su naturaleza, lo que hace que una cosa sea tal como ella es.
- Calidad "valor relativo": aquello que hace que una cosa sea más o menos
recomendable, porque ocupa un lugar más o menos elevado en una escala de valor
práctico.
En cualquier caso la calidad en general, respecto a un producto consumible, puede
definirse como "la satisfacción de los deseos y exigencias del consumidor" y de
forma comparada "la superioridad o excelencia de un producto frente a otro".
Este concepto va a ser valorado por el consumidor, por lo que puede hablarse de
calidad percibida, que es diferente de la calidad real u objetiva. La calidad objetiva
se relaciona con la superioridad técnica de un producto, mientras que en la percibida
inciden criterios subjetivos.
Asimismo el concepto de calidad varía en el tiempo y en el espacio, así no son
iguales los criterios para la calidad del cordero considerado hace 50 años y los
actuales, ni los existentes en Argentina, respecto a los de España (SIERRA, 1977).
El término "calidad de la carne" resulta complejo y difícil de expresar, muestra de ello
es que en la bibliografía se encuentran un gran número de definiciones (BRAY,
1963; PEARSON, 1968; COLOMER, 1973; PIERCE et al., 1974; WANDERSTOCK,
1974; SIERRA, 1977; GARCIA DE SILES, 1978; SAÑUDO, 1980; CUTHBERSON y
KEMPSTER, 1982; FORCADA, 1985; ALLEN, 1991; APARICIO, 1992), pero
podemos intentar definirlo como "la totalidad de las cualidades positivas que
constituyen el valor sensorial y nutritivo de la carne".
La calidad de la carne deriva de la suma e interrelaciones de una gran cantidad de
factores:
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- Intrínsecos o dependientes del propio animal como son: raza, sexo, edad,
nutrición, sanidad, etc., que definen en el matadero la calidad natural inicial de la
canal (composición anatómica, conformación, composición química de los tejidos), y
que posteriormente determinan la de la carne.
- Extrínsecos, que influyen también en la calidad real de utilización con que la carne
llega al consumidor:
* Condiciones pre-sacrificio: transporte hasta el matadero, factores de tensión
(BRISKLEY y LISTER, 1968), tiempo de ayuno, naturaleza y cantidad de la última
ingesta alimenticia,
* Sacrificio: faenado, oreo, maduración, conservación, etc., si bien el proceso de
sacrificio en ovinos no afecta la calidad tanto como en el caso de la carne de cerdo
(TROEGER, 1992),
* Distribución, venta, conservación en el hogar y tratamiento culinarios.
Todas estas circunstancias han sido ampliamente estudiadas por numerosos
autores en diversas especies desde hace ya tiempo (HEDRICK, 1965; KIRTON,
1967; JUDGE, 1969; CERVENKA, 1969; SIERRA, 1973a; BRAZAL y BOCCARD,
1977; SORNAY, 1978; SAÑUDO, 1980; FORCADA, 1985; LÓPEZ, 1988; CALVO,
1990; RONCALÉS et al., 1993).
En el "mundo de la carne" los diferentes actores económicos (productor,
transformador, distribuidor y consumidor) que intervienen en la cadena atribuyen al
término calidad una denominación muy variable, no existiendo uniformidad de
apreciación del valor, ni están todos interesados por las mismas características de
calidad. Todo depende de la influencia que las diversas propiedades del producto,
en sus diferentes etapas, ejerzan sobre sus propios intereses.
CUADRO 5: Valoración relativa de la importancia de distintos factores que determina
la calidad de la canal y de la carne ovina en los distintos niveles de su
comercialización. (SAÑUDO, 1991)
Productor Transformador Distribuidor Comprador
ganadero
Rto canal
**
Peso canal
***
Conformación
*
Engrasamiento
**
pH carne
C.R.A.
Color
Terneza
Sabor
-
matadero
***
**
**
***
**
**
*
-
carnicero
**
*
***
*
*
*
-
venta
*
*
**
*
**
-
Consumidor
consumo
*
**
**
***
***
La calidad es un arma para afrontar la competencia comercial y ningún problema de
producción puede emprenderse sin tener en consideración este aspecto
fundamental. La cantidad, la economía y la competencia de la producción animal
están supeditadas a la calidad, pero a la vez la misma calidad depende de la
economía.
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El primer motor de la calidad está en el animal y el último receptor de la calidad es el
consumidor:
a) Para el productor: los principales criterios de calidad son el coste de producción y
el precio de venta (SIERRA, 1977).
Dada la amplia diversidad en el peso medio de las canales los países comunitarios,
el peso canal es importante para determinar el destino comercial de las canales
ovinas y por tanto el precio.
b) Para la industria: su interés estriba principalmente en ofrecer canales con aquellos
parámetros de calidad que sus clientes desean como puede ser: peso de la canal,
contenido de grasa y conformación, junto con escasas pérdidas en el despiece y
preparación.
c) Para los consumidores: la elección se realiza principalmente por el precio y por su
apariencia, pero bajo diferentes ópticas. El criterio relación calidad/precio, es
significativo (SIERRA, 1977).
Tipos de calidades según el consumidor
Calidad organoléptica o sensorial
Basada en las características, que percibidas por los sentidos en el momento de la
compra o del consumo, influyen en la satisfacción sensorial. Son intrínsecas a la
propia naturaleza de la carne y determinantes en la compra, sin embargo es posible
su medición y modificación.
* vista (aspecto): color, forma, firmeza, tamaño, superficie.
* oído: crujiente, crepitante.
* olfato: olor, aroma.
Sabor o flavor.
* gusto: gusto.
dureza
kinesia
jugosidad
textura
untuosidad
tacto
rugosidad
aspereza
Estos parámetros varían de un mercado a otro.
Calidad bromatológica
Por su contenido en elementos que responden a las diferentes necesidades
metabólicas del organismo: proteínas (aminoácidos esenciales y no esenciales),
glúcidos, lípidos (ácidos grasos saturados e insaturados, colesterol, etc.), vitaminas,
minerales y agua.
Situándonos ya en el cordero, los consumidores buscan hoy la carne magra
separando en el plato el tejido adiposo. La riqueza en triglicéridos del músculo
aumenta con la edad de los animales y está correlacionada con el engrasamiento de
la canal.
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Por otro lado, está demostrado (LÓPEZ FRANCOS, 1991) que las proporciones en
ácidos grasos saturados varían en función del régimen alimenticio del cordero. En el
músculo las proporciones de ácidos grasos saturados varían desde el 59% con
raciones ricas en forrajes al 38% en raciones ricas en concentrados. Las carnes de
nuestros corderos dan pues en la diana de las normas dietéticas que hoy se
imponen: son jóvenes, blancas, magras y con cocientes ácidos grasos
poliinsaturados/saturados muy favorable (CAMPO et al., 1995).
Calidad higiénica
Como cualidad primera ningún alimento debe suponer el más mínimo riesgo para la
salud del consumidor, cualquier defecto en ese sentido impedirá la comercialización
del producto. Agentes bacterianos, microbianos, parasitarios y residuos (pesticidas,
metales pesados, medicamentos, promotores, etc.) son los principales responsables
de alteraciones de la carne (GRACEY, 1989; HERRERA, 1991). Además es
conocido (FRERES y BORIES, 1970; PANTALEON, 1972) que los residuos y
metabolitos de las sustancias adicionales al alimento quedan en el músculo o en la
grasa.
El cordero es considerado un producto natural y verde (KEMPSTER, 1989) ya que
no presenta tan agudamente los problemas asociados con la cría intensiva de
cerdos o las unidades de cebo de terneros. Sin embargo, en nuestro país el cebo
intensivo es la norma, aunque todavía la carne de la especie ovina es por el
momento la menos contaminada.
En el futuro los aspectos ecológicos cobrarán más importancia entre los
consumidores. Se exigirá la promesa de que el cordero sea un producto natural libre
de residuos de antibióticos y sustancias químicas. La única forma de ofrecer
seguridad es que todos los eslabones de la cadena, desde la producción a la
comercialización estén comprometidos en preparar productos de calidad controlada.
Ante la actual situación en materia de utilización de drogas prohibidas en el cebo de
los animales, se impone como una exigencia ineludible la reflexión profunda, el
intercambio de ideas y la toma de decisión para la supresión generalizada de su
utilización.
Por ello, merecen un comentario especial, aunque breve, por lo actual del tema los
estimuladores o promotores del crecimiento. Los que despiertan una mayor
polémica en estos momentos son los β−agonistas (los más comunes son el
clembuterol y el cimaterol) que poseen una estructura análoga a la de la adrenalina.
Actúan además incrementando el rendimiento de la canal, mejorando la morfología,
disminuyendo el contenido graso y elevando el muscular, es decir afectan a la
repartición grasa/proteína. La administración oral de estos productos 0,25-4 ppm
(VANBELLE, 1992) en las raciones conduce a una modificación profunda de la canal
de corderos, bovinos, cerdos y aves. Según HANRAHAN (1987), los resultados
muestran que la administración de cimaterol tiene efecto en la ganancia, en la
eficiencia de la alimentación y la composición de la canal que es deseable para
productores; el contenido graso de la canal y de los depósitos de grasa interna
respecto al peso de la canal se ven reducidos en aproximadamente el 20%. El peso
de los músculos individualmente se ha incrementando de un 10% a un 20%. Sin
embargo parece que aumentan la dureza de la carne. La salud del animal y la
seguridad del consumidor son los problemas preocupantes para resolver. Con los
conocimientos actuales estos productos están prohibidos pues pueden ser
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peligrosos, siendo detectados actualmente a nivel de hígado y de la retina del animal
(ELLIOTT et al., 1993).
Calidad de servicio
Relacionada con la facilidad de utilización por el consumidor, tanto en la compra
como en el cocinado.
En los sistemas de distribución de libre servicio se presentan las carnes al público
comprador en embalajes transparentes resaltando el aspecto de los productos,
principalmente los parámetros que intervienen como caracteres de "reclamo" (y por
tanto de rechazo", si son desfavorables). Así por ejemplo: importancia del color y su
estabilidad, exudados, uniformidad de presentación, etc.
Calidad subjetiva o imaginaria
Características difícilmente mensurables, ligadas a la imagen pre-establecida sobre
un producto, pero que pueden ser determinantes. Así prohibiciones religiosas,
hábitos adquiridos, campañas publicitarias de distintas marcas, incidencia de
noticias de prensa desfavorables (MENENDEZ y RODRÍGUEZ, 1991).
Específicamente en el ganado ovino la realización de campañas publicitarias
tendenciosas sobre su sistema de sacrificio ha perjudicado las exportaciones a
determinados países comunitarios muy sensibilizados con los derechos de los
animales como es el caso de Gran Bretaña (no olvidemos que el Hombre es un gran
consumidor de símbolos y mitos).
Calidad de presentación
Las modificaciones de la misma en los cortes tradicionales o el desarrollo de nuevos
productos con nuevas presentaciones pueden variar la intención de compra y por lo
tanto su calidad.
Calidad funcional o tecnológica
Relacionada con las propiedades de la carne que determinan su aptitud para las
transformaciones y su conservación, dependiendo de su pH final, de su maduración,
de su aptitud a la retención de agua (RENERRE, 1986; JULLA, 1988), etc., factores
todos que varían con el sexo, el acabado, la preparación para el sacrificio, etc.
En todo caso, la garantía de calidad se fundamenta en: sabor, salud, seguridad y
precio adecuado.
RELACIÓN CALIDAD-PRECIO
Se puede considerar la calidad óptima en términos de cantidad máxima que el
consumidor está dispuesto a pagar.
Así, además de la consideración de la calidad total, es fundamental considerar el
precio, es decir la valoración de las distintas calidades en términos monetarios.
A menudo el poder adquisitivo de los consumidores es el factor clave a considerar
para explicar el comportamiento alimenticio de los distintos grupos socioprofesionales.
En consecuencia para cada grupo la calidad puede ser diferente.
CALIDAD NUTRITIVA Y SANITARIA DE LA CARNE
288
La carne es una fuente importante de proteínas ricas en aminoácidos
indispensables, en determinados minerales (hierro hemínico, zinc, etc.) vitaminas y
lípidos. En general, la composición química de lo músculos es muy constante (75 %
de agua, 19-25% de proteínas, 1-2% de minerales, 1-2% de glúcidos y 1-6% de
lípidos), el contenido en lípidos es muy variable: 2,5% en lomo a 17,55 en costillar.
También es muy variable la composición química de dichos lípidos. En los
rumiantes, que hidrogenan en el rumen gran parte de los ácidos grasos insaturados
que ingieren, el contenido intramuscular en ácidos grasos insaturados es
notablemente inferior al de cerdos, aves, conejos, etc. Los músculos de los
rumiantes vienen a contener un 50% de ácidos grasos insaturados y un 50% de
ácidos grasos saturados, predominando el ácido oleico.
En la nutrición humana se recomienda que la relación AGPI / AG sea de 0,45,
mientras que en la carne de bovino y de ovino dicha relación es 0,11-0,15.
ÁCIDOS GRASOS
Los ácidos grasos son ácidos orgánicos monoenoicos, que se encuentran presentes en las grasas,
raramente libres, y casi siempre esterificando al glicerol y eventualmente a otros alcoholes. Son
generalmente de cadena lineal y tienen un número par de átomos de carbono. La razón de esto es que
en el metabolismo de los eucariotas, las cadenas de ácido graso se sintetizan y se degradan mediante la
adición o eliminación de unidades de acetato. No obstante, hay excepciones, ya que se encuentran
ácidos grasos de número impar de átomos de carbono en la leche y grasa de los rumiantes, procedentes
del metabolismo bacteriano del rumen, y también en algunos lípidos de vegetales, que no son
utilizados comúnmente para la obtención de aceites.
Los ácidos grasos como tales (ácidos grasos libres) son poco frecuentes en los alimentos, y además
son generalmente producto de la alteración lipolítica. Sin embargo, son constituyentes fundamentales
de la gran mayoría de los lípidos, hasta el punto de que su presencia es casi definitoria de esta clase de
sustancias.
En la nomenclatura de los ácidos grasos se utilizan con más frecuencia los nombres triviales que los
sistemáticos. La nomenclatura abreviada es muy útil para nombrar los ácidos grasos. Consiste en
una C, seguida de dos números, separados por dos puntos. El primer número indica la longitud de la
cadena hidrocarbonada, mientras que el segundo indica el número de dobles enlaces que contiene.
Ácidos grasos saturados
Dada su estructura, los ácidos grasos saturados son sustancias extremadamente estables desde el punto
de vista químico. La longitud de la cadena va desde los cuatro carbonos del ácido butírico a los 35 del
ácido ceroplástico, y por lo general, contienen un número par de átomos de carbono. Los ácidos grasos
saturados más abundantes son el palmítico (hexadecanoico, o C16:0) y el esteárico (octadecanoico, o
C18:0). Los ácidos grasos saturados de menos de 10 átomos de C son líquidos a temperatura ambiente
y parcialmente solubles en agua. A partir de 12 C, son sólidos y prácticamente insolubles en agua. En
estado sólido, los ácidos grasos saturados adoptan la conformación alternada todo-anti, que da un
máximo de simetría al cristal, por lo que los puntos de fusión son elevados. El punto de fusión
aumenta con la longitud de la cadena.
Los ácidos grasos de cadena impar probablemente derivan de la metilación de un ácido graso de
cadena par. En ellos, la simetría del cristal no es tan perfecta, y los puntos de fusión son menores.
Ejemplos son el ácido propiónico (C3:0), valeriánico (pentanoico, o C5:0) y pelargónico (nonanoico, o
C9:0).
Los lípidos ricos en ácidos grasos saturados constituyen las grasas. Conviene en este punto hacer una
distinción entre los términos lípidos, grasas y aceites. Grasas son aquellos lípidos que son sólidos a
temperatura ambiente, mientras que aceites son aquellos lípidos que son líquidos a temperatura
ambiente. Tanto los aceites como las grasas son lípidos
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Estructura
ACIDOS GRASOS SATURADOS MAS COMUNES
Nombre común
Se encuentra en
C 4:0
butírico
leche de rumiantes
C 6:0
caproico
leche de rumiantes
C 8:0
caprílico
leche de rumiantes, aceite de coco
C 10:0
cáprico
leche de rumiantes, aceite de coco
C 12:0
láurico
aceite de coco, aceite de nuez de palma
C 14:0
mirístico
coco, nuez de palma, otros aceites vegetales
C 16:0
palmítico
abundante en todas las grasas
C 18:0
esteárico
grasas animales, cacao
Ácidos grasos insaturados
Con mucha frecuencia, aparecen insaturaciones en los ácidos grasos, mayoritariamente en forma de
dobles enlaces, aunque se han encontrado algunos con triples enlaces, en un número que va de 1 a 6.
Cuando hay varios dobles enlaces en la misma cadena, estos no aparecen conjugados (alternados),
sino cada tres átomos de carbono. Los que tienen una sola insaturación se llaman monoinsaturados,
quedando para el resto el término de poliinsaturados, aunque evidentemente también puede hablarse
de diinsaturados, triinsaturados, etc.
En la nomenclatura abreviada, se indica la longitud de la cadena y el número de dobles enlaces. La
posición de los dobles enlaces se indica como un superíndice en el segundo numero. Así, el ácido
oleico (9-octadecenoico) se representa como C18:19, y el linoleico (9,12-octadecadienoico) como
C18:29,12, y el linolénico (9,12,15-octadecatrienoico) como C18:39,12,15.
En los ácidos grasos habituales, es decir, en la inmensa mayoría de los procedentes del metabolismo
eucariota que no han sufrido un procesado o alteración químicos, los dobles enlaces están siempre en
la configuración cis. Esto hace que la disposición de la molécula sea angulada, con el vértice en la
insaturación. Esta angulación hace que los puntos de fusión de las ácidos insaturados sean más bajos
que los de sus homólogos saturados. Los dobles enlaces en trans distorsionan poco la simetría
cristalina, que es muy parecida a la de los ácidos grasos saturados.
La configuración en cis o en trans de un doble enlace en la cadena hidrocarbonada también puede
indicarse en la nomenclatura abreviada. Así, el ácido araquidónico (5, 8, 11, 14-eicosatetraenoico) se
representa como C20:45c,8c,11c,14c ó C20:4 (5c, 8c, 11c, 14c).
La configuración modifica las características químicas y físicas de la molécula. El ácido oleico y
elaidico tienen la misma fórmula pero distinta configuración.
Algunos ácidos grasos poliinsaturados (linoleico, linolénico y araquidónico) no pueden ser
sintetizados por los animales superiores (incluido el hombre), y como su función biológica es
fundamental, deben ser suministrados en la dieta. Por este motivo reciben el nombre de ácidos grasos
esenciales.
Los ácidos grasos insaturados manifiestan las propiedades inherentes al doble enlace:
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- Reaccionan fácilmente con ácido sulfúrico para dar sulfonatos, que se emplean frecuentemente
como detergentes domésticos.
- Los dobles enlaces pueden adicionar hidrógeno. La hidrogenación catalítica (completa) de los
ácidos grasos insaturados constituye la base de la transformación industrial de aceites en grasas sólidas
(la margarina es el resultado de la hidrogenación de aceites vegetales).
- Los dobles enlaces pueden autooxidarse con el oxígeno del aire. Es una reacción espontánea en la
que se producen radicales peróxido y radicales libres, muy reactivos, que provocan en conjunto el
fenómeno de enranciamiento de las grasas, que resulta en la formación de una compleja mezcla de
compuestos de olor desagradable.Una cuestión de nomenclatura
Según las normas de la IUPAC, utilizadas de forma general, la cadena de los ácidos grasos se
numera a partir del carbono del carboxilo, que es entonces el número 1. La posición de los
dobles enlaces se indica utilizando la letra griega ∆, delta mayúscula. Ahora bien, en las
ramas científicas que consideran los ácidos grasos desde el punto de vista biológico y no
puramente químico, se utiliza otra nomenclatura, numerado la cadena a partir del metilo. En
este caso, la posición de los dobles enlaces se indica con la letra griega ω omega minúscula, o
con la letra n. El carbono terminal es denominado “omega”. Los dobles enlaces se encuentran
en el carbono 3, 6, 9, etc. Los omega 3 protegen contra riesgos coronarios, mientras que los
omega 6 los aumentan
La razón de este sistema de numeración es que en los seres vivos la elongación, insaturación y corte de
los ácidos grasos se produce a partir del extremo carboxilo, por los que numerando desde el metilo se
mantiene la relación entre los que pertenecen a la misma serie metabólica. Además, como en los
ácidos grasos habituales, y especialmente en las series metabólicas correspondientes al linoleico y
linolénico los dobles enlaces están situados siempre con un CH2 entre ellos, solamente se especifica la
posición del primero (contando desde el metilo)
Por ejemplo, utilizando las normas de la IUPAC:
El ácido 18:2∆ 9,12 se elonga para dar 20:2∆ 11,14, que a su vez se puede insaturar para dar 20:3 ∆ 5,
11, 14 o elongar hasta 24:2∆ 15, 18.
Utilizando el sistema bioquímico:
El ácido 18:2 n-6 se elonga para dar 20:2 n-6 que a su vez se puede insaturar para dar 20:3 n-6, o
elongar hasta 24:2 n-6. Es evidente cual de los dos sistemas es el más útil para el estudio del
metabolismo.
Estructura
ACIDOS GRASOS MONOINSATURADOS
Nombre común
Se encuentra en
C 10:1 n-1
caproleico
leche de rumiantes
C 12:1 n-3
lauroleico
leche de vaca
C 16:1 n-7
palmitoleico
C 18:1 n-9
oleico
C 18:1 n-7
vaccénico
grasas de rumiantes
C 20:1 n-11
gadoleico
aceites de pescado
C 22:1 n-11
cetoleico
aceites de pescado
C 22:1 n-9
erúcico
nuez de macadamia, aceites de pescado
aceites vegetales (muy extendido en la naturaleza)
aceite de colza
Ácidos grasos poliinsaturados y esenciales
Los ácidos grasos poliinsaturados más frecuentes pertenecen a las series n-6 y n-3, que tienen como
cabezas respectivas al ácido linoleico (18:2 n-6) y al linolénico (18:3 n-3). Estos dos ácidos grasos son
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esenciales, es decir, no pueden sintetizarse en el organismo, y deben obtenerse de la dieta. Todos los
demás ácidos grasos de sus series sí pueden obtenerse a partir de ellos.
En todos los casos, los dobles enlaces se encuentran separados por un carbono, es decir, formando un
sistema dieno no conjugado.
Estructura
ACIDOS GRASOS POLIINSATURADOS
Nombre común
Se encuentra en
C 18:2 n-6
linoleico
girasol, maíz, soja, algodón, cacahuete.
C 18: 3 n-3
linolénico
soja, otros aceites vegetales
C 18:3 n-6
gamma linolénico
C 18:4 n-3
estearidónico
aceites de pescado, semillas de borraja, onagra
C 20:4 n-6
araquidónico
aceites de pescado
C 22:5 n-3
clupanodónico
aceites de pescado
C 22:6 n-3
docosahexaenoico
aceites de pescado
aceite de onagra, borraja
Los ácidos grasos poliinsaturados son fácilmente oxidables, tanto más cuanto mayor sea el número de
dobles enlaces. A partir de tres insaturaciones, son francamente inestables, y las grasas en las que
abundan solamente pueden utilizarse en buenas condiciones en la industria alimentaria tras su
hidrogenación.
Ácidos grasos menos frecuentes
En la mayoría de las grasas comunes, la longitud de la cadena de los ácidos grasos saturados y
monoinsaturados es de 18 átomos de carbono como máximo, y de 24 carbonos para los
poliinsaturados. Se exceptúan las ceras, en las que pueden encontrarse toda una serie de ácidos grasos
saturados de hasta 35 carbonos de longitud. También en los aceites de pescado, procedentes del
metabolismo de las ceras que acumula el zooplancton, se encuentran diversos ácidos grasos
monoinsaturados largos.
Estructura
ACIDOS GRASOS SATURADOS RAROS
Nombre común
Se encuentra en
C 20:0
araquídico
C 22:0
behénico
C 24:0
lignocérico
C 26:0
cerótico
aceite de cacahuete
ceras
aceite de cacahuete
cera de abejas
Ácidos grasos con estructuras peculiares
Como ya se ha indicado, los ácidos grasos comunes tienen la cadena con un número par de átomos de
carbono. Sin embargo, las bacterias sintetizan frecuentemente ácido grasos con un número impar de
átomos de carbono, que pasan a las grasas animales. En el caso de los rumiantes, la peculiaridad de su
alimentación, muy dependiente de la fermentación bacteriana del rumen, hace que estos ácidos grasos
se encuentre en su grasa y especialmente en la leche en un porcentaje pequeño, pero significativo. Los
más abundantes son el También en algunos vegetales aparecen ácidos grasos de número impar de
átomos de carbono, como el ácido pelargónico, de nueve átomos de carbono, producido por la ruptura
oxidativa del ácido oleico. Por la misma razón, aparecen en la leche y grasa de los rumiantes indicios
de ácidos grasos de cadena ramificada y ácidos grasos con dobles enlaces en configuración trans. Los
ácidos grasos trans se encuentran también en pequeñas cantidades en algunos aceites de semillas poco
frecuentes, pero son muy abundantes en las grasas procesadas por hidrogenación.
Estructura
C 17:0
OTROS ACIDOS GRASOS PECULIARES
Nombre común
Se encuentra en
margárico
grasas de rumiantes
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C 18:1 n-9 trans
elaídico
grasas hidrogenadas
Existen también, en diversos vegetales, ácidos grasos con estructuras peculiares, que precisamente con
su presencia hacen que el aceite que puede obtenerse de ellos no sea comestible, aunque puede ser
muy útil en algunas industrias. El ácido crepenínico, presente en algunas semillas, tiene 18 carbonos,
con un enlace triple y uno doble. El ácido ricinoleico tiene un grupo hidroxilo en el carbono Y como
su nombre indica, es abundante en el aceite de ricino El ácido coriólico, presente en algunas semillas,
también tiene un grupo OH. El floionólico, presente en el corcho, tiene tres grupos hidroxilo. Los
ácidos vernólico y coronárico tienen anillos de epóxido (tres eslabones, uno de ellos un oxígeno).
Otras estructuras aún más peculiares son, por ejemplo, la del ácido colnelhénico, con un grupo éter en
su cadena, que se forma en las patatas por oxidación enzimática del ácido linolénico. El ácido
hidnocárpico y otros ácidos grasos de Hydnocarpus tienen formando parte de la cadena un anillo
insaturado de cinco eslabones. Se han utilizado en medicina.
ACIDO LINOLEICO CONJUGADO: UN ACIDO GRASO CON
ISOMERIA TRANS POTENCIALMENTE BENEFICIOSO.
Julio Sanhueza C, Susana Nieto K y Alfonso Valenzuela B.
Laboratorio de Lípidos y Antioxidantes
Instituto de Nutrición y Tecnología de los Alimentos ( INTA), Universidad de Chile.
Revista chilena de nutrición, vol. 29, n 2, 2002
ABSTRACT
Conjugated linoleic acid (CLA) is a type of isomeric trans fatty acid that has been demonstrated to
have diverse health beneficial effects. The most common naturally existing structural form of CLA is
the 9c (cis), 11t (trans) isomeric configuration. CLA, which is commonly found in the tissues and/or
secretions (i.e., milk) of ruminants, is formed from the isomerization of linoleic acid by the ruminal
bacteria Butyrivibrio fibrisolvens. CLA may also be synthesized, in both ruminants and non
ruminants, by desaturation of vaccenic acid (18:1, 11t) at the intestinal tract and/or the at liver of these
animals. Daily ingestion of CLA in humans highly variable (0.5g/day-1.5g/day), pending on the
individual and the country nutritional habits, and on the amount of meat, milk and milk-derived
products consumed. Different biological and nutritional properties have been described for CLA, the
most relevant being related to its hipocholesterolemic, antiatherogenic and immuno-stimulant action,
the protective action against certain types of cancer, and its antioxidant and body-weight reduction
effects ascribed.for the isomeric fatty acid. However, the definitive confirmation of these health
beneficial effects needs more experimental and clinical evidences supporting these actions.
Meanwhile, diverse products containing CLA are now offered at the retail market with increasing
success, especially those preparations claiming body weight reduction properties for the isomeric fatty
acid.
Key words: Conjugated linoleic acid; trans isomers; polyunsaturated fatty acids and health; ruminal
Butyrivibrio fibrisolvens.
INTRODUCCION
Los ácidos grasos son componentes importantes de la dieta de los animales superiores y del hombre.
Constituyen no solo un aporte energético considerable que casi duplica al aporte de los carbohidratos y
de las proteínas, y varios tienen funciones metabólicas específicas. Algunos de ellos se caracterizan
por su esencialidad, como es el caso de los ácidos grasos omega-6 y omega-3 (1). Otros, destacan por
sus efectos ya sea beneficiosos o potencialmente dañinos para la salud humana, como es el caso de los
ácidos grasos monoinsaturados y poliinsaturados, dentro de los primeros, y de los ácidos grasos
saturados en el segundo caso (2). La isomería geométrica de los ácidos grasos es importante en
términos nutricionales. La gran mayoría de los ácidos grasos que se encuentran naturalmente poseen
isomería cis, sin embargo en nuestra dieta habitual consumimos una pequeña, pero no despreciable
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porción (1g a 7g/día) de ácidos grasos con isomería trans (3). Estos ácidos grasos provienen
esencialmente de la manipulación tecnológica a que son sometidas las grasas y aceites para adaptarlas
a nuestro consumo. La hidrogenación industrial, que permite la obtención de mantecas ("shortenings")
y margarinas de mesa, y la desodorización de los aceites a alto vacío y temperatura, son las dos fuentes
de origen tecnológico más importantes de formación de isómeros trans de los ácidos grasos (4). El
consumo de ácidos grasos trans ha sido fuertemente cuestionado por los Comités de Expertos en
Nutrición, ya que la evidencia científica indica que estos isómeros son dañinos para la salud, por sus
efectos a nivel de los lípidos sanguíneos (5), por su acción inhibitoria sobre la actividad de enzimas
hepáticas (6), por la modificación que producen en la fluidez de las membranas celulares (7) entre
otras, que se traducen, entre otros efectos, en un mayor potencial aterogénico (8). La recomendación
es evitar el consumo de ácidos grasos trans, y la legislación sanitaria de muchos países obliga a
declarar el contenido total de ácidos grasos trans de productos como las margarinas y las mantecas.
Sin embargo, a la luz del conocimiento actual, la generalización del concepto sobre el efecto dañino de
los ácidos grasos trans deberá ser revisada, ya que algunos de estos isómeros pueden tener efectos
beneficiosos en la nutrición y salud humana. Este es el caso de ácido linoleico conjugado (ALC) con
isomería trans.
QUE ES UN ACIDO GRASO CONJUGADO: EL CASO DEL ALC
La estructuración de los dobles enlaces (insaturación) de los ácidos grasos naturales obedece a un
patrón muy característico y conservado. En un ácido graso diinsaturado, ambos dobles enlaces siempre
estarán separados por un carbono intermedio que no participa de la estructura de insaturación. Esto es,
en un ácido graso donde los dobles enlaces están entre los carbones 9-10 y 12-13, el carbono 11 no
participará de la estructura de insaturación. Esta sería una estructura "no conjugada" y al carbono 11 se
le designaría como un carbono metilénico intermedio. Este es el caso de la estructura de la mayoría de
los ácidos grasos en su forma natural. Sin embargo, como consecuencia de la manipulación
tecnológica de las grasas y aceites ya comentada, o en casos muy particulares, por efecto de la
metabolización a nivel celular de ciertos ácidos grasos, es posible que un doble enlace cambie de
posición, siguiendo el ejemplo anterior, desde la posición 9-10 a la 10-11, o de la posición 12-13 a la
11-12. En ambos casos desaparecería el carbono metilénico intermedio y el ácido grasos formado se
transformaría en una estructura "conjugada", o sea, en un ácido graso conjugado. La conjugación de
los dobles enlaces puede, además, ocasionar un cambio en la isomería espacial del ácido graso. Esto
es, en un ácido graso diinsaturado cuyos dos dobles enlaces tienen isomería cis (c), uno de estos
dobles enlaces, o ambos, pueden adoptar la isomería trans (t). Por lo cual podrán existir ácidos grasos
conjugados diinsaturados con isomería c,c (poco probable) o c,t, o t, c o t, t.
El ácido linoleico (18:2, 9c-12c), es un ácido graso esencial omega-6 muy abundante en el reino
vegetal y también animal. La gran mayoría de los aceites vegetales (con algunas excepciones como el
aceite de oliva, el de palma, o el aceite de coco) aportan cantidades significativas de ácido linoleico.
En la grasa animal también se le encuentra, junto con los ácidos grasos saturados y monoinsaturados.
Con la incorporación de una mejor tecnología para el análisis y la identificación de los ácidos grasos
componentes de grasas, aceites o de muestras de tejidos (aplicación de cromatografía gasesosa capilar,
HPLC de alta resolución, y espectrometría de masas), fue posible identificar que en toda muestra de
aceite o de grasa, particularmente en aquellas de origen animal, siempre está presente una pequeña
cantidad de ALC (9). Este ácido graso se presenta con diferente isomería (7c-9t, 9c-11t, 11c-13t,
principalmente), aunque siempre predomina la estructura 9c-11t. Si bien el ALC se encuentra en
pequeñas proporciones en los aceites vegetales, su concentración es particularmente alta en la carne y
en la leche de los rumiantes, donde puede alcanzar hasta un 0,65% de los lípidos totales (10). La figura
1 muestra en forma comparativa las estructura del ácido linoleico (C18:2, 9c-12c) y del isómero del
ácido linoleico conjugado (C18:2, 9c-11t).
EL ORIGEN DEL ALC EN LOS TEJIDOS ANIMALES
Puesto que el ALC se encuentra en una proporción muy pequeña en los granos y en el forraje que
constituyen la alimentación de los rumiantes, significa que son estos animales los que transforman el
ácido linoleico en alguno de los isómeros del ALC. Es en el poderoso ambiente reductor del rúmen
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donde se produce el proceso de biohidrogenación del ácido linoleico (11). Dentro de la abundante y
variada flora microbiológica del rúmen, constituida por bacterias y protozoos principalmente, es la
bacteria identificada como Butyrivibrio fibrisolvens, quien al realizar la hidrogenación del ácido
linoleico para transformarlo en un ácido graso monoinsaturado, genera como intermediario del
proceso a los diferentes isómeros del ALC (12). Por su origen ruminal al ALC se le identifica como
"ácido ruménico" (13). Existe otra vía metabólica para la formación de ALC. Esta puede ocurrir en el
hígado de los rumiantes, y posiblemente también en los mamíferos no rumiantes. El ácido vaccénico
(18:1, 11t) es producido por la hidrogenación del ácido linoleico en el rúmen. Este ácido graso puede
ser desaturado en el carbono 9 por las enzimas desaturasas intestinales y/o hepáticas de los rumiantes,
transformándose en ALC (forma 9c-11t) (14). Esta podría ser la razón por la que en los mamíferos no
rumiantes, incluidos los humanos, también se encuentra ALC en sus tejidos y secreciones (leche) (15),
aunque en menor proporción que en los rumiantes. Al consumir carne de rumiantes (o productos
lácteos), conteniendo ácido vaccénico, este sería transformado a ALC por la desaturación enzimática,
proceso que incrementaría el aporte de ALC proveniente de la carne y de la leche de rumiantes (16).
En los tejidos animales el ALC se distribuye en los fosfolípidos, particularmente en la
fosfatidiletanolamina, por lo cual de alguna manera estaría participando en la determinación de las
propiedades químicas y biológicas de las membranas celulares (fluidez, permeabilidad, transmisión de
señales, etc.) (17). Cuando el aporte dietario de ácido linoleico es alto, sobre el 5% del aporte de grasa,
como el que se puede obtener en forma experimental en ratas, es posible encontrar ALC ampliamente
distribuido en el hígado, en los pulmones, y en el tejido muscular y adiposo (18). En humanos también
se ha observado la presencia de ALC, ya sea en la leche o en el plasma sanguíneo (19). En la leche, el
isómero mas frecuente es el 9c-11t, cuyos niveles fluctúan en 0,15%-0,22% (20). También se ha
encontrado el isómero 7t-9c en la leche humana, aunque en concentraciones iguales o inferiores a
0,03% de los lípidos totales (15). En el suero sanguíneo humano el isómero 9c-11t llega a constituir
hasta el 0,4-0,5% del total de los lípidos circulantes (21). De cualquier forma, los niveles de ALC
determinados en los humanos pueden ser muy variables, ya que dependerán de la cantidad y tipo de
carne que se consume y del tipo de alimentación que reciben los animales, de los hábitos de consumo
individuales, de la composición total de la dieta, entre otras (16). No existe información si en humanos
es posible la transformación de ácido vaccénico en ALC.
APORTE DIETARIO DE ALC
A partir de lo comentado en el párrafo precedente, es posible deducir que la mejor fuente dietaria de
ALC es el consumo de carnes y productos lácteos procedentes de rumiantes. En una dieta mixta
promedio occidental se estima que el consumo de ALC puede ser hasta 1,5 g/día (22). Sin embargo, el
consumo es muy variable y depende de los hábitos de cada país y también del porcentaje de ALC
aportado por las carnes de animales rumiantes. Por ejemplo, dentro de los países cuyo consumo se ha
establecido, Australia presenta los valores mas altos (1,5-1,8 g/día), en tanto que Alemania muestra los
valores mas bajos (0,5 g/día) (23). La carne consumida en los países germanos proviene
principalmente del cerdo, un no rumiante. En Estados Unidos el consumo promedia los 0,9-1,2 g/día
(24). Se desconoce el consumo de ALC en América Latina, aunque se puede presumir que en países
con alta tradición de consumo de carne bovina, como es el caso de Argentina y Uruguay, la ingesta
promedio de ALC debería ser alta (sobre 1g/día). En Chile, Brasil, Perú y en Ecuador, ocurriría todo lo
contrario, ya que la ingestión de carne está representada principalmente por el consumo de aves (pollo,
principalmente), las que por su tipo de alimentación, principalmente de origen vegetal, no constituyen
un aporte significativo de ALC.
EFECTOS NUTRICIONALES Y EN LA SALUD DERIVADOS DEL CONSUMO DE ALC
Fue el grupo encabezado por Pariza y colaboradores quienes comunicaron por primera vez
información relacionada con los posibles efectos beneficiosos derivados del consumo de ALC (25).
Desde la primera publicación sobre las actividades biológicas del ALC, son muchas las
comunicaciones científicas que informan sobre las propiedades atribuidas al ácido graso. En la
actualidad se le considera como un "regulador metabólico", y a continuación, aunque en forma no
exhaustiva, se resumen sus principales efectos y/o funciones.
Efectos hipocolesterolémicos.
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En modelos experimentales de hipercolesterolemia, el ALC ha demostrado producir disminución de
los niveles plasmáticos de colesterol, con respuestas muy similares a las que se obtienen con los ácidos
grasos omega-3, aunque el ALC no pertenece a esta serie de ácidos grasos (26). En Hamsters
alimentados con dietas que aportan 0,06% a 1,1% de ALC, con un aporte además de 1,1% de ácido
linoleico, se produce una disminución progresiva, en relación a la dosis de ALC, del colesterol-LDL,
pero no del colesterol-HDL (26). Sin embargo, la relación tocoferol plasmático/colesterol total
aumenta hasta en un 86%, y en forma proporcional al aporte de ALC (26). La información acumulada
sugiere que el ALC tendría un efecto de ahorro de la capacidad antioxidante del plasma, actividad que
de alguna manera se podría relacionar con efectos antiaterogénicos (26). Estudios realizados en
conejos, han demostrado que la adición de tan solo 0,5 g/día de ALC a una dieta semisintética que
aporta 14% de grasa, produce una disminución significativa del colesterol-LDL y de los triglicéridos
plasmáticos, produciendo al mismo tiempo una disminución de la relación colesterol-LDL/colesterolHDL, y una disminución de la acumulación de placas ateroscleróticas en los grandes vasos (27).
Resultados similares se han obtenido con ratones de la cepa C57BL/6 que constituyen un modelo de
estudio experimental de aterogenesis. En estos animales, la suplementación de la dieta aterogenica
(aporta altas cantidades de colesterol y grasa saturada) con 2,5 g/Kg de ALC, produce una franca
disminución del proceso aterogenico (28). Estos resultados, y muchos otros similares, han motivado
atribuir al ALC un efecto antiaterogénico, a través de su acción hipocolesterolémica e
hipotrigliceridémica. Sin embargo, el mecanismo de este efecto es aún desconocido, como lo es
también la real proyección nutricional que tienen estos resultados experimentales.
Efectos en el sistema inmune
Los efectos del ALC sobre el sistema inmune constituyen conocimientos mas recientes y se refieren,
principalmente en el estímulo que ejerce en la síntesis de IgA, IgG, IgM y a la disminución
significativa de los niveles de IgE, por lo cual se presume que el ácido graso podría tener efectos
favorables en la prevención y/o tratamiento de ciertas alergias alimentarias (29). Estudios similares
han demostrado, en una relación dosis dependiente, que el ALC aumenta el nivel de linfocitos en el
bazo de ratones y la secreción de IgG e IgM por parte de estas células (30). El ALC disminuye, la
producción de interleukina 6 inducida por polisacáridos en macrófagos peritoneales, la producción del
factor de necrosis tumoral, y la producción de prostaglandina E en el hígado de la rata (31). Una dieta
que contiene un 1% de ALC produce un efecto protector de la acción mitogénica de las
fitohemoaglutininas y de la concanavalina A en las ratas, respuesta que es más efectiva cuando se trata
de animales jóvenes (30). Una observación interesante es la demostración del efecto protector del
ALC en la anorexia inducida por endotoxinas en las ratas, acción que se refleja en la prevención de la
detención del crecimiento de los animales por efecto de las toxinas (32). Las acciones sobre el sistema
inmune atribuidas al ALC guardan estrecha relación con su efecto en la prevención del desarrollo de
ciertos cánceres.
Efectos anticarcinogénicos
Los efectos anticarcinogénicos del ALC son quizás los mejor documentados y que a diferencia de los
anteriores, están respaldados por estudios realizados en humanos. Dentro de los diferentes tipos de
cáncer en los que se ha estudiado el efecto de ALC, su acción sobre el cáncer mamario parece ser la
más significativa. El ALC es más eficiente en su efecto de prevención de este tipo de cáncer que el
ácido oleico, linoleico y que los ácidos grasos omega-3 eicosapentaenoico y docosahexaenoico (33).
Estudios realizados en finlandesas post-menopausicas han demostrado una correlación negativa entre
el consumo de ALC, proveniente de la leche y el queso de consumo habitual en esta población, y el
desarrollo de cáncer mamario (34). El efecto preventivo parece ser dosis dependiente, la que se ha
estudiado en rangos de aporte de ALC desde un 0,05% hasta un 2%. Experimentalmente se ha
demostrado en ratones inmunodeficientes con trasplante de tumores mamarios una disminución de
hasta un 73% del crecimiento tumoral si se le aporta a los animales, antes de la inoculación del tumor,
una dieta que contiene un 1% de ALC (35). Se ha demostrado que el ALC ejerce efectos citotóxicos
en cultivos de células de melanoma colo-rectal y de cáncer mamario (36), así como también un efecto
de detención del ciclo celular en Go/G1 en cultivo de células del tipo MCF-7 (37). El ALC muestra,
además, efectos antimutagénicos, ya que inhibe la inducción de cáncer de piel de ratas producida por
7,12 trimetilbencil antraceno, un poderoso agente carcinogénico (38). El mecanismo de los efectos
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inhibitorios que ejerce el ALC sobre la diferenciación celular anormal, que finalmente conduce al
desarrollo de un cáncer, no es conocido en la actualidad, y la investigación apunta a caracterizar su
ación a nivel de la expresión de ciertos tipos de mRNA que codifican para receptores de membrana
involucrados en la transducción de señales, o en la traducción de receptores activados por
proliferadores peroxisomales (PPARs) (17). Sin lugar a dudas es un campo muy fértil de investigación
que requiere de muchos más antecedentes experimentales.
Efectos antioxidantes
La información sobre el posible efecto antioxidante atribuido al ALC es menos clara y más
controversial que las acciones biológicas ya descritas. Dependiendo del modelo de estudio, es el efecto
observado. En modelos in vivo el ALC produce una disminución significativa de los niveles de
peróxidos y de sustancias reactivas al ácido tiobarbitúrico, dos procedimientos analíticos utilizados
para evaluar efectos de antioxidantes o de inhibidores del estrés oxidativo (39). Estudios realizados in
vitro, han demostrado que el ALC posee una efectiva capacidad atrapadora de radicales libres
prooxidantes (40), lo cual es atribuible a una actividad antioxidante (41). El ALC ha sido considerado
como un efectivo inhibidor del estrés oxidativo cuando se le compara con los tocoferoles y con
antioxidantes sintéticos como el butilhidroxitolueno (BHT) (42), y en numerosas revisiones se
menciona su actividad antioxidante como comparable a la de los antioxidantes sintéticos
convencionales (43, 44, 45). Sin embargo, aunque existe evidencia sobre los efectos antioxidantes del
ALC la controversia deriva del hecho que el ácido graso in vitro oxida con mayor velocidad aún que
ácidos grasos de mayor poliinsaturación como es el caso de los ácidos eicosapentaenoico (20:5) y
docosahexaenoico (22:6) (46), por lo cual podría hasta atribuírsele al ALC un efecto pro-oxidante. La
inducción de la oxidación por efecto de la temperatura en aceites vegetales, es más rápida si el aceite
se adiciona de ALC, lo cual demostraría su posible efecto prooxidante (47). Como se puede observar,
esta es otra área de investigación sobre el ALC que requiere de mucho mas información y exactitud en
el desarrollo de los modelos de estudio y en la interpretación de los resultados.
Efectos sobre el peso corporal
Este es quizás el efecto del ALC que despierta más curiosidad y que tendría también mas impacto
nutricional. La acción reductora del peso corporal atribuída al ALC, ha derivado en una creciente
explotación comercial del ácido graso sin tener, por el momento, un sustento científico sólido. La
administración de una dieta que contiene 5% de aceite de maíz suplementada con un 0,5 % de ALC a
ratas desde las seis semanas de edad, produce a las cuatro semanas de administración de la dieta, una
reducción del 60% del contenido de grasa del tejido adiposo (48). Ratones de la cepa AKR/J que
recibieron dietas donde el 15% o el 45% de la energía fue aportado por las grasas y que fueron
suplementadas con 1% o 2% de ALC respectivamente, presentaron al cabo de seis semanas una
disminución de la ingestión de energía, y del depósito de grasas en el tejido adiposo, y un aumento de
la velocidad metabólica y del cuociente respiratorio, efectos que resultan en una disminución
significativa del peso de los animales (49). En estudios similares, no se ha observado una disminución
de la ingestión de alimento, pero sí una reducción de la grasa y del peso corporal (50). Estudios
realizados con personas que presentan sobrepeso, o que son obesas, han demostrado que la ingestión
diaria de 3,4 g de ALC produce una disminución de la masa grasa total sin afectar otros parámetros
metabólicos, como el recuento eritrocitario y la cantidad de masa magra (51). La información obtenida
respecto al efecto del ALC en la reducción del peso corporal sugiere que el ácido graso afectaría la
interconversión metabólica de los ácidos grasos y produciría una activación de la lipolisis,
probablemente por una activación de la beta oxidación mitocondrial (52). Produciría, además, una
disminución de los niveles de leptina (48), y una estimulación de la actividad de la enzima carnitina
palmitoil-transferasa (48). La inhibición de la actividad de la enzima lipoproteína lipasa dependiente
de heparina, también podría estar involucrada en el efecto modulador del peso corporal que produce el
ALC, ya que disminuiría la biodisponibilidad de los ácidos grasos hacia lo tejidos extra hepáticos (53).
Este es otro aspecto interesante del ALC que requiere aún de mucha información científica.
CONCLUSIONES Y PERSPECTIVAS DEL ALC
El estado actual sobre la investigación de los efectos nutricionales del ALC, no permite obtener
conclusiones inequívocas, sino más bien conjeturas con mayor o menor apoyo experimental. El ácido
297
graso puede ser consumido como tal o en la forma de glicéridos (mono, di o triglicéridos) ya que
cuenta con la categoría GRAS por parte del FDA (USA). Esta categorización ha despertado el
entusiasmo por incrementar el aporte de ALC de algunos alimentos. Mediante un manejo nutricional
adecuado de los animales, se puede incrementar hasta en un 100% el aporte de ALC a través de la
carne de bovinos o de otros rumiantes, de la leche y de los productos derivados de esta (54, 55).
También se han desarrollado alimentos suplementados con diferentes cantidades de ALC, todo dentro
del concepto de los llamados "alimentos funcionales". Sin embargo, es preciso ser muy cuidadosos en
la interpretación de los efectos del ALC y de sus reales resultados nutricionales. Un producto que
consumido en forma habitual permita bajar de peso, o prevenir ciertos tipos de cáncer, además de
constituirse en un poderoso aliado de las campañas de salud pública sobre el sobrepeso o la obesidad,
puede también convertirse en un fenómeno comercial sin precedentes si no se ejerce el debido control.
Para que esto pueda realmente ocurrir, es preciso contar con mayor investigación sobre la bioquímica
básica y nutricional del ALC, tener mayor información sobre sus efectos en modelos animales y
humanos, con estudios clínicos y epidemiológicos de largo plazo y en diferentes poblaciones y grupos
etarios, que aseguren así la real efectividad de este ácido graso con isomería trans de características
tan particulares.
RESUMEN
El ácido linoleico conjugado (ALC) es un ácido graso que presenta un tipo de isomeria trans, y que
tiene variados efectos beneficiosos para la salud. La estructura de ALC más común que existe en la
naturaleza, corresponde a la configuración del isómero 9c (cis), 11t (trans). El ALC se encuentra
normalmente en tejidos y/o secreciones (leche) de rumiantes y es formado por la isomerización del
ácido linoleico, por acción de la bacteria del rúmen llamada Butyrivibrio fibrisolvens. ALC puede ser
sintetizado, tanto en rumiantes como en no rumiantes, por la desaturación del ácido vaccenico (18:1,
11t) en el tracto intestinal y/o en el hígado de estos animales. La ingestión diaria de ALC es muy
variable (0,5 g/día-1,5g/día), ya que depende por una parte de los hábitos nutricionales ya sea
individuales o regionales, y por otra, del consumo de carne, leche o derivados de la leche. Se han
descritos diversas propiedades nutricionales y biológicas para los diversos isómeros de ALC, entre las
más relevantes se destacan: su efecto hipocolesterolémico y antiaterogénico, su acción inmunoestimulante, la protección que ofrece contra cierto tipo de cánceres, su función antioxidante y la
participación en la reduccción de peso corporal. Sin embargo, la confirmación definitiva de todos estos
efectos beneficiosos para la salud, requiere de un mayor cuerpo de evidencias clínicas y
experimentales que avalen sin lugar a dudas estas acciones de ALC. En la actualidad, diversos
productos que contienen ALC se ofrecen en los mercados para la venta, los de mayor éxito, son
aquellos productos que muestran que los isómeros de ALC que contienen, permiten reducir peso.
Palabras claves: Acido linoleico conjugado; isómeros trans; ácidos grasos poliinsaturados y salud;
Butyrivibrio fibrisolvens ruminal.
Agradecimientos: El trabajo de investigación de los autores es financiado por FONDECYT,
FONDEF, Fondo de Ayuda a la Investigación de la Universidad de los Andes, Laboratorios Ordesa
(España) y Alltech Inc. (USA).
BIBLIOGRAFIA
1.- Simopoulos A, Leaf A, Salem N. Essentiality of and recomended dietary intakes for omega-6 and
omega-3 fatty acids. Ann Nutr Metab 1999;43: 127-130.
2.- Valenzuela A, Sanhueza J, Nieto S. Acidos grasos omega-3 de cadena larga en la nutrición humana
y animal. Rev Chil Nutr 2000; 27: 351-354.
3- Valenzuela A, Morgado N. Trans fatty acid isomers in human health and in the food industry. Biol
Res 1999; 32: 273-287.
4.- Beare-Rogers J.L. Trans and positional isomers of common fatty acid. Adv Nutr Res 1988; 5: 171200.
5.- Bouziane M, Prost J y Belleville J. Changes in fatty acid composition of total serum and
lipoprotein particles, in growing rats given protein-deficients diet with either hydrogenated coconut or
salmon oils as fat sources . Brit J Nutr 1994; 71: 375-387.
298
6.- Morgado N, Galleguillos A, Sanhueza J, Garrido A, Nieto S, and Valenzuela, A. Effect of the
degree of hydrogenation of dietary fish oil on the trans acid content and enzimatic activity of rat
hepatic microsomes. Lipids 1998; 33: 669-673.
7.- Mann G. Metabolic consequences of dietary trans fatty acids. Lancet. 1994; 343: 1268-1271.
8.- Mensink RP, Katan M.B, and Hornstra G. Efefects of dietary cis and trans fatty acids on serum
lipoprotein (a) levels in humans. J Lipids Res 1992; 33:1493-1501.
9.- Willians W, Dosson CG, and Gunstone, F. Isomers in commercial samples of conjugated linoleic
acid. J Am Oil Chem Soc 1997; 74 :1231-1233.
10.- Fritsche J, and Steinhart H. Analysis, occurrence and physiological properties of trans fatty acids
(TFA) with particular emphasis on conjugated linoleic acid isomers (CLA)- a review. Fett. / Lipid
1998; 100: 190-210.
11- Chin SF Storkson JM, Karan WL, Albright J, and Pariza MW. Conjugated linoleic acid ( 9-11 and
10,12-octadecadienoic acid) is produced in conventional but not germ free rats fed linoleic acid. J Nutr
1994; 124: 694-710.
12.- Kim YJ, Liu RH, Bond DR and Russell, J.B. Effect of linoleic acid concentration on conjugated
linoleic acid production by Butyrivibrio fibrisolvens A38. Appl Envirom Microbiol 2000; 12:
5226.5230.
13.- Kramer JK, Parodi PW, Jensen RG, Mossoba MM, Yurawecz MP and Adlof R.O. Rumenic acid:
A proposed common name for the major conjugated linoleic acid isomer found in natural products.
Lipids 1998; 33: 835-840.
14.- Mahfouz MM, Valicenti A.J and Holman RT. Desaturation of isomeric trans-octadecenoic acid
by rat liver microsomes. Biochim. Biophys. Acta 1980; 618: 1-12.
15.- Yurawecz, M.P., . Roach, J.A., Sehat, N., Mossoba, M.M., Kramer, J.K., Fristsche, J., Steinhart,
H., and ku, K. A new conjugated linoleic acid isomers, 7 trans, 9 cis-octadecadienoic acid, in cow
milk, cheesse, beef and human milk and adipose tissue. Lipids 1998; 33: 803-809.
16.- Ackman, R.G., Eaton, c.A., Sipos, J.C., and Crewe, N.F. Origin of cis-9, trans-11 and trans-9,
trans 11-octadecadienoic acid in the depot fat of primates fed a diet rich in lard and corn oil and
implications for the human diet. Can Inst Food Sci Technol J 1981; 14: 103-107.
17.- Sébédio JL, Gnaedig, S and Chardigny JM. Recent Advances in Conjugated Linoleic Acid
Research. Curr Opin Clin Nutr Metab Care 1999; 2: 499-506.
18.- Kramer JK, Sehat N, Dugan M, Mossoba MM, Yurawecz MP, Roach JA, Eulitz K, Aalhus JL,
Schaefer AL and Ku Y. Distribution of conjugated linoleic acid (CLA) isomers in tissue lipids classes
of pigs fed a commercial CLA mixture determined by gas chromatography and silver ion-highperformance liquid chromatography. Lipid 1998; 33: 549-558.
19.- Jahreis G, Fritsche J, Mockel P, Schone F, Moller U, Steinhart H. The potential anticarcinogenic
conjugated linoleic acid, cis-9,trans-11 C18:2, in milk of different species: cow, goat. ewe, sow, mare,
woman. Nutr Res 1999; 19: 1541-1549.
20.- Jensen RG, lammi-Keep CJ, Hill DH, Kind AJ, Henderson BA. The anticarcinogenic conjugated
fatty acid, 9c,11t-18:2, in human milk: Conformation of its presence. J Human Lact 1998; 14: 23-27.
21.-Salminen I, Mutanen M, Jauhiainen M and Aro A. Dietary trans fatty acids increase conjugated
linoleic acid levels in human serum. J Nutr Biochem 1998; 9: 93-98.
22.- Parodi, P.W. Conjugated linoleic acid content: An anticarcinogenic fatty acid present in milk fat.
Austr J.Dairy Technol 1994; 49: 93-97.
23.- Fritsche J and Steinhart H. Amounts of conjugated linoleic acid (CLA) in German foods and
evaluation of daily intake. Z. Lebensm Unters Forsch. 1998; 206: 77-82.
24.- Hunter Je, Applewhite T.H. Isomeric fatty acids in the US diet: levels and health perspectives.
Am J Clin Nutr 1986; 44: 707-717.
25.- Pariza MW, Ha YL. Conjugated dienoic derivaties of linoleic acid a new class of anticarcinogens.
Med Oncol Tumor Pharmacother 1990; 7: 169-171.
26.- Nicolisi RJ, Rogers EJ, Kritchevky D, Scimeca JA and Huth P.J. Dietary conjugated linoleic acid
reduces plasma lipoprotein and early aortic atherosclerosis in hypercholesterolemic hamsters. Artery
1997; 22: 266-277.
27.-Lee KN, Kritschevky D, Pariza MW. Conjugated linoleic acid and atherosclerosis in rabbits.
Atherosclerosis 1994; 108: 19-25.
299
28.- Munday JS, Thompson KG and james K.A. Dietary conjugated linoleic acids promote fatty streak
formation in the C57BL/6 mouse atherosclerosis model. Br J Nutr 1999; 81: 251-255.
29.- Sugano M, Tsujita A, Yamasaki M, Noguchi M and Yamada K. Conjugated linoleic acid
modulates tissue levels of chemical mediator and inmune globulins in rats. Lipids 1998; 33: 521-527.
30.- Hayek MG, Han SN, Wu D, Watkins BA, Meydani M, Dorsey JL, Smith DE, Meydani S.N.
Dietary conjugated linoleic acid influences the immune response of young and old C57BL/6N CrlBr
mice. J Nutr 1999; 129: 32-38.
31.- Tarek JJ, Li Y, Schoenlein IA, Alle K and Watkins BA. Modulation of macrophage citokine
production by conjugated linoleic acid is influenced by dietary n-6:n-3 fatty acid ratio. J Nutr Biochem
1998; 9: 258-266.
32.- Miller CC, Park, Y Pariza, MW, Cook M.E. Feeding conjugated linoleic acid to animal partially
overcomes catabolic responses due to endotoxin injectio. Biochem Biophys Res Commun 1994; 198:
1107-1112.
33.- Ip C. Review of the effects of trans fatty acid, oelic acid, n-3 polyunsaturated fatty acids, and
conjugated linoleic acid on mammary carcinogenesis in animals. Am J Clin Nutr 1997; 66: 1523-1529.
34.- Aro A, Mannisto S, Salminen I, Ovaskainen ML, Kataja V and Uusitupa M. Inverse association
between dietary and serum conjugated linoleic acid and risk of breast cancer in postmenopausal
women. Nutr Cancer 2000; 38: 151-157.
35.-Visonneau S., Cesano A., Tepper S.A., Scimeca J.A., Santoli D., and Kritchevsky D. Conjugated
linoleic Acid suppresses the growth of human breast adenocarcinoma cells in SCID Mice. Anticancer
Res. 1997; 17: 969-973.
36.- Shultz T.D., Chew B.P., Seaman W., and Leudecke L.O. Inhibitory effect of conjugated linoleic
acid and beta-carotene on the in Vitro Growth of Human cancer cells. Cancer Lett. 1992; 63: 125-133.
37.-Shulz TD, Chew BP, and Seaman WR. Differential stimulatory and inhibitory response of human
MCF-7 breast cancer cells to linoleic acid and conjugated linoleic acid in culture. Anticancer Res
1992; 12: 2143-2145.
38.- Pariza MW, Hargraves WA. A beef-derived mutagenesis modulator inhibits initiation of mouse
epidermal tumors by 7,12-dimethylbenz(a) antracene. Carcinogenesis 1985; 8: 1881 – 1887.
39.- Pariza MW, Park Y, Cook ME. The biologically active isomers of conjugated linoleic acid. Prog
Lipid Res 2001; 40: 283-298.
40.- Banni S, Angioni E, Contini M, Carta G, Casu V, Lengo G, Melis P, Deiana M, Dessi A,
Corongiu F. Conjugated linoleic acid and oxidative stree. J. Am Oil Chem Soc 1998; 75: 261-267.
41.-Yu L. Free radical scavenging properties of conjugated linoleic acid. J Agric Food Chem 2001; 49
3452-3456.
42.- Ha YL, Storkson J, Pariza MW. Inhibition of benzo(a)pyrene-induce mouse forestomach
neoplasia by conjugated derivatives of linoleic acid. Cancer Res 1990; 50: 1097-10101.
43.- O` Quinn, PR, Nelssen JL, Goodband RD, Tokach MD. Conjugated linoleic acid. Anim Health
Res Rev 2000; 1: 35-46.
44.- Kelly GS. Conjugated linoleic acid. Alter Med Rev 2001; 6: 367-382.
45.- Devery R, Miller A, Stanton C. Conjugated linoleic acid and oxidative behaviour in cancer cells.
Biochem Soc Trans 2001; 29: 341-344
46.- Zhang A, Chen ZY. Oxidative stability of conjugated linoleic acid relative to the other
polyunsaturated fatty acid. J Am Oil Chem Soc 1997; 74: 1611-1613.
47.- Chen ZY, Chan PT, Kwan KY, Zhan A. Reassessment of the antioxidant activity of conjugated
linoleic acid. J Am Oil Chem Soc 1997; 73: 749-753.
48.- Rahman SM, Wang YM, Yotsumoto H, Cha JY, Han SY, Inoue S and Yanagita T. Effects of
conjugated linoleic acid on serum leptin concentration, body-fat accumulation, and β -oxidation of
fatty acid in OLETF Rats Nutr 2001; 17: 385-390.
49.-West DB, Delany JP, Camet PM, Blohm F, Truett A and Scimeca J. Effects of conjugated linoleic
acid on body fat and energy metabolims in the mouse. Am J Physiol 1998; 275: R 667- 672.
50.- Delany JP, Blohm F, Truett AA, Scimeca JA and West DB. Conjugated linoleic acid rapidly
reduces body fat content in mice withouth affecting energy intake. Am J Physiol 1999; 276: R 1172R1179.
51.- Blankson H, Stakkestad JA, Erling HF, Wadstein TJ and Gudmundsen O. Conjugated linoleic
acid reduces body fat mass in overweigth and obese humans. J Nutr 2000; 130: 2943-2948.
300
52.- Clouet P, Demizieux L, Gresti J and Degrace P. Mitochondrial respiration on rumenic and linoleic
acids. Biochem Soc Trans 1998; 29: 320-325.
53.- Lin Y, Kreeft A, Schuurbiers JA, Draijer R. Different effects of conjugated linoleic acid Isomers
on lipoprotein lipase activity in 3T3-L1 adipocyte. Nutr Biochem 2001; 12: 183-189.
54.- Ramsay, T.G., Evock-Clover, C.M., Steele, N.C., and Azain, M.J. Dietary conjugated linoleic
acid alters fatty acid composition of pig skeletal muscle and fat. J Anim Sci 2001; 79: 2152-2161.
55.- Ramaswamy N, Baer RJ, Schingoethe DJ, Hippen AR, Kasperson KM, Whitlock LA. Consumer
evaluation of milk high in conjugated linoleic acid. J Dairy Sci 2001; 84: 1607-1609
EFFECTS OF FATTY ACIDS ON MEAT QUALITY: A REVIEW
J. D. Wood , , R. I. Richardson, G. R. Nute, A. V. Fisher, M. M. Campo, E. Kasapidou, P. R.
Sheard and M. Enser
Department of Clinical Veterinary Science, Division of Farm Animal Science, University of Bristol,
Langford, Bristol BS40 5DU, UK
Meat Science Volume 66, Issue 1, January 2004, Pages 21-32
Abstract
Interest in meat fatty acid composition stems mainly from the need to find ways to produce healthier
meat, i.e. with a higher ratio of polyunsaturated (PUFA) to saturated fatty acids and a more favourable
balance between n-6 and n-3 PUFA. In pigs, the drive has been to increase n-3 PUFA in meat and this
can be achieved by feeding sources such as linseed in the diet. Only when concentrations of αlinolenic acid (18:3) approach 3% of neutral lipids or phospholipids are there any adverse effects on
meat quality, defined in terms of shelf life (lipid and myoglobin oxidation) and flavour. Ruminant
meats are a relatively good source of n-3 PUFA due to the presence of 18:3 in grass. Further increases
can be achieved with animals fed grain-based diets by including whole linseed or linseed oil,
especially if this is “protected” from rumen biohydrogenation. Long-chain (C20–C22) n-3 PUFA are
synthesised from 18:3 in the animal although docosahexaenoic acid (DHA, 22:6) is not increased
when diets are supplemented with 18:3. DHA can be increased by feeding sources such as fish oil
although too-high levels cause adverse flavour and colour changes. Grass-fed beef and lamb have
naturally high levels of 18:3 and long chain n-3 PUFA. These impact on flavour to produce a ‘grass
fed’ taste in which other components of grass are also involved. Grazing also provides antioxidants
including vitamin E which maintain PUFA levels in meat and prevent quality deterioration during
processing and display. In pork, beef and lamb the melting point of lipid and the firmness/hardness of
carcass fat is closely related to the concentration of stearic acid (18:0).
Author Keywords: Cattle; Fatty acids; Meat quality; Pigs; Sheep
1. Introduction
There has been an increased interest in recent years in ways to manipulate the fatty acid composition
of meat. This is because meat is seen to be a major source of fat in the diet and especially of saturated
fatty acids, which have been implicated in diseases associated with modern life, especially in
developed countries. These include various cancers and especially coronary heart disease. In the UK,
the [Department of Health, 1994] recommended that fat intake be reduced to 30% of total energy
intake (from about 40%) with a figure of 10% of energy intake for saturated fatty acids (from 15%).
At the same time, the recommended ratio of polyunsaturated fatty acids (PUFA) to saturated fatty
acids (P:S) should be increased to above 0.4. Since some meats naturally have a P:S ratio of around
0.1, meat has been implicated in causing the imbalanced fatty acid intake of today's consumers. For
this reason, ways to improve the P:S ratio during meat production are required. More recently,
nutritionists have focussed on the type of PUFA and the balance in the diet between n-3 PUFA formed
from α-linolenic acid (18:3) and n-6 PUFA formed from linoleic acid (18:2) ([Williams, 2000]). The
ratio of n-6:n-3 PUFA is also a risk factor in cancers and coronary heart disease, especially the
formation of blood clots leading to a heart attack ([Enser, 2001]). The recommendation is for a ratio of
301
less than 4 and again some meats are higher than this. As with the P:S ratio, meats can be manipulated
towards a more favourable n-6:n-3 ratio.
The increasing awareness of the need for diets to contain higher levels of n-3 PUFA has focused on
the importance of meat as a natural supplier of these to the diet. The ratio of n-6:n-3 PUFA is
particularly beneficial (low) in ruminant meats, especially from animals that have consumed grass
which contains high levels of 18:3. Ruminants also naturally produce conjugated linoleic acids (CLAs)
which may have a range of nutritional benefits in the diet ([Enser, 2001]).
Fatty acids are involved in various “technological” aspects of meat quality. Because they have very
different melting points, variation in fatty acid composition has an important effect on firmness or
softness of the fat in meat, especially the subcutaneous and intermuscular (carcass fats) but also the
intramuscular (marbling) fat. Groups of fat cells containing solidified fat with a high melting point
appear whiter than when liquid fat with a lower melting point is present, so fat colour is another aspect
of quality affected by fatty acids. The ability of unsaturated fatty acids, especially those with more
than two double bonds, to rapidly oxidise, is important in regulating the shelf life of meat (rancidity
and colour deterioration). However, this propensity to oxidise is important in flavour development
during cooking.
The aim of this article is to summarise the main effects of fatty acid composition on meat quality and
to review recent work showing the effects on meat quality of changes in fatty acid composition
achieved during production.
2. Fatty acid composition of meat
A survey conducted by [Enser et al., 1996] illustrated the differences in fatty acid composition and
content between beef, lamb and pork. Fifty loin steaks or chops from each species were purchased
from four supermarkets to represent the meat on sale to the public (Table 1). The total fat content of
the steaks (obtained by dissection) was highest in lamb, probably because of a lower level of fat
trimming during butchery. The total fatty acid composition of the longissimus muscle, including some
fat attached to the perimysium, was also highest in lamb and was least in pork. The most obvious
difference in fatty acid composition was that 18:2 was higher in pork, causing a higher P:S ratio. This
is due to the high content of 18:2 in the cereal-based diets consumed by meat animals and this
produced an undesirably high n-6:n-3 ratio.
Table 1. Fat and fatty acid composition of beef, lamb and pork loin steaks purchased from four
supermarkets ([Enser et al., 1996])
ND, not detectable.
The ruminant meats had a more favourable n-6:n-3 ratio, due both to less18:2 than in pork and
relatively high levels of n-3 PUFA, especially 18:3. The study also showed that the long chain (C20–
C22) n-3 PUFA were at low but significant levels in pork subcutaneous fat but not detectable in beef
and lamb, reflecting a relatively greater deposition of long chain derivatives of 18:3 in pig neutral
lipids (triacylglycerols). In ruminant muscle and adipose tissue, PUFA are restricted almost
exclusively to the phospholipid fraction. An illustration of this species effect on 18:2 and 18:3 is in
Table 2. Groups of control animals from two studies are compared. The percentage of 18:2 in
longissimus phospholipids was 12 times greater than that in neutral lipids in the steers and 3 times
greater in pigs. Ratios were 6 and 1 for 18:3 in the steers and pigs, respectively.
Differences in muscle fibre type between muscles are reflected in differences in fatty acid
composition. “Red” muscles have a higher proportion of phospholipids than “white” muscles and
therefore a higher percentage of PUFA. An example is given in Table 3 comparing the longissimus
muscle with the redder leg muscle gluteobiceps. The muscles were taken from 30 grass-fed steers
302
examined by [Enser et al., 1998]. The P:S ratio was significantly higher in gluteobiceps due to higher
concentrations of most PUFA.
Studies on poultry meat have shown similarities with pork i.e. the meat fatty acids are relatively
unsaturated although 18:2 is at a higher level ([Enser, 1999]). This similarity with pork has caused the
US pig industry to label pork as the “other white meat”.
3. Manipulation of fatty acid composition and the effects on meat quality
3.1. Components of meat quality
The components of technological meat quality influenced by fatty acids are fat tissue firmness
(hardness), shelf life (lipid and pigment oxidation) and flavour. Although there have been suggestions
that dietary fatty acids influence tenderness and juiciness, these are more likely to be affected by the
total amount of fatty acids rather than individual ones. The effect of fatty acids on firmness is due to
the different melting points of the fatty acids in meat. In the 18C fatty acid series, stearic acid (18:0)
melts at 69.6 °C, oleic acid (18:1) at 13.4 °C, 18:2 at -5 °C and 18:3 at -11 °C. Thus as unsaturation
increases, melting point declines. Variation in the structure of the molecule are also important. For
example, trans fatty acids melt at a higher temperature than their cis-isomers and branched chain fatty
acids have lower melting points than the straight chain fatty acids with the same number of carbon
atoms ([Enser, 1984]).
The effect of fatty acids on shelf life is explained by the propensity of unsaturated fatty acids to
oxidise, leading to the development of rancidity as display times increases. The colour change is due
to the oxidation of red oxymyoglobin to brown metmyoglobin, this reaction generally proceeding in
parallel to that of rancidity. Several studies have shown that lipid oxidation products can promote
pigment oxidation and vice versa although the strength of the relationship between these two aspects
of shelf life is sometimes low ([Renerre, 2000]). Antioxidants, especially α-tocopherol (vitamin E)
have been used to delay lipid and colour oxidation and to extend shelf life.
The effect of fatty acid on meat flavour is due to the production of volatile, odourous, lipid oxidation
products during cooking and the involvement of these with Maillard reaction products to form other
volatiles which contribute to odour and flavour. The unsaturated phospholipid fatty acids are
particularly important in flavour development. Early research showed that the fat tissues in meat were
the source of the characteristic species flavour ([Mottram, 1998]).
3.2. Fatty acids and meat quality in pigs
Studies conducted at Bristol in the 1970s and 1980s showed that 18:0 and 18:2 are particularly
important contributors to fat tissue firmness. As fatty acid composition was changed for reasons of
diet, genetics, sex or fatness, these two showed the highest correlations with firmness measured
subjectively (a finger test) or objectively (using a compression tester or penetrometer). The ratio of
18:0:18:2 was found by [Whittington et al., 1986] to provide the best prediction of firmness. In a study
by [Wood et al., 1978] of pigs selected for lean content, the melting point of extracted lipid was also
closely related to the concentrations of 18:0 and 18:2, with 18:0 showing the highest correlation. The
role of 18:0 is particularly interesting since it varies across a smaller range than 18:2.
Fat tissue consists not only of fatty acids contained in fat cells but also the connective tissue matrix
associated with water. In pigs, the concentration of water in thin (i.e. underdeveloped) backfat is very
high as is that of collagen (Table 4). These constituents are also good predictors of tissue firmness
along with the concentrations of 18:0 and 18:2 and the thickness of the fat tissue itself. These results
show that fat tissue development in the pig is an extremely ordered process with all the major
constituents closely interrelated.
As subcutaneous fat tissue develops and changes in composition, it becomes more cohesive i.e. is less
easily separated within itself layer by layer. The problem of fat tissue separation is unsightly in fresh
pork and particularly in bacon or ham. Studies have shown that cohesiveness is closely related to
water, collagen, 18:0 and 18:2 fatty acid concentrations, just as is firmness (Table 4).
After slaughter, various changes occurring in pig meat favour oxidation, for example the release of
iron from within cells and the loss of the glutathione peroxidase enzyme system ([Morrissey et al.,
303
1998]). Because the lipids in pig meat are relatively unsaturated, attempts to further increase
concentrations of PUFA risk the generation of lipid oxidation products, leading to off-odours and
flavours and colour changes.
Several papers have examined the effects of dietary oils containing a high proportion of 18:2 on the
fatty acid composition and quality of pigmeat. Examples of such oils are soya, peanut, maize and
sunflower. Concentrations of 18:2 can easily be raised from basal levels of around 10–15% of fatty
acids to over 30% ([Hartman et al., 1985 and West and Myer, 1987]), the effect being rapidly
achieved. For example in one study, [Warnants et al., 1999] showed the full effect of feeding full fat
soya oil to pigs from 30 kg live weight was achieved in 6 weeks and 50% of this was achieved in 2
weeks.
[Larick et al., 1992] showed that muscles with raised levels of 18:2 oxidised rapidly when heated,
producing various volatile compounds, including the aldehydes pentanal and hexanal. However, there
was no change in the flavour of ground pork patties made from meat with low or high concentrations
of 18:2 and no effect on muscle colour. [Hartman et al., 1985] raised the 18:2 concentration from 15 to
33% of total fatty acids and also found no effects on the flavour or colour of pork chops. A similar
result was found by [West and Myer, 1987]. [Melton, 1990] speculated that because pork was
naturally high in 18:2, its oxidation products are recognised by consumers as natural components of
pork flavour.
Supplementing pig diets with 18:3 to lower the n-6:n-3 ratio has been examined by several workers.
Canola (rapeseed) oil and especially flaxseed (linseed) are good sources of this. In some papers, no
effects on meat quality parameters have been observed ([Enser et al., 2000 and Leskanich et al., 1997])
but in others, adverse effects on odours and flavours have been detected, especially when oxidative
stress in meat is increased by preparation treatment (e.g. salt injection, comminution, freezing and
reheating; [Myer et al., 1992 and Shackelford et al., 1990]). A possible explanation for these results
lies in the level of 18:3 achieved in the fat or muscle tissue. Above about 3% of total fatty acids, the
mix of volatile compounds produced on cooking seems to adversely impact on flavour as detected by
taste panellists. [Campo et al., 2003], in a model system, found that odour scores were often higher for
18:3 than for 18:2, i.e. 18:3 produces more intense odours.
[Enser et al., 2000 and Sheard et al., 2000] showed that the n-6:n-3 ratio in pork could be reduced
close to the target level (less than 4) by feeding crushed whole linseed, with no detectable adverse
effects on meat quality. They showed that increasing the 18:3 content of longissimus muscle total lipid
from 1% in controls to 1.6% in those fed linseed, which lowered the n-6:n-3 ratio to five (compared
with nine in controls), had no effects on lipid oxidation measured using thiobarbituric acid reacting
substances test (TBARSs), colour saturation (vividness of red colour) or the eating quality of grilled
loin chops.
[Kouba et al., 2002] showed that feeding a diet containing 6% whole crushed linseed reduced the n6:n-3 ratio in longissimus muscle to 3.9 in only 20 days from 40 kg live weight compared with a ratio
of 7.6 in controls. Ratios were 3.0 at 60 days and 3.1 at 100 days on the linseed diet, corresponding to
18:3 concentrations of 3.0 and 2.2% in longissimus total lipid at 60 and 100, days respectively. This
supports the conclusion of [Warnants et al., 1999] that maximal feeding effects with essential fatty
acids can be achieved within 40 days, with half of the effect occurring within 2 weeks. Results in Fig.
1a from the study of Kouba et al. show the similarity of 18:3 concentrations in pig neutral lipids and
phospholipids, whereas the long-chain PUFAs, e.g. eicosapentaenoic acid (EPA, 20:5) are much
higher in phospholipids. For both fatty acids, the concentration at 100 days on the linseed diet was
significantly lower than at 60 days. Levels of n-3 PUFA in the pigs fed the linseed diet produced
higher TBARS levels following conditioning for 10 days followed by simulated retail display for a
further 7 days (Fig. 1b) but this did not impact on muscle colour (saturation) during the display period
(Fig. 1c). However, there were detectable differences in odours and flavours between the diets in
grilled pork chops as identified by the trained taste panel (Fig. 1d). The pigs fed linseed had lower
scores for pork odour and pork flavour and higher scores for abnormal odour and abnormal flavour.
These results confirm the US data (e.g. [Shackelford et al., 1990]) showing that 18:3 concentrations of
304
above about 3% in total lipid or neutral lipid can produce relatively undesirable flavours if processing
conditions accelerate lipid oxidation.
In the study of [Kouba et al., 2002]; Fig. 1), the concentration of vitamin E in longissimus was lower
in the pigs fed linseed after 60 days than in controls (2.1 vs. 2.9 µg/g). Vitamin E added to the diet was
the same in both groups (150 mg/g) so this effect could be associated with greater utilisation of the
antioxidant to protect the more unsaturated phospholipid fatty acids.
Changes in fatty acid composition have not been directly linked to changes in myoglobin oxidation
and muscle colour in many of the pig studies reported ([Kouba et al., 2002, Larick et al., 1992, Sheard
et al., 2000 and West and Myer, 1987]). In several studies in which supranutritional vitamin E has
been used to inhibit fatty acid oxidation, concomitant improvements in colour stability have also not
been observed ([Jensen et al., 1997 and Phillips et al., 2001]). [Jensen et al., 1997] speculated that the
beneficial effect of added vitamin E on muscle colour depends on the relative muscle vitamin E level
in controls. Where these are above a critical level, say 3.5 µg/g, no beneficial effect is seen. Where the
level is low, for example, in the study of [Asghar et al., 1991]; Table 5), supplementation to the critical
level improves colour retention. In contrast, suppression of lipid oxidation is consistently observed at
all muscle levels of added vitamin E.
The total fatty acid content of muscle (i.e. neutral lipid plus phospholipid fatty acids), termed marbling
fat, has long been recognised as a factor in eating quality, especially juiciness and tenderness although
the strength of the relationship has been questioned ([Wood, 1990]). There are several possible
explanations for a positive effect of lipid on tenderness, including the location of neutral lipid in fat
cells within the perimysium which could have a physical effect in separating muscle fibre bundles,
beginning the process of tenderisation by “opening up the muscle structure”. Lipids could also trap
moisture in muscle, improving juiciness. There are clear genetic effects on the concentrations of total
fatty acids in muscle, for example, [Wood et al., 2003] found that Duroc and Berkshire pure bred pigs
had higher concentrations of both neutral lipids and phospholipids in longissimus and psoas muscles
than Large Whites and Tamworths (Table 6). The two “traditional” breeds (Berkshire and Tamworth)
had by far the fattest carcasses so the results indicated a big genetic effect on “fat partitioning”
between intramuscular and carcass fat depots. The fatty acid composition results were also not as
predicted. When neutral lipid increases, the percentage of 18:2 is expected to decline as in the
Berkshires compared with the Large Whites and as observed in backfat ([Wood, 1984 and Wood et al.,
1985]). The high percentage of 18:2 in Durocs was therefore unexpected and they also had the highest
concentration of 18:3 in neutral lipid. Values for phospholipid were more similar between the breeds.
3.3. Fatty acids and meat quality in ruminants
Ruminant fat tissue is naturally firmer than that of pigs, because the fatty acid profile is more
saturated. In the first stages of fattening in cattle, the concentration of saturated relative to unsaturated
fatty acids increases as in pigs, but beyond a certain fat level in the animal this ratio then declines. In
very fat cattle, fat is soft and oily, mainly due to an increase in 18:1 relative to 18:0 and 16:0 ([Leat,
1975 and Wood, 1984]). [Wood, 1984] recorded a value for 18:0 of 14.7% of total fatty acids in a
young heifer and 2.7% in an 11-year-old fat steer. In 1000 lambs selected in four abattoirs and
sampled throughout the year, [Enser and Wood, 1993] found that the concentration of 18:0, as with
pigs, showed the highest correlation with melting point ( Fig. 2). Average melting point of
subcutaneous fat was 39.5 °C (range 30–49 °C) and correlations were 0.89, −0.42 and −0.31 for 18:0,
18:1 and 18:2 fatty acid concentrations, respectively. It was calculated that only 35% of these fat
samples would melt in the mouth of the consumer, confirming the hard nature of lamb fat and its
tendency to feel sticky in the mouth. The lowest melting points were in the summer months May–
August corresponding with the arrival of “new seasons” lamb.
In lambs, especially ram lambs, soft fat develops in animals fed grain-based (concentrate) diets. This is
due not only to a lower concentration of 18:0 but also to an increased deposition of medium to longchain (C10–C17) branched chain fatty acids formed from methylmalonate, a metabolite of propionate
([Busboom et al., 1981]). These authors found that the total concentration of branched chain fatty
acids was a good predictor of lamb fat firmness but the correlation with 18:0 was equally strong (
305
The presence of the rumen makes fatty acid composition in beef and sheep more difficult to
manipulate by changing diet than in pigs. Nevertheless, there are some clear effects of diet on tissue
fatty acid composition. [Scollan et al., 2001 and Vatansever et al., 2000] fed different oils to cattle in a
forage:concentrate diet in which total oil content was 6% of dry matter of which 3% was the test oil.
Animals were fed for 120 days, after which steaks from longissimus and burgers from the forequarter
muscles infraspinatus, supraspinatus and triceps brachi were examined ([Vatansever et al., 2000]). A
loin joint was conditioned for 11 days at 1 °C after which steaks were cut, wrapped in oxygenpermeable film and displayed for up to 16 days under simulated retail conditions. Lipid oxidation and
colour measurements were made during this time. After 5 days of display, steaks were taken for
subsequent analysis by the trained taste panel. Burgers were also used for lipid oxidation and colour
measurements, being packed in a modified atmosphere (O2:CO2 75:25) in sealed plastic containers.
Lipid oxidation tests for the burgers were conducted after heating in a plastic bag to 78 °C, cooling
and 24 h storage. This procedure was used to enhance lipid oxidation and test the stability of the highPUFA beef. The results (Fig. 3) show that n-3 PUFA concentrations were greatly influenced by diet.
The linseed diet doubled the 18:3 concentration in phospholipids compared with controls, which led to
a higher level of EPA but not docasahexanoic acid (DHA 22:6; Fig. 3a). These two fatty acids were
increased in the fish oil and linseed/fish oil diets. Lipid oxidation in the steaks increased at 8 and 11
days of display (Fig. 3b) and was especially high in the fish oil diet, exceeding the cut off value of 2
mg malonaldehyde per kg of meat, at which rancidity may be detected by consumers ([Younathan and
Watts, 1959]). Lipid oxidation in the burgers was much more pronounced than in the steaks, a TBARS
value of 2 mg malonaldehyde per kg being achieved at only 3 days of display ([Vatansever et al.,
2000]). Colour saturation was also affected by feeding treatment, declining fastest in the fish oil diet in
which lipid oxidation was greatest (Fig. 3c).
In order to understand the links between meat composition and flavour, the beef produced from the
linseed, fish oil and linseed/fish oil diets was analysed for aroma volatile production after cooking in
an autoclave. The results (Figs. 3d and e) showed that the samples with high n-3 PUFA concentrations
produced higher concentrations of lipid degradation products, particularly saturated and unsaturated
aldehydes, alcohols and ketones. Aldehydes were quantitatively the most important and since they
have low odour thresholds they are thought to be the reason for the changes in flavour of the modified
beef ([Elmore et al., 1999]). Some of these aldehydes are more likely to derive from 18:1 and 18:2
than from 18:3. It is suggested that free radicals formed from the more unsaturated and easily oxidised
n-3 PUFA initiated the oxidation of these more abundant fatty acids ([Elmore et al., 1999]). The taste
panel detected a difference in flavour attributes of steaks from the fish oil group and the rest (Fig. 3f),
recording higher values for rancidity and fishy notes and a lower score for overall liking, however
these differences were not large on the 100-point scale.
Fig. 3. Effects of dietary n-3 PUFA on fatty acid composition and meat quality in steers. (a)
Phospholipid fatty acids in minced forequarter muscles (%) ([Vatansever et al., 2000]). (b) Lipid
oxidation in longissimus after 11 days conditioning at 1 °C and display in overwrapped packs at 4 °C.
Assessed as TBARS (mg malonaldehyde/kg) ([Vatansever et al., 2000]). (c) Colour saturation of
burgers prepared from forequarter muscles during retail display in modified atmosphere packs
([Vatansever et al., 2000]). (d) Saturated aldehydes (ng/100 g) detected in headspace volatiles of
cooked longissimus ([Elmore et al., 1999]). (e) Unsaturated aldehydes (ng/100 g) detected in
headspace volatiles of cooked longissimus ([Elmore et al., 1999]). (f) Taste panel results for grilled
longissimus steaks (0–100 scales; [Vatansever et al., 2000]).
[Campo et al., 2003] have studied the effects of individual fatty acids on aromas in an in vitro system
in which the fatty acids were heated alone and with cysteine and ribose. The results (Table 8) show
that meaty aromas are much more pronounced when cysteine and ribose are also present, i.e. they
derive from interactions between Maillard reaction products and fatty acids. On the other hand, some
flavour notes were more associated with the fatty acids alone, e.g. oily. The fatty acids18:1, 18:2 and
18:3 produced different odour profiles, e.g. 18:3 produced high scores for fishy, linseed/putty and
306
creosote. The term “grassy” was also scored higher for 18:3 plus cysteine and ribose, especially when
Fe SO4 was used to catalyse the oxidation reactions.
Although some dietary PUFA in linseed and other plant oils escapes rumen biohydrogenation, a high
proportion (>90%) is hydrogenated leading to high values for saturated fatty acids in ruminant meats
([Scollan et al., 2001]). So studies such as that by [Scollan et al., 2001 and Vatansever et al., 2000]
have usually not increased the P:S ratio in meat beyond the 0.1 level normally seen. To achieve higher
values, two options are to feed a predominantly cereal (concentrate) diet in which rumen
biohydrogenation is less effective or to “protect” the dietary oil using a procedure such as
formaldehyde treatment of dietary protein which protects the oil within a matrix structure ([Scott et al.,
1971]). We have a fed a 2:1 soya oil:linseed oil supplement in recent work and by so doing have raised
the P:S ratio to around 3. The n-6:n-3 ratio was raised slightly, but still remained below the target
value of 4.0 ([Enser et al., 2001]).
Studies with beef and lamb have shown that the concentrations of 18:3 and 20:5 in muscle
phospholipids are higher when animals have consumed grass than when they have been fed grainbased (concentrate) diets. In the latter case, 18:2 and arachidonic (20:4 n-6) fatty acids are increased
relative to 18:3 ([Enser et al., 1998, Fisher et al., 2000 and Marmer et al., 1984]). These results are due
to the predominance of 18:3 in grass lipids and 18:2 in most other plants and seeds.
In the study of [Fisher et al., 2000], Suffolk cross lambs were reared on lowland grass or on a standard
concentrate diet. The total lipid of semimembranosus contained higher concentrations of 18:3, 20:5
and 22:6 in the grass-fed group and higher concentrations of 18:2 and 20:4 in the concentrate group
(Fig. 4). In grilled loin chops, taste panellists gave higher scores for lamb flavour and overall liking to
the grass group and higher scores for abnormal lamb flavour, metallic, bitter and rancid to the
concentrate group.
In a study involving British lambs fed grass and Spanish lambs fed milk and concentrates, analgous
differences in fatty acid composition were observed, i.e. the grass fed animals had higher muscle
concentrations of n-3 PUFA and the concentrate-fed animals had higher concentrations of the n-6
PUFA ([Sanudo et al., 2000]). When the meat was assessed by British and Spanish taste panels, both
found the British lamb (higher in n-3 PUFA) to have a higher odour and flavour intensity, but whereas
the British panel preferred the flavour and overall eating quality of the grass-fed lamb, the Spanish
panel scored flavour liking and overall liking higher in the Spanish lamb ( Fig. 5). This preference for
grain-finished products is also expressed by US taste panellists and consumers who are more used to
the taste of beef and lamb produced in feedlot conditions and prefer it to grass-fed beef and lamb
([Kemp et al., 1981, Larick and Turner, 1990 and Medeiros et al., 1987]).
In the British/Spanish data set, wide ranges of n-3 and n-6 PUFA concentrations were found and quite
strong correlations were seen between these and the taste panel scores, the strongest relationships
involving 18:2, 20:4 and 18:3 (Table 9). For example, the concentration of 18:3 was positively
correlated with odour and flavour intensity scores given by both taste panels. The correlations with
flavour liking and overall liking were positive for the British panel and negative for the Spanish panel.
An explanation for these positive relationships between 18:3 and meat flavour is that the oxidation
products of 18:3 and it's derivatives are directly responsible for the differences in flavour observed
between grass-fed cattle and sheep. [Larick and Turner, 1990] also found that the headspace volatile
compounds produced on cooking beef fed grass or grains were dominated by lipid oxidation products,
especially aldehydes and [Priolo et al., 2001] concluded in a review that n-3 PUFA oxidation products
are mainly responsible for the particular flavour of grass-fed lamb. However, another explanation for
the results is that n-6 and n-3 PUFA are markers for grain and grass diets, respectively and other
components of meat are more directly responsible for the flavours produced. In sheep, several authors
have shown that branched chain fatty acids of medium chain length are important constituents of lamb
odours and flavours ([Wong et al., 1975]) and [Young et al., 1997] showed that 4-methyloctanoic acid
and 4-methylnonanoic acid were increased on a grass compared with a grain diet. Grass feeding also
307
increased concentrations of diterpenoids which derive from chlorophyll breakdown in the rumen.
Similar results have been found in cattle ([Melton, 1990]). [Young et al., 1997] also found that the
concentration of 3-methylindole (skatole), which is responsible for boar taint in pigs, was increased in
grass diets and was partly responsible for the grass-fed effect.
Several authors have shown that lipid oxidation and colour development in ruminant meats is
influenced by both fatty acid composition and the concentration of the tissue antioxidant, vitamin E
([Arnold et al., 1993 and Renerre, 2000]). In a recent comparison of grass-fed and grain-fed cattle by
our group ([Warren et al., 2002]), the bright red colour associated with oxymyoglobin was retained
longer in retail display in the grass-fed group. Although the total concentration of unsaturated fatty
acids was similar in both, grass feeding produced higher concentrations of more oxidisable n-3 PUFA
and grain feeding increased levels of n-6 PUFA. The conclusion was that antioxidants in grass
probably caused higher tissue levels of vitamin E in these animals with benefits for lower lipid
oxidation and better colour retention despite greater potential for lipid oxidation. [Yang et al., 2002]
reported high tissue levels of vitamin E in grass-fed beef, similar to those recorded in grain-fed cattle
supplemented with 2.5 g vitamin E/head/day. In studies with sheep, [Kasapidou et al., 2001] showed
that low tissue concentrations of vitamin E are associated with lower amounts of both n-6 and n-3
PUFA in tissues. This suggests that loss of PUFA occurs in vivo when antioxidant status is low. These
studies also showed that muscle concentrations of vitamin E in sheep were often well below the level
of 3.0–3.5 µg/g suggested by [Arnold et al., 1993 and Liu et al., 1996] as necessary for optimum
antioxidant status in cattle. This was particularly true when the lambs were fed a grain-based
(concentrate) diet alone. When grass was included in a mixed diet with concentrates, vitamin E levels
were usually restored to around 3 µg/g. The associations found between lipid oxidation, colour
development and vitamin E concentration in steers by [Liu et al., 1996] show that the interrelationship
between fatty acid composition, in both lipid fractions and tissue vitamin E in ruminants is crucial to
many aspects of metabolism, with eventual implications for meat quality.
Acknowledgements
We are grateful to our collaborators in providing many of the results presented here, including Institute
of Grassland and Environmental Research, Harper Adams University College and University of
Reading. Funding was provided by Department for Environment, Food and Rural Affairs (DEFRA),
Meat and Livestock Commission, ABN Ltd, JSR Farms Ltd, Tesco Stores Ltd, Roche Products Ltd,
International Fishmeal and Oil Manufacturers Association and Southern Counties Fresh Foods Ltd.
We gratefully acknowledge the technical assistance of Kathy Hallett, Fran Whittington, Kevin Gibson,
Anita Robinson, Rose Ball, Anne Baker and Sue Hughes
References
Arnold et al., 1993. R.N. Arnold, S.C. Arp, K.K. Scheller, S.N. Williams and D.M. Schaefer, Tissue
equilibration and subcellular distribution of vitamin E relative to myoglobin and lipid oxidation in
displayed beef. Journal of Animal Science 71 (1993), pp. 105–118.
Asghar et al., 1991. A. Asghar, J.I. Gray, A.M. Booren, E.A. Gomaa, M.M. Abouzied and E.R. Miller,
Effects of supranutritional dietary vitamin E levels on subcellular disposition of α-tocopherol in the
muscle and on pork quality. Journal of the Science of Food and Agriculture 57 (1991), pp. 31–41.
Busboom et al., 1981. J.R. Busboom, G.J. Miller, R.A. Field, J.D. Crouse, M.L. Riley, G.E. Nelms and
C.L. Ferrell, Characteristics of fat from heavy ram and wether lambs. Journal of Animal Science 52
(1981), pp. 83–92.
Campo et al., 2003. Campo, M. M., Nute, G. R., Wood, J. D., Elmore, S. J., Mottram, D. S., & Enser,
M. (2003). Modelling the effect of fatty acids in odour development of cooked meat in vitro: Part I—
sensory perception. Meat Science, 63, 367–375.
Choi et al., 2000. N.-J. Choi, M. Enser, J.D. Wood and N.D. Scollan, Effect of breed on the deposition
in beef muscle and adipose tissue of dietary n-3 polyunsaturated fatty acids. Animal Science 71 (2000),
pp. 509–519.
Department of Health, 1994. Department of Health, Nutritional Aspects of Cardiovascular Disease.
Report on Health and Social Subject No. 46. , Her Majesty's Stationery Office, London (1994).
308
Elmore et al., 1999. J.S. Elmore, D.S. Mottram, M. Enser and J.D. Wood, Effect of polyunsaturated
fatty acid composition of beef muscle on the profile of aroma volatiles. Journal of Agricultural and
Food Chemistry 47 (1999), pp. 1619–1625.
Enser, 1984. M. Enser, The chemistry, biochemistry and nutritional importance of animal fats. In: J.
Wiseman, Editor, Fats in animal nutrition, Butterworths, London (1984), pp. 23–51.
Enser, 1999. M. Enser, Nutritional effects on meat flavour and stability. In: R.I. Richardson and G.C.
Mead, Editors, Poultry Meat Science. Poultry Science Symposium Series (Vol. 25), CABI Publishing,
Wallingford, UK (1999), pp. 197–215.
Enser, 2001. M. Enser, The role of fats in human nutrition. In: B. Rossell, Editor, Oils and fats, Vol. 2.
Animal carcass fats, Leatherhead Publishing, Leatherhead, Surrey, UK (2001), pp. 77–122.
Enser et al., 1996. M. Enser, K. Hallett, B. Hewett, G.A.J. Fursey and J.D. Wood, Fatty acid content
and composition of English beef, lamb and pork at retail. Meat Science 44 (1996), pp. 443–458.
Enser et al., 1998. M. Enser, K.G. Hallett, B. Hewett, G.A.J. Fursey, J.D. Wood and G. Harrington,
Fatty acid content and composition of UK beef and lamb muscle in relation to production system and
implications for human nutrition. Meat Science 49 (1998), pp. 329–341
Enser et al., 2000. M. Enser, R.I. Richardson, J.D. Wood, B.P. Gill and P.R. Sheard, Feeding linseed
to increase the n-3 PUFA of pork: fatty acid composition of muscle, adipose tissue, liver and sausages.
Meat Science 55 (2000), pp. 201–212
Enser et al., 2001. M. Enser, N. Scollan, S. Gulati, I. Richardson, G. Nute and J. Wood, The effects of
ruminally-protected dietary lipid on the lipid composition and quality of beef muscle. Proceedings of
the 47th International Congress of Meat Science and Technology 1 (2001), pp. 12–13.
Enser and Wood, 1993. M. Enser and J.D. Wood, Effect of time of year on fatty acid composition and
melting point of UK lamb. Proceedings of the 39th International Congress of Meat Science and
Technology 2 (1993), p. 74.
Fisher et al., 2000. A.V. Fisher, M. Enser, R.I. Richardson, J.D. Wood, G.R. Nute, E. Kurt, L.A.
Sinclair and R.G. Wilkinson, Fatty acid composition and eating quality of lamb types derived from
four diverse breed×production systems. Meat Science 55 (2000), pp. 141–147.
Hartman et al., 1985. A.D. Hartman, W.J. Costello, G.W. Libal and R.C. Walhlstrom, Effect of
sunflower seeds on performance, carcass quality, fatty acids and acceptability of pork. Journal of
Animal Science 60 (1985), pp. 212–219.
Jensen et al., 1997. C. Jensen, J. Guidera, I.M. Skovgaard, H. Staun, L.H. Skibsted, S.K. Jensen, A.J.
Moller, J. Buckley and G. Bertelsen, Effects of dietary α-tocopheryl acetate supplementation on αtocopherol deposition in porcine m. psoas major and m.longissimus dorsi and on drip loss, colour
stability and oxidative stability in pork meat. Meat Science 45 (1997), pp. 491–500.
Kasapidou et al., 2001. E. Kasapidou, J.D. Wood, L.D. Sinclair, R.G. Wilkinson and M. Enser, Diet
and vitamin E metabolism in lambs: effects of dietary supplementation on meat quality. Proceedings
of the 47th Congress of Meat Science and Technology 1 (2001), pp. 42–43.
Kemp et al., 1981. J.D. Kemp, L. Mahyuddin, D.J. Ely, J.D. Fox and W.G. Moody, Effect of feeding
systems, slaughter weight and sex on organoleptic properties and fatty acid composition of lamb.
Journal of Animal Science 51 (1981), pp. 321–330.
Kouba et al., 2002. Kouba, M., Enser, M., Whittington, F. M., Nute, G. R., & Wood, J. D. Effect of a
high linolenic acid diet on lipogenic enzyme activities, fatty acid composition and meat quality in the
growing pig. Journal of Animal Science (in press).
Larick and Turner, 1990. D.K. Larick and B.E. Turner, Head space volatiles and sensory
characteristics of ground beef from forage- and grain fed heifers. Journal of Food Science 54 (1990),
pp. 649–654.
Larick et al., 1992. D.K. Larick, B.E. Turner, W.D. Schoenherr, M.T. Coffey and D.H. Pilkington,
Volatile compound contents and fatty acid composition of pork as influenced by linoleic acid content
of the diet. Journal of Animal Science 70 (1992), pp. 1397–1403.
Leat, 1975. W.M.F. Leat, Fatty acid composition of adipose tissue of Jersey cattle during growth and
development. Journal of Agricultural Science, Cambridge 85 (1975), pp. 551–558.
Leskanich et al., 1997. C.O. Leskanich, K.R. Matthews, C.C. Warkup, R.C. Noble and M. Hazzledine,
The effect of dietary oil containing n-3 fatty acids on the fatty acids, physiochemical and organoleptic
characteristics of pigmeat and fat. Journal of Animal Science 75 (1997), pp. 673–683.
309
Liu et al., 1996. Q. Liu, K.K. Scheller, S.C. Arp, D.M. Schaefer and S.N. Williams, Titration of fresh
meat stability and malondialdehyde development with Holstein steers fed vitamin E-supplemented
diets. Journal of Animal Science 74 (1996), pp. 117–126.
Marmer et al., 1984. W.N. Marmer, R.J. Maxwell and J.E. Williams, Effects of dietary regimen and
tissue site on bovine fatty acid profiles. Journal of Animal Science 59 (1984), pp. 109–121.
Medeiros et al., 1987. L.C. Medeiros, R.A. Field, D.J. Menkhaus and W.C. Russell, Evaluation of
range-grazed, concentrate-fed beef by a trained sensory panel, a household panel and a laboratory test
market group. Journal of Sensory Studies 2 (1987), pp. 259–272.
Melton, 1990. S.L. Melton, Effects of feeds on flavour of red meat: a review. Journal of Animal
Science 68 (1990), pp. 4421–4435.
Morrissey et al., 1998. P.A. Morrissey, P.J.A. Sheehy, K. Galvin, J. Kerry and D.J. Buckley, Lipid
stability in meat and meat products. Proceedings of the 44th International Congress of Meat Science
and Technology 1 (1998), pp. 120–131.
Mottram, 1998. D.S. Mottram, Flavour formation in meat and meat products: a review. Food
Chemistry 62 (1998), pp. 415–424.
Myer et al., 1992. R.O. Myer, D.D. Johnson, D.A. Knauft, D.W. Gorbet, J.H. Brendemuhl and W.R.
Walker, Effect of feeding high-oleic acid peanuts to growing-finishing swine on resulting carcass fatty
acid profile and on carcass and meat quality characteristics. Journal of Animal Science 70 (1992), pp.
3734–3741.
Phillips et al., 2001. A.L. Phillips, C. Faustman, M.P. Lynch, K.E. Govoni, T.A. Hoagland and S.A.
Zinn, Effect of dietary α-tocopherol supplementation on colour and lipid stability on pork. Meat
Science 58 (2001), pp. 389–393.
Priolo et al., 2001. A. Priolo, D. Mikol and J. Agabaiel, Effects of grass feeding systems on ruminant
meat colour and flavour: a review. Animal Research 50 (2001), pp. 185–200.
Renerre, 2000. M. Renerre, Oxidative processes and myoglobin. In: E. Deker, C. Faustman and C.J.
Lopez-Bote, Editors, Antioxidants in muscle foods, John Wiley, New York, NY (2000), pp. 113–133.
Sanudo et al., 2000. C. Sanudo, M. Enser, M.M. Campo, G.R. Nute, G. Maria, I. Sierra and J.D.
Wood, Fatty acid composition and fatty acid characteristics of lamb carcasses from Britain and Spain.
Meat Science 54 (2000), pp. 339–346
Scollan et al., 2001. N.D. Scollan, N.-J. Choi, E. Kurt, A.V. Fisher, M. Enser and J.D. Wood,
Manipulating the fatty acid composition of muscle and adipose tissue in beef cattle. British Journal of
Nutrition 85 (2001), pp. 115–124.
Scollan et al., 2001. N.D. Scollan, M.S. Dhanoa, N.-J. Choi, W.J. Maeng, M. Enser and J.D. Wood,
Biohydrogenation and digestion of long chain fatty acids in steers fed on different sources of lipid.
Journal of Agricultural Science, Cambridge 136 (2001), pp. 345–355.
Scott et al., 1971. T.W. Scott, L.J. Cook and S.C. Mills, Protection of dietary polyunsaturated fatty
acids against microbial hydrogenation in ruminants. Journal of the American Oil Chemists Society 48
(1971), pp. 358–364.
Shackelford et al., 1990. S.D. Shackelford, J.O. Reagan, K.D. Haydon and M.F. Miller, Effects of
feeding elevated levels of monounsaturated fats to growing-finishing swine on acceptability of
boneless hams. Journal of Food Science 55 (1990), pp. 1485–1517.
Sheard et al., 2000. P.R. Sheard, M. Enser, J.D. Wood, G.R. Nute, B.P. Gill and R.I. Richardson, Shelf
life and quality of pork and pork products with a raised n-3 PUFA. Meat Science 55 (2000), pp. 213–
221.
Vatansever et al., 2000. L. Vatansever, E. Kurt, M. Enser, G.R. Nute, N.D. Scollan, J.D. Wood and
R.I. Richardson, Shelf life and eating quality of beef from cattle of different breeds given diets
differing in n-3 polyunsaturated fatty acid composition. Animal Science 71 (2000), pp. 471–482.
Warnants et al., 1999. N. Warnants, M.J. Van Oeckel and C.V. Boucqué, Incorporation of dietary
polyunsaturated fatty acids into pork fatty tissues. Journal of Animal Science 77 (1999), pp. 2478–
2490.
Warren et al., 2002. H.E. Warren, N.D. Scollan, K. Hallett, M. Enser, R.I. Richardson, G.R. Nute and
J.D. Wood, The effects of breed and diet on the lipid composition and quality of bovine muscle.
Proceedings of the 48th Congress of Meat Science and Technology 1 (2002), pp. 370–371.
310
West and Myer, 1987. R.L. West and O.L. Myer, Carcass and meat quality characteristics and backfat
fatty acid composition of swine as affected by the consumption of peanuts remaining in the field after
harvest. Journal of Animal Science 65 (1987), pp. 475–480.
Whittington et al., 1986. F.M. Whittington, N.J. Prescott, J.D. Wood and M. Enser, The effect of
dietary linoleic acid on the firmness of backfat in pigs on 85kg live weight. Journal of the Science of
Food and Agricultural 37 (1986), pp. 753–761.
Williams, 2000. C.M. Williams, Dietary fatty acids and human health. Annales Zootechnie 49 (2000),
pp. 165–180.
Wong et al., 1975. E. Wong, L.N. Nixon and C.B. Johnson, Volatile medium chain fatty acids and
mutton flavour. Journal of Agricultural and Food Chemistry 23 (1975), pp. 495–498.
Wood, 1984. J.D. Wood, Fat deposition and the quality of fat tissue in meat animals. In: J. Wiseman,
Editor, Fats in animal nutrition, Butterworths, London (1984), pp. 407–435.
Wood, 1990. J.D. Wood, Consequences for meat quality of reducing carcass fatness. In: J.D. Wood
and A.V. Fisher, Editors, Reducing fat in meat animals, Elsevier Applied Science, London (1990), pp.
344–397.
Wood et al., 1978. J.D. Wood, M. Enser, H.J.H. MacFie, W.C. Smith, J.P. Chadwick and M. Ellis,
Fatty acid composition of backfat in Large White pigs selected for low backfat thickness. Meat
Science 2 (1978), pp. 289–300.
Wood et al., 1985. J.D. Wood, R.C.D. Jones, J.A. Bayntun and E. Dransfield, Backfat quality in boars
and barrows at 90 kg live weight. Animal Production 40 (1985), pp. 481–487.
Wood et al., 2003. Wood, J. D., Whittington, F. M., Nute, G. R., Richardson, R. I., Sheard, P. R., &
Chang, K. C. Muscle fatty acids and eating quality in traditional and modern pig breeds. Meat Science
(in preparation).
Yang et al., 2002. A. Yang, M.J. Brewster, M.C. Lanari and R.K. Tume, Effect of vitamin E
supplementation on α-tocopherol and β-kerotene concentrations in tissues from pasture-and grain-fed
cattle. Meat Science 60 (2002), pp. 35–40.
Younathan and Watts, 1959. M.T. Younathan and B. Watts, Relationship of meat pigments to lipid
oxidation. Food Research 24 (1959), pp. 728–734.
Young et al., 1997. O.A. Young, J.L. Berdagué, C. Viallon, S. Rousset-Akrim and M. Theriez, Fatborne volatiles and sheep meat odour. Meat Science 45 (1997), pp. 183–200.
INFLUENCE OF INTRAMUSCULAR FAT CONTENT ON THE
QUALITY OF PIG MEAT. 1. COMPOSITION OF THE LIPID
FRACTION
AND
SENSORY
CHARACTERISTICS
OF
M.
*1
LONGISSIMUS LUMBORUM
X. Fernandez , , a, G. Monina, A. Talmanta, J. Mourotb and B. Lebretb
a
INRA, Meat Research Centre, Theix, 63122 Saint-Genés Champanelle, France
b
INRA, Pig Research Centre, 35590 L'Hermitage, France
Meat Science Volume 53, Issue 1, September 1999, Pages 59-65
Abstract
The present study is part of a project which aimed to examine the influence of intramuscular fat (IMF)
content on the sensory attributes and consumer acceptability of pork. Two experiments were
conducted to evaluate the influence of IMF level on the composition of the lipid fraction and on the
sensory qualities of muscle longissimus lumborum (LL). Each of these experiments used 32 castrated
male pigs selected after slaughter either from 125 Duroc×Landrace (Experiment 1) or 102 Tia
Meslan×Landrace (Experiment 2) crossbred animals, and showing large variability in LL IMF content:
from <1.5 to >3.5% in Experiment 1 and from 1.25 to 3.25% in Experiment 2. Results from lipid
analyses indicate that in both experiments, an increase in IMF content is almost entirely reflected by
an increase in the triglycerides content of the muscle. In Experiment 2, higher IMF content was
associated with higher free fatty acids. Marbling score was significantly affected by IMF level in
Experiment 1 but not in Experiment 2. In Experiment 1, a trend towards a favourable effect of high
IMF levels on flavour (p=0.09) and tenderness (p=0.055) was observed. In experiment 2, increased
311
IMF level was associated with significantly higher juiciness and flavour scores. The results from the
present study indicate that the variability in IMF level of LL muscle was almost entirely due to the
variability in triglyceride contents. Favourable effects of increased IMF levels on the sensory attributes
of pork were demonstrated in both experiments using different types of animals, but the nature and the
magnitude of these effects depended on the experiment considered.
Author Keywords: Pig meat; Sensory qualities; Intramuscular fat
1. Introduction
It is generally accepted that an increased level of intramuscular fat (IMF) has a positive influence on
the sensory qualities of pig meat. However, a careful examination of the literature reveals
contradictory results. Some studies indicate, or suggest, a positive effect of IMF level on the sensory
attributes of pork (Barton; Bejerholm & Barton-Gade, 1986; Touraille; Gandemer and Eikelenboom),
whereas some others do not show any influence (Judge; Lundstom; Wood; Purchas; Lentsch and
Tornberg et al., 1993), or even a negative influence of IMF level (Cameron and Lan).
These discrepancies could originate from the fact that there was a confusion between IMF level and
breed, or genetic type, since the latter has often been retained as a source of variability in IMF level.
Furthermore, none of these studies has taken into account other possible sources of variability in
sensory qualities. In particular, the segregation of two major genes influencing the qualities of pork,
the halothane and the RN− genes, has never been considered in the above cited studies.
The present study is part of a project which aimed to examine the influence of IMF level on the
sensory attributes and consumer acceptability of pork. In this project, care has been taken to ensure
that the influence of IMF level was assessed under conditions where other factors, known to affect
sensory qualities, were kept to a minimum level of variation. This article reports the results from
various measurements taken at slaughter, lipid composition and sensory analyses. Results concerning
the acceptability of meat by consumers are presented in a second article (Fernandez, Monin, Talmant,
Mourot, & Lebret, 1999).
2. Material and Methods
2.1. Animals
Two similar experiments were conducted using two different genetic types of pigs.
2.1.1. Experiment 1
Animals were 125 castrated male pigs from the Duroc×Landrace crossbreeding. They originated from
the same farm and were reared in collective pens on straw bedding, with ad libitum feeding up to a
live weight of 100–110 kg. The number of pigs per pen (n=32, 55 and 38) correspond to the number of
pigs per slaughter day.
2.1.2. Experiment 2
Animals were 102 castrated male pigs from the Tia Meslan× Landrace crossbreeding. The Tia Meslan
sires are from a synthetic line containing Chinese blood. The pigs originated from the same farm and
were reared in collective pens (nine pigs per pen) until slaughter at 100–110 kg live weight. The pigs
were slaughtered in three series (n=41, 39 and 22).
For both experiments, a sample of muscle longissimus lumborum (LL) was taken at 70 kg live weight,
using the biopsy technique described by Talmant, Fernandez, Sellier, and Monin (1989). This sample
was used for the determination of glycolytic potential (Monin & Sellier, 1985) in order to identify the
pigs carriers of the RN− allele (Fernandez, Tornberg, Naveau, Talmant, & Monin, 1992). In addition,
a blood sample was taken for the determination of halothane genotype using the PCR technique (Fujii
et al., 1991).
2.2. Sampling and measurements at slaughter
312
The pigs were delivered at the abattoir in the afternoon preceding the slaughter day and were
slaughtered after manual low voltage (250 V, Experiment 1) or automatic high voltage (700 V,
Experiment 2) electrical stunning.
At 40 min post mortem, a 2 g sample of LL was taken at the level of the last rib for the measurement
of pH after homogenisation in 18 ml of 5 mM iodocatétate (pH40). The pH was measured using a
combined glass electrode (Metler Toledo, Switzerland) connected to a portable pH-meter (SchottGeräte, Germany).
At 24 h after slaughter, the left half carcass of each animal was cut according to the usual French
practice and the following measurements were carried out on muscle LL, at the level of the last rib:
• ultimate pH (pHu), directly in the muscle using the apparatus described above,
• reflectance spectra between 400 and 700 nm using a Minolta spectrophotometer (Minolta Camera
Ltd., Japan). The color coordinates (Lightness, L*; redness, a*; yellowness, b*) were calculated in the
CIELAB system.
A 50 g sample of LL was taken at the level of the last rib for the determination of intramuscular fat
content according to Folch, Lees, and Sloane-Stanley (1957). The remaining part of the left loin was
vacuum-packed in polyethylene bags, stored at +4°C for 5 days and frozen at −20°C until analyses.
2.3. Selection of experimental animals
In each experiment, a group of 32 experimental pigs was selected in order to obtain a significant
variability in IMF content. Apart from IMF content, several criteria were retained for the selection of
the 32 pigs among the slaughtered animals. The criteria to fulfil were the following:
• non carrier of the n allele of the halothane gene,
• non carrier of the RN− allele, on the basis of glycolytic potential (Fernandez et al., 1992),
• pH40 >6.1 (to exclude PSE meat),
• pHu <6.0 (to exclude DFD meat).
Each of the 32 selected animals was assigned to one of the four IMF groups determined on the basis of
IMF variability in the corresponding population (Table 1).
2.4. Determination of lipid composition
The lipid composition was assessed by high performance liquid chromatography coupled to an
evaporative light-scattering detector (Sedere, Paris, France) according to Leseigneur-Meynier and
Gandemer (1991) and Stolywho, Martin, and Guichon (1987). The concentrations of the different
components were expressed as mg per 100 g fresh muscle tissue.
2.5. Sensory analyses
Sensory analyses were carried out on LL samples after about 1 month frozen storage. Vacuum-packed
loins were thawed for 24 to 36 h at +4 °C. The LL muscle was cut in slices of 1 cm depth. Raw
samples were evaluated individually by a trained panel of 12 members (the same panel was used in
Experiments 1 and 2). The order of presentation followed a factorial design in order to take into
account the effect of rank. Colour and smell intensities, and marbling were evaluated on raw samples.
Smell intensity, flavour, juiciness and toughness were evaluated after cooking on a grill (2×2′30′′ at
180 °C). Sensory attributes were scored on a 7 points discrete scale from 1=very low to 7=very high
intensity.
Each member of the jury received one sample per IMF group with two replicates. Thus, after four
sessions, 48 responses per IMF group were collected.
2.6. Statistical analyses
313
Analyses of variance were performed using the GLM procedure of SAS (1989). The model included
the main effect of slaughter day and IMF group. Where appropriated, differences between IMF groups
were tested using Duncan's multiple range test.
3. Results
3.1. Carcass characteristics and quality traits
3.1.1. Experiment 1
As shown in Table 2, most of the traits under study were not significantly affected by IMF group. The
percentage of muscle in the carcass tended to decrease with increased IMF level, the difference being
significant between Groups 1 and 4. A significant effect of IMF group was found for pH40. This effect
was due to the lower pH40 observed in Group 2. It is worth noting that the difference was of low
magnitude and furthermore, none of the pH value was lower than 6.1.
3.1.2. Experiment 2
None of the traits under study significantly differed between the IMF group (Table 2). There was a
trend towards an effect of IMF group on L* value (p=0.09) since LL muscles from Group 4 showed a
significantly higher L* value than those from Group 3.
3.2. Composition of the lipid fraction
3.2.1. Experiment 1
A marked effect of IMF group on the amount of triglycerides (TG) in the LL was observed (Table 3).
In Group 4 (IMF >3.5%), the amount of TG was 4-fold higher than that obtained in group 1 (IMF
1.5%). None of the other neutral lipids were influenced by IMF group, neither were the different
classes of phospholipids.
Table 3. Composition of the lipid fraction according to the level of intramuscular fat (IMF) in the
m.longissimus lumborum of experimental pigs (µ±SEM; n=8 per group)a
3.2.2. Experiment 2
IMF group significantly influenced the amount of TG. As in Experiment 1, higher IMF level was
associated with increased TG (Table 3). In addition, there was a significant increase in the amount of
FFA, and a significant decrease in the amount of sphingomyelin, with increasing IMF level. A trend
towards an effect of IMF group on the amount of cardiolipids was observed (p=0.07) but no clear
relationship between this trait and IMF level could be drawn up.
3.3. Sensory qualities
3.3.1. Experiment 1
IMF level significantly affected marbling score (Table 4). The latter increased with IMF (Figure 1) but
no difference was found between the two first groups (IMF level ranging from 1.5 to 2.5%). A trend
was observed towards an effect of IMF group on flavour and toughness (Table 4). As illustrated in
Fig. 1, significant but slight differences in flavour were found between the four IMF groups. Larger
differences were observed for toughness, the third group (2.5< IMF <3.5) getting the lower score, i.e.
the higher tenderness (Fig. 1).
3.3.2. Experiment 2
None of the traits evaluated on raw meat was affected by IMF group (Table 4). On cooked meat
however, a significant effect of IMF level was recorded for flavour and juiciness. Samples with IMF
level over 2.25% got a higher juiciness score than samples with IMF level <2.25% (Fig. 2). Flavour
score gradually increased with IMF level up to 2.75% (Fig. 2).
314
4. Discussion
In the present work, the influence of IMF level on the sensory qualities of pig meat was assessed in
two trials using distinct genetic types of pigs raised and slaughtered under different conditions.
Therefore, direct comparisons of the data from both experiments are not possible.
4.1. Carcass characteristics, quality traits and lipid composition
In Experiment 1, a relationship between percentage of muscle in the carcass and IMF level in the LL
was found, whereas no such relationship was found in Experiment 2. However, lean percentage in
Experiment 1 was low (approximately 50%) and in anyway lower than expected with this genetic type
of pig (approximately 55%). This can be most likely explained by the fact that breeding conditions
were not optimised in the private farm where the pigs were kept. Indeed, pigs were raised in large
collective pens with ad libitum feeding and in an old building. The pigs were kept on straw bedding
and it is likely that environmental conditions were not at an optimum. Therefore, the link between lean
percentage and IMF level in Duroc crossbred found in the present study should not be considered as a
general rule. In Experiment 2, the lack of relationships between IMF level and lean percentage is in
accordance with previous works showing poor, if any, phenotypic correlations between IMF level and
lean percentage and/or subcutaneous fat depth (Jensen; Malmfors; Schworer and Cameron).
The fact that, overall, the IMF groups did not differ significantly for meat quality measurements at
slaughter, allows the assessment of the effect of IMF level on sensory qualities without interference
with factors known to strongly affect sensory qualities, such as rate and extent of pH fall.
Results from lipid composition are in accordance with previous works in pigs (Leseigneur and
Fernandez) showing that triglycerides are the main components of muscle lipids and that
phosphatidyl-choline represents the main constituent of the phospholipid fraction. Our data show that
the increase in IMF level is mostly due to an increase in triglycerides content, and a relative decrease
of the two main phospholipids (phosphatidyl-choline and sphingomyeline). To our knowledge, data
comparing the lipid composition of a given muscle showing variable IMF levels are not available.
Nevertheless, some authors have compared several muscles showing different IMF levels ( Leseigneur
and Fernandez). According to the muscles considered, they usually report that differences in IMF
content between muscles are mostly due to differences in triglycerides content.
4.2. Effect of IMF level on sensory qualities
The sensory attributes of meat from Duroc crossbred (Experiment 1) were only slightly affected by
IMF level, with the exception of marbling. The observed trends towards an effect of IMF level on
flavour and toughness were of low magnitude. In Experiment 2 however, flavour and juiciness were
significantly enhanced when IMF levels increased above approximately 2.5%. The latter results are in
accordance with previous works showing positive effects of IMF level on sensory qualities of pork
(Barton; Bejerholm & Barton-Gade, 1986; Touraille; Gandemer and Eikelenboom). Barton-Gade and
Bejerholm (1985) noted that IMF level had to reach values above 2% before any noticeable effects on
sensory qualities could be detected, as was the case in the present work in Experiment 2.
Nevertheless, our results show that under two situations with comparable range of variation in IMF
levels, the observed effects on sensory qualities differed in nature and magnitude. Numerous factors
could explain this observation (e.g. differences in genetic background, breeding and slaughter
conditions) but the present data indicate that an effect of IMF level on the sensory qualities of pork is
not systematic, even when other known sources of sensory quality variation are under control.
Acknowledgements
The authors are indebted to P. Vernin (INRA, Meat Research Centre) and A. Mounier (INRA, Porcine
Research Centre) for technical assistance. We thank S. Gilbert (ADIV) for carrying out the sensory
test.
References
Barton-Gade, P. and Bejerholm, A.C., 1985. Eating quality in pork. Pig Farming 33, p. 56.
Bejerholm, A. C., & Barton-Gade, P. (1986). Effect of intramuscular fat level on eating quality of pig
meat. Proceed. 30th Europ. Meet. Meat Res. Workers, Bristol, pp. 389–391..
315
Cameron, N.D., 1990. Genetic and phenotypic parameters for carcass traits, meat and eating quality
traits in pigs. Livestock Production Science 26, pp. 119–135.
Cameron, N.D., Warriss, P.D., Porter, S.J. and Enser, M.B., 1990. Comparison of Duroc an British
Landrace pigs for meat and eating quality. Meat Science 27, p. 227.
Eikelenboom, G., Hoving-Bolink, A.H. and Van der Wal, P.G., 1996. The eating quality of pork. 2.
The influence of intramuscular fat. Fleischwirtschaft 76, pp. 559–560.
Fernandez, X., Tornberg, E., Naveau, J., Talmant, A. and Monin, G., 1992. Bimodal distribution of
muscle glycolytic potential in French and Swedish populations of Hampshire crossbred pigs. Journal
of the Science Food and Agriculture 59, p. 307.
Fernandez, X., Mourot, J., Mounier, A. and Ecolan, P., 1995. Effect of muscle type and food
deprivation for 24 hours on the composition of the lipid fraction in muscles of Large White pigs. Meat
Science 41, p. 335.
Fernandez, X., Monin, G., Talmant, A., Mourot, J., & Lebret. (1999). Influence of intramuscular fat on
the quality of pig meat — 2. Consumer acceptability of muscle longissimus lumborum. Meat Science,
53, 67–72..
Folch, J., Lees, M. and Sloane-Stanley, G.H., 1957. A simple method for the isolation and purification
of total lipids from animal tissue. Journal Biological Chemistry 226, pp. 497–509.
Fujii, J., Otsu, K., Zorzato, F., De Leon, S., Khanna, V.K., Weiler, J., O'Brien, P.J. and Maclennan,
D.H., 1991. Identification of a mutation in the porcine ryanodine-receptor that is associated with
malignant hyperthermia. Science 253, pp. 448–451.
Gandemer, G., Pichou, D., Bouguennec, B., Caritez, J.C., Berge, P., Briand, E. and Legault, C., 1990.
Influence du systéme d'élevage et du génotype sur la composition chimique et les qualités
organoleptiques du muscle long dorsal chez le porc. Journées Recherche Porcine en France 22, pp.
101–110.
Jensen, P., Craig, H.B. and Robinson, O.W., 1965. Phenotypic and genetic association among carcass
traits in swine. Journal of Animal Science 26, pp. 1252–1260.
Judge, M.D., Cahill, V.R., Kunkle, L.E. and Deatherage, F.E., 1958. Pork quality II: physical,
chemical and organoleptic relationships in fresh pork. Journal of Animal Science 36, pp. 145–149.
Lan, Y.H., McKeith, F.K., Novakofski, J. and Carr, T.R., 1993. Carcass and muscle characteristics of
Yorkshire, Meishan, Yorkshire×Meishan, Meishan×Yorkshire, Fengjing×Yorkshire, and
Minzhu×Yorkshire pigs. Journal of Animal Science 71, pp. 3344–3349.
Lentsch, D.M., Pruska, K.J., Fedler, C.A., Meisinger, D. and Goodwin, R., 1991. Factors influencing
the sensory quality of pork loin chops. Journal of Animal Science 66 Suppl. 1, p. 346 (Abstract).
Leseigneur-Meynier, A. and Gandemer, G., 1991. Lipid composition of pork muscle in relation to the
metabolic type of the fibres. Meat Science 29, pp. 229–241.
Lundström, K., Nilsson, H. and Malmfors, B., 1979. Interrelations between meat quality
characteristics in pigs. Acta Agriculturae Scandinavica 21, pp. 71–80.
Malmfors, G. and Nilsson, R, 1979. Meat quality traits in Swedish Landrace and Yorkshire pigs with
special emphasis on genetics. Acta Agriculturae Scandinavica 21, pp. 81–90.
Monin, G. and Sellier, P., 1985. Pork of low technological quality with a normal rate of muscle pH fall
in the immediate postmortem period: the case of the Hampshire breed. Meat Science 13, pp. 49–63.
Purchas, R.W., Smith, W.C. and Pearson, G., 1990. A comparison of the Duroc, Hampshire, Landrace
and Large White as terminal sire breeds of crossbred pigs slaughtered at 85 kg liveweight. 2. Meat
quality. New Zealand Journal of Agricultural Research 33, pp. 97–104.
SAS, SAS/STAT User's Guide NC.
Schworer, D., Blum, J. and Rebsamen, A., 1980. Parameters of meat quality and stress resistance in
pigs. Livestock Production Science 7, p. 337.
Stolywho, A., Martin, M. and Guichon, G., 1987. Analysis of lipid classes by HPLC with the
evaporative light scattering detector. Journal of Liquid Chromatogrophy 10, pp. 1237–1253.
Talmant, A., Fernandez, X., Sellier, P., & Monin, G. (1989). Glycolytic potential in longissimus dorsi
of Large White pigs, as measured after in vivo sampling. Proceed. 35th Int. Cong. Meat Sci. Technol.,
Copenhagen 1129-1132..
Tornberg, E., Andersson, A., Göransson, A., & Von Seth, G. (1993). Water and fat distribution in pork
in relation to sensory properties. In E. Puolanne & D. Demeyer (Eds.), Pork quality, genetic and
metabolic factors (pp. 239–258). Townbridge: CAB International..
316
Touraille, C., Monin, G. and Legault, C., 1989. Eating quality of meat from european×chinese
crossbred pigs. Meat Science 25, pp. 177–186.
Wood, J.E., Dransfield, E. and Rhodes, D.N., 1979. The influence of breed on the carcass and eating
quality of pork. Journal of the Science of Food and Agriculture 30, p. 493 .
FAT DEPOSITION, FATTY ACID COMPOSITION AND MEAT
QUALITY: A REVIEW
JD Wooda, M Ensera, AV Fishera, GR Nutea, PR Shearda, RI Richardsona, S I Hughesa and FM
Whittingtona,
aDivision of Farm Animal Science, Department of Clinical Veterinary Science, University of Bristol,
Langford, Bristol, BS40 5DU, UK
Corresponding author: tel +44 117 928 9293 ; fax +44 117 928 9582
E-mail address: [email protected] (Jeff Wood)
Abstract
This paper reviews the factors affecting the fatty acid composition of adipose tissue and muscle in
pigs, sheep and cattle and shows that a major factor is the total amount of fat. The effects of fatty acid
composition on meat quality are also reviewed. Pigs have high levels of polyunsaturated fatty acids
(PUFA), including the long chain (C20-22) PUFA in adipose tissue and muscle. The full range of
PUFA are also found in sheep adipose tissue and muscle whereas cattle ‘conserve’ long chain PUFA
in muscle phospholipid. Linoleic acid (18:2 n-6) is a major ingredient of feeds for all species. Its
incorporation into adipose tissue and muscle in relation to the amount in the diet is greater than for
other fatty acids. It is deposited in muscle phospholipid at a high level where it and its long chain
products eg aracidonic acid (20:4n-6) compete well for insertion into phospholipid molecules. Its
proportion in pig adipose tissue declines as fat deposition proceeds and is an index of fatness. The
same inverse relationships are not seen in ruminant adipose tissue but in all species the proportion of
18:2n-6 declines in muscle as fat deposition increases. The main reason is that phospholipid, where
18:2n-6 is located, declines as a proportion of muscle lipid and the proportion of neutral lipid, with its
higher content of saturated and monounsaturated fatty acids, increases. Oleic acid (18:1cis-9), formed
from stearic acid (18:0) by the enzyme stearoyl CoA-desaturase, is a major component of neutral lipid
and in ruminants the same enzyme forms conjugated linoleic acid (CLA), an important nutrient in
human nutrition. Like 18:2n-6, α linolenic acid (18:3n-3) is an essential fatty acid and is important to
ruminants since it is the major fatty acid in grass. However it does not compete well for insertion into
phospholipid compared with 18:2n-6 and its incorporation into adipose tissue and muscle is less
efficient.
Greater biohydrogenation of 18:3n-3 and a long rumen transit time for forage diets also limits the
amount available for tissue uptake compared with 18:2n-6 from concentrate diets. A positive feature
of grass feeding is that levels of the nutritionally important long chain n-3 PUFA are increased ie EPA
(20:5n-3) and DHA (22:6n-3).
Future research should focus on increasing n-3 PUFA proportions in lean carcasses and the use of
biodiverse pastures and conservation processes which retain the benefits of fresh leafy grass offer
opportunities to achieve this. The varying fatty acid compositions of adipose tissue and muscle have
profound effects on meat quality.
Fatty acid composition determines the firmness/oiliness of adipose tissue and the oxidative stability of
muscle, which in turn affects flavour and muscle colour. Vitamin E is an essential nutrient, which
stabilises PUFA and has a central role in meat quality, particularly in ruminants.
1. Introduction
In many countries, fat is an unpopular constituent of meat for consumers, being considered unhealthy.
Yet fat and fatty acids, whether in adipose tissue or muscle, contribute importantly to various aspects
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of meat quality and are central to the nutritional value of meat. This review considers the factors
controlling fat deposition and fatty acid composition in adipose tissue and muscle of pigs, sheep and
cattle and the roles of fat in meat quality in these different species.
2. Fatty acid composition of adipose tissue and muscle in meat animals
The fatty acid composition and total fatty acid content of subcutaneous adipose tissue and longissimus
muscle from loin chops or steaks of pigs, sheep and cattle purchased at retail are shown in Table 1
(Enser, Hallett, Hewitt, Fursey and Wood, 1996).
The concentrations of total fatty acids in longissimus are higher than in other studies in which cores
from the central part of the muscle, with no adhering subcutaneous or intermuscular adipose tissue,
have been examined. The intention of the study of Enser et al (1996) was to examine muscle and fat
tissues as normally consumed, so only rough dissection was performed, as for someone separating
muscle from fat on the dinner plate. Cores from the centre of longissimus typically contain 1% total
lipid in pigs. The data show that adipose tissue has a much higher fatty acid content than muscle but
the fatty acid composition of the two tissues is broadly similar. However, there are important species
differences. Pigs have much higher proportions of the major polyunsaturated fatty acid (PUFA)
linoleic acid (18:2n-6) in both tissues than cattle and sheep. In this study, the proportions were similar
in the 2 tissues but most reports show higher proportions in pig adipose tissue than muscle (Teye,
Sheard, Whittington, Nute, Stewart and Wood, 2006a; Teye, Wood, Whittington, Stewart and Sheard,
2006b). Linoleic acid is derived entirely from the diet. It passes through the pig’s stomach unchanged
and is then absorbed into the blood stream in the small intestine and incorporated from there into
tissues. In ruminants, the fatty acid, which is at high levels in concentrate feedstuffs (grains and
oilseeds), is degraded into monounsaturated and saturated fatty acids in the rumen by microbial
biohydrogenation and only a small proportion, around 10% of dietary 18:2n-6, is available for
incorporation into tissue lipids. In both sheep and cattle, the fatty acid is at higher levels in muscle
than adipose tissue. The second most important PUFA is α linolenic acid (18:3n-3), which is present
in many concentrate feed ingredients but at lower levels than 18:2n-6. In pigs, the proportion is higher
in adipose tissue than muscle. This is a major dietary fatty acid for ruminants since it constitutes over
50% of total fatty acids in grass and grass products. Again, a high proportion is biohydrogenated to
saturated fatty acids in the rumen. In a review, Doreau and Ferlay (1994) found that a variable
proportion of dietary 18:3n-3 is biohydrogenated (85 – 100%) but this is more than for 18:2n-6 (70 –
95%), so less is available for incorporation into tissues. As with 18:2n-6, proportions in ruminants are
higher in muscle than adipose tissue.
Muscle contains significant proportions of long chain (C20-22) PUFAs which are formed from 18:2n6 and 18:3n-3 by the action of _5 and _6 desaturase and elongase enzymes. Important products are
arachidonic acid (20:4n-6) and eicosapentaenoic acid (EPA, 20:5n-3) which have various metabolic
roles including eicosanoid production. Greater incorporation of 18:2n-6 into pig muscle fatty acids
compared with ruminants produces higher levels of 20:4n-6 by synthesis and the net result is a higher
ratio of n-6:n-3 PUFA compared with the ruminants (Table 1). Nutritional advice is for ratios < 4.0
(Scollan, Hocquette, Nuernberg, Dannenberger, Richardson and Maloney, 2006a) so pig muscle is
unbalanced relative to that of the ruminants.
On the other hand, the ratio of all PUFA to saturated fatty acids (P:S), the target for which is 0.4 or
above, is much higher, beneficially so, in pigs and other monogastrics compared with the ruminants.
Results in Table 2 (Kouba, Enser, Whittington, Nute and Wood, 2003; Wachira, Sinclair, Wilkinson,
Enser, Wood and Fisher, 2002) confirm those in other studies showing that ruminants have higher
proportions of the two main PUFAs in muscle than adipose tissue whereas the opposite is true for pigs.
3. Fatty acid composition of triacylglycerol (neutral lipid) and phospholipid
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The major lipid class in adipose tissue (>90%) is triacylglycerol or neutral lipid. In muscle, a
significant proportion is phospholipid, which has a much higher PUFA content in order to perform its
function as a constituent of cellular membranes.
Values for the fatty acid composition of longissimus muscle neutral lipid and phospholipid from
studies on pigs, sheep and cattle conducted with collaborators at Bristol are shown in Table 3 (Wood
et al, 2004; Demirel, Wachira, Sinclair, Wilkinson, Wood and Enser, 2004; Warren, Scollan, Enser,
Hughes, Richardson and Wood, 2007a). The three studies are not directly comparable because
different diets were fed but the trends within each species are typical. In all three species, oleic acid
(18:1cis-9), the major fatty acid in meat, was much more predominant in neutral lipid. This fatty acid
is formed from stearic acid (18:0) by the enzyme stearoyl Co-A desaturase, a major lipogenic enzyme.
On the other hand, 18:2n-6 was at much higher proportions in phospholipid than neutral lipid. The
proportion of 18:3n-3 was slightly higher in neutral lipid than phospholipid in pigs but in sheep and
cattle the proportions were higher in phospholipid. The differences between sheep and cattle for
18:2n-6, 18:3n-3 and the long chain n-6 and n-3 PUFA in Table 3 are partly due to the different
concentrate diets fed. In the work with sheep, dried grass (high in 18:3n-3) formed 75% of the
concentrate whereas in the cattle study the concentrate contained a high proportion of full fat soyabean
meal, high in 18:2n-6. Nevertheless, we have often seen higher values for individual phospholipid
PUFAs in sheep compared with cattle.
Long chain n-3 and n-6 PUFA are mainly found in phospholipid but are detected in pig and sheep
muscle neutral lipid and adipose tissue (Enser, Richardson, Wood, Gill and Sheard, 2000; Cooper,
Sinclair, Wilkinson, Hallett, Enser and Wood, 2004). We have never seen these fatty acids in beef
muscle neutral lipid or adipose tissue (Scollan, Choi, Kurt, Fisher, Enser and Wood, 2001; Warren et
al, 2007a), confirming other studies showing ‘conservation’ of essential fatty acids in cattle muscle
where they are less likely to be used for energy production (Crawford, Hare and Whitehouse, 1984).
The double bonds in unsaturated fatty acids are usually of the cis type, ie the hydrogen atoms attached
to the carbon atoms in the fatty acid chain point in the same direction. In ruminants, as a result of
biohydrogenation in the rumen, a significant proportion of double bonds are of the trans type, ie the
hydrogen atoms point in different directions. These fatty acids have particularly low melting points as
a result of this structure. A major trans fatty acid is 18:1 trans vaccenic which is a biohydrogenation
product of 18:2n-6. This fatty acid is converted to conjugated linoleic acid (CLA, 18:2cis-9, trans-11)
in adipose tissue by the action of stearoyl Co-A desaturase, the same enzyme responsible for the
production of 18:1cis-9 from 18:0.
Like 18:1cis-9, both 18:1 trans vaccenic and CLA are at higher proportions in neutral lipid than
phospholipid and higher in adipose tissue than muscle. CLA is also produced in the rumen but
synthesis from 18:1 trans vaccenic in tissues is quantitatively the most important contributor to tissue
levels (Scollan et al, 2006).
CLA has health benefits in the human diet although meat from ruminants makes only a small
contribution towards nutritionally significant levels.
4. Effects of fat content on fatty acid composition
4.1 Adipose tissue
As the fat content of the animal and meat increases between early life and the time of slaughter, the
proportions of fatty acids change. In pig subcutaneous adipose tissue, Wood (1984) showed that the
C18 fatty acids 18:0 and 18:1cis-9 increased in proportion and 18:2n-6 declined during this period.
This was ascribed to an increasing role for de novo tissue synthesis of saturated and monounsaturated
fatty acids and a relatively declining role for the direct incorporation of 18:2n-6 from the diet. A
similar result was found by Kouba et al (2003). Pigs were fed a control diet from 40kg live weight for
20, 60 or 100 days. During this time, the proportion of 18:0 increased from 10% to 13%, 18:1cis-9
increased from 38% to 42% and the proportion of 18:2n-6 fell from 19% to 11% of total fatty acids.
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The inverse relationship between the proportion of 18:2n-6 in subcutaneous adipose tissue and the
amount of fat or an index of it such as backfat thickness, has been observed in several studies in pigs.
Wood et al (1978) observed correlations of about 0.3 between the proportion of 18:2n-6 in the inner
layer of subcutaneous adipose tissue and loin fat thickness in Large White pigs from a line selected for
fast growth and low fat thickness and a control line. The values for 18:2n-6 were 9.3% in the control
line and 10.7% in the selection line. Similarly, in 300 pigs with 8mm, 12mm and 16mm P2 backfat
thickness, average values for 18:2n-6 in subcutaneous adipose tissue fell from 14.9% to 12.4% to
10.6% (Wood, Enser, Whittington, Moncrieff and Kempster ,1989) (Table 4). This study also
compared entire male and female pigs.
Proportions of PUFA tend to be high in subcutaneous adipose tissue from entire males and this study
showed this was mainly due to their thinner backfat. However, even at the same backfat thickness,
there was a higher proportion of 18:2n-6 and a lower proportion of 18:1cis-9 in subcutaneous adipose
tissue from entires as the results in Figure 1 show. At the same fat thickness as females, subcutaneous
adipose tissue from entires contained a higher proportion of water and a lower proportion of lipid,
signifying a less mature tissue. These results help explain why fat quality tends to be lower in entire
male pigs than castrates and females.
The changes in adipose tissue fatty acid composition with age and fatness are different between pigs
and cattle. Leat (1975) examined fatty acid composition in subcutaneous fat of Jersey cattle of
different sexes using biopsies at different ages.
Both 16:0 and 18:0 fell in proportion as age increased from 3 to 30 months, whereas 18:1cis-9
increased, similar to the observation in pigs. In a comparison of extremes, Wood (1984) found
proportions of 14.7 and 2.7% for 18:0 and 41.5 and 56.4% for 18:1cis-9 in a young heifer and an old
fat steer respectively. We have recently observed an increase in the proportion of 18:1cis-9 in
subcutaneous adipose tissue of Aberdeen Angus crossbred steers fed a concentrate diet between 14
and 24 months of age (Table 5). Carcass fat greatly increased during the period as shown by the
carcass fat score (values are approximately the percentage of subcutaneous fat in the carcass x 10).
The proportion of 18:0 fell during the same period (as in the study of Leat) and this allowed the
proportion of 18:2n-6 to remain constant (Table 5). This study also showed that the proportion of CLA
increased with fatness, as did that of 18:1 trans vaccenic acid.
4.2 Muscle
Early work on meat fatty acid composition concentrated on adipose tissue, since that is where the bulk
of the body’s fatty acids are located. Recently, there has been more emphasis on muscle because of its
greater significance as food and an increasing aversion to visible fat at retail. Muscle also contains
higher concentrations of the long chain n-6 and n-3 fatty acids, the importance of which in human
nutrition has been recognised relatively recently. Separation and identification procedures for low
levels of unsaturated fatty acids in muscle have also greatly improved in recent years.
The overall fat content of the animal and muscle have an important impact on proportionate fatty acid
composition because of the different fatty acid compositions of neutral lipid and phospholipid (Table
3). Phospholipid is an essential component of cell membranes and its amount remains fairly constant,
or increases little, as the animal increases in fatness. In young lean animals, genetically lean animals or
animals fed a low energy diet, the lower 18:1cis-9 and higher 18:2n-6 content of phospholipid has a
major influence on total muscle fatty acid composition. But as body fat increases, neutral lipid
predominates in overall fatty acid composition.
Results from the study of Kouba et al (2003) of pigs fed a control diet from 40kg live weight for 20,
60 or 100 days are shown in Table 6. Phospholipid declined from 46% of total lipid at 20 days to 28%
at 100 days. This was associated with an increase in the proportion of 18:1cis-9 and a decrease in the
proportion of 18:2n-6.
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Warren et al (2007a) examined the fatty acid content and composition of neutral lipid and
phospholipid in cattle of three ages, 14, 19 and 24 months. There were two breeds, Aberdeen Angus
cross and Holstein-Friesian, and two diets, concentrate and grass silage, fed from 6 months of age. A
plot of the concentrations of total neutral lipid and phospholipid fatty acids in muscle in relation to
total lipid fatty acids for all 96 steers in the trial is in Figure 2. This illustrates the increasing
importance of neutral lipid in total lipid as fattening proceeds and the fairly constant level of
phospholipid.
Results for Aberdeen Angus steers fed the concentrate diet are in Table 7. The proportion of
phospholipid in total lipid fell from 30% at 14 months to 12% at 24 months and this was accompanied
by an increase in the proportion of 18:1cis-9 and a decrease in the proportion of 18:2n-6 in total lipid.
Data were statistically analysed within age group in this trial so age groups themselves were not
directly compared.
However, comparison with other results in the trial suggests that the age effects on neutral lipid, total
lipid and fatty acid proportions were statistically significant. The trends in Table 7 are similar to those
in the pig study in Table 6. In both studies, there was an increase in the proportion of 18:1cis-9 and a
decrease in the proportion of 18:2n-6 in neutral lipid during the periods under investigation, evidence
of the increasingly important role of stearoyl Co-A desaturase and the declining importance of dietary
fat as a source of muscle fatty acids as fat deposition accelerates, in muscle triacylglycerol as in
adipose tissue.
5. Genetic effects on fatty acid composition
Breeds or genetic types with a low concentration of total lipid in muscle, in which phospholipid is a
high proportion of the total, will have higher proportions of PUFA in total lipid, for the reasons given
in section 4. This was illustrated in sheep by Fisher et al (2000) (Table 8). Welsh Mountain and Soay
sheep were reared on grass diets and slaughtered at the same body weight. Soays had much leaner
carcasses and less lipid in muscle. They had lower proportions of 18:1cis-9 and higher proportions of
all PUFA in semimembranosus muscle.
Raes, De Smet and Demeyer (2001) have shown that the double muscling genotype (mh/mh) within
the Belgian Blue Breed has low proportions of 18:1 cis-9 and high proportions of 18:2n-6 in muscle
lipid compared with the normal genotype (+/+). This is due to a low concentration of total lipid in
muscle and a higher ratio of phospholipid to total lipid. Average values for the total lipid content of 5
muscles in young bulls were 0.9 g/100g and 2.6 g/100g in mh/mh and +/+ respectively. The
proportions of 18:1cis-9 were 23.1 and 37.8 and the proportions of 18:2n-6 were 16.3 and 6.5 in
mh/mh and +/+ respectively. The mh/mh animals had a P:S ratio of 0.55, above the minimum
recommended for the diet as a whole and much higher than reported elsewhere for beef (Table 1). This
study, in common with others, showed only small differences between muscles in fatty acid
composition.
In the study by Warren et al (2007a) of beef fatty acid composition involving two diets and slaughter
at three ages (Table 7), Aberdeen Angus cross and Holstein-Friesian breeds were compared. Results
for proportions of 18:1cis-9 and 18:2n-6 in phospholipid and neutral lipid in the 14 and 24 month
groups fed concentrate are in Table 9. Aberdeen Angus had much fatter carcasses than HolsteinFriesian, but amounts of neutral lipid and phospholipid in longissimus muscle were not very different
and consequently proportions of 18:1cis-9 and 18:2n-6 in both lipid fractions were also quite similar.
Bigger differences would have been expected if muscle lipid concentration had mirrored subcutaneous
fat. These results show that the dairy breed Holstein-Friesian had a higher ratio of muscle lipid to
carcass fat than the beef breed Aberdeen Angus. This is consistent with other work showing
differences in the partitioning of body fat between dairy and beef breeds, with dairy breeds having
more “internal” and less “external” (subcutaneous) fat (Truscott, Wood and MacFie, 1983).
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The Duroc pig breed is notable in having a high muscle lipid (marbling fat) content relative to
subcutaneous fat compared with other breeds. Wood et al (2004) examined purebred Berkshire, Duroc,
Large White and Tamworth breeds fed for 12 weeks on a standard concentrate diet. The 2 traditional
breeds (Berkshire and Tamworth) grew slowly and were lighter and fatter than the 2 modern breeds at
slaughter (Table 11).
The amount of phospholipid in longissimus was similar between the breeds but the amounts of neutral
lipid and total lipid were higher in Berkshire and Duroc than in Large White and Tamworth. Durocs
had the highest ratio of muscle lipid to subcutaneous fat thickness. The proportion of phospholipid in
total lipid was 18.8, 23.8, 38.9 and 31.7 in Berkshire, Duroc, Large White and Tamworth,
respectively.
Values for the proportions of 18:1cis-9 and 18:2n-6 in total lipid were as expected based on these
figures except for Duroc, the proportion of 18:1cis-9 being lower and the proportion of 18:2n-6 being
higher than expected. A possible explanation for these results is the slightly higher proportion of
phospholipid in Duroc longissimus muscle (Table11) associated with their ‘redder’ muscle fibre type
profile compared with the other breeds reported in a companion paper by Chang et al (2003). Their
fatty acid profile would be expected to be closer to psoas than longissimus, with higher 18:2n-6 and
lower 18:1cis-9 proportions.
Analysis of long chain n-3 PUFA proportions in the steers fed grass silage in the study of Warren et al
(2007a) and referred to in Tables 7 and 9, suggested that Holstein-Friesians formed more
docosahexaenoic acid (DHA, 22:6n-3) than Aberdeen Angus from its precursor 18:3n-3 in
phospholipid. Values for these phospholipid fatty acids and the index DHA/18:3n-3 for the 14 and 24
month silage-fed groups are in Table 10. Most fatty acid proportions were significantly different
between the breeds at 24 months (P<0.05) but not at 14 months. The DHA/18:3n-3 ratio was
significantly different between the breeds at both ages (P<0.05). These results suggest that HolsteinFriesians have a greater activity or a greater expression of _5 and _6 desaturase enzymes. Evidence
that the double muscled (mh/mh) Belgian Blue genotype converts a higher proportion of 18:3n-3 to
20:5n-3 and 22:5n-3 but not 22:6n-3 was presented by Raes et al (2001).
6. Diet effects on fatty acid composition
6.1 Pigs
The pig, being a monogastric species, is amenable to changes in the fatty acid composition of adipose
tissue and muscle using diets containing different oils.
Spectacular results can be achieved using diets with high levels of 18:2n-6, which is a common fatty
acid in grains and oilseeds. In general, the proportion of this fatty acid in tissues increases linearly as
the dietary intake increases (Wood, 1984). In early studies of Ellis and Isbell (1926) the proportion of
18:2n-6 in subcutaneous adipose tissue increased from 1.9% on a low fat diet to over 30% on diets
containing a high level of soyabeans.
Other dietary lipid sources containing particular fatty acids can be used to influence meat fatty acid
composition. Teye et al (2006a and 2006b) fed concentrate diets containing 2.8% added oil coming
from palm kernel oil high in lauric acid (12:0), myristic acid (14:0) and 18:0; palm oil high in palmitic
(16:0) and palmitoleic (16:1) acids; and soyabean oil high in 18:2n-6. The greatest dietary impact in
adipose tissue and muscle was on proportions of 12:0, 14:0 (these had very low proportions) and
18:2n-6, with the C16 and C18 saturated and monounsaturated fatty acids hardly affected by dietary
concentrations. These results are explained by the fact that 12:0 and 14:0 are mainly derived from the
diet and 18:2 n-6 is entirely derived from the diet. Conversely, the C16 and C18 saturated and
monounsaturated fatty acids are mainly the products of synthesis in the animal and interconversions
between them limit the impact of dietary additions. The clearest effect was that of soyabean oil on
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18:2n-6 in adipose tissue. Proportions in muscle were lower than in adipose tissue and the dietary
effect was smaller.
Several studies have examined the effect of 18:3n-3 in linseed/flaxseed on its concentration in pork.
The motivation for this research is the high n-6:n-3 fatty acid ratio in pork and the need to reduce this
for human nutritional reasons. An example is the work of Enser et al (2000). Two diets were fed,
differing in the ratio of 18:2n-6:18:3n-3, to 80 entire male and female pigs between 25kg and 95kg
live weight.
The aim was to favour deposition of 18:3n-3 and its long chain products in triacylglycerol and
phospholipid. The n-6 and n-3 PUFA compete for access to desaturase enzymes and for incorporation
into lipids. A control diet contained 1.5g 18:3n-3 and 16g 18:2n-6/kg and a linseed-rich diet contained
4.5g 18:3n-3 and 10g 18:2n-6/kg. This gave 18:2n-6:18:3n-3 ratios of 11.0 and 2.0 respectively. The
results (Table 12) show that the linseed diet increased the deposition of 18:3n-3 in adipose tissue and
muscle, particularly muscle phospholipid. Conversion of this extra 18:3n-3 into the C20-22n-3 PUFA
20:5n-3, docosapentaenoic (DPA, 22:5n-3) and 22:6n-3 occurred and these were deposited in muscle
phospholipid but not in muscle neutral lipid (results not shown). Only 20:5n-3 of the long chain n-3
PUFA was significantly higher in muscle total lipid of pigs fed the linseed diet. However, there was
evidence of extra long chain n-3 PUFA deposition (except for 20:5n-3) in adipose tissue, albeit the
levels of these fatty acids were very low.
Nguyen, Nuijens, Everts, Salden and Beynen (2003) studied the uptake of dietary n-6 and n-3 PUFA
into pig adipose tissue and muscle in their own and in published work and concluded that the
efficiency of uptake, defined as the slope of the line relating tissue level to dietary intake, was greater
for 18:2n-6 than 18:3n-3 in both adipose tissue and muscle. They found that in the case of 18:2n-6, the
slope was higher for adipose tissue than muscle but for 18:3n-3, efficiency of uptake into the two
tissues was similar. The results of Enser et al (2000) are consistent with these conclusions.
The study of Kouba et al (2003) showed that incorporation of 18:3n-3 from a 6% crushed linseed diet
into muscle neutral lipid and phospholipid reached a maximum in terms of proportions after 60 days of
feeding. However, 91% and 87% of the effect had occurred in neutral lipid and phospholipid
respectively at 20 days. For 20:5n-3 incorporation into neutral lipid and phospholipid, the maximum
proportions were also reached at 60 days, with 85% and 71% of the effect having occurred at 20 days
in neutral lipid and phospholipids respectively. These results confirm the rapid uptake of n-3 PUFA
into pork found by Warnants, Van Oeckel and Boucque (1999) and show that incorporation of chain
elongation products is more rapid in neutral lipid than phospholipid.
In a recent study, Teye et al (2006a) used low protein diets (18% versus 20% crude protein) with the
same energy content to increase the concentration of total lipid in longissimus muscle. Low protein
limits muscle deposition and the energy which would have been used for muscle synthesis is diverted
to fat synthesis. In the later stages of growth, intramuscular fat is particularly affected. This strategy
increased total lipid from 1.7% to 2.8% and had a marked effect on the proportion of 18:1cis-9 which
increased from 32.1% to 39.0% of total muscle lipid. Proportions of all n-6 and n-3 PUFA were
reduced when this diet was fed. A companion paper by Doran, Moule, Teye, Whittington, Hallett and
Wood (2006) showed that low protein diets increased the expression of stearoyl Co-A desaturase in
longissimus muscle and there was a linear relationship between the expression of stearoyl Co-A
desaturase and the amount of 18:1cis-9 in muscle. These data also show that de novo synthesis of fatty
acids can dominate fatty acid profiles in some circumstances.
6.2 Cattle and sheep
Several studies have shown that dietary n-6 and n-3 PUFA can be incorporated into adipose tissue and
muscle of ruminants despite the biohydrogenation of dietary fatty acids in the rumen. The study of
Warren et al (2007a) of steers of 2 breeds fed a concentrate or grass silage diet from 6 months of age
to 14, 19 and 24 months contrasts the incorporation of 18:2n-6 from a grain-based concentrate diet
with 18:3n- 3 from a grass silage diet. Results in Tables 5 and 7 show that 18:2n-6 in steers fed the
concentrate diet was at higher proportions in muscle than adipose tissue at 14 and 24 months of age.
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The same was true for 18:3n-3 from the grass silage diet. For example, the proportions of 18:3n-3 in
adipose tissue lipid and total muscle lipid at 14 months were 0.52 and 1.17g/100g respectively. At 24
months, the figures were 0.45 and 0.62 g/100g respectively. These results show that ruminants
preferentially incorporate essential fatty acids, with their important metabolic roles, into muscle rather
than storing them in adipose tissue.
In the study of Warren et al (2007a), the proportion of 18:2n-6 in total muscle lipid varied from 1% to
12%. As total lipid increased, the proportion fell steeply (Figure 3a) before plateauing at about
6g/100g total lipid. This curvilinear pattern was explained by the high proportion of 18:2n-6 in
phospholipid and a declining proportion of phospholipid in total lipid as total lipid increased.
Proportions of 18:2n- 6 in muscle from steers given the two diets were closely related to the
percentage of phospholipid in total lipid (Figure 3b). The proportions of 18:2n-6 and 18:3n-3 in
phospholipid and neutral lipid plotted against total muscle lipid for all steers fed the concentrate and
grass silage diets are shown in Figures 4a and 4b. These graphs emphasise the much greater
incorporation of 18:2n-6 than 18:3n-3 into muscle lipids, especially phospholipid, and the declining
proportions of these PUFA as muscle lipid increased. The content of phospholipid fatty acids
remained fairly constant but neutral lipid, with its high proportions of saturated and monounsaturated
fatty acids, increased markedly as total lipid increased (Figure 2). These differences in tissue levels of
the 2 essential fatty acids are the more surprising considering that intakes of the fatty acids were
similar. For example in the 14 month groups, the approximate daily intakes were 74g 18:2n-6 and
73.5g 18:3n-3 from the concentrate and grass silage diets respectively.
Higher levels of 18:2n-6 than 18:3n-3 in tissues are not only due to a higher affinity for incorporation
into phospholipid molecules as illustrated in Figures 4a and 4b but also reduced biohydrogenation in
the rumen. This occurs when the form of the diet is similar (Doreau and Ferlay, 1994) and particularly
in typical 18:2n-6 -rich concentrate diets. These have a small particle size and a shorter rumen transit
time than fibrous forage diets, limiting the opportunities for microbial biohydrogenation. Our studies
with sheep have mainly used concentrate – based diets and this may be one reason why concentrations
and proportions of PUFA in muscle are higher than in the studies on beef which have mainly used
diets containing 60% forage and 40% concentrate (Demirel et al, 2004; Scollan et al, 2001).
Incorporation of 18:2n-6 from the concentrate diet and 18:3n-3 from the grass silage diet into muscle
in the study of Warren et al (2007a) led to synthesis of the long chain n-6 and n-3 PUFA in
phospholipid. Results for the 14 month Aberdeen Angus steers are in Table 13. These data are
concentrations in muscle (mg/100g) rather than proportions in phospholipid. The concentrate diet
produced relatively high levels of 18:2n-6 and all its long chain products and the grass silage diet
produced high levels of 18:3n-3 and its long chain products, including 22:6n-3. Feeding linseed in
previous research had not led to synthesis of 22:6n-3 (DHA) and a block on DHA synthesis or a
failure to compete for incorporation has been noted in other studies (Scollan et al, 2001). It seems that
grass feeding has a special ability to raise DHA levels.
In the 19 and 24 month age groups in the study of Warren et al (2007a), there was evidence of extra
incorporation of 18:2n-6 and synthesis of 20:4n-6 in phospholipid beyond 14 months (Figure 5a).
However, the amounts of 18:3n-3 and its products remained constant, despite continued consumption
of the grass silage diet. These results suggest that the capacity for incorporation of PUFA into
phospholipid is limited and that 18:2n-6 competes for incorporation much more effectively than
18:3n-3. Evidence suggests that the n-3 PUFA are the preferred substrates for the _5 and _6
desaturase enzymes (Williams and Burdge, 2006) so limited access to the enzyme systems cannot
explain low values for long chain n-3 PUFA. In contrast to these results for phospholipid, extra
incorporation of 18:2n-6 and 18:3n- 3 into muscle triacylglycerol (neutral lipid) occurred beyond 14
months of age (Figure 5b). The level and rate of incorporation was greater for 18:2n-6 than for 18:3n-
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3. Levels of n-3 PUFA in ruminant tissues can be increased by feeding dietary lipid which is
‘protected’ from biohydrogenation in the rumen using formaldehyde treatment of linseed. In a study
by Scollan, Enser, Gulati, Richardson and Wood (2003), in which a protected lipid supplement
comprised of soyabean, linseed and sunflower seeds was fed, the concentration of 18:3n-3 in muscle
phospholipid increased from 12.7 to 16.0mg/100g, a small increase and no chain elongation and
desaturation to long chain n-3 PUFA occurred. However, the supplement doubled the concentration of
18:2n-6 in phospholipid and substantially increased the concentration of this fatty acid in neutral lipid
compared with 18:3n-3. Because of the high incorporation of 18:2n-6, the P:S ratio in muscle was
increased from 0.1 in controls to 0.4 in animals given a high level of the supplement. These results
again demonstrate the higher efficiency of incorporation of 18:2n-6 into muscle compared with 18:3n3.
In Australian research, Cook, Scott, Faichney and Davies (1972) observed that the proportion of
18:2n-6 increased to 35g/100g fatty acids in perirenal fat of steers given a protected sunflower
supplement for 8 weeks. A value of 20g/100g was achieved after 2 weeks.
In the work of Warren et al (2007a), a group of steers was fed fresh grazed grass rather than grass
silage between 14 and 19 months of age. The results in subcutaneous adipose tissue (Table 14) showed
that the proportion of 18:3n-3 was slightly higher in the steers fed grazed grass. This group also had
higher proportions of 18:1 trans vaccenic acid and CLA than those fed grass silage, showing that the
process of rumen biohydrogenation is different between fresh and conserved grass. A similar result
was found by French et al (2000). The CLA values were similar in the groups fed grazed grass and
concentrate in our work (Table 14).
Changes in grassland management, such as harvesting at different times of the grass growing season or
allowing the grass to wilt before harvesting and conservation have an effect on fatty acid proportions
in grasses and also in the meat of cattle and sheep (Wood et al, 2007). Different grasses and pasture
plants also produce different concentrations of PUFA in meat due to higher levels of certain PUFA or
because of differences in the way the feed is processed in the rumen. Scollan, Costa, Hallett, Nute,
Wood and Richardson (2006b) showed that the proportions of both 18:2n-6 and 18:3n-3 in muscle
were significantly increased when steers were fed silage comprised of red clover rather than perennial
ryegrass. Other research (Lee, Winters, Scollan, Dewhurst, Theodoru and Minchin, 2004) suggests
that the pattern of rumen fermentation and biohydrogenation for red clover is different from that of
perennial ryegrass due to the inhibition of lipolysis in clover by the plant enzyme polyphenol oxidase.
7. Effects of fat and fatty acids on meat quality
7.1 Adipose tissue
Work with pigs and ruminants has shown that the fatty acid composition of adipose tissue affects its
firmness, because the different fatty acids have different melting points. The composite fatty acids of
meat melt between about 25 ºC and 50 ºC, with saturated fatty acids melting at higher and
polyunsaturated fatty acids at lower temperatures e.g. 18:0 melts at 69 ºC and 18:2n-6 at -5 ºC (Wood,
1984).
In pigs, the differences in fatty acid composition of subcutaneous fat between carcasses of different P2
fat thickness have an important effect on fat quality defined in terms of firmness and the degree of
cohesiveness between lean and fat tissues (fat separation). In a study of carcasses with 8mm, 12mm
and 16mm P2 fat thickness, the proportion of 18:0 increased and that of 18:2n-6 decreased as fat
thickness increased (Table 4). The backfat of pigs with 16mm P2 was firmer and there was less
separation between fat and underlying muscle than in backfat from the 8mm P2 group (Wood, Jones,
Francombe and Whelehan, 1986). Firmness, measured both objectively and subjectively in the
shoulder and loin regions, was correlated with fatty acid proportions, the highest correlations being
with 18:0 (positive) and 18:2n-6 (negative). The proportion of 18:2n-6 provided the best prediction of
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fat firmness (Table 15). In an earlier study of Large White pigs from two genetic selection lines, 18:0
and 18:2n-6 proportions were correlated with the melting point of extracted lipid from subcutaneous
fat and in this case the proportion of 18:0 provided the best prediction of melting point (Wood et al,
1978).
Changing the fatty acid composition of subcutaneous adipose tissue using different dietary oils also
changes lipid melting point and fat firmness. For example, palm kernel oil produced firmer fat than
soyabean oil in the study of Teye et al (2006b). When all the data were pooled, the proportions of 12:0
and 14:0 (high in pigs given palm kernel oil) were strongly correlated with fat quality parameters, as
also were 18:0 and 18:2n-6.
In lamb subcutaneous fat sampled throughout the year in four abattoirs, Enser and Wood (1993) found
that melting point varied with the time of year, being lowest in the Spring and Summer and highest
later in the year. Melting (slip) point ranged from 30ºC to 49ºC and 18:0, which ranged from 7.0 to
32.9% of fatty acids (mean 18.8%) was the fatty acid most highly correlated with melting point (r
0.89). Linoleic acid was 1.3% of fatty acids overall and its correlation with melting point was -0.3.
Lamb subcutaneous fat is unusual in having significant concentrations of methyl branched fatty acids
of medium to long chain length (C8-17) with low melting points. Their concentration reached 4% of
the total in the study of Enser and Wood (1993).
These fatty acids are responsible for the soft, oily fat found in sheep that have consumed high grain
diets which produce high levels of propionic acid in the rumen.
7.2 Muscle
The total lipid content of muscle (intramuscular fat, often termed marbling fat, although this is strictly
the flecks of adipose tissue composed mainly of neutral lipid) has a role in the tenderness and juiciness
of cooked meat although the strength of the correlation varies considerably between studies, with
some showing an important role for marbling fat and others showing only a weak relationship with
sensory traits. The role of marbling fat is of particular interest in pigs because genetic selection for
lean pigs has reduced the level of marbling fat to below 1% of muscle weight in modern pigs (e.g.
Large Whites in Table 11) compared with 2-4% in US studies in the 1960s (Wood, 1990). In the study
of 4 breeds of Wood et al, 2004, the highest correlation between marbling fat concentration and
sensory traits across all four breeds was 0.17, for tenderness. The correlation in Berkshires was 0.34.
The study of Wood et al (1986) showed that total lipid (marbling fat) in longissimus muscle was 0.55,
0.66 and 0.96g/100g in pig carcasses having 8mm, 12mm and 16mm P2 fat thickness respectively.
These were very light carcasses, weighing 58kg on average. Correlations across all pigs between
marbling fat and sensory traits were 0.13 for tenderness and 0.31 for juiciness. Juiciness was
significantly lower in the 8mm than the 16mm P2 fat thickness group. In a recent comparison of lamb
chops produced in organic and conventional production systems, Angold, Wood, Nute, Whittington,
Hughes and Sheard (2007) showed that the correlations between the total fatty acid content of
longissimus (marbling fat) and eating quality scores given by the taste panel were 0.36 and -0.06 for
juiciness and toughness respectively. It seems from these results that juiciness is the trait most affected
by increasing levels of marbling fat, associated with greater retention of water in meat during cooking.
The location of marbling fat in the perimysial connective tissue between muscle fibre bundles may
also be important in ‘opening up’ the structure of muscle, allowing it to be more easily broken down in
the mouth (Wood, 1990). There are therefore good reasons to expect a positive role for marbling fat in
meat quality.
The use of low protein diets to increase marbling fat in pigs has sometimes produced a higher score for
tenderness and juiciness in cooked pork. In the study of Teye et al (2006a), total lipid was increased to
2.8% of longissimus using an 18% protein diet compared with 1.7% in a standard diet containing 20%
protein. The scores for tenderness and juiciness (1-8 range) were increased from 4.2 and 3.9 in the
20% protein diet to 4.8 and 4.4 in the 18% protein diet (both P <0.01).
Despite contradictory results between studies for the role of marbling fat in the tenderness and
juiciness of fresh pork, beef and lamb, incorporation of adipose tissue at different levels into burgers
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or patties has been linked positively to tenderness and juiciness in several studies (e.g. Kregel, Prusa
and Hughes, 1986). In these cases, positive effects on tenderness and juiciness are observed at between
10 and 20% lipid rather than at the lower levels seen for marbling fat.
The fatty acid composition of muscle affects its oxidative stability during processing and retail
display, the polyunsaturated fatty acids in phospholipid being liable to oxidative breakdown at this
stage. A standard test for lipid oxidative stability in foods is the thiobarbituric acid reacting substances
(TBARS) test of Tarladgis, Watts, Younathan and Dugan (1960) which measures the oxidation
product malondialdehyde. Values above about 0.5 are considered critical since they indicate a level of
lipid oxidation products which produce a rancid odour and taste which can be detected by consumers.
Values of TBARS in our studies with pork have usually been well below 0.5, even when PUFA
proportions have been increased to high levels using soyabean oil or linseed (Riley, Enser, Nute and
Wood, 2000; Kouba et al, 2003; Sheard, Enser, Wood, Nute, Gill and Richardson, 2000). In the
studies of Riley et al (2000) and Sheard et al (2000), minced and comminuted products were produced
which develop higher levels of oxidation because the fatty acids are exposed to pro-oxidants such as
iron released from muscle cells. Even here, TBARS values remained below 0.5 except in the case of
bacon in the work of Sheard et al (2000). In this study, several factors contributed to high levels of
oxidation. The loin joint was conditioned at 1ºC for 10 days, after which it was injected with brine to a
target level of 10%. The loin was immersed in brine for 3 days after which the bacon was sliced, blast
frozen, stored at -18ºC for 8 weeks, thawed, packed in overwrapped trays and kept under retail display
conditions for up to 9 days. Injection of salt followed by freezing and thawing were probably the most
important contributors to lipid oxidation. Even after this treatment, TBARS values were below 0.5 at 5
days of retail display, increasing to about 1.5 after 9 days.
The bacon with a high level of 18:3n-3 (1.3%) had a similar TBARS value to the controls (18:3n-3
0.85%). The bacon was assessed by the trained taste panel after the freezing stage and no differences n
flavour characteristics between feeding treatments were detected.
It is possible that in the study of Sheard et al (2000), 18:3n-3 proportions in muscle of treated pigs
were below those likely to produce oxidation products having adverse effects on pork flavour. In the
work of Kouba et al (2003), in which the proportion of 18:3n-3 was increased to 3.0% of muscle fatty
acids compared with 0.65% in controls, an increase in TBARS after 7 days of retail display was
observed, although only to 0.15 mg malondialdehyde/kg compared with 0.10 in controls. A slightly
higher level of abnormal odour was detected by the taste panel in subcutaneous adipose tissue
compared with the controls, and the ‘flavour liking’ score of longissimus muscle was significantly
reduced. It is at levels of around 3% 18:3n-3 in muscle fatty acids that other workers have detected
off-flavours as a result of feeding linseed (Shackleford, Reagan, Haydon and Miller, 1990).
Feeding fish oils to pigs increases levels of long chain n-3 PUFA in adipose tissue and particularly in
muscle and fishy odours and flavours are detected when critical tissue levels are exceeded. In the work
of Overland, Taugbol, Haug and Sundstol (1996), feeding a 1% fish oil diet between 10 and 100kg
live weight increased the proportions of 20:5n-3 and 22:6n-3 from 0.6 and 0.9% of muscle fatty acids
in controls to 1.5 and 1.8% respectively. This caused significantly higher ‘off odour’ and ‘off flavour’
scores in cooked subcutaneous adipose tissue sampled both fresh and after 6 months frozen storage. A
3% fish oil diet increased these scores even more.
Several studies with pigs have shown that high levels of vitamin E in the diet are incorporated into
tissues where they are effective in reducing lipid oxidation in stored and displayed pork (Buckley,
Morrissey and Gray, 1995). However, a level of 150 mg/kg diet did not prevent the deterioration in
flavour when linseed feeding raised the level of 18:3n-3 to 3% of muscle fatty acids in the study of
Kouba et al (2003) and extra vitamin E did not increase storage stability in pigs given diets containing
0.5% fish oil in a study by Hertzman, Goransson and Ruderus (1988). In some studies,
‘supranutritional’ vitamin E has reduced drip loss and improved colour stability in pork, probably by
preventing oxidation of muscle pigments by lipid oxidation products but in others, limited effects on
drip loss and colour stability have been seen (Jensen et al, 1997).
In ruminants, we have frequently seen higher values of TBARS than in our studies on pork. In a recent
study, Nute et al (2007) examined oxidative stability and eating quality in lambs which had been fed
327
different levels of n-3 PUFA from linseed oil, fish oil, a protected lipid supplement (PLS) made from
linseed, sunflower seed and soyabean meal, marine algae (contains long chain n-3 PUFA) and
combinations of these different oil sources. Leg steaks were conditioned for 6 days at 0 ºC then
packed in modified atmosphere packs (O2:CO2 75:25) and displayed under retail conditions.
Lipid oxidation was measured on the semimembranosus muscle at 7 days of display.
The lowest TBARS value was in muscles from the group given linseed oil (0.6mg/kg) and all other
groups had values above 2.0mg/kg, the highest value being 6.2 in the group given a combination of
algae and fish oil. All the groups, except those given linseed, had low taste panel scores for lamb
flavour and high scores for abnormal lamb flavour. These scores were correlated with fatty acid
proportions in phospholipid, negative correlations being found between long chain n-3 PUFA and
lamb flavour (Table 16). The fatty acid composition of semimembranosus phospholipid was greatly
affected by diet in this study. For example, 18:2n-6 varied from 11.5 (fish oil) to 33.7% (PLS), 18:3n3 from 1.4 (combination of fish oil and marine algae) to 6.9% (linseed) and 22:6n-3 from 0.6 (PLS) to
5.35% (combination of PLS and marine algae). Significant proportions of long chain n-3 PUFA were
also detected in adipose tissue. A companion paper by Elmore et al (2005) showed that very high
levels of lipid oxidation products were produced during the cooking of these samples to affect the
flavour scores. Muscle samples from the fish oil/marine algae treatments had the highest lipid
oxidation and the lowest concentration of vitamin E. Other work has shown low vitamin E levels in
pig tissues containing high PUFA proportions, suggesting utilization of the vitamin to control
oxidation (Kouba et al, 2003).
In cattle, consumption of concentrate produced higher TBARS values in steaks than consumption of
grass silage in a study of Warren, Scollan, Nute, Hughes, Wood and Richardson (2007b). This is a
companion study to that of Warren et al (2007a).
Aberdeen Angus cross and Holstein-Friesian steers were fed the diets from 6 to 14 months of age.
After slaughter, loin joints were conditioned at 1ºC for 10 days.
Steaks were then placed in modified atmosphere packs (O2:CO2 75:25) and displayed under retailtype conditions. Lipid oxidation measurements were made at 4 and 7 days of display. The results
(Table 17) show that the concentrate diet increased lipid oxidation in the steaks, values increasing to
over 2.0 after 7 days of display in both breeds. On the other hand, TBARS values remained at low
levels in the grass silagefed groups, albeit these were higher than we normally see in pork. These
TBARS values were apparently inversely related to the vitamin E concentration in muscle and plasma.
Steers fed grass silage had higher values for muscle and plasma vitamin E than those fed concentrate.
Muscle values for the grass silage groups were around the 3.3 to 3.5 mg/kg level found by Arnold,
Scheller, Arp, Williams and Schaefer (1993) to give optimum lipid stability in longissimus while
values in the concentrate group were considerably lower. The high vitamin E values in the steers fed
grass silage are partly the result of lower PUFA levels in muscle but mainly due to greater uptake of
vitamin E from the diet. When the data from all animals slaughtered at 14, 19 and 24months was
combined, TBARS were higher in the concentrate-fed animals than in those fed grass silage at all
levels of PUFA in muscle (Figure 6). TBARS increased with PUFA level only in those fed
concentrate. For the steers fed grass silage it appears that vitamin E was sufficiently high to protect the
PUFA from oxidation, at least for the 7 days during which the beef was displayed.
In the study of Warren et al (2007b), the concentrate diet contained a standard level of vitamin E (25
mg/kg). In work with sheep, Demirel et al (2004) fed concentrate diets containing different oil sources
(5%) and either 100 or 500 mg/kg vitamin E. Despite these ‘supranutritional’ levels, concentrations of
the vitamin in muscle were 0.27 and 0.52 mg/kg for the 100 and 500 mg/kg diets respectively. Values
around 5 mg/kg would be expected. The reason for these very low levels is unclear but these results,
together with those of Warren et al (2007b) point to excessive utilisation of antioxidants in concentrate
– type diets.
328
A change in muscle colour seen during retail display in the study of Warren et al (2007b) suggested a
link between lipid oxidation, vitamin E concentration and colour.
The intensity of the red colour, termed saturation or chroma, declined gradually as the display period
progressed but the decline was more rapid in the muscles from the groups fed concentrate than the
groups fed grass silage. A value of 18 for colour saturation, which has been used as an index of the
end of shelf life, was reached 2-3 days sooner in the concentrate groups.
Elmore et al (2004) examined the flavour volatile compounds produced when beef samples from the
study of Warren et al (2007b) were grilled. Products of 18:2n-6 oxidation such as pentanal and
hexanal were detected in steaks produced using concentrate and the alcohols 1-penten-3-ol and cis-2penten-1-ol, products of 18:3n-3 oxidation, were detected in steaks from the grass silage - fed group.
A compound formed from chlorophyll, 2-phytene, was higher in samples from the grass-fed groups.
Despite these differences in lipid oxidation, the trained taste panel at Bristol could detect few clear
differences in sensory (eating) quality between the concentrate and grass silage groups. On balance,
the panel preferred loin steaks from steers fed grass silage. This result is consistent with papers which
have shown that when grain- and grass-fed cattle grow at similar rates, sensory scores are similar
(Bidner et al, 1986).
Comparisons of well finished grain-fed with poorly finished grass-fed steers have often found results
in favour of those fed grain (Medeiros, Field, Menkhaus and Russell, 1987).
Campo, Nute, Hughes, Enser, Wood and Richardson (2006) examined eating quality in 73 beef loins
produced using different feeding treatments and containing different concentrations of n-6 and n-3
PUFA. Lipid oxidation was promoted by conditioning for 10 days, freezing, thawing and storing
steaks in modified atmosphere packs (O2:CO2 75:25) before sensory analysis. This series of
procedures promoted high levels of lipid oxidation, TBARS values up to 12.0 being recorded. As the
TBARS value increased, the scores for beef flavour, bloody, metallic and livery declined, and scores
for abnormal flavour, rancid and greasy increased (Table 18). This study identified a TBARS value of
2.3 as the point where rancid and other abnormal flavours overpower beef flavour to produce an
unacceptable flavour profile in beef.
Below this, rancidity was detected but beef flavour remained high. These results suggest that the upper
limit for TBARS of 0.5 suggested by Tarladgis et al (1960) based on pork may not be appropriate for
beef (or lamb) where the natural level of lipid oxidation is higher.
8. Conclusions
This review has shown that the fatty acid composition of adipose tissue and muscle in pigs, sheep and
cattle depends on the amount of fat in the carcass and in muscle.
Effects of diet and breed have to be judged against the amount of fat. Also, there are important
differences between the species which are only partly explained by differences in the digestive
process. These include: ruminants conserve PUFA in muscle whereas in pigs, concentrations are
higher in adipose tissue; long chain (C20- 22) PUFA are found in adipose tissue and muscle neutral
lipid in pigs and sheep but not in cattle; and the ratio of 18:0/18:2n-6 in adipose tissue increases as
fattening proceeds in pigs but declines in ruminants.
In muscle, the high proportion of 18:2n-6 in phospholipid compared with neutral lipid in all species
means that muscle from lean animals has high proportions of this major PUFA. As the animal is
fattened for meat, the decline in PUFA proportions is more dramatic in the ruminants because PUFA
levels in neutral lipid are so low. Since desirable sensory characteristics tend to increase with fatness,
there is potentially an inverse relationship between nutritional value and eating quality in ruminants.
Of the 2 major PUFA, 18:2n-6 is more rapidly taken up into meat tissues than 18:3n-3 and reaches
much higher levels. Synthesis of long chain PUFA from these precursors occurs in phospholipid but
329
the available sites for incorporation are soon filled and long term feeding of linseed to pigs or grass to
cattle does not increase levels and so proportions decline.
Oxidation of fatty acids proceeds at a naturally higher level in ruminants than pigs after slaughter
despite the lower PUFA proportions. Vitamin E is a vital meat quality enhancing nutrient, particularly
in ruminants where high concentrations resulting from concentrations, often seen after the feeding of
concentrate diets, lead to a shorter colour shelf life and unfavourable beef flavour notes.
Acknowledgements
We are grateful to many collaborators in the research presented including Professor Nigel Scollan and
Helen Warren of the Institute of Grassland and Environmental Research, Drs Liam Sinclair and Robert
Wilkinson of Harper Adams University College and Professor Don Mottram and Dr Stephen Elmore
of Reading University.
We gratefully acknowledge the technical assistance at Bristol of Kathy Hallett, Kevin Gibson, Ann
Baker, Rose Ball, Duncan Marriott and Jackie Bayntun. We also gratefully acknowledge funding from
the Department for Environment, Food and Rural Affairs (Defra) and Meat and Livestock
Commission. Finally we thank many colleagues in industry for their cooperation.
References
Angold, K.M., Wood, J.D., Nute, G.R., Whittington, F.M., Hughes, S.I. and Sheard, P.R. (2007). A
comparison of organic and conventionally – produced lamb purchased from 3 major UK supermarkets
: price, eating quality and fatty acid composition. Meat Science In press.
Arnold, R.N., Scheller, K.K., Arp, S.C., Williams, S.N. and Schaefer, D.M. (1993). Dietary _tocopheryl acetate enhances beef quality in Holstein and Beef breed steers. Journal of Food Science,
58, 28-33.
Bidner, T.D., Schupp, A.R., Mohamad, A.B., Rumore, N.C., Montgomery, R.E., Bagley, C.P. and
MacMillin, K.W. (1986). Acceptability of beef from Angus-Hereford or Angus-Hereford-Brahman
steers finished on all-forage or a high-energy diet. Journal of Animal Science, 62, 381-387.
Buckley, D.J., Morrissey, P.A. and Gray, J.I. (1995). Influence of dietary vitamin E on the oxidative
stability and quality of pigmeat. Journal of Animal Science, 73, 3122-3130.
Campo, M.M., Nute, G.R., Hughes, S.I., Enser, M., Wood, J.D. and Richardson, R.I. (2006). Flavour
perception of oxidation in beef. Meat Science, 72, 303-311.
Chang, K.C., Da Costa, N., Blackley, R., Southwood, O., Evans, G., Plastow, G., Wood, J.D. and
Richardson, R.I. (2003). Relationships of myosin heavy chain fibre types to meat quality traits in
traditional and modern pigs. Meat Science, 64, 93-103.
Cook, L.J., Scott, T.W., Faichney, G.J. and Davies, H.L. (1972). Fatty acid interrelationships in
plasma, liver, muscle and adipose tissues of cattle fed sunflower oil protected from ruminal
hydrogenation. Lipids 7, 83-99.
Cooper, S.L., Sinclair, L.A., Wilkinson, R.G., Hallett, K.G., Enser, M. and Wood, J.D. (2004).
Manipulation of the n-3 polyunsaturated acid content of muscle and adipose tissue in lambs. Journal
of Animal Science, 82, 1461-1470.
Crawford, M.A., Hare, W.R. and Whitehouse, D.B. (1984). Nutrient partitioning in domesticated and
non-domesticated animals. In: J. Wiseman (Ed.) Fats in Animal Nutrition (pp.471-479) London:
Butterworth’s.
Demirel, G., Wachira, A.M., Sinclair, L.A., Wilkinson, R.G., Wood, J.D. and Enser, M. (2004).
Effects of dietary n-3 polyunsaturated fatty acids, breed and dietary vitamin E on the fatty acids of
lamb muscle, liver and adipose tissue. British Journal of Nutrition, 91, 551-565.
Doran, O., Moule, S.K., Teye, G.A., Whittington, F.M., Hallett, K.G. and Wood, J.D. (2006). A
reduced protein diet induces stearoyl-CoA desaturase protein expression in pig muscle but not in
subcutaneous adipose tissue: relationship with intramuscular lipid formations. British Journal of
Nutrition, 95, 609-617.
Doreau, M. and Ferlay, A. (1994). Digestion and utilisation of fatty acids by ruminants. Animal Feed
Science and Technology 45, 379-396.
330
Ellis, N.R. and Isbell, H.S. (1926). Soft pork studies. 3. The effect of food fat upon body fat, as shown
by the separation of the individual fatty acids of the body fat. Journal of Biological Chemistry, 69,
239-248.
Elmore, J.S., Cooper, S.L., Enser, M., Mottram, D.S., Sinclair, L.S., Wilkinson, R.G. and Wood, J.D.
(2005). Dietary manipulation of fatty acid composition in lamb meat and its effect on the volatile
aroma compounds of grilled lamb. Meat Science, 69, 233-242.
Elmore, J.S., Warren, H.E., Mottram, D.S., Scollan, N.D., Enser, M., Richardson, R.I. and Wood, J.D.
2004. A comparison of the aroma of volatiles and fatty acid compositions of grilled beef muscle from
Aberdeen Angus and Holstein-Friesian steers fed diets based on silage or concentrates. Meat Science,
68, 27-33.
Enser,M. and Wood, J.D. (1993). Effect of time of year on fatty acid composition and melting point of
UK lamb. Proceedings of the 39th International Congress of Meat Science and Technology, 2, 74.
Enser, M., Hallett, K., Hewitt, B., Fursey, G.A.J. and Wood, J.D. (1996). Fatty acid content and
composition of English beef, lamb and pork at retail. Meat Science, 42, 443-456.
Enser, M., Richardson, R.I., Wood, J.D., Gill, B.P. and Sheard, P.R. (2000). Feeding linseed to
increase the n-3 PUFA of pork: fatty acid composition of muscle, adipose tissue, liver and sausages.
Meat Science, 55, 201-212.
Fisher, A.V., Enser, M., Richardson, R.I., Wood, J.D., Nute, G.R., Kurt, E., Sinclair, L.A. and
Wilkinson, R.G. (2000). Fatty acid composition and eating quality of lamb types derived from four
diverse breed x production systems. Meat Science, 55, 141-147.
French, P.C., Stanton, C., Lawless, F., O’Riordan, G., Monahan, F.J. and Caffrey, P.J. (2000). Fatty
acid composition including conjugated linoleic acid, of intramuscular fat from steers offered grazed
grass, grass silage or concentrate-based diets. Journal of Animal Science, 78, 2849-2855.
Hertzman, C., Goransson, L. and Ruderus, H. (1988). Influence of fish meal, rapeseed and rape-seed
meal in feed on the fatty acid composition and storage stability of porcine body fat. Meat Science, 23,
37-53.
Jensen, C., Guidera, J., Skovgaard, I.M., Staun, H., Skibsted, L.H., Jensen, S.K., Moller, A.J.,
Buckley, J. and Bertelsen, G. (1997). Effects of dietary _-tocopheryl acetate supplementation on _tocopherol deposition in porcine m.psoas major and m. longissimus dorsi and on drip loss, colour
stability and oxidative stability of pork meat. Meat Science, 45, 491-500.
Kouba, M., Enser, M., Whittington, F.M., Nute, G.R. and Wood, J.D. (2003). Effect of a highlinolenic acid diet on lipogenic enzyme activities, fatty acid composition and meat quality in the
growing pig. Journal of Animal Science, 81, 1967-1979.
Kregel, K.K., Prusa, K.J. and Hughes, K.V. (1986). Cholesterol content and sensory analysis of
ground beef as influenced by fat level, heating and storage. Journal of Food Science, 51, 1162-1190.
Leat, W.M.F. (1975). Fatty acid composition of adipose tissue of Jersey cattle during growth and
development. Journal of Agricultural Science, 85, 551-558.
Lee, M.R.F., Winters, A.L., Scollan, N.D., Dewhurst, R.J., Theodorou, M.K. and Minchen, F.R.
(2004). Plant-mediated lipolysis and proteolysis in red clover with different polyphenol oxidase
activities. Journal of the Science of Food and Agriculture, 84, 1639-1645.
Medeiros, L.C., Field, R.A., Menkhaus, D.J. and Russell, W.C. (1987). Evaluation of range-grazed
and concentrate-fed beef by a trained sensory panel, a household panel and a laboratory test market
group. Journal of Sensory Studies, 2, 259-272.
Nguyen, L.Q., Nuijens, M.C.G.A., Everts, H., Salden, N. and Beynen, A.C. (2003). Mathematical
relationships between the intake of n-6 and n-3 polyunsaturated fatty acids and their contents in
adipose tissue of growing pigs. Meat Science, 65. 1399-1406.
Nute, G.R., Richardson, R.I., Wood, J.D., Hughes, S.I., Wilkinson, R.G., Cooper, S.L. and Sinclair,
L.A. (2007). Effect of dietary oil source on the flavour and the colour and lipid stability of lamb meat.
Meat Science. In press.
Overland, M., Taugbol, O., Haug, A. and Sundstol, E. (1996). Effect of fish oil on growth
performance, carcass characteristics, sensory parameters and fatty acid composition in pigs. Acta
Agriculturae Scandinavica, 46, 11-17.
Raes, K., De Smet, S. and Demeyer, D. (2001). Effect of double-muscling in Belgian Blue young bulls
on the intramuscular composition with emphasis on conjugated linoleic acid and polyunsaturated fatty
acids. Animal Science, 73, 253-260.
331
Riley, P.A., Enser, M., Nute, G.R. and Wood, J.D. (2000). Effects of dietary linseed on nutritional
value and other quality aspects of pig muscle and adipose tissue. Animal Science, 71, 483-500.
Scollan, N.D., Choi, N.J., Kurt, E., Fisher, A.V., Enser, M. and Wood, J.D. (2001). Manipulating the
fatty acid composition of muscle and adipose tissue in beef cattle. British Journal of Nutrition, 85,
115-124.
Scollan, N.D., Enser, M., Gulati, S.K., Richardson, R.I. and Wood, J.D. (2003). Effects of including a
ruminally protected lipid supplement in the diet on the fatty acid composition of beef muscle. British
Journal of Nutrition, 90, 709-716.
Scollan, N.D., Hocquette, J-F., Nuernberg, K., Dannenberger, D., Richardson, R.I. and Maloney, A.
(2006a). Innovations in beef production systems that enhance the nutritional and health value of beef
lipids and their relationship with meat quality. Meat Science, 74, 17-33.
Scollan, N.D., Costa, P., Hallett, K.G., Nute, G.R., Wood, J.D. and Richardson, R.I. (2006b). The fatty
acid composition of muscle fat and relationships to meat quality in Charolais steers: influence of level
of red clover in the diet. Proceedings of the British Society of Animal Science, 2006, 23.
Shackelford, S.D., Miller, M.F., Haydon, K.D. and Reagan, J.O. (1990). Effects of feeding elevated
levels of monounsaturated fats to growing-finishing swine on acceptability of low-fat sausage. Journal
of Food Science, 55, 1497-1500.
Sheard, P.R., Enser, M., Wood, J.D., Nute, G.R., Gill, B.P. and Richardson, R.I. (2000). Shelf life and
quality of pork and pork products with raised n-3 PUFA. Meat Science, 55, 213-221.
Tarladgis, B.G., Watts, B.M., Younathan, N.T. and Dugan, L. (1960). A distillation method for the
quantitative determination of malonaldehyde in rancid foods. Journal of the American Oil Chemists
Society, 37, 44-48.
Teye, G.A., Sheard, P.R., Whittington, F.M., Nute, G.R., Stewart, A. and Wood, J.D. (2006a).
Influence of dietary oils and protein level on pork quality. 1. Effects on muscle fatty acid composition,
carcass, meat and eating quality. Meat Science, 73, 157-165.
Teye, G.A., Wood, J.D., Whittington, F.M., Stewart, A. and Sheard, P.R. (2006b). Influence of dietary
oils and protein level on pork quality. 2. Effects on properties of fat and processing characteristics of
bacon and frankfurter-style sausages. Meat Science, 73, 166-177.
Truscott, T.G., Wood, J.D. and MacFie, H.J.H. (1983). Fat deposition in Hereford and Friesian steers.
1. Body composition and partitioning of fat between depots. Journal of Agricultural Science, 100,
257-270.
Wachira, A.M., Sinclair, L.A., Wilkinson, R.G., Enser, M., Wood, J.D. and Fisher, A.V. (2002).
Effects of dietary fat source and breed on the carcass composition, n-3 polyunsaturated fatty acid and
conjugated linoleic acid content of sheepmeat and adipose tissue. British Journal of Nutrition, 88, 697709.
Warren, H.E., Scollan, N.D., Enser, M., Richardson, R.I., Hughes, S.I. and Wood, J.D. (2007)a.
Effects of breed and a concentrate or grass silage diet on beef quality. I. Animal performance, carcass
quality and muscle fatty acid composition. Meat Science. In press.
Warren, H.E., Scollan, N.D., Nute, G.R., Hughes, S.I., Wood, J.D. and Richardson, R.I. (2007b).
Effects of breed and a concentrate or grass silage diet on beef quality. II. Meat stability and flavour.
Meat Science. In press.
Warnants, N., Van Oeckel, M.J. and Boucque, C.V. (1999). Incorporation of dietary polyunsaturated
fatty acids into pork fatty tissues. Journal of Animal Science, 77, 2478-2490.
Williams, C.M. and Burdge, G. (2006). Long-chain n-3 PUFA: plant v. marine sources. Proceedings
of the Nutrition Society, 65, 42-50.
Wood, J.D. (1984). Fat deposition and the quality of fat tissue in meat animals. In: J. Wiseman (Ed.)
Fats in Animal Nutrition (pp. 407-435). London: Butterworths.
Wood, J.D. (1990). Consequences for meat quality of reducing carcass fatness. In: J.D. Wood and
A.V. Fisher (Eds.) Reducing Fat in Meat Animals. (pp. 344-397), London: Elsevier Applied Science.
Wood, J.D., Enser, M.B., MacFie, H.J.H., Smith, W.C., Chadwick, J.P., Ellis, M. and Laird, R. (1978).
Fatty acid composition of backfat in Large White pigs selected for low backfat thickness. Meat
Science, 2, 289-300.
Wood, J.D., Jones, R.C.D., Francombe, M.A. and Whelehan, O.P. (1986). The effects of fat thickness
and sex on pig meat quality with special reference to the problems associated with overleanness. 2.
Laboratory and trained taste panel results. Animal Production, 43, 535-544.
332
Wood, J.D., Enser, M., Whittington, F.M., Moncrieff, C.B. and Kempster, A.J. (1989). Backfat
composition in pigs: differences between fat thickness groups and sexes. Livestock Production
Science, 22, 351-362.
Wood, J.D., Nute, G.R., Richardson, R.I., Whittington, F.M., Southwood, O., Plastow, G.,
Mansbridge, R., da Costa, N. and Chang, K.C. (2004). Effects of breed, diet and muscle on fat
deposition and eating quality in pigs. Meat Science, 67, 651-667.
Wood, J.D., Richardson, R.I., Scollan, N.D., Hopkins, A., Dunn, R., Buller, H. and Whittington, F.M.
(2007). Quality of meat from biodiverse grassland. In: J. Hopkins, A.J. Duncan, D.I. McCracken, S.
Peel and J.R.B. Tallowin. (Eds.) High Value Grassland (pp. 107-116). Cirencester, Gloucestershire:
British Grassland Society.
MEAT QUALITY, FATTY ACID COMPOSITION AND FLAVOUR
ANALYSIS IN BELGIAN RETAIL BEEF
K. Raesa, A. Balcaena, P. Dirinckb, A. De Winneb, E. Claeysa, D. Demeyera and S. De Smet , , a
a
Department of Animal Production, Faculty of Agricultural and Applied Biological Sciences, Ghent
University, Proefhoevestraat 10, 9090, Melle, Belgium
b
Chemical and Biochemical Research Centre (CBOK), Department of Chemistry and Biochemistry,
KaHo Sint-Lieven, Gebroeders Desmetstraat 1, 9000, Ghent, Belgium
Meat Science Volume 65, Issue 4, December 2003, Pages 1237-1246
Abstract
The objective of this study was to evaluate the differences in biochemical, sensorial and quality
characteristics of retail beef in Belgium. Four types of beef (Belgian Blue double-muscled, Limousin,
Irish and Argentine) and two different muscles (longissimus lumborum and semimembranosus) were
bought at the retail level and compared with regard to colour, shear force, collagen content, fatty acid
analysis, taste panel evaluation as well as flavour analysis. Belgian Blue and Limousin beef had a
paler colour, lower collagen and intramuscular fat contents. Fatty acid profiles were significantly
different between the four types, with significantly higher PUFA/SFA and n-6/n-3 ratios for Belgiam
Blue and Limousin beef compared to Argentine and Irish beef. There were significant differences
between the meat types for taste panel tenderness and shear force, however both measurements did not
fully correspond. Flavour analysis by gas chromatography–mass spectrometry as well as sensory
analysis demonstrated that Irish and Argentine beef had a higher flavour intensity related to higher
contents of volatile compounds. Differences in tenderness and flavour between the meat types were
probably affected by differences in ageing time, related to import vs local production of meat.
Author Keywords: Beef quality; Meat origin; Fatty acid composition; Flavour
BB Belgian Blue double-muscled
CLA conjugated linoleic acid
GC–MS gas chromatography–mass spectrometry
LL longissimus lumborum
MUFA monounsaturated fatty acids
PCA Principal Component Analysis
PUFA polyunsaturated fatty acids
SFA saturated fatty acids
SM semimembranosus
WBSF Warner–Bratzler shear force
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1. Introduction
Variation in beef quality is large and is due to many factors, such as differences in genetic
background, sex, age, management, nutrition. In Belgium, beef cattle are mostly of the Belgian Blue
breed and are fattened indoors on high-concentrate diets. However, at the retail level, imported meat
from more extensive grass-based production systems is available and is labelled accordingly. Often,
labels on these meats claim specific sensory or health benefits and generally have a positive public
image due to their more ‘natural’ character. Beef from a specific production system represents the
combined effects of breed, genotype, sex, age, nutrition and management, and these effects can
interact at many points. As a consequence, a comparison of retail meat samples does not allow us to
attribute differences in meat quality to one particular factor. However, from a consumer's point of
view, only the overall differences in meat quality are of interest, and one can question whether meat
labels differentiate meat objectively.
The consumer's decision to purchase beef is guided by the perception of healthiness and a variety of
sensory traits including colour, tenderness, juiciness, and aroma or flavour ([Verbeke ]). It is therefore
worthwhile considering differences in meat quality at the consumer level, with respect to both sensory
traits and health aspects. The purpose of this work is to present objective measurements of meat
quality characteristics (colour, tenderness, juiciness, fatty acid composition, sensory and instrumental
flavour analyses) of retail beef samples of four different origins, either produced locally or imported.
2. Material and methods
2.1. Meat samples
Meat samples of four different origins (combination of breed and nutrition) were obtained in
collaboration with a local supermarket: Belgian Blue double-muscled (BB), Limousin, Irish and
Argentine beef. Beef from BB and Limousin animals originated from animals fattened under high
intensive production conditions in Belgium, while Irish and Argentine beef originated from animals
fattened in their respective countries and were claimed to represent more extensive production systems
compared to the Belgian situation. For each type of beef, eight samples from two muscles each
[longissimus lumborum (LL) and semimembranosus (SM)] were purchased. Steaks (2.5 cm thick)
from each sample were cut, as possible perpendicular to the fibre direction. Steaks of BB and
Limousin animals were vacuum packed and aged for 14 days at 4 °C. Argentine and Irish steaks were
vacuum packed and frozen (-20 °C) after the determination of colour at arrival. It was stated that the
ageing time for Argentine and Irish beef was 29 and 22 days, respectively, at day of purchase.
Anatomical sites of steaks were similar for similar analyses. One steak was taken for collagen content,
one for fatty acid analysis, one for shear force and sarcomere length, and three steaks were taken for
flavour analysis and taste panel evaluation (taste, tenderness and juiciness).
2.2. Meat quality characteristics
After cutting the muscles into steaks, colour was measured in duplicate on different fresh samples
further used for shear force determination, flavour analysis and sensory analysis. The samples were
allowed to bloom for 1 h. The Hunterlab L*, a* and b* values were measured with a Hunterlab
Miniscan colorimeter (D65 light source, 10° standard observer, 45°/0° geometry, 1 in light surface,
white standard). After the colour measurements, the samples were vacuum packed, aged (BB and
Limousin samples) and stored at −20 °C until shear force, flavour or sensory analysis.
Warner–Bratzler shear force (WBSF) measurements were performed using a Lloyd TA 500 Texture
Analyser. After thawing, samples were heated by hanging them into plastic bags and immersing them
into a water bath (75 °C) for 60 min. Fifteen to twenty cores (ø 1.27 cm) were cut from the steaks
parallel to the muscle fibre orientation. The mean value of the replicate determinations of the
maximum force needed to shear the samples was taken as the shear force value (WBSF). The total
area under the shear force curve, representing total work, was allocated to a collagen and a
myofibrillar component ([Harris]), as described by [Claeys et al].
Collagen measurements were performed on minced meat samples by measuring the hydroxyproline
content (ISO/DIS 3496.2).
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Sarcomere length was determined on the samples used for shear force, before heating
([Vandenriessche et al]).
2.3. Fatty acid analysis
Intramuscular fat was extracted by means of a modification of [Folch et al] using chloroform/methanol
(2/1; v/v). Fatty acids were analysed by gas chromatography as described by [Raes et al]. Briefly,
nonadecanoic acid was added as an internal standard. After methylation (NaOH/MeOH followed by
HCl/MeOH), the fatty acids were analysed on a HP6890 gas chromatograph with a CP-Sil 88 column
(100 m×0.25 mm×0.2 µm). The following temperature program was used: 150 °C during 2 min
followed by an increase of 1.5 °C/min to 175 °C, followed by an increase of 5 °C/min to 215 °C, and
then held at this temperature until C22:6 n-3 had been detected.
2.4. Sensory evaluation
Sensory characteristics were evaluated by a 10-member, inhouse trained panel (22–55 years of age).
As roasting is the most used preparation method in Belgium, meat samples (3×3×2 cm) were grilled
for 2 min on a 2-contact grill and served on pre-heated plates. The panellists were asked to assess the
following attributes: tenderness, juiciness and flavour intensity. A ranking test was used for flavour
intensity, while tenderness and juiciness were scored on an 8-point scale (1=extremely tough/dry to
8=extremely tender/juicy).
2.5. Instrumental flavour analysis
Gas chromatography–mass spectrometry (GC–MS) analyses were performed on extracts of 3
separately grilled samples of the LL muscles (without visible fat) of each beef type (7×7×2.5 cm).
Meat samples were grilled for 4 min (SEB, grill minute). After grilling, the meat was cut into pieces
(1×1 cm). Aroma compounds were isolated by Likens-Nickerson extraction (4 h reflux time) using
600 ml distilled water and 60 ml dichloromethane as extraction solvent. Semi-quantitative data of the
flavour compounds were obtained by relating the peak intensities to the intensity of nonane, added to
the dichloromethane phase as an internal standard. The extracts were concentrated to 0.2 ml by
Kuderna-Danish evaporation and stored at −18 °C until analysis. Analyses were performed on a
HP5890 gas chromatograph coupled to a HP5971A mass spectrometer. The gas chromatographic
conditions were: injector temperature: 250 °C; detector temperature: 280 °C; methylsilicone capillary
column (50 m×0.2 mm×0.5 µm); carrier gas: He; flow: 1 ml/min; oven temperature: 40 °C for 5 min,
followed by an increase of 5 °C/min to 250 °C and then held there for 13 min. The mass spectrometer
operated in an electron impact mode with an electron energy of 70 eV, a source temperature and
pressure of 191 °C and 25–30 mTorr respectively. The mass spectrometer scanned from m/z 40 to 260.
Identification of the volatile components was based on comparison of the spectra with the spectra of
the Wiley/NBS library and of a self-made library.
2.6. Statistical analysis
Data were subjected to analysis of variance (ANOVA), using Duncan's post-hoc test (SPSS 9.0).
Discriminant analysis and principal component analysis (PCA) was carried out using data of the fatty
acid analysis and flavour analysis, respectively.
3. Results
3.1. Meat quality characteristics (Table 1)
Table 1. Mean values for some biochemical properties of longissimus lumborum and
semimembranosus meat samples according to their origin (n=8)
Arg=Argentine beef; BB=Belgian Blue double-muscled beef; Limo=Limousin beef; Irish=Irish beef.
a, b, c: Means with different letters are significantly different for LL (P<0.05). x, y, z: Means with
different superscripts are significantly different for SM (P<0.05)
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For both muscles, meat from BB and Limousin animals had lower a*-values and higher L*-values,
reflecting a paler colour. The highest collagen content was found in the Irish meat, while the lowest
value was measured for BB beef. The Warner-Bratzler shear force of the LL muscle was highest for
BB meat and lowest for Argentine meat, indicating that the LL of BB beef was less tender. This
difference was not apparent for the SM muscle. For the four beef types, the ‘collagen work’ was lower
for the LL muscle than for the SM muscle. Large differences in ‘collagen work’ between the meat
types were found for both muscles, with the highest values being for Limousin and Irish beef, for the
LL and SM muscle, respectively. No significant differences in ‘myofibrillar work’ were measured
between meat types. Also no differences in sarcomere length were found between the muscles and
meat types.
3.2. Fatty acid composition
Total intramuscular fatty acid content (mg/100 g meat) was the lowest for BB and Limousin meat
(Table 2), compared to Irish and Argentine beef. Also, the variation in total intramuscular fatty acid
content of BB and Limousin meat was much smaller than for Irish and Argentine meat (data not
shown). For the four meat types, the intramuscular fatty acid content was lower in the SM muscle than
in the LL muscle. This difference was mainly due to lower saturated (SFA) and monounsaturated
(MUFA) fatty acid contents, while the polyunsaturated fatty acid (PUFA) contents were similar (Table
2). This means that with increasing intramuscular fat content the proportion of PUFA decreased (as a
% of total fatty acids), while the absolute PUFA contents (mg/100 g muscle) did not differ.
Table 2. Proportions (% of total fatty acids) and concentrations (mg/100 g meat) of saturated (SFA),
monounsaturated (MUFA) and polyunsaturated (PUFA) fatty acids and some nutritional values for
longissimus lumborum and semimembranosus according to their origin (n=8)
Arg=Argentine beef; BB=Belgian Blue double-muscled beef; Limo=Limousin beef; Irish=Irish beef.
a, b, c: Means with different letters are significantly different for LL (P<0.001). x, y, z: Means with
different letters are significantly different for SM (P<0.001). P/S=(C18:2n-6+C18:3n3)/(C14:0+C16:0+C18:0).
n-6/n-3=(C18:2n-6+C18:3n-6+C20:3n-6+C20:4n-6+C22:4n-6)/(C18:3n3+C20:5n-3+C22:5n-3+C22:6n-3).
It can be deduced from Table 3 that within the individual fatty acids (mg/100 g meat),
C16:0+C18:0+C18:1 represented more than 90% of the SFA+MUFA. The relative proportion of n-6
fatty acids was 2.5–4 times higher for BB and Limousin meat compared to Irish and Argentine meat,
but no differences in the absolute amounts of total and individual n-6 fatty acids in the 2 muscles were
observed between the meat types (Table 3). The most abundant n-6 fatty acids were C18:2 n-6 and
C20:4 n-6. The relative proportion of n-3 fatty acids was approximately 1.5 times higher for BB and
Limousin meat compared to Irish and Argentine meat, but inversely the absolute amount of total n-3
fatty acids (mg/100 g meat) was significantly higher for the Irish and Argentine meat compared to BB
and Limousin beef, reflecting a higher content of individual n-3 fatty acids (C18:3 n-3, C20:5 n-3,
C22:5 n-3 and C22:6 n-3).
Table 3. Fatty acid profile (mg/100 g meat) of longissimus lumborum and semimembranosus
depending on their origin (n=8)
Arg=Argentine beef; BB=Belgian Blue double-muscled beef; Limo=Limousin beef; Irish=Irish beef.
a, b, c: Means with different letters are significantly different for LL (P<0.001). x, y, z: Means with
different letters are significantly different for SM (P<0.001).
Fig. 1. Discriminant analysis based on intramuscular fatty acid profile of beef samples of different
origin. Arg=Argentine beef; BB=Belgian Blue double-muscled beef; Limo=Limousin beef; Irish=Irish
beef.
336
Irish and Argentine meat clearly contained more cis-9,trans-11 conjugated linoleic acid (CLA)
(between 20 and 35 mg/100 g meat) compared to BB and Limousin meat (between 2.5 and 10 mg/100
g meat) (Table 3). Expressed as mg/g fat the CLA content varied for BB and Limousin beef between 4
and 6 mg/g fat, and for Argentine and Irish meat between 8 and 10 mg/g fat. Fig. 1 shows a
discriminant analysis based on the fatty acid profile, using the proportions of all individual fatty acids
of the two muscles of the four different beef types. BB and Limousin beef were clearly distinguished
from the closely related Irish and Argentine beef.
In view of nutritional guidelines the ratios PUFA/SFA and n-6/n-3 are important (Table 2). The
PUFA/SFA ratio was clearly lower for Argentine and Irish beef (0.10–0.15) compared to BB and
Limousin (0.35–0.77). A higher PUFA/SFA ratio is found for the SM muscle than for the LL muscle
and this difference is more obvious for the leanest meat (BB and Limousin). For the n-6/n-3 ratio
higher values are found for BB and Limousin (5–7), compared with values of 2.5–3 for Argentine and
Irish beef.
3.3. Sensory evaluation
Meat samples from Limousin and BB animals showed significantly lower flavour intensity compared
with Irish and Argentine meat for both muscles (Table 4). Argentine meat showed the highest flavour
intensity, which is most obvious for the LL muscle.
Table 4. Mean values for longissimus lumborum and semimembranosus of taste panel evaluation for
flavour intensity, tenderness and juiciness according to their origin (n=8)
Arg=Argentine beef; BB=Belgian Blue double-muscled beef; Limo=Limousin beef; Irish=Irish beef.
a, b, c: Means with different letters are significantly different for LL (P<0.05). x, y, z: Means with
different letters are significantly different for SM (P<0.05).
With regard to tenderness no significant differences in the LL muscles were observed between the
meat types (Table 4). However, for the SM muscle the BB and Limousin meat showed the lowest
value, corresponding to more tender meat. The LL muscle of the BB meat was the most juicy (Table
4), while for the SM muscle the Limousin meat tended to be the most juicy.
3.4. Instrumental flavour analysis (GC–MS)
Based on experience in our laboratory we preferred to use the Likens-Nickerson extraction method for
the isolation of the volatiles in grilled meat. Using this extraction method to obtain ‘a total volatile’
analysis has several advantages compared to headspace procedures, that do not allow isolation of the
less volatile key aroma compounds. Also the ‘total volatile’ isolation procedure eliminates the problem
of aroma release, which in the case of heterogeneous products, like meat, hinder reproducibility
([Demeyer et al, Dirinck et al and Schmidt]). It has been reported that the type of isolation method
affects the number and the relative proportion of the volatile compounds ([Demeyer et al]). This study
deals with the flavour of roasted meat (the general preparation method of beef in Belgium). Roasting
meat is already a severe heat treatment and for this type of meat Likens-Nickerson extraction should
be good practice, since we have shown in our laboratory it is the preferred method to extract volatile
compounds of other roasted products, like coffee. In these type of roasted products good correlations
between sensory and GC–MS profiling using Likens-Nickerson extraction as an isolation procedure
for the volatile compounds have been found.
Sixty-seven volatiles were identified in the GC-MS analyses of the grilled meat samples. The semiquantitative volatile composition of the grilled meat samples is presented in Table 5.
Table 5. Semi-quantitative determination of volatile compounds (µg/kg meat) of longissimus
lumborum depending on their origin (grouped according to their chemical nature) (n=3).
Arg=Argentine beef; BB=Belgian Blue double-muscled beef; Limo=Limousin beef; Irish=Irish beef.
337
The volatile compounds were classified according to their chemical nature: aldehydes, ketones,
pyrazines, pyrroles, furane derivatives, thiazoles, sulphur compounds, esters and alcohols. Aldehydes
were the chemical family of highest concentration and a distinction could be made between the higher
and the lower molecular weight saturated and unsaturated aldehydes. Because of their low volatility
the higher molecular weight aldehydes, which also occur in raw meat, should have a minor impact on
roasted meat flavour and for this reason they are not individually presented. The low molecular weight
aldehydes were classified into: saturated straight-chain alkanals (pentanal, hexanal, heptanal, nonanal),
unsaturated aldehydes (2-butenal, 2-octenal, 2-nonenal, 2-decenal, 2,4-decadienal and 2-undecenal),
branched aldehydes (2- and 3-methylbutanal) and aromatic aldehydes (benzaldehyde and
phenylacetaldehyde). Among the ketones, considerable amounts of 3-hydroxy-2-butanone and diacetyl
were detected.
Argentine and Irish beef clearly contained higher concentrations of the lower saturated and
unsaturated aldehydes, resulting from fat oxidation, as well as branched and aromatic aldehydes,
resulting from proteolysis and amino acid degradation (Table 5). Irish beef had the highest content of
both pyrazines and pyrrole derivatives.
To visualise the volatile composition of the roasted beef samples a PCA-analysis with 67 individual
aroma compounds was performed. PC1 and PC2 are plotted in Fig. 2. BB and Limousin beef were
situated at the lower right quadrant of the PCA-plot, reflecting the lowest content of aroma
compounds. The Irish meat was situated at the positive side of PC2 and was characterised by high
amounts of aroma compounds. The high concentrations of pyrazines should be important contributors
to the pronounced roasted meat flavour of the Irish beef, which had also the highest level of potent
aroma unsaturated aldehydes. The Argentine beef was situated in the region of the saturated, branched
and aromatic aldehydes, probably as a result of the longer ageing of the meat.
4. Discussion
The paler colour of BB and Limousin beef, compared to Irish and Argentine beef, may be the result of
both nutritional and genetic factors. A darker colour of Irish and Argentine meat is probably related to
the more extensive grass-based production systems, as is apparent from the fatty acid composition, and
corresponds with literature data ([Priolo et al]). Also, [Vestergaard et al] found that muscles from
pasture-fed animals had a higher proportion of oxidative fibres and a darker colour than muscles from
grain-fed animals. According to these authors, difference in feeding levels and physical activity
between grain- and pasture-fed animals could be responsible for a change in the metabolic
characteristics as well as the colour of the muscles. In addition, it is known that lean breeds like the
double-muscled BB have more glycolytic fibre type ([Fiems et al]), which would also contribute to the
differences in colour observed.
Tenderness evaluation by the taste panel did not fully correspond with the WBSF values. No
differences in taste panel tenderness were observed between the beef types for the LL muscle in spite
of differences in WBSF values, whereas tenderness scoring was in line with WBSF values for the SM
muscle. On the other hand, differences in juiciness between beef types were larger in the LL than in
the SM muscle. In this study, the taste panel tenderness evaluations appeared to be more related to the
collagen content and to the ‘collagen work’ rather than to the ‘myofibrillar work’ during shearing.
Myofibrillar and collagen resistance to shearing are affected by the heat treatment, being different for
WBSF preparation than for taste panel evaluations. Additionally, the fragmentation of myofibrillar
proteins during ageing affects tenderness, and in line with trade practices ageing times were longer for
the imported beef in this study. The complexity of these interactions prevents a meaningful discussion
of the differences observed, but nonetheless the differences may be relevant to consumer preference.
The very low intramuscular fatty acid content (less than 1%) for BB beef corresponds with previous
studies ([De Smet et al, Raes et al and Webb et al]). Breed and sex differences are probably the main
reason for the lower intramuscular fatty acid content of the BB and Limousin beef compared to the
Irish and Argentine beef. Probably breed differences are also the main reason for the smaller
variability in intramuscular fatty acid content for BB and Limousin beef. As these two breeds are
selected for lower fat contents, they are closer to the physiological lower limit of intramuscular fatty
338
acid content. Higher intramuscular fat content in the Argentine and Irish beef is also associated with a
higher SFA and MUFA content, whereas the PUFA content remains constant across the beef types.
This is mainly due to the relatively constant proportion of phospholipids in the cell membranes, and
increasing deposition of triglycerides in the adipocytes with increasing intramuscular fat content (
[Vernon ]). Differences in PUFA content between the LL and SM muscle can be traced to differences
in oxidative nature of the muscles. [Turkii and Enser et al] found higher PUFA contents in more
oxidative muscles, corresponding to the higher PUFA content in the more oxidative SM muscle
compared to the LL muscle found in this study.
Grass-fed ruminants deposit a higher amount of n-3 fatty acids in their intramuscular and adipose fat
([Enser et al, French et al, Marmer et al and Miller et al]), while concentrate-fed animals normally
have higher n-6 PUFA. Despite biohydrogenation of unsaturated fatty acids in the rumen, higher n-3
fatty acids in grass fed animals can be explained by the high C18:3n-3 contents in grass, while grains
are normally high in n-6 fatty acids. Irish and Argentine beef, probably originating, at least partly,
from extensive production based on grass (silage) feeding displayed higher n-3 fatty acid contents than
BB and Limousin beef, originating from animals raised on high concentrate diets. In line with this, the
latter two meat types have a much higher proportion of n-6 fatty acids. The content of cis-9, trans-11
CLA varied between 4 and 9 mg/g fat, depending on its origin, in agreement with other studies ([Enser
et al, French et al and Shantha et al]). Higher CLA contents (mg/100 g meat) in the Argentine and
Irish muscle can be partly explained by the higher fat content of these samples, since it is well known
that the CLA content of meat is closely related to the total fatty acid content ([Raes et al]). It is also
known that meat ([Shantha et al]) and milk ([Dhiman et al]) from grass-fed animals have a higher
content of CLA than concentrate fed animals. Both these factors, the higher intramuscular fat content
and the diet, can explain the higher CLA content (mg/g fat) of the Argentine and Irish beef.
Increasing the muscle n-3 fatty acid content resulted in a lower n-6/n-3 ratio. The values obtained for
Argentine and Irish meat are similar to other studies using grass-fed animals ([Enser et al and French
et al]). For the BB and Limousin beef these results correspond to earlier studies using lean beef breeds
([De Smet et al and Raes et al]) and are much lower than the values reported by [Enser et al] for beef
from concentrate fattened animals with a higher fat content. Compared to the nutritional guidelines
([National Raad voor Voeding, 1996]) for the n-6/n-3 ratio to be 5 or lower, only BB meat was slightly
too high. On the contrary, the PUFA/SFA ratio was much higher for BB and Limousin beef and
approached most closely the nutritional recommendation of 0.7. This is the result of the (genetically
determined) lower fat level of these breeds, resulting in lower SFA and MUFA contents.
The analytical flavour analyses corresponded with the results observed by the taste-panel. Taste-panel
evaluations indicated the highest flavour intensity for Irish and Argentine meat. Both meat types were
situated in the PCA-plot in the region of very potent aroma compounds, such as pyrazines, saturated
and unsaturated aldehydes. The members of the taste panel noticed also the weaker flavour of
Limousin, and especially of BB beef, which corresponds to their location in the PCA-plot. Again there
may be several factors involved in these differences, e.g. differences in fat content, feeding, sex,
slaughter age, ageing time.
In roasted products pyrazines, resulting from Maillard reaction and Strecker degradation, are important
flavour compounds, associated with the roasty flavour ([Mottram, 1985]). No differences in the
pyrazine content were observed between the four beef types, which is in agreement with findings of
[Elmore et al] showing that the dietary fat source has no effect on the pyrazine volatiles. The higher
flavour intensity described by the taste-panel for the Irish and Argentine beef is probably linked with
higher amounts of lower molecular weight unsaturated aldehydes. These lower molecular weight
unsaturated aldehydes are derived from fat oxidation, especially from long chain PUFA ([Mottram]).
These volatiles have a low threshold value and are thus probably making a major contribution to the
higher flavour intensity of the Irish as well as the Argentine beef. In both these beef types, the absolute
PUFA content was much higher than for the leaner BB and Limousin.
The higher amount of lower molecular weight saturated, branched and aromatic aldehydes, products
derived from protein degradation, in the Argentine beef is probably due to the longer ageing time and
as a consequence of more pronounced proteolysis. Beef from BB and Limousin animals showed
339
higher concentrations of products derived from carbohydrates (acetoine, diacetyl). This may be
associated with the more glycolytic nature of the muscles of these breeds and the high-concentrate
feeding that was applied.
Among the ketones, considerable amounts of 3-hydroxy-2-butanone and diacetyl were detected, that
are known to impart buttery notes to food products. The presence of 2,3-octanedione has been
attributed to pasture-fed animals by [Young et al] Accordingly, in our study this volatile compound
was only detected in the Irish and Argentine beef, representing the more extensive production system,
and not in the BB and Limousin beef.
The pyrazines, pyrroles, thiazoles and furanes are typical Maillard reaction products contributing to
roasted meat flavour. Also methional and 1-(methylthio)-propane are potent aroma compounds and
originate from sulphur containing amino acids. The compounds 4-methylphenol and 1-octen-3-ol,
which impart a mushroom odour, have low threshold values. The higher content of 4-methylphenol in
the Argentine and Irish beef could be due to the more extensive production system for both these beef
types. [Ha] speculated that higher concentrations of methylphenols could be encountered in pasturefed beef, confirming the findings of [Young et al] for grass and grain fed lambs.
5. Conclusions
Distinct differences in fat content, fatty acid composition and flavour characteristics of beef can be
expected at the retail level, depending on the origin and treatment of the meat, whereas differences in
colour and tenderness are less evident. Based on a series of objective measurements, beef sources
could be well discriminated in this study.
Acknowledgements
This study was funded by the Ministry of Small Enterprises, Traders and Agriculture, Directorate
Research and Development. The authors are grateful for the technical assistance of S. Coolsaet, D.
Baeyens and B. Lammertyn. Mr. Broeckaert and Mr. Van der Weeën are gratefully acknowledged for
their help in the meat supply.
References
Claeys et al., 2000. Claeys, E., De Smet, S. Balcaen, A., & Demeyer, D. (2000). Analyse du profil de
la mesure de la force de cisaillement. In Compte rendu des VIIIe journées des sciences du muscle et
technologies de la viande (pp. 237–240), 21–22 November 2000, Paris, France.
Demeyer et al., 2000. D. Demeyer, M. Raemaekers, A. Rizzo, A. Holck, A. De Smedt, B. ten Brink,
B. Hagen, C. Montel, E. Zanardi, E. Murbrekk, F. Leroy, F. Vandendriessche, K. Lorentsen, K.
Venema, L. Sunesen, L. Stahnke, L. De Vuyst, R. Talon, R. Chizzolini and S. Eerola, Control of
bioflavour and safety in fermented sausages: first results of a European project. Food Research
International 33 (2000), pp. 171–180.
De Smet et al., 2000. S. De Smet, E.C. Webb, E. Claeys, L. Uytterhaegen and D.I. Demeyer, Effect of
dietary energy and protein levels on fatty acid composition of intramuscular fat in double-muscled
Belgian Blue bulls. Meat Science 56 (2000), pp. 73–79.
Dhiman et al., 1999. T.R. Dhiman, G.R. Anand, L.D. Satter and M.W. Pariza, Conjugated linoleic acid
content of milk from cows fed different diets. Journal of Dairy Science 82 (1999), pp. 2146–2156.
Dirinck et al., 1997. P. Dirinck, F. Van Opstaele and F. Vandendriessche, Flavour differences between
Northern and Southern European cured hams. Food Chemistry 59 (1997), pp. 511–521.
Elmore et al., 1999. J.S. Elmore, D.S. Mottram, M. Enser and J.D. Wood, Effect of the
polyunsaturated fatty acid composition of beef muscle on the profile of aroma volatiles. Journal of
Agriculture and Food Chemistry 47 (1999), pp. 1619–1625.
Enser et al., 1998. M. Enser, K.G. Hallett, B. Hewitt, G.A.J. Fursey, J.D. Wood and G. Harrington,
Fatty acid content and composition of UK beef and lamb muscle in relation to production system and
implications for human nutrition. Meat Science 49 (1998), pp. 329–341.
340
Enser et al., 1999. M. Enser, N.D. Scollan, N.J. Choi, E. Kurt, K. Hallett and J.D. Wood, Effect of
dietary lipid on the content of conjugated linoleic acid (CLA) in beef muscle. Animal Science 69
(1999), pp. 143–146.
Fiems et al., 1995. L.O. Fiems, J. Van Hoof, L. Uytterhaegen, C.H. Boucque and D.I. Demeyer,
Comparative quality of meat from double-muscled and normal beef cattle. In: A. Ouali, D.I. Demeyer
and F.J.M. Smulders, Editors, Expression of tissue and regulation of protein degradation as related to
meat quality, ECCEAMST, Utrecht, The Netherlands (1995), pp. 381–393.
Folch et al., 1957. J. Folch, M. Lees and S.G.H. Stanley, A simple method for the isolation and
purification of total lipids from animal tissues. Journal of Biological Chemistry 226 (1957), pp. 497–
509.
French et al., 2000. P. French, C. Stanton, F. Lawless, E.G. O'Riordan, F.J. Monahan, P.J. Caffrey and
A.P. Moloney, Fatty acid composition, including conjugated linoleic acid, of intramuscular fat from
steers offered grass, grass silage or concentrate-based diets. Journal of Animal Science 78 (2000), pp.
2849–2855.
Ha & Lindsay, 1991. J.K. Ha and R.C. Lindsay, Volatile alkylphenols and thiophenols in speciesrelated characterising flavors of red meat. Journal of Food Science 56 (1991), pp. 1197–1202.
Harris & Shorthose, 1988. P.V. Harris and W.R. Shorthose, Meat texture. In: R.A. Lawrie, Editor,
Developments in meat science-4, Elsevier Applied Science, London, UK (1988), pp. 245–296.
Marmer et al., 1984. W.N. Marmer, R.J. Maxwell and J.E. Williams, Effects of dietary regimen and
tissue site on bovine fatty acid profiles. Journal of Animal Science 59 (1984), pp. 109–121.
Miller et al., 1981. G.J. Miller, M.L. Masor and M.L. Riley, Intramuscular lipids and triglyceride
structures in range and feedlot steers. Journal of Food Science 46 (1981), pp. 1333–1335.
Mottram, 1985. D.S. Mottram, The effect of cooking conditions on the formation of volatile
heterocyclic compounds in pork. Journal of the Science of Food and Agriculture 36 (1985), pp. 377–
382.
Mottram & Edwards, 1983. D.S. Mottram and R.A. Edwards, The role of triglycerides and
phospholipids in the aroma of cooked beef. Journal of the Science of Food and Agriculture 34 (1983),
pp. 517–522.
National Raad voor Voeding, 1996. National Raad voor Voeding, Voedingsaanbevelingen voor
België. , G. De Backer, Zevekotestraat 43, B-9830 Sint-Martens-Latem, Belgium (1996).
Priolo et al., 2001. A. Priolo, D. Micol and J. Agabriel, Effects of grass feeding systems on ruminant
meat colour and flavour. A review. Animal Research 50 (2001), pp. 185–200.
Raes et al., 2001. K. Raes, S. De Smet and D. Demeyer, Effect of double-muscling in Belgian Blue
young bulls on the intramuscular fatty acid composition with emphasis on conjugated linoleic acid and
poly-unsaturated fatty acids. Animal Science 73 (2001), pp. 253–260.
Raes et al., 2003. Raes, K., Balcaen, A., Claeys, E., Demeyer, D., & De Smet, S. (2003). Effect of
duration of feeding diets rich in n-3 fatty acids on the fatty acid composition of Belgian Blue doublemuscled young bulls. Reproduction, Nutrition Development (accepted for publication).
Shantha et al., 1997. N.C. Shantha, W.G. Moody and Z. Tabeidi, Conjugated linoleic acid
concentration in semimembranosus muscle of grass- and grain-fed and zeranol-implanted beef cattle.
Journal of Muscle Foods 8 (1997), pp. 105–110.
Schmidt & Berger, 1998. S. Schmidt and R.G. Berger, Aroma compounds in fermented sausages of
different origines. Zeitschrift für Lebensmittel Untersuchung Forschung 31 (1998), pp. 559–567.
Turkii & Cambell, 1967. P.R. Turkii and A.M. Cambell, Relation of phospholipids to other lipid
components in two beef muscles. Journal of Food Science 32 (1967), pp. 151–154.
Vandenriessche et al., 1984. Vandendriessche, F., Buts, B., Claeys, E., Dendooven, R., & Demeyer, D.
(1984). Sarcomere length measurement by laser diffraction and light microscopy. In Proceedings 30th
European Meeting of Meat Research Workers (pp. 110–111), Bristol, UK.
Verbeke & Viaene, 1999. W. Verbeke and J. Viaene, Beliefs, attitude and behaviour towards fresh
meat consumption in Belgium: empirical evidence from a consumer survey. Food, Quality and
Preference 10 (1999), pp. 437–445.
Vernon & Flint, 1988. R.G. Vernon and D.F. Flint, Lipid metabolism in farm animals. Proceedings of
the Nutrition Society 47 (1988), pp. 283–287.
341
Vestergaard et al., 2000. M. Vestergaard, N. Oksbjerg and P. Henckel, Influence of feeding intensity,
grazing and finishing feeding on muscle fibre characteristics and meat colour of semitendinosus,
longissimus dorsi and supraspinatus muscles of young bulls. Meat Science 54 (2000), pp. 177–185.
Webb et al., 1998. E.C. Webb, S. De Smet, C. Van Nevel, B. Martens and D. Demeyer, Effect of
anatomical location on the composition of fatty acids in double-muscled Belgian Blue cows. Meat
Science 50 (1998), pp. 45–53.
Young et al., 1997. O.A. Young, J.-L. Berdagué, C. Viallon, S. Rousset-Akrim and M. Theriez, Fatborne volatiles and sheepmeat odour. Meat Science 45 (1997), pp. 183–200.
STRESS DES ANIMAUX ET QUALITÉS DE LEURS VIANDES. RÔLES
DU
PATRIMOINE
GÉNÉTIQUE
ET
DE
L'EXPÉRIENCE
ANTÉRIEURE
E.M.C. TERLOUW
INRA, Station de Recherches
[email protected]
sur
la
Viande,
Theix,
63122
St-Genès-Champanelle
2002, INRA Prod. Anim., 15, 125-133
Les qualités sensorielles et technologiques de la viande dépendent des conditions d'évolution du
métabolisme musculaire au moment de l'abattage. Or ces conditions sont largement influencées
par l'état physiologique de l'animal et notamment de ses éventuelles réactions de stress.
Résumé
Les réactions de stress aux procédés de l'abattage influencent la vitesse du métabolisme musculaire
avant et après la mise à mort, et par ce biais, les qualités des viandes. Ce phénomène est
essentiellement lié à une baisse des réserves glycolytiques et à une augmentation de l'activité
ATPasique. Les réactions comportementales, physiologiques et métaboliques aux événements
stressants dépendent du patrimoine génétique des animaux et de leur expérience antérieure. Par
exemple, certaines races sont plus réactives à l'Homme ou à un changement d'environnement. L'effet
des changements physiologiques sur le métabolisme dépend entre autres du nombre et du
fonctionnement des récepteurs des cellules musculaires ; ce nombre est également influencé par le
patrimoine génétique. Concernant l'expérience antérieure, une défaite dans un combat ou l'élevage en
isolement ou attaché peut augmenter la réactivité comportementale et physiologique à un objet non
familier ou à la distribution du repas quotidien. Il est probable qu'une telle élévation de la réactivité au
stress renforce les effets du stress de l'abattage sur les qualités des viandes. La facilité du chargement,
du déchargement et des manipulations et par conséquent les réactions de l'animal à ces situations,
dépendent de la familiarité de la situation. Chez le veau de boucherie, l'attitude de l'éleveur vis-à-vis
de ses animaux influence dans une certaine mesure les réactions du veau aux procédés d'abattage et les
qualités de ses viandes. En résumé, nous connaissons une partie des rôles du patrimoine génétique, du
mode d'élevage et des réactions de l'animal aux conditions d'abattage dans le déterminisme des
qualités des viandes. Il est nécessaire d'étendre ces connaissances et d'en étudier les mécanismes sousjacents.
Introduction
Alors que la préoccupation d'une meilleure maîtrise des qualités organoleptiques et technologiques des
viandes est toujours d'actualité, d'autres intérêts ont émergé, notamment celui porté au bien-être
animal, qui joue un rôle important dans l'image de la viande auprès du consommateur. Le stress à
l'abattage est associé au manque de respect pour le bien-être animal et est à l'origine de variations dans
les qualités des viandes. Le présent article a pour objectif de décrire les liens entre les réponses
physiologiques et comportementales de stress et certaines qualités technologiques des viandes,
notamment celles liées au métabolisme glycolytique. Est en particulier discutée l'influence de deux
facteurs importants, le patrimoine génétique et l'expérience antérieure sur la façon dont l'animal évalue
et réagit à la situation. Les propos sont illustrés par des données expérimentales, obtenues dans des
342
expérimentations contrôlées sur le porc, et, dans une moindre mesure, sur le bovin. Les autres espèces
ne sont pas abordées pour des raisons de concision. Ces expérimentations ne reflètent pas forcément la
situation exacte des pratiques commerciales d'abattage, mais elles permettent d'apprécier l'effet des
facteurs qui nous intéressent. Tout d'abord, quelques notions sur les concepts de stress et de bien-être
et sur la transformation du muscle en viande sont introduites.
1 / Stress, qualités des viandes: rappels
1.1 / Stress
Les pionniers des recherches sur le stress furent Walter Cannon (1914) et Hans Selye (1932). Cannon
a démontré que le système sympatho-médullo-surénalien (notamment la sécrétion de l'adrénaline et de
la noradrénaline) est nécessaire pour faire face à des perturbations physiques et physiologiques. Le
rôle important du système cortico-surrénalien (notamment la sécrétion des glucocorticoides) dans la
réponse de stress a été reconnu par Selye. La théorie de Selye associait le terme stress surtout au stress
physique (fatigue, maladie) et à des réponses physiologiques. Plus tard, cette théorie a été critiquée par
Mason (1971), car elle n'intégrait pas la dimension émotionnelle de l'état de stress. Actuellement, il
n'existe toujours pas de définition précise du concept de stress. La définition de l'état de stress chez
l'animal la plus souvent citée est 'le résultat de la sollicitation exagérée des capacités d'ajustement
comportementale et physiologique de l'animal' (Fraser et al 1975). Cette définition ne fait toujours pas
référence à l'état mental ou physiologique de l'animal de manière explicite. De plus, l'imprécision
notamment du terme 'exagérée' rend difficile de déterminer, pour certaines situations, si un individu
donné est stressé.
On peut dire que plus un individu se sent menacé par rapport au bon fonctionnement de son corps
(impossibilité de se coucher et de se tourner, problèmes de soif, de faim, de douleur ou de maladie…)
et de son équilibre mental (contexte social inadapté, problèmes de peur, de frustration, de sur- ou sousstimulation par l'environnement…), plus il sera stressé. Dans cet article, le terme d'état de stress fera
référence à l'état physiologique, comportemental et psychologique de l'animal, face à une situation
supposée menaçante.
Nous ne pouvons qu'estimer l'état psychologique de l'animal à l'aide de mesures physiologiques et
comportementales, car nous manquons d'indicateurs directs. En fonction de l'origine du stress,
différentes mesures peuvent être choisies. Les mesures comportementales concernent généralement les
réponses d'adaptation à la situation (fuite, agression, immobilisation, exploration…). Concernant la
physiologie, les taux sanguins de cortisol, principal glucocorticoïde chez de nombreuses espèces, sont
souvent utilisés car ils augmentent suite à l'application de facteurs de stress très différents. L'activité
du système nerveux autonome est une autre mesure couramment utilisée. Le système nerveux
autonome a deux branches, le système (ortho) sympathique et le système parasympathique. Le premier
inhibe entre autres les organes digestifs et stimule les poumons et le cœur. Le système
parasympathique a un effet contraire. L'activité cardiaque reflète l'équilibre des activités des deux
branches. La sécrétion des catécholamines (adrénaline et noradrénaline) dans le sang est sous le
contrôle de la branche sympathique. Contrairement au système cortico-surrénalien, le système
autonome est rapide: les variations de cortisolémie apparaissent après une vingtaine de minutes et
peuvent durer plusieurs heures, alors que la fréquence cardiaque et les taux sanguins d'adrénaline et de
noradrénaline varient en quelques secondes ou minutes. La difficulté de l'interprétation de ces mesures
réside dans le fait que toutes ces variations peuvent se produire en dehors de tout état de stress,
simplement suite à une activité physique ou à une vigilance accrue.
Enfin, il est important de noter que l'état de stress de l'animal dépend non pas de la situation, mais de
son évaluation de la situation. Chaque individu est forgé de manière unique par son patrimoine
génétique et son expérience antérieure. Par conséquent, l'état de stress d'un animal est une expérience
individuelle et subjective. Sa façon de réagir à différentes situations de stress est appelée la réactivité
au stress (physiologique et/ou comportementale; figure 1). La réactivité au stress est donc une
caractéristique de l'animal.
Figure 1. Représentation schématique des liens entre la réactivité au stress, le stress à l'abattage et les
qualités des viandes. Le stress d'un animal dépend de la nature des manipulations qui précèdent
l'abattage, de son patrimoine génétique et de son expérience antérieure. Il provoque des réponses
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comportementales et physiologiques. L'effet de ces réponses sur le métabolisme dépend de leur
ampleur, et du patrimoine génétique et de l'expérience antérieure de l'animal.
1.2 / Qualités des viandes
Après la saignée, le métabolisme musculaire est profondément modifié en raison de l'arrêt de la
circulation sanguine. Le muscle se trouvant en anoxie, la synthèse de l'ATP repose alors sur la
dégradation de la phosphocréatine et surtout sur la glycogénolyse anaérobie (pour revue : Monin
1988). A mesure que le taux d'ATP diminue et que le glycogène est dégradé, des protons et des
molécules de lactate sont formés, entraînant une diminution du pH du muscle. La valeur à laquelle le
pH se stabilise est appelée le pH ultime. La vitesse de la chute du pH dépend de la vitesse de
dégradation de l'ATP, c'est-à-dire de l'activité ATPasique. L'amplitude de la diminution du pH dépend
des réserves musculaires, essentiellement en glycogène, au moment de la mort. Les qualités
organoleptiques et technologiques sont influencées à la fois par la vitesse et par l'amplitude de chute
du pH. Une diminution du pH trop rapide entraîne la dénaturation des protéines musculaires qui
conduit à une viande pâle, flasque et exudative. Elle est dure à manger. D'une façon générale, plus le
pH ultime est bas, plus la couleur de la viande est claire. Les viandes à pH ultime élevé sont de couleur
sombre et ont une plus grande sensibilité aux développements microbiens. Le pH ultime explique une
partie importante de la variabilité de la tendreté, de la jutosité et de la flaveur, celles-ci augmentant
avec le pH. Mais il convient de noter que la couleur dépend également du taux de pigment, et donc de
fer présent dans le muscle sous forme héminique. Le fer entre dans la composition de l'hème, luimême constituant des pigments qui donnent leur couleur rouge au sang et au muscle, de l'hémoglobine
et de la myoglobine.
La maturation de la viande, qui est associée à la dégradation des protéines et des lipides musculaires,
se traduit par l'augmentation de la tendreté de la viande et le développement de sa flaveur. Ce
processus, qu'il est souhaitable de laisser se dérouler pendant quelques jours, commence quelques
heures après l'abattage dès l'installation de la rigor mortis (Ouali 1990).
1.3 / Facteurs de stress et qualités des viandes
Le transport et l'abattage des animaux sont associés à une multitude de facteurs potentiellement
stressants. Ces facteurs sont d'origine physique, comme l'absence d'aliments, la restriction de la prise
d'eau, les mouvements du camion, les chocs provoqués par des pertes d'équilibre, par des coups reçus
d'autres animaux ou du manipulateur, et d'origine psychologique, car tout changement de la situation
habituelle est susceptible de provoquer la peur chez l'animal. Le départ du milieu habituel, le
changement du milieu social, l'introduction dans des environnements inconnus et la présence de
personnes non familières sont des exemples. Les qualités des viandes sont fortement influencées par le
comportement et par l'état physiologique des animaux pendant la période de pré-abattage et au
moment de l'abattage (cf figure 1). L'activité physique entraîne une diminution des réserves
énergétiques musculaires, induite par une activation de la phosphorylase et la glycogénolyse. Cette
activation métabolique est sous-tendue par des changements physiologiques tels que l'augmentation de
la fréquence cardiaque et la libération d'hormones (cortisol, (nor)adrénaline). L'état de stress, dû aux
facteurs énumérés ci-dessus, ne fait que renforcer les réponses comportementales et physiologiques, et
par conséquent les changements métaboliques.
Concrètement, pendant la période pré-abattage (transport, attente à l'abattoir), une activité physique
accrue diminue les réserves glucidiques du muscle, et ce d'autant plus si elle est associée à un état de
stress. Selon le muscle étudié, cette diminution peut se traduire par un pH ultime plus élevé et une
couleur plus sombre. Souvent on obtient des viandes plus tendres et juteuses, mais plus difficile à
conserver (Lewis et al 1962a et 1962b, Hendrick et al 1964, Monin 1988, Lewis et al 1989). Une
activité physique élevée et/ou un état de stress importants immédiatement avant l'abattage (conduite et
passage au restrainer) se traduisent par l'augmentation de l'activité ATPasique, qui provoque une
glycogénolyse et une acidification plus rapide des muscles concernés, pouvant conduire à des viandes
avec un pouvoir de rétention d'eau réduit (Monin 1988, Terlouw et al 1997, D'Souza et al 1999).
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Cependant, les effets des conditions d'abattage sur les qualités des viandes varient selon l'individu et
selon la situation. La façon de réagir au stress et l'influence des réactions de stress sur le métabolisme
musculaire dépendent entre autres de l'expérience antérieure et du patrimoine génétique de l'animal.
Ces idées sont développées ci-dessous.
2 / Patrimoine génétique et réponses de stress
Il est bien connu qu'à l'intérieur d'une espèce, certaines races répondent de manière plus prononcée à
des facteurs de stress que d'autres. Notre étude sur des porcs, comparant des Duroc et des Large White
illustre ces différences raciales (Terlouw et al 1997). Les animaux ont été élevés de manière identique
dans une même animalerie. Chaque porc a été soumis individuellement à deux tests, l'exposition à un
objet non familier et l'exposition à l'Homme, chacun durant 20 minutes. Dans ces tests, l'animal est
introduit dans une case expérimentale (3,80 x 2,60 m) où il reste seul pendant 10 minutes. Pour le test
d'exposition à un objet non familier, un cône de circulation est ensuite descendu du plafond. Pour le
test d'exposition à l'Homme une personne entre et se positionne contre une des barrières. Chaque fois
que le porc touche la personne, celle-ci se déplace et se positionne contre une autre barrière. Il s'est
avéré que les Duroc ont une fréquence de contact avec l'Homme significativement plus élevée que les
Large White (figure 2). En plus, cette différence comportementale était associée à une différence
physiologique: en présence de l'Homme, les Duroc avaient une fréquence cardiaque plus élevée que
les Large White. Cette augmentation s'explique par la plus grande activité physique des Duroc: en
effet, on observe une corrélation positive entre la fréquence de contact avec l'Homme et la fréquence
cardiaque (figure 3).
Figure 2. Nombre de contacts avec l'objet non familier et avec l'Homme lors de tests d'exposition de
porcs Duroc et Large White (voir texte).
Ces résultats montrent que la présence de l'Homme n'était pas évaluée de la même manière par les
porcs des deux races. Les données ne permettent pas de déterminer laquelle des races était la plus
stressée dans la situation du test: l'approche de l'Homme dépend à la fois de la peur que sa présence
engendre chez l'animal (la tendance de celui-ci à garder une distance) et de la motivation de l'animal
de le toucher ou de l'explorer (sa tendance à diminuer la distance). Ainsi, pour les Duroc, l'ensemble
de ces tendances penchait plus vers une attirance pour l'Homme que pour les Large White. Les Duroc
avaient moins peur et/ou étaient plus attirés par l'Homme que les Large White. Quelle que soit la
raison, les Duroc avaient des réponses comportementales et physiologiques plus prononcées à ce test.
Dans certains cas, la génétique a une influence directe sur la physiologie. L'exemple le plus connu
dans l'espèce porcine est celui des porteurs de l'allèle n du gène majeur de la sensibilité à l'halothane
(un anesthésique volatil d'usage courant). Les porteurs de cet allèle présentent une anomalie
métabolique, liée à la mutation génétique d'une protéine d'un canal calcique du réticulum
sarcoplasmique. L'entrée du calcium dans le cytoplasme est mal contrôlée et la réabsorption du
calcium par le réticulum sarcoplasmique est déficiente (MacLennan et al 1990). Le calcium est un des
principaux régulateurs de l'activation métabolique dans la cellule musculaire. Chez les porcs sensibles
à l'halothane, l'inhalation de ce produit ou un état de stress peuvent provoquer le syndrome
d'hyperthermie maligne, qui se caractérise par d'intenses contractures musculaires donnant une rigidité
généralisée de la musculature, une élévation rapide de la température et une acidose métabolique des
tissus, pouvant aboutir à la mort. Chez ces mêmes animaux, assez souvent, les réactions de stress avant
l'abattage provoquent l'élévation de la température et la chute précoce du pH, entraînant la formation
de viandes pâles, flasques et exudatives (dites PSE). Chez les hétérozygotes, l'effet du stress sur les
qualités des viandes varie selon le caractère considéré. On connaît peu l'effet de la présence d'un seul
allèle n sur le comportement et la physiologie des porcs.
Figure 3. Fréquence cardiaque (bpm : battements par minute) chez des porcs Duroc et Large White
lors d'un test d'exposition à l'Homme et corrélation entre la fréquence cardiaque et le nombre de
contacts avec l'Homme.
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La grande majorité des porcs Piétrain sont homozygotes pour l'allèle n. Cependant, des lignées de
Piétrain non porteurs de l'allèle n (Piétrain NN) ont été créées à des fins expérimentales ou par des
sociétés de sélection. Ces lignées nous ont permis de comparer les réactions au stress de Piétrain NN
avec celles de Large White NN et avec celles de Piétrain Nn (Terlouw et al 2000 et 2002). Dans un
test d'isolement, chaque porc était introduit dans une cage expérimentale (3,80 x 2,60 m) où il restait
seul pendant 10 minutes. L'étude du comportement n'a révélé aucun effet de la race, ni de la présence
ou de l'absence de l'allèle n. Des prises de sang avant et après l'isolement montrent que l'isolement a
induit des élévations des taux de lactate beaucoup plus prononcées chez les Piétrain Nn que chez les
Piétrain NN et les Large White NN (figure 4). Ainsi, malgré l'absence de différences
comportementales, le métabolisme accéléré des Piétrain Nn libère plus de pyruvate que le cycle de
Krebs ne peut en absorber; du lactate était donc libéré dans le sang.
Figure 4. Effet du test d'isolement (de 0 à 10 min) sur le taux du lactate sanguin chez des porcs Large
White et des porcs Piétrain porteurs de l'allèle n du gène de sensiblilité à l'halothane (Piétrain Nn) ou
non (Piétrain NN).
L'effet de la race sur les réactions de stress existe aussi dans l'espèce bovine: des génisses Salers ont
par exemple des réactions comportementales plus prononcées à l'isolement que des Frisonnes (Le
Neindre 1989). L'auteur indique que l'interprétation de ces différences est complexe puisqu'elles
peuvent être dues à différents facteurs. Plus récemment on a constaté en race Limousine, que la facilité
de manipulation des génisses dépend partiellement de celle du père (héritabilité de 20 %; Le Neindre
et al 1995). Au moment de l'abattage, des réactions prononcées à la séparation d'avec les congénères et
à la manipulation par l'Homme pourraient, bien sûr, avoir des conséquences négatives sur les qualités
des viandes.
3 / Expérience antérieure et réponses de stress
L'évaluation par l'animal d'une situation et sa réponse comportementale et physiologique dépendent
aussi de son expérience antérieure. Ainsi, chez la truie, la réponse cardiaque à la distribution d'aliment
est influencée par le type du logement (Schouten et al 1991). Ce changement est lié à un changement
d'équilibre entre les systèmes sympathique et parasympathique. Pour un bon fonctionnement des
organes, l'activité de ces deux systèmes doit être en équilibre. Cet équilibre peut être perturbé par un
stress chronique, provoqué dans ce cas par un logement mal adapté aux besoins de l'animal. L'étude
montre chez la truie en gestation, attachée en permanence, une fréquence de base tout à fait normale
par rapport à des truies témoins en stabulation libre sur paille. La différence s'observe lors
d'événements significatifs comme la distribution d'aliment qui provoque des réactions importantes
chez des animaux sous restriction alimentaire sévère. Schouten et al (1991) ont montré une
accélération cardiaque, la fréquence étant de 10 à 15 battements par minute (bpm) pour des truies
témoins et de 30 à 33 bpm pour les truies à l'attache. Ces chercheurs ont ensuite bloqué
successivement le système parasympathique et sympathique à l'aide de produits pharmacologiques.
L'étude a démontré qu'au repos, l'activité de chacun des deux systèmes est similaire quel que soit le
type de logement. La plus forte accélération cardiaque en réponse à la distribution de la nourriture
chez les truies à l'attache était liée à une augmentation de la réactivité du système sympathique. Ainsi,
le type de logement peut influencer l'équilibre physiologique ; l'effet apparaît quand l'animal est
soumis à un facteur de stress.
D'autres études montrent que chez les porcs en engraissement également, les réactions de stress sont
influencées par l'expérience préalable. Ainsi chez des porcs ayant subi une défaite dans un test de
combat, la réaction cardiaque à un objet non familier est plus importante. De même, des porcs élevés
en isolement touchent moins rapidement un objet non familier (40 s) que des porcs logés par paires
(20 s). Cette différence, associée à une fréquence cardiaque plus élevée chez les porcs élevés en
isolement, suggère que le test a provoqué une peur plus intense chez les animaux de ce groupe (Ruis et
al 2001). Le système sympathique stimule la mobilisation des réserves de glycogène musculaires. Une
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élévation de la réactivité sympathique chez les porcs au moment de l'abattage renforcerait ainsi l'effet
du stress de l'abattage sur les qualités des viandes. Il est donc important d'éviter au maximum le stress
durant la période d'élevage.
Chez les bovins, plusieurs études ont montré que le mode d'élevage et le type et la fréquence de
contact avec l'éleveur ont un effet beaucoup plus marqué que la génétique sur la facilité avec laquelle
les animaux se laissent manipuler (Boissy et Bouissou 1988, Boivin et al 1992, Le Neindre et al
1995).
4 / Patrimoine génétique, stress et qualités des viandes
Le patrimoine génétique influence aussi la façon dont l'état de stress influe sur les qualités des viandes.
Premièrement, il y a des différences génétiques musculaires de base, comme par exemple la teneur en
glycogène au repos (ex. Estrade et al 1994). Deuxièmement, la génétique peut influencer la façon dont
les changements physiologiques se répercutent sur le muscle. Par exemple, l'effet stimulateur de
l'adrénaline sur le métabolisme glycolytique musculaire dépend de la quantité des récepteurs betaadrénergiques fonctionnels sur la membrane de la cellule musculaire (Böhm et al 1997). Afin de
savoir si des différences génétiques existent pour la quantité de ces récepteurs, nous avons comparé
des veaux de boucherie, élevés ensemble, de races Holstein et Montbéliarde (observations
personnelles). Des échantillons du muscle Longissimus Lumborum ont été prélevés à l'abattage et les
quantités des récepteurs beta-adrénergiques ont été déterminées par des techniques de liaison ligandrécepteur. Les résultats montrent que les Holstein ont significativement plus de récepteurs que les
Montbéliards, suggérant qu'une même quantité d'adrénaline pourrait avoir plus d'effet sur leur
métabolisme musculaire que sur celui des Monbéliards (figure 5).
Figure 5. Capacité maximale de liaison spécifique (Bmax) des récepteurs beta-adrénergiques chez
deux races de veaux de boucherie. Les Holstein ont plus de récepteurs par gramme de tissu musculaire
que les Montbéliards.
Enfin, en comparant les qualités des viandes de porcs Duroc et Large White (Terlouw et al 1997)
abattus sur le site expérimental (pas de mélange d'animaux, pas d'attente, peu de transport, jeûne de 14
h), ou dans un abattoir industriel (mélange, attente, transport, jeûne de 34 h), nous avons constaté que
les muscles des Large White sont beaucoup plus sensibles aux conditions d'abattage. En particulier, les
pH ultimes des muscles Adductor femoris, Biceps femoris et Semimembranosus des Large White
étaient significativement plus élevés après abattage industriel qu'après abattage expérimental (figure
6). L'indice de jaune des muscles Longissimus Lumborum, Adductor femoris et Semimembranosus de
ces mêmes animaux était moins élevé. Chez les Duroc, les pH ultimes et la couleur de ces mêmes
muscles n'étaient pas influencés par les conditions d'abattage. L'absence d'effet des conditions
d'abattage chez les Duroc ne s'explique pas par une différence raciale de poids corporel (et donc pas
par une différence de dépenses énergétiques), comme l'indique l'absence de corrélations entre le poids
et le pH ultime, le poids et la couleur. Ces résultats pourraient indiquer qu'à la différence des Large
White, l'état comportemental et physiologique des Duroc était peu influencé par les conditions
d'abattage. Toutefois, l'étude avait mis en évidence des réactions comportementales et physiologiques
similaires pour les deux races (test d'exposition à un objet non familier), voire plus prononcées pour
les Duroc (test d'exposition à l'Homme). Il est donc possible que chez les Duroc, aussi bien que chez
les Large White, l'état comportemental et physiologique soit influencé par les conditions d'abattage.
Cet état aurait eu en revanche moins d'effet sur le métabolisme musculaire des Duroc. Par ailleurs, cet
exemple montre que la production de viandes de bonne qualité n'indique pas forcément que l'animal
n'ait pas subi de stress, comme cela semble être le cas pour les Duroc.
Figure 6. pH ultime du muscle Adductor femoris de porcs Duroc et Large White abattus dans un
abattoir industriel ou expérimental.
5 / Expérience antérieure, stress et qualités des viandes
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Le chargement, le transport et le déchargement font partie des événements provoquant le plus de
perturbations comportementales et physiologiques à l'abattage (Geverink et al 1998a). Sachant que la
non familiarité des situations est souvent source de peur chez les animaux, Geverink et al (1998b) ont
habitué un groupe de porcs à être manipulé en dehors de sa loge d'élevage. Le jour du départ à
l'abattoir, les porcs manipulés sortaient plus facilement de leur loge (27 s) que les témoins (54 s).
Toutefois, une part des résultats était contraire aux attentes. En effet, chez les animaux manipulés, à 60
minutes post-mortem les taux de glycogène du Longissimus Lumborum était plus bas que chez les
témoins, et à 26 h la luminosité du même muscle était plus élevée. On peut donc supposer que la partie
connue du transport (sortie de cage, manipulation) était moins stressante pour les porcs manipulés,
mais que la suite des événements (transport, attente à l'abattoir) présentait un stress plus important
pour ce groupe, expliquant la réduction plus importante des réserves glycolytiques avant l'abattage.
L'explication de cet effet paradoxal peut être qu'à la différence des témoins, les porcs manipulés
s'attendaient à rentrer dans leur loge après les manipulations. Ainsi, la disparité entre les attentes et la
réalité était plus importante pour le groupe manipulé, provoquant plus de stress. Ce travail montre que
l'expérience antérieure et les attentes des porcs peuvent avoir un effet significatif sur les qualités de
leurs viandes.
Lensink et al (2000) ont démontré que l'attitude de l'éleveur vis-à-vis de ses veaux de boucherie
influence aussi le comportement de ces animaux lors du transport à l'abattoir. Ainsi, les éleveurs qui
ont tendance à avoir moins de contacts brutaux avec leurs animaux, fournissent des veaux qui se font
charger et décharger plus facilement et qui ont une réponse cardiaque moins élevée au transport. Ces
veaux donnent des viandes à pH ultime légèrement mais significativement plus bas. Lensink et al
expliquent l'effet par un moindre stress, d'où une moindre dépense énergétique pendant le transport et
donc des réserves glycolytiques musculaires plus importantes.
6 / Réactivité individuelle au stress et qualités des viandes
Des différences de réponse de stress existent non seulement entre des animaux de type génétique ou de
mode d'élevage différents, mais aussi entre des individus d'une même lignée et d'un même élevage.
Les individus montrent une certaine cohérence dans leur réactivité au stress : dans certains cas, la
réactivité d'un animal dans une situation X prédit sa réactivité dans une situation Y, suggérant un
profil comportemental/neurophysiologique général sous-jacent à cette réactivité. Ainsi, pour des
cochettes, il a été établi que les notes données pour la facilité de sortir l'animal de sa loge et de le
séparer du groupe social, la facilité pour lui faire parcourir un couloir, et le niveau de réactivité de
l'animal à l'approche soudaine d'un humain, tendaient à être corrélées entre elles (Lawrence et al
1991). Les porcs de réactivité extrême, soit très élevée, soit très basse, ont été sélectionnés et soumis à
d'autres tests. Dans un test d'exposition à un objet non familier, les porcs caractérisés comme ayant
une forte réactivité touchaient et regardaient l'objet plus souvent que les porcs peu réactifs. Dans un
test de compétition pour la nourriture, les porcs réactifs gagnaient un pourcentage plus élevé
d'interactions agressives (Lawrence et al 1991). Une cohérence dans la réactivité à différentes
situations a été observée pour différentes espèces et à différents âges (ex. porcs en engraissement,
bovins, animaux de laboratoire, humains: Bohus et al 1987, Boissy et Bouissou 1995, Schrama et al
1997, Waldstein et al 1997).
Il est utile de disposer de tests de réactivité simples, qui peuvent être réalisés tôt dans la vie de l'animal
et qui ont une valeur prédictive pour sa réactivité à d'autres situations, y compris à l'abattage. Hessing
et al (1993) ont testé une forme de réactivité chez des porcs âgés de 1 à 3 semaines. Il s'agit du test de
retournement : l'animal est placé sur le dos et maintenu par la main de l'expérimentateur qui détermine
si l'animal lui résiste. Après plusieurs répétitions, il s'est avéré qu'une grande partie des porcelets
étaient constants dans leur réponse comportementale au test : 44 % résistaient toujours et 35 % ne
résistaient jamais. Seulement 21 % des animaux avaient des réponses variables. Lors d'un test de
rencontre sociale, les porcelets classés comme résistants se sont avérés plus souvent agressifs. Enfin,
les expérimentateurs ont sélectionné les animaux qui avaient des niveaux élevés pour la résistance et
pour l'agressivité ou, au contraire, des niveaux bas. Ces animaux différaient pour des variables
comportementales et physiologiques dans un test d'exposition à un objet non familier. Ainsi, les
animaux résistants/agressifs faisaient plus de tentatives pour s'échapper et avaient une réponse
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cardiaque plus prononcée à l'introduction de l'objet (Hessing et al 1994). A l'heure actuelle, nous ne
savons pas si ces animaux ont également une plus forte réactivité au stress de l'abattage.
Figure 7. Corrélation entre le nombre de contacts lors d'un test d'exposition à un objet non familier et
le pH ultime de l'Adductor femoris (résiduels après déduction de l'effet des conditions d'abattage) chez
des porcs Large White et Duroc.
Nos différentes études réalisées chez le porc (Terlouw et al, en préparation) montrent que des
corrélations existent entre certains comportements dans des tests de réactivité et les qualités des
viandes. Ainsi, le nombre de contacts avec l'objet non familier dans un champ clos est corrélé
positivement avec le pH ultime de l'Adductor femoris après l'abattage (figure 7). Ces résultats
suggèrent que les animaux touchant plus souvent l'objet sont plus réactifs aux événements précédant
l'abattage, conduisant à une consommation plus importante des réserves glucidiques du muscle de la
cuisse et, par conséquent, à une diminution post-mortem du pH moins importante. Ces corrélations ont
été observées pour différentes races. Cependant, on ne trouve pas toujours les mêmes corrélations pour
toutes les races. Ainsi, chez le Large White, la réactivité à l'Homme est corrélée avec différentes
caractéristiques musculaires du Longissimus Lumborum après l'abattage, effet qui n'a pas été observé
chez les Duroc (Terlouw et al 1997). Des études américaines et australiennes ont montré que des
corrélations entre des caractéristiques comportementales et des qualités des viandes existent également
chez les bovins (Fordyce et al 1988, Voisinet et al 1997). Des études approfondies sont nécessaires
afin d'élucider les mécanismes sous-jacents à ces corrélations.
Conclusion
Le présent article décrit et illustre l'impact du patrimoine génétique et de l'expérience antérieure de
l'animal sur sa façon de réagir à des facteurs de stress y compris ceux rencontrés pendant la période
avant l'abattage. Ainsi, chez le porc et chez le bovin, la race peut influencer les réactions
comportementales et/ou physiologiques à l'Homme ou à la séparation d'avec les congénères. Chez le
porc, la présence de l'allèle de la sensibilité à l'halothane influence les réponses physiologiques à
l'isolement. L'expérience antérieure, comme l'expérience sociale ou la familiarité des situations, ou le
stress chronique lié au logement et l'attitude de l'éleveur vis-à-vis de ses animaux influent sur la façon
dont l'animal réagit à des situations nouvelles et aux manipulations par l'Homme, et sur la réactivité du
système physiologique. Les réactions de stress pendant la période du pré-abattage accélèrent le
métabolisme musculaire péri-mortem et peuvent modifier, par ce biais, les qualités des viandes. La
sensibilité des muscles aux effets des réactions de stress dépend également du patrimoine génétique.
Il est nécessaire de quantifier l'impact des différents facteurs de stress, en fonction du patrimoine
génétique et de l'expérience de l'animal, sur les qualités des viandes et d'en d'étudier les mécanismes
sous-jacents. Ces connaissances devraient ensuite permettre de faire des choix adaptés concernant les
conditions d'abattage, les génotypes et les conditions d'élevage des animaux de boucherie, dans le but
d'améliorer les qualités des viandes et de respecter le bien-être animal.
Remerciements
La rédaction de cet article a bénéficié des commentaires de V. Santé et de deux relecteurs anonymes.
Les dosages de récepteurs adrénergiques (veaux) ont été réalisés en collaboration avec I. Veissier, T.
Astruc et C. Astier (INRA-Theix) et avec R. Garcia-Villar (INRA-Toulouse).
Références
Böhm S.K., Grady E.F., Bunnet N.W., 1997. Regulatory mechanisms that modulate signalling by Gprotein-coupled receptors. Biochem. J., 322, 1-18.
Bohus B., Benus R.F., Fokkema D.S., Koolhaas J.M., Nyakas C., Van Oortmerssen G.A., Prins
A.J.A., De Ruiter A.J.H., Scheurink A.J.W., Steffens A.B., 1987. Neuroendocrine states and
behavioral and physiological stress responses. In: De Kloet E.R., Wiegant V.M., De Wied D. (eds),
Neuropeptides and brain function, Progr. Brain Res., 72, 57-70. Elsevier, Amsterdam/New
York/Oxford.
Boissy A., Bouissou, M.F., 1988. Effects of early handling on heifer's subsequent reactivity to humans
and to unfamiliar situations. Appl. Anim. Behav. Sci., 20, 259-273.
349
Boissy A., Bouissou M.F., 1995. Assessment of individual differences in behavioural reactions of
heifers exposed to various fear-eliciting situations. Appl. Anim. Behav. Sci., 46, 17-31.
Boivin X., Braastad B.O., 1996. Effects of handling during temporary isolation after early weaning on
goat kids' later response to humans. Appl. Anim. Behav. Sci., 48, 61-71.
Broom D.M., 1986. Indicators of poor welfare. Br. Vet. J., 142, 524-526.
Cannon W.B., 1914. The emergency function of the adrenal medulla in pain and the major emotions.
Am. J. Physiol., 33, 356-372.
D'Souza D.N., Dunshea F.R., Leury B.J., Warner R.D., 1999. Effect of mixing boars during lairage
and pre-slaughter handling on pork quality. Aust. J. Agric. Res., 50, 109-113.
Estrade M., Ayoub S., Talmant A., Monin G., 1994. Enzyme activities of glycogen metabolism and
mitochondrial characteristics in muscles of RN- carrier pigs (Sus scrofa domesticus). Comp. Biochem.
Physiol. Biochem. Molec. Biol., 108, 295-301.
Fordyce G., Wythes J.R., Shorthose W.R., Underwood D.W., Shepherd R.K., 1988. Cattle
temperaments in extensive beef herds in Northern Queensland. 2. Effect of temperament on carcass
and meat quality. Austr. J. Exp. Agr., 28, 689-693.
Fraser D., Ritchie J.S., Fraser A.F., 1975. The term 'stress' in a veterinary context. Br. Vet. J., 131,
653-662.
Geverink N.A., Buhnemann A., Van De Burgwal J.A., Lambooij E., Blokhuis H.J., Wiegant V.M.,
1998a. Responses of slaughter pigs to transport and lairage sounds. Physiol. Behav., 63, 667-673.
Geverink N.A., Kappers A., Van de Burgwal J.A., Lambooij E., Blokhuis H.J., Wiegant V.M., 1998b.
Effects of regular moving and handling on the behavioral and physiological responses of pigs to
preslaughter treatment and consequences for subsequent meat quality. J. Anim. Sci., 76, 2080-2085.
Hedrick H.B., Parrish F.C.J., Bailey M.E., 1964. Effect of adrenaline stress on pork quality. J. Anim.
Sci., 23, 225-229.
Hessing M.J.C., Hagelso A.M., Van Beek J.A.M., Wiepkema P.R., Schouten W.G.P., Krukow R.,
1993. Individual behavioural characteristics in pigs. Appl. Anim. Behav. Sci., 37, 285-295.
Hessing M.J.C., Hagelso A.M., Schouten W.G.P., Wiepkema P.R., Van Beek J.A.M., 1994. Individual
behavioral and physiological strategies in pigs. Physiol. Behav., 55, 39-46.
Lawrence A.B., Terlouw E.M.C., Illius A.W., 1991. Individual differences in behavioural responses of
pigs exposed to non-social and social challenges. Appl. Anim. Behav. Sci., 30, 73-86.
Le Neindre P., 1989. Influence of rearing conditions and breed on social behaviour and activity of
cattle in novel environments. Appl. Anim. Behav. Sci., 23, 129-140.
Le Neindre P., Trillat G., Sapa J., Ménissier F., Bonnet J. N., Chupin J.M., 1995. Indidivual
differences in docility in limousin cattle. J. Anim. Sci., 73, 2249-2253.
Lensink B.J., Fernandez X., Boivin X., Pradel P., Le Neindre P., Veissier I., 2000. The impact of
gentle contacts on ease of handling, welfare, and growth of calves and on quality of veal meat. J.
Anim. Sci., 78, 1219-1226.
Lewis P.K., Brown C.J., Heck M.C., 1962a. Effect of preslaughter treatments on certain chemical and
physical charateristics of certain beef muscles. J. Anim. Sci., 21, 433-438.
Lewis P.K., Brown C.J., Heck M.C., 1962b. Effect of stress on certain pork carcass characteristics and
eating quality. J. Anim. Sci., 21, 196-198.
Lewis P.K.J., Rakes L.Y., Brown C.J., Noland P.R., 1989. Effect of exercise and preslaughter stress
on pork muscle characteristics. Meat Science, 26, 121-129.
MacLennan D.H., Duff C., Zorzato F., Fujii J., Phillips M., Korneluk R.G., Frodis W., Britt B.A.,
Worton R.G., 1990. Ryanodine receptor gene is a candidate for predisposition to malignant
hyperthermia. Nature, 343, 559-61.
Mason J.M., 1971. A re-evaluation of the concept of 'non specificity' in stress theory. J. Psychiatr.
Res., 8, 323-333.
Monin G., 1988. Stress d'abattage et qualités de la viande. Rec. Med. Vet., 164, 835-842.
Ruis M.A.W., De Groot J., Te Brake J.H.A., Ekkel E.D., Van de Burgwal J.A., Erkens J.H.F., Engel
B., Buist W.G., Blokhuis H.J., Koolhaas J.M., 2001. Behavioural and physiological consequences of
acute social defeat in growing gilts: effects of the social environment. Appl. Anim. Behav. Sci., 70, 3,
201-225.
Schouten W.G.P., Rushen J., De Passille A.M.B., 1991. Stereotypic behavior and heart rate in pigs.
Physiol. Behav., 50, 617-624.
350
Schrama J.W., Schouten W.G.P., Swinkels J.W.G.M., Gentry J.L., Reilingh G.D., Parmentier H.K.,
1997. Effect of hemoglobin status on humoral immune response of weanling pigs differing in coping
styles. J. Anim. Sci., 75, 2588-2596.
Selye H., 1932. The general adaptation syndrome and the diseases of adaptation. J. Clin. Endocrin., 6,
117-152.
Terlouw C., Rybarczyk P., Fernandez X., Blinet P., Talmant A., 1997. Comparaison de la réactivité au
stress des porcs de races Large White et Duroc. Journées Recherches Porcine en France, 29, 383-390.
Terlouw E.M.C., Ludriks A., Schouten W.G.P., Vaessen S., Fernandez X., 2000. Stress reactivity and
meat quality in pigs: effects of breed and halothane gene. Proceedings of the 34th International Society
of Applied Ethology, Floriapolis, Brésil.
Terlouw E.M.C., Ludriks A., Schouten W.G.P., Vaessen S., Fernandez X., 2002. Race et sensibilité à
l'halothane chez le porc: comparaison de la réactivité au stress et des qualités des viandes. Viande et
Produits carnés (soumis).
Voisinet B.D., Grandin T., O'Connor S.F., Tatum J.D., Deesing M.J., 1997. Bos indicus-Cross feedlot
cattle with excitable temperaments have tougher meat and a higher incidence of borderline dark
cutters. Meat Sci., 46, 367-377.
Waldstein S.R., Bachen E.A., Manuc S.B., 1997. Active coping and cardiovascular reactivity: A
multiplicity of influences. Psychosom. Med., 59, 620-625.
L'AMÉLIORATION GÉNÉTIQUE DE LA QUALITÉ DE LA VIANDE
DANS LES DIFFÉRENTES ESPÈCES: SITUATION ACTUELLE ET
PERSPECTIVES À COURT ET MOYEN TERME
G. RENAND 1, C. LARZUL 2, E. LE BIHAN-DUVAL 3 , P. LE ROY 1
1
INRA, Station de Génétique Quantitative et Appliquée, 78352 Jouy-en-Josas
2
INRA, Station d'Amélioration Génétique des Animaux, 31326 Castanet-Tolosan
3
INRA, Station de Recherches Avicoles, 37380 Nouzilly.
[email protected]
2003, INRA Prod. Anim., 16, 159-173.
La qualité de la viande englobe des critères d'importances différentes suivant l'espèce animale
considérée. Pour les porcs et les volailles, la qualité technologique a un impact économique important
lors de la transformation; elle a fait l'objet de nombreux travaux d'amélioration. Pour les bovins, la
tendreté de la viande est plus importante puisque la viande est commercialisée en frais et provient
d'animaux plus âgés. Pour toutes les espèces, l'amélioration des qualités organoleptiques nécessite de
mettre en évidence les relations génétiques entre caractères de production et qualités sensorielles de la
viande.
Résumé
Les efforts d'amélioration génétique de nos populations d'animaux domestiques exploitées pour la
production de viande ont porté jusqu'à présent essentiellement sur les critères de production,
principalement la vitesse de croissance en vif mais aussi, de plus en plus, la croissance musculaire.
Seules les qualités technologiques de la viande de porc sont actuellement intégrées dans les schémas
d'amélioration génétique du fait de leur impact économique, de la mise en évidence de gènes à effet
majeur (HAL sur la viande 'pisseuse' et RN sur la viande 'acide') et de l'existence de prédicteurs du
rendement technologique mesurables en abattoir (pH, réflectance, perte en eau). Il est ainsi possible de
poursuivre l'amélioration de la croissance musculaire tout en maintenant le niveau des qualités
technologiques dans nos populations porcines. Chez les volailles, une part croissante de la production
est utilisée par les industries de transformation. Comme chez le porc, il a été montré que les mesures
de pH, de réflectance et de perte d'eau sont génétiquement liées au rendement technologique. Par
contre, alors qu'il existe une relation génétique légèrement défavorable chez le porc, ces critères
n'apparaissent pas liés génétiquement aux caractères de production chez les volailles.
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La sélection des qualités sensorielles se heurte pour l'instant à l'absence de prédicteurs mesurables en
abattoir. Les recherches actuelles visent principalement à mettre en évidence les relations génétiques
entre caractères de production et qualités sensorielles. Chez les volailles et le lapin, une sélection sur la
croissance n'a pas d'impact sur les qualités sensorielles si l'âge à l'abattage n'est pas modifié. Par contre
la réduction de l'âge à l'abattage des volailles, consécutive à la sélection sur la croissance, induit un
accroissement de la tendreté et une réduction de la flaveur liés à la moindre maturité des animaux.
Chez le porc, les relations génétiques entre croissance musculaire et qualités sensorielles sont assez
nettement défavorables et une dégradation de ces dernières pourrait être évitée si une sélection pour
accroître la teneur en lipides intramusculaires était possible. Chez les bovins, les quelques études
menées en France permettent d'assurer qu'une sélection sur la croissance musculaire devrait être plutôt
favorable à la tendreté, mais défavorable à la flaveur. Comme dans le cas du porc, une sélection sur la
teneur en lipides intramusculaires permettrait de pallier cet effet négatif. Dans ces deux espèces,
l'amélioration simultanée de la croissance musculaire et de la teneur en lipides intramusculaires se
heurte non pas tant à l'existence d'une relation génétique négative entre ces deux objectifs, mais
surtout à la difficulté d'obtenir un prédicteur fiable et non destructif de cette teneur chez des animaux
qui sont particulièrement maigres. Cette difficulté milite pour la recherche de gènes qui soient à la fois
impliqués dans ces qualités et sélectionnables grâce à un polymorphisme facilement détectable.
Introduction
L'amélioration de la qualité de la viande dans les différentes espèces doit se raisonner en intégrant la
phase de production et la phase de transformation. La production de viande exploite la capacité des
animaux d'élevage à transformer des aliments d'origine végétale en tissu musculaire. La transformation
du tissu musculaire en viande consommable concerne aussi bien la viande consommée directement en
frais, après cuisson bien entendu, que celle qui a subi divers traitements technologiques pour la
transformer et/ou la conserver. Il va de soi que la qualité du produit consommé résulte alors de l'action
combinée de nombreux facteurs qui, pour la majorité d'entre eux, sont en fait contrôlés par l'homme.
Si le mode de cuisson est déterminant sur la qualité sensorielle de la viande, le mode d'abattage et tous
les traitements ultérieurs le sont également: ressuage, refroidissement, maturation, transformation,
conservation. De même, avant l'abattage, l'action de l'homme, en l'occurrence l'éleveur engraisseur,
s'avère prépondérante de par ses décisions quant au choix du système de production (régime
alimentaire, rythme de croissance) et du stade d'abattage (poids, âge, état d'engraissement).
Si les actions de l'homme sont primordiales, l'animal a tout de même sa part de responsabilité sur la
qualité de la viande produite. L'ensemble de son génome contrôle en effet la mise en place des tissus et
leur métabolisme jusqu'à l'abattage. Mais ce génome s'exprime en interaction avec le milieu
environnant et la variabilité observée résulte de ces deux composantes. Vouloir améliorer la qualité de
la viande via la génétique dépend de notre capacité à discerner dans la variabilité de la qualité la part
qui est effectivement d'origine génétique et utilisable par la sélection pour être cumulée au cours des
générations. Cette discrimination sera d'autant moins hasardeuse qu'on aura réduit la part de la
variabilité non génétique en standardisant au mieux les conditions de milieu ante et post mortem.
Toutes choses étant égales par ailleurs (conduite, abattage, traitements, etc), les différences entre
animaux expriment alors ce qui est communément appelé la variabilité individuelle et que les
généticiens appellent la variabilité phénotypique.
Pour ce qui concerne la qualité de la viande, nos connaissances sur la variabilité individuelle et son
déterminisme génétique sont encore limitées. Mis à part le cas des productions sous label, la principale
raison réside dans le manque de lisibilité et donc de quantification de la demande des consommateurs.
En l'absence de réelle plus-value économique pour les viandes de qualité supérieure, aucune mesure en
abattoir de la qualité n'a donc été développée. De plus, la difficulté d'obtenir des enregistrements,
même indirects, de cette qualité limite les possibilités de mettre en place des programmes
expérimentaux pour entreprendre des études génétiques de dimension suffisante. Les seules qualités de
la viande particulièrement bien étudiées concernent des défauts majeurs de la viande de porc qui ont
un impact économique important et quantifiable au niveau de la transformation. En conséquence, le
déterminisme génétique de ces qualités technologiques a été mis en évidence et la gestion des défauts
est désormais possible de même que l'amélioration génétique de nos races et lignées.
352
Même dans le cas du porc, les qualités sensorielles sont peu ou pas du tout prises en compte dans les
programmes d'amélioration génétique. Nos connaissances sont en cours d'élaboration. Leurs relations
avec les caractéristiques du muscle et les caractères de production actuellement sélectionnés sont en
cours d'étude. L'objectif de ces études est de pouvoir alerter les responsables professionnels si une
dégradation des qualités est à redouter suite à l'accroissement du potentiel de production des animaux
et, éventuellement, de proposer des critères de sélection utilisables dans ces programmes. Selon les
espèces, le progrès génétique réalisé sur la productivité de l'engraissement peut être fort variable.
Celui-ci est essentiellement obtenu par une sélection de la vitesse de croissance, parfois complétée par
une sélection indirecte sur la composition corporelle pour améliorer la croissance musculaire aux
dépens de la croissance adipeuse. La principale conséquence visible de cette sélection est la réduction
de la durée d'engraissement et donc de la maturité des animaux à l'abattage. A ce premier effet peuvent
s'ajouter d'éventuelles modifications des caractéristiques musculaires. Dans les deux cas, il est
nécessaire de quantifier les éventuelles modifications des qualités sensorielles de la viande qui sont
associées à ces deux effets.
Entre espèces, il existe d'énormes différences de la maturité des animaux au moment de l'abattage. Si
les animaux des espèces monogastriques (porcs, volailles, lapins) sont abattus à un stade très précoce
(avant la maturité sexuelle), les bovins, eux, sont abattus à un degré de maturité nettement plus élevé
(figure 1). Les relations avec les qualités de la viande sont donc certainement fort variables selon
l'espèce considérée et les possibilités de les améliorer par sélection seront présentées séparément pour
chaque type de production.
Figure 1. Âge et poids des animaux de boucherie (relatifs à l'âge à la puberté et au poids adulte des
femelles reproductrices de ces espèces).
1 / La sélection des porcs et l'amélioration de la qualité de leur viande
L'amélioration génétique du porc charcutier a depuis une trentaine d'années intégré la nécessité de
prendre en compte les qualités technologiques de la viande puisqu'une part importante de la carcasse
de porc (environ 2/3) est destinée à l'industrie de la transformation, en particulier pour fournir le
marché en jambon cuit. Jusqu'à présent, les actions génétiques conduites en France chez le porc ont
porté sur des gènes individuels à effet majeur sur la qualité de la viande (HAL et RN) ou ont emprunté
les voies plus conventionnelles de la génétique quantitative (indices de sélection combinant plusieurs
caractères, dont la qualité de la viande sous la forme de la variable IQV).
1.1 / Viande exsudative: le gène majeur halothane (HAL)
Dès le début des années 70, l'incidence d'un défaut majeur de la viande de porc (viande PSE pour
Pale, Soft, Exudative ou viande 'pisseuse') a fait l'objet de nombreuses études qui ont mis en évidence
son origine génétique (locus HAL) et son lien avec la prédisposition au syndrome de stress du porc,
appelé aussi syndrome d'hyperthermie maligne (Christian 1972, Ollivier et al 1975). Le locus HAL
comporte deux allèles: N (normal) et n (sensible). Le défaut PSE lié à l'allèle n est causé par une chute
excessivement rapide du pH post mortem (pH1 < 6) et induit, entre autres conséquences, une moindre
tendreté de la viande fraîche et de mauvais rendements de fabrication du jambon cuit ou cru, alors que
ce même allèle n a des effets favorables sur la teneur en muscles de la carcasse. La mise au point d'un
test de détection des sujets sensibles à l'halothane (test halothane, Eikelenboom et Minkema 1974),
puis l'utilisation des marqueurs sanguins Phi et Pgd, génétiquement liés à HAL (Saugère et al 1989) et,
enfin, la découverte de la mutation responsable sur le gène du récepteur de la ryanodine (Fujii et al
1991), rapidement suivie de la mise au point d'un test moléculaire ad hoc, ont permis l'éradication
quasi complète de l'allèle n dans les grandes populations porcines exploitées comme lignées
maternelles. Cet allèle est par contre pratiquement fixé dans la race Piétrain, fréquemment utilisée
pour fabriquer des verrats de croisement terminal (Sellier 1998). Une question longuement débattue a
concerné la valeur exacte des sujets hétérozygotes “Nn” en termes de qualités technologiques et
sensorielles de la viande (Larzul et al 1997a, Monin et al 1999). Du fait de qualités légèrement
moindres, une tendance se dessine actuellement dans plusieurs organisations de sélection porcine
françaises en faveur de l'emploi de verrats terminaux non porteurs de l'allèle n (cf. les projets de
353
création de lignées Piétrain NN) malgré l'avantage des hétérozygotes en terme de composition des
carcasses.
1.2 / Indice de qualité de la viande
Dans les populations porcines, des progrès génétiques importants ont été réalisés sur les caractères de
croissance, mais aussi sur la composition corporelle grâce à la mise en place de programmes de
sélection combinant l'évaluation individuelle des verrats sur l'épaisseur du gras dorsal (mesurée in vivo
par ultrasons) et l'évaluation du pourcentage de muscles d'animaux collatéraux abattus. Depuis plus de
vingt ans, cette sélection a été complétée par l'utilisation d'une variable composite nommée IQV
(Indice Qualité de la Viande). Cet indice combine trois mesures réalisables en site industriel sur la
coupe du jambon: le pH ultime, la clarté (réflectance) et la capacité de rétention d'eau (temps
d'imbibition d'un papier buvard) dans le but de prédire le rendement technologique de la fabrication du
jambon de Paris (Jacquet et al 1984, Guéblez et al 1990): un meilleur rendement va de pair avec un
pH et un temps d'imbibition plus élevés et une couleur moins claire. Grâce à la base de données ainsi
constituée, les paramètres génétiques de ces mesures ont été estimés et des indices de sélection
synthétiques ont été proposés. Il existe de nombreuses études (cf. revue de Sellier 1998) qui montrent
que l'héritabilité (h2) de ces mesures de la qualité technologique et celle de l'IQV ne sont pas
négligeables (h2 entre 0,15 et 0,25 en général), bien que plus faibles que celles des caractères de
croissance (h2 de 0,30 environ) ou de composition corporelle (h2 entre 0,40 et 0,55). Les estimées des
corrélations génétiques du pH ultime avec le rendement à la cuisson sont suffisamment élevées (rg =
0,70 en moyenne) pour espérer améliorer ce dernier en sélectionnant sur le pH ultime ou l'IQV. Il
s'avère par ailleurs que si les qualités technologiques de la viande de porc sont génétiquement
indépendantes de la vitesse de croissance, elles sont par contre défavorablement corrélées avec la
composition corporelle. Tribout et al (1996) ont ainsi montré que dans les races Large White et
Landrace la corrélation génétique entre pH ultime et épaisseur de lard est positive (respectivement
0,10 et 0,53) et que celle existant entre pH ultime et pourcentage de muscle est négative
(respectivement -0,21 et -0,56). Pour tenir compte de cet antagonisme génétique entre caractères de
production, essentiellement la composition de la carcasse, et caractères de qualité technologique et
ainsi répondre à l'objectif de sélection qui est d'améliorer les premiers tout en maintenant les seconds à
un niveau acceptable, la sélection porte actuellement sur un indice synthétique avec une pondération
non négligeable sur IQV. Des études réalisées dans les années 90 montrent qu'il n'existe effectivement
qu'une évolution génétique très légèrement défavorable de l'IQV dans les races Large White et
Landrace (Ducos et al 1995). Afin de quantifier les réponses génétiques effectivement obtenues suite à
la sélection pratiquée pendant 20 ans en race Large White, une expérience a été mise en place pour
comparer des porcs charcutiers issus de verrats d'insémination nés en 1977 et en 1998 (Tribout et al
2001). Plusieurs caractères concernant les qualités de la viande (et du gras) sont bien évidemment
mesurés à cette occasion, mais les résultats ne sont pas encore disponibles.
1.3 / Viande acide: le gène majeur RN
Entre-temps, un nouveau défaut est apparu suite à l'utilisation de la race américaine Hampshire pour
constituer de nouvelles lignées synthétiques de verrats pour le croisement terminal: la viande acide,
qui se traduit par un faible rendement technologique. Afin d'évaluer ce défaut dans les populations
concernées, Naveau (1986) a mis au point un test de fabrication de type jambon cuit sur un échantillon
de muscle semi-membraneux, conduisant à la mesure du rendement technologique Napole (RTN).
Cette mesure, lourde mais efficace, a permis de mettre en évidence l'origine génétique de ce défaut: un
seul gène dont l'allèle dominant provoque une réduction significative du rendement Napole (Le Roy et
al 1990) et qui était originellement en ségrégation dans la race Hampshire. L'étude des phénomènes
biologiques impliqués a montré que ce défaut était lié à une amplitude trop importante de la chute du
pH post mortem, elle-même conséquence d'un stock de glycogène particulièrement élevé dans les
fibres musculaires blanches et rapides (Estrade et al 1993). Cette faible valeur du pH ultime
s'accompagne d'autres effets sur la qualité de la viande: la viande est plus pâle, a une moindre capacité
de rétention en eau et est moins tendre, alors que sa flaveur est accrue (Le Roy et al 1996). Grâce à
l'utilisation de la carte génétique porcine et à une démarche de recherche de locus à effet quantitatif, ou
QTL pour Quantitative Trait Locus, le gène RN a pu être localisé dans un premier temps sur le
chromosome 15 (Milan et al 1995). La mutation causale a ensuite été identifiée dans le gène PRKAG3
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codant pour une molécule intervenant dans la régulation d'une protéine kinase (AMPK), elle-même
impliquée dans la biosynthèse du glycogène (Milan et al 2000). Il est donc désormais possible, à l'aide
d'un test moléculaire, de sélectionner directement sur le génotype au locus PRKAG3 pour éliminer le
défaut 'viande acide' dans les populations concernées.
Il a été montré depuis longtemps que le rendement technologique de la viande de porc dépend de
l'amplitude de la chute du pH musculaire et cette dernière du potentiel glycolytique (PG) du muscle
(Monin et Sellier 1985), c'est-à-dire de l'importance des réserves intra vitam en composés musculaires
susceptibles de se transformer en acide lactique au cours de la glycolyse post mortem. La valeur du PG
peut être estimée in vivo sur un échantillon de muscle long dorsal prélevé par biopsie. Il s'avère que,
même en l'absence de l'allèle défavorable RN- au locus RN, il existe une variabilité génétique non
négligeable (h2 = 0,25) de ce potentiel glycolytique (Le Roy et al 1998) et qu'il présente une
corrélation génétique négative avec le rendement technologique (rg = -0,42; Larzul et al 1999). La
possibilité de sélectionner directement les verrats candidats à la reproduction contre leur PG mesuré in
vivo permet en théorie d'accroître l'efficacité des programmes d'amélioration génétique de la qualité
technologique de la viande (Larzul et al 1998). Toutefois, une expérience de sélection sur six
générations n'a pas permis de mettre en évidence de réponse corrélative significative sur le rendement
technologique de la fabrication du jambon cuit (Larzul et al 1999).
1.4 / Qualités sensorielles et teneur en lipides intramusculaires
La prise en compte des qualités sensorielles de la viande de porc est une préoccupation relativement
récente. En effet, les progrès génétiques réalisés pour réduire l'adiposité des carcasses et les
corrélations génétiques défavorables entre le rapport muscle/gras de la carcasse et les qualités
sensorielles de la viande fraîche (rg = -0,25 avec la tendreté et la jutosité et rg = -0,35 avec la flaveur,
en moyenne) font craindre une détérioration de ces qualités (Sellier 1998). Bien que les liaisons
phénotypiques soient assez peu marquées, une plus forte teneur en lipides intramusculaires est
favorablement corrélée avec les résultats des tests de dégustation de la viande fraîche (Fernandez et al
1999, Van Laack et al 2001), même si le comportement d'achat du consommateur ne traduit pas cette
préférence (Fernandez et al 1996). La teneur en lipides intramusculaires influe également sur la qualité
du jambon sec. Comment améliorer simultanément la teneur en lipides intramusculaires et le rapport
muscle/gras des carcasses lorsque la relation génétique entre les deux caractères est défavorable: rg = 0,35 environ (Sellier 1998) ? Une première solution est de tirer parti de la particularité de la race
américaine Duroc qui se caractérise par une teneur en lipides intramusculaires nettement supérieure à
celle des races Large White et Landrace, alors que la composition de la carcasse est pratiquement
identique chez le Duroc, le Large White et le Landrace. La race Duroc a ainsi été introduite en France
pour la constitution de nouveaux types génétiques de verrats de croisement terminal.
L'antagonisme génétique entre teneur en muscle de la carcasse et teneur en lipides intramusculaires est
réel, mais n'est cependant pas si marqué qu'il annihile tout espoir de conduire une sélection efficace
sur un index synthétique combinant les deux informations. La limite réside plus dans la difficulté
d'introduire la teneur en lipides intramusculaires dans les programmes de sélection du fait du coût de
leur dosage. Des recherches sont donc menées pour trouver des mesures physiques réalisables in vivo
(Baas et Newcom 2002) ou en routine dans les abattoirs et suffisamment précises pour discriminer la
teneur en lipides entre animaux dont la teneur moyenne est très faible (1,5 à 2 %). Une mesure
systématique de la teneur en lipides intramusculaires par spectrophotométrie est toutefois réalisée dans
les stations de testage en Suisse et a été incluse avec un certain succès parmi les critères de sélection
(Schwörer et al 2000). La mise en évidence de gènes responsables de l'aptitude à stocker des lipides
dans les adipocytes intramusculaires permettrait un travail de sélection efficace à condition qu'un
polymorphisme existe dans les populations porcines exploitées et qu'il soit facilement détectable. Par
une analyse de ségrégation appliquée au taux de lipides intramusculaires de porcs provenant de
croisements F2 entre la race chinoise Meishan et des lignées européennes, Janss et al (1997) ont
montré qu'un gène majeur devait être en ségrégation chez ces animaux croisés: l'allèle récessif
assurerait aux homozygotes porteurs une teneur de 3,9% contre 1,8 % pour les hétérozygotes et les
homozygotes non porteurs. Des résultats similaires ont été obtenus par Sanchez et al (2002) avec des
animaux résultant du croisement F2 entre le Duroc et le Large White. Cette approche ne permet pas
toutefois de localiser ce gène sur le génome. L'approche QTL a par ailleurs mis en évidence plusieurs
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zones du génome (sur les chromosomes 1, 2, 4, 6 et X) susceptibles de contenir un gène à effet majeur
sur la teneur en lipides intramusculaires (cf. revue de Bidanel et Rothschild 2002). Récemment,
Bidanel et al (2002) ont détecté un QTL de ce type sur le chromosome 7, dans la même zone qu'un
QTL affectant l'adiposité des carcasses. Il s'avère que l'allèle originaire de la race Meishan est associé
à une teneur en lipides intramusculaires plus élevée, tout en étant aussi associé à une moindre
épaisseur de gras dorsal. L'exploitation d'un tel QTL permettrait de 'rompre', au moins partiellement, la
liaison génétique positive entre lipides intramusculaires et teneur en gras des carcasses. Cette dernière
étude a également mis en évidence dans la même zone du chromosome 7 un QTL affectant l'activité
de l'enzyme malique, enzyme impliquée dans la lipogenèse dont le gène codant se trouve en fait sur le
chromosome 1. Grâce à une carte génétique toujours plus fine et à la cartographie comparée, les
travaux s'orientent vers la recherche du ou des gènes responsables d'effet majeur et en particulier vers
l'identification des gènes régulant l'activité de l'enzyme malique. Toutefois, dans cette région du
chromosome 7 se trouvent également le complexe majeur d'histocompatibilité du porc (système SLA)
et donc de très nombreux gènes candidats.
1.5 / Autres caractères de qualité
La variabilité génétique d'autres caractères ayant trait à la qualité du produit porc ont fait l'objet de
travaux de recherche dans les deux dernières décennies, mais sans qu'ils aient débouché pour le
moment sur une véritable prise en considération dans les programmes d'amélioration génétique. Des
travaux sont entrepris pour déterminer la variabilité de la composante myofibrillaire des
caractéristiques musculaires et leurs relations avec les qualités de la viande. Les muscles sont en effet
constitués d'une proportion variable de fibres très nettement différenciées quant à leur propriété
contractile et leur métabolisme énergétique. De ce fait, les caractéristiques biochimiques (stocks de
composés énergétiques et équipement enzymatique) du muscle et les qualités de la viande qui leur sont
associées varient notablement en fonction de la proportion de ces fibres (Karlsson et al 1999). A
l'heure actuelle, il n'existe encore que très peu de résultats sur le déterminisme génétique de ces
caractéristiques musculaires, si ce n'est l'étude de Larzul et al (1997b). Ces travaux ne permettent pas
pour l'instant de conclure sur l'utilité d'inclure des mesures sur les fibres musculaires dans les
programmes de sélection en vue d'améliorer la qualité de la viande de porc. Mentionnons également
les travaux visant à l'estimation des paramètres génétiques des caractéristiques de composition
chimique du gras de porc, qui sont impliquées dans le risque d'apparition de 'gras mou' (Maignel et al
1998) et la série d'études sur le déterminisme génétique de l'odeur sexuelle de la viande de porc mâle
entier (boar taint), abordé sous l'angle de la teneur en androsténone du tissu gras (Fouilloux et al 1997,
Sellier et al 2000). Plus récemment, il a été montré qu'une variabilité génétique existe pour la
prédisposition à un phénomène connu sous le nom de 'viande déstructurée', qui touche principalement
la musculature profonde du jambon et se traduit notamment par une augmentation des pertes au
tranchage du jambon cuit (Franck et al 2000, Le Roy et al 2001, Bouffaud et al 2002).
2 / La sélection des volailles et l'amélioration de la qualité de leur viande
La sélection génétique a largement contribué à l'amélioration de la productivité des volailles de chair,
notamment du poulet et de la dinde. Après une période où la sélection ne portait que sur la croissance,
l'amélioration du rendement en viande commercialisable a également été recherchée pour répondre
aux besoins croissants des industries de transformation (Pollock 1997). De plus, la réduction des
dépôts adipeux abdominaux permet d'améliorer indirectement l'indice de consommation, caractère
économiquement très important mais difficile à sélectionner directement. Des coefficients
d'héritabilité élevés et la possibilité de contrôler des collatéraux abattus permettent de sélectionner les
reproducteurs simultanément sur leur propre croissance et la composition corporelle de leurs
collatéraux pour améliorer efficacement le rendement en filet et réduire les dépôts adipeux internes
(Le Bihan-Duval et al 1998).
2.1 / Qualités sensorielles
Les qualités sensorielles des volailles de chair dépendent étroitement de l'âge à l'abattage. La réduction
drastique de l'âge à l'abattage du poulet de chair ou de la dinde standards, suite à l'amélioration de leur
croissance, a largement contribué à l'accroissement de la tendreté aux dépens de la flaveur (Sauveur
1997). Le déterminisme génétique de la qualité sensorielle de la viande de volaille a essentiellement
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été étudié lors de comparaisons de souches différant par leur croissance et/ou leur composition
corporelle. Tout d'abord, Ricard et Touraille (1988) constatent qu'une sélection divergente appliquée
sur le pourcentage de gras abdominal modifie essentiellement les caractéristiques de la cuisse, avec
une viande plus ferme et de saveur plus forte chez les oiseaux les plus maigres. Ils n'observent pas de
différences pour les autres qualités organoleptiques et pour la teneur en lipides intramusculaires.
Aucune différence n'a été détectée par Touraille et al (1981) et Rabot et al (1996) pour les qualités
sensorielles de la viande de poulets abattus à 16 semaines et issus de la sélection divergente sur la
croissance initiée par Ricard (1975). En fait, pour répondre aux attentes des consommateurs français
qui préfèrent une viande plus ferme et de goût plus prononcé, la filière avicole a développé les
productions de poulet Label grâce à l'exploitation de lignées à croissance plus lente qui permettent
d'atteindre le poids commercial à 12 semaines au lieu de 6 semaines. Dans ce contexte de production
avec contrainte sur la qualité sensorielle, la réponse fut donc de changer drastiquement de type
génétique et non pas de modifier par la sélection les lignées alors exploitées en poulet standard.
2.2 / Qualités technologiques
L'utilisation d'une proportion accrue de la viande de volaille dans les industries de découpe et de
transformation conduit à étudier les possibilités d'améliorer les qualités technologiques par la voie
génétique. L'aptitude la plus importante concerne le rendement lors de la transformation. La tenue et
les qualités organoleptiques du produit transformé sont également à prendre en compte dans ce
nouveau contexte. Le rendement technologique dépend étroitement de la capacité de rétention en eau
des protéines musculaires, que ce soit pour la viande fraîche vendue en barquette ou au moment de la
cuisson du produit élaboré. Dans une étude menée en site industriel, Fernandez et al (2002) ont montré
le rôle prépondérant joué par l'évolution du pH post mortem lors de la fabrication de 'Blanc de Dinde'
ou de 'Jambon de Dinde': une chute trop rapide du pH conduit à des rendements à la transformation
significativement plus faibles et à des pertes d'exsudat plus élevées caractéristiques des viandes PSE.
Les comparaisons de souches permettent une première approche du déterminisme génétique des
qualités de la viande et des caractéristiques musculaires associées. Berri et al (2001) rapportent, pour
le poulet, les résultats d'une expérience de sélection divergente sur la croissance, le rendement en filet
et le gras abdominal et ceux d'une comparaison d'une souche commerciale sélectionnée depuis plus de
25 ans avec une souche témoin. Les résultats de ces deux comparaisons concordent aussi bien pour les
mesures de la qualité technologique que pour celles des caractéristiques musculaires. Les poulets ayant
la plus forte croissance musculaire ont une viande significativement plus claire. Alors qu'il est
généralement observé une relation positive entre clarté et perte d'exsudat, d'une part, et une relation
négative entre clarté et pH d'autre part, aucune différence de perte d'exsudat n'est observée et la viande
de ces poulets a un pH ultime significativement plus élevé en accord avec un moindre potentiel
glycolytique. La différence de clarté est en partie explicable par la moindre teneur en pigments de leur
muscle, qui est d'ailleurs moins rouge. Par ailleurs, du fait d'un pH plus élevé, la viande des poulets
avec la plus forte croissance musculaire n'apparaît nullement du type PSE, comme pouvait le laisser
craindre sa couleur plus pâle. Sur le plan histologique, Rémignon et al (1995) ont montré que
l'augmentation de la croissance musculaire par sélection était due à un accroissement de la taille et du
nombre de fibres musculaires sans modification de leur typologie moyenne.
2.3 / Paramètres génétiques
Des premières estimations des paramètres génétiques des qualités technologiques et des
caractéristiques musculaires ont été obtenues par Le Bihan-Duval et al (2001) à partir de plus de 1000
poulets de l'expérience de sélection rapportée par Berri et al (2001) et mentionnée ci-dessus. Les
qualités technologiques de la viande concernaient le pH, à 15 minutes post mortem et à 24 heures, la
couleur (clarté, intensités dans le rouge et dans le jaune) et la perte d'exsudat. Tous ces caractères
présentent des coefficients d'héritabilité élevés, entre 0,35 et 0,57, du même ordre de grandeur que
ceux des caractères de production. Des actions de sélection efficaces peuvent donc être envisagées si
ces caractères sont utilisés comme critères de sélection. De très fortes oppositions génétiques ont été
mises en évidence entre le pH ultime d'une part et les mesures de clarté et de perte d'exsudat d'autre
part (rg=-0,91 et rg=-0,83 respectivement). Ces valeurs confirment l'impact de l'amplitude de la chute
du pH post mortem sur la couleur et la capacité de rétention en eau et sont encore plus marquées que
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les corrélations génétiques estimées chez le porc: rg=-0,53 et rg=-0,71 en moyenne (Sellier 1998). Une
sélection sur le pH ultime représente donc un moyen sûr pour éviter l'apparition de viandes pâles et
exsudatives et améliorer la capacité de rétention en eau. Le rendement lors de la cuisson de la viande
de volaille étant de plus en plus important pour la filière, il est prévu de compléter la présente étude
par l'estimation des relations génétiques de ce rendement technologique avec les caractères étudiés
jusqu'à présent.
Les corrélations génétiques estimées sont particulièrement instructives quant aux possibilités de
modifier conjointement les caractères de production et les qualités technologiques de la viande. En
effet si les trois caractéristiques technologiques précédentes apparaissent pratiquement indépendantes
de la croissance et du rendement en filet, elles sont génétiquement liées au potentiel génétique
d'engraissement. Les oiseaux avec le plus fort potentiel d'engraissement ont un pH ultime plus bas, une
viande plus claire et une plus forte perte d'exsudat: rg=-0,54 rg=0,50 et rg=0,29 respectivement. Ces
estimations sont actuellement les seules disponibles et ne suggèrent donc pas d'antagonisme génétique
entre caractères de production et qualité de la viande chez le poulet. Elles diffèrent notablement de ce
qui se passe chez le porc (rg=0,15, rg=-0,21 et rg=-0,10 en moyenne respectivement; Sellier 1998).
Ces valeurs très spécifiques peuvent expliquer que les lignées sélectionnées pour la croissance
musculaire ne donnent pas de viande de type PSE, puisqu'une sélection conduisant à une réduction du
gras abdominal doit induire un accroissement du pH ultime du fait de la forte corrélation négative
entre ces deux caractères. Ces paramètres génétiques ont toutefois été obtenus dans des conditions
expérimentales favorables qui ont limité l'incidence des problèmes de qualité consécutifs à des stress
avant abattage. Or, en conditions industrielles d'abattage, l'incidence des défauts de qualité n'est pas
négligeable. L'estimation des paramètres génétiques des qualités technologiques de la viande de
volaille apparaît donc nécessaire dans ces conditions industrielles. Une première étude a ainsi été
menée en production de viande de dinde (Le Bihan-Duval et al 2002). La variabilité génétique
apparente de tous les caractères est plus faible qu'en conditions expérimentales, surtout pour les
mesures de qualité technologique (pH et couleur) avec des héritabilités inférieures à 0,20. Une
corrélation génétique très fortement négative (rg =-0,80) est obtenue entre pH à 20 minutes post
mortem et clarté de la viande, résultat classique décrit dans le cas du syndrome PSE. Dans cette étude
également, l'augmentation du niveau génétique pour les performances de croissance et de
développement musculaire n'apparaît pas associée à une dégradation de la qualité. Il est nécessaire de
poursuivre ces travaux en intégrant la susceptibilité aux conditions stressantes qui peut interagir
significativement avec l'aptitude à produire une viande de qualité.
3 / La sélection des lapins et l'amélioration de la qualité de leur viande
Actuellement la sélection des aptitudes bouchères du lapin porte principalement sur la vitesse de
croissance après sevrage, c'est-à-dire sur une phase de croissance relativement précoce. L'héritabilité
de ce caractère, environ 0,30 (revue de Khalil et al 1986), et les différentiels de sélection applicables
sont suffisamment élevés pour obtenir des progrès génétiques significatifs dans diverses expériences
de sélection (Estany et al 1992, Piles et al 2000, Gondret et al 2002) et chez les sélectionneurs. En
effet, l'âge à l'abattage pratiqué en France est passé de 12 semaines avant 1989 à 10 semaines
actuellement, pour un poids à l'abattage qui est resté d'environ 2,4 kg.
Les expériences de sélection ont également montré qu'une amélioration génétique de la vitesse de
croissance s'accompagne d'une augmentation des dépôts adipeux internes sans dégradation du
rendement en carcasse si l'âge à l'abattage n'est pas modifié (Gondret et al 2002). Or, nous avons vu
que les lapins de boucherie sont abattus de plus en plus jeunes pour maintenir constant le poids moyen
à l'abattage. Si ce rajeunissement permet de réduire la proportion de gras interne, il induit également
une dégradation du rendement en carcasse (Pla et al 1998). Cette dégradation du rendement est liée à
la croissance relative du 5ème quartier, plus rapide que celle de la carcasse chez le lapereau de
boucherie. Seule une sélection conjointe de la croissance et des qualités des carcasses doit permettre
de concilier l'évolution génétique de ces caractères. Des études sont actuellement en cours pour
développer des mesures in vivo de la composition et de la conformation corporelle (tomographie,
Tobec, etc) afin d'éviter d'avoir à pratiquer une sélection sur collatéraux abattus.
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Chez le lapin, il n'existe que de très rares estimations des paramètres génétiques des qualités de la
viande et des caractéristiques musculaires associées dans les populations exploitées pour la
production. Il existe toutefois un certain nombre d'expériences de sélection dans lesquelles ont été
mesurées les réponses corrélées sur les caractéristiques musculaires ou les qualités de la viande. Pla et
al (1998) et Piles et al (2000) ont montré que lorsque la comparaison se fait à poids constant, la
sélection sur la vitesse de croissance induit une réduction de la teneur en lipides intramusculaires
corrélativement avec la réduction d'âge et une tendance pour des pertes d'eau à la cuisson accrues,
malgré un pH plus élevé dans la première expérience. Par ailleurs, Gondret et al (2002) ont montré
que la teneur en lipides intramusculaires ne change pas, bien que la proportion de gras péri-rénal
augmente lorsque la comparaison se fait à âge constant. Leurs résultats montrent que l'amélioration de
la croissance musculaire est liée à une augmentation de la taille des fibres (hypertrophie) sans
augmentation de leur nombre et sans modification des proportions des différents types de fibres
musculaires. Enfin, aucune différence n'a été observée sur le pH final, la couleur, la capacité de
rétention en eau et sur la force de cisaillement de la viande crue. Ces derniers résultats obtenus à âge
constant permettent d'analyser les modifications des composantes biologiques de la croissance
musculaire et devraient être complétés par des études à poids constant pour quantifier l'impact réel sur
les qualités de la viande en situation de production, c'est-à-dire lorsqu'il faut réduire l'âge à l'abattage
par suite d'une amélioration génétique de la croissance. Pour l'instant, il n'existe pas de programme de
détection de QTL sur les qualités de la viande, l'essentiel des efforts portant sur la mise au point de la
mesure des caractéristiques musculaires et des qualités de la viande pour en étudier la variabilité
individuelle et en déduire de nouveaux critères de sélection.
Si la sélection actuellement pratiquée sur la vitesse de croissance détériore les qualités des carcasses,
elle ne modifie pas intrinsèquement les caractéristiques du muscle classiquement mesurées si ce n'est
un accroissement de la taille des fibres musculaires. Les conséquences sur les qualités de la viande
sont peu marquées, en particulier du fait de l'absence d'altération du pH de la viande. Toutefois, une
meilleure connaissance des mécanismes biologiques mis en jeu lors de l'élaboration des qualités de la
viande, combinée à l'estimation des paramètres génétiques, permettra éventuellement d'orienter la
sélection vers des produits de qualité en proposant des critères de sélection qui font actuellement
défaut.
4 / La sélection des bovins à viande et l'amélioration de la qualité de leur viande
Les races à viande spécialisées, exploitées en race pure en France, sont essentiellement sélectionnées,
à travers le contrôle de performances en ferme, sur la production de veaux sevrés, c'est-à-dire sur des
aptitudes qui s'expriment chez l'animal jeune (croissance, morphologie) et sur des aptitudes
maternelles (reproduction, allaitement). Ces aptitudes sont peu ou pas corrélées avec les aptitudes
bouchères pendant l'engraissement ou à l'abattage. Seuls les taureaux d'insémination artificielle font
l'objet d'une sélection sur ces aptitudes bouchères, d'abord en station de contrôle individuel
(croissance, efficacité alimentaire et conformation bouchère en vif), puis en station de contrôle sur
descendance (croissance, rendement à l'abattage et conformation bouchère des carcasses). En utilisant
des données commerciales recueillies en abattoir, il a été montré que cette sélection était efficace pour
améliorer le poids de carcasse (Fouilloux et al 2001). En testant 60 taureaux Charolais extrêmes (30
supérieurs et 30 inférieurs) sélectionnés parmi 510 contrôlés en station de contrôle individuel, Renand
et al (1998) ont montré qu'une sélection sur un indice combinant la croissance et l'efficacité
alimentaire permettait d'améliorer la croissance musculaire sans modifier celle des dépôts adipeux. La
sélection pour améliorer le rapport muscle/gras pourrait s'intensifier, si la méthode d'estimation in vivo
de la composition corporelle basée sur la vitesse des ultrasons était effectivement mise en place
(Renand et Fisher 1997).
4.1 / Réponses potentielles des qualités de la viande à une sélection sur la croissance musculaire
Actuellement, aucune évaluation et donc aucune sélection n'est réalisée sur les qualités de la viande.
Faute de mesures de ces qualités il n'est pas possible de prévoir leur évolution suite à la sélection
pratiquée dans les stations de contrôle individuel pour améliorer la croissance musculaire. Pour fournir
des éléments de réponse, l'expérience citée ci-dessus a été mise en place de façon à estimer les
paramètres génétiques des aptitudes bouchères conjointement avec ceux de caractéristiques
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musculaires susceptibles d'être en relation avec les qualités de la viande (Renand et al 1994, Gamand
1998). Les relations génétiques sont peu marquées avec la croissance en vif, mais nettement plus avec
la composition du croît. Au vu des corrélations génétiques, une sélection pour accroître la masse
musculaire aux dépens des dépôts adipeux devrait se traduire par une réduction des teneurs en lipides
intramusculaires et en pigments, du diamètre des fibres musculaires et par une augmentation du pH et
de la solubilité du collagène. Les relations avec le type de fibre sont nettement moins marquées.
Quelles conséquences peuvent avoir ces modifications attendues des caractéristiques musculaires sur
les qualités de la viande, sachant que seules les qualités organoleptiques sont concernées?
Dans cette expérience, les relations phénotypiques entre texture, flaveur et jutosité, d'une part, et les
caractéristiques musculaires du muscle long dorsal, d'autre part, ont été évaluées (Renand et al 2001).
Ces relations sont relativement modestes puisque les coefficients de corrélation ne dépassent pas
r=0,40, ce qui est généralement le cas dans ce type d'étude. Sur ces jeunes bovins de boucherie, des
taurillons de 17 mois en moyenne et relativement maigres, la flaveur dépend en premier lieu de la
teneur en lipides intramusculaires (r=0,35). La tendreté dépend essentiellement de deux composantes:
la taille des fibres et le collagène. Des fibres de petite taille, une moindre teneur en collagène et un
collagène plus soluble sont favorables à la tendreté. Une relation négative a également été mise en
évidence avec le pH. Les animaux dont le métabolisme du muscle long dorsal est plus oxydatif ont
tendance à produire une viande qui mature moins vite et qui est donc plus dure. Enfin, il n'existe
aucune relation entre tendreté et teneur en lipides intramusculaires. Par ailleurs, aucune relation n'a été
mise en évidence entre jutosité et caractéristiques musculaires. Une étude réalisée sur des jeunes
bovins des races Aubrac, Gasconne et Salers a confirmé les relations mises en évidence chez les
Charolais (Renand et al 2002). Ainsi, mise à part la réponse corrélée sur le pH, les relations génétiques
entre composition de la carcasse et caractéristiques musculaires d'une part et les relations
phénotypiques entre ces dernières et les qualités organoleptiques d'autre part, indiquent qu'une
sélection pour accroître le rapport muscle/gras devrait avoir un effet favorable sur la tendreté, mais
défavorable sur la flaveur et la couleur.
Si l'amélioration simultanée de la croissance musculaire, de la tendreté et de la flaveur devenait une
nécessité dans un nouveau contexte économique, il deviendrait indispensable de sélectionner
simultanément ces aptitudes. Pour ceci, il faudrait disposer de critères de sélection indirects des
qualités organoleptiques puisqu'un testage sur descendants incluant des tests de dégustation serait
économiquement irréalisable. Pour ceci, les exemples étrangers peuvent être utiles. Malheureusement,
bien qu'il existe une littérature bien documentée en Amérique du Nord et plus récemment en Australie
sur le déterminisme génétique des qualités de la viande conjointement aux caractères de production, il
est difficile d'extrapoler leurs résultats car les qualités de la viande, tout comme leur variabilité et leurs
corrélations, dépendent très fortement des conditions de production (sexe, âge, vitesse
d'engraissement), de transformation (abattage, refroidissement, maturation) et de consommation
(cuisson).
4.2 / Sélectionner pour améliorer la tendreté?
La tendreté est très certainement le critère de qualité le plus important à améliorer chez les bovins. Elle
diffère notablement entre muscles. Or il est difficilement envisageable d'évaluer d'autres muscles que
le long dorsal qui est le muscle de référence, bien que les relations entre muscles soient loin d'être
parfaites: corrélations phénotypiques de 0 à 0,56 pour la force de cisaillement du long dorsal avec
celle de neuf autres muscles (Shackelford et al 1995); corrélation génétique de 0,34 entre les forces de
cisaillement mesurées sur le long dorsal et le semi-tendineux de plus de 3700 jeunes bovins (Johnston
et al 2001). La principale source de variation de la tendreté entre muscles est liée à la teneur en
collagène et à sa solubilité. Pour un même muscle, Dikeman et al (1986), Seideman et al (1987),
Whipple et al (1990a), Harris et al (1992) et Shackelford et al (1992) ne mettent en évidence aucun
effet du collagène sur la tendreté chez des bouvillons dans des études nord-américaines. Le fait de
travailler avec des animaux castrés et avec des températures de cuisson élevées réduit très
certainement l'impact du collagène sur la tendreté. Dans les études génétiques réalisées dans ces pays,
cette composante n'est donc jamais prise en considération. Pour une production de taurillons, la
composante collagénique serait certainement à prendre en compte du fait de son impact sur la tendreté
360
comme cela a été montré dans l'étude rapportée plus haut et du fait de l'existence d'une variabilité
génétique non négligeable de sa teneur et de sa solubilité (Renand et al 1994, Gamand 1998).
La tendreté de la viande, soit évaluée directement par un jury de dégustation, soit mesurée
indirectement par la force de cisaillement, présente une variabilité génétique suffisamment élevée pour
être sélectionnée: h2= 0,20-0,25 en moyenne (revues de Bertrand et al 2001 et de Burrow et al 2001).
Toutefois, seule la mesure de la force de cisaillement pourrait éventuellement être réalisée lors d'un
testage sur descendance, mais à un coût élevé. En France, au début des années 80, une mesure de la
force de cisaillement sur viande fraîche était réalisée dans des programmes de testage. Bien qu'une
variabilité génétique non négligeable ait été mise en évidence (h2=0,30; Renand 1985) cette mesure a
été abandonnée car trop coûteuse et non valorisée par la filière. Aux Etats-Unis, c'est seulement en
race Brahman que quelques taureaux sont testés sur la force de cisaillement, les animaux de type Bos
indicus ayant une viande particulièrement dure comparativement aux animaux de type Bos taurus
(Koch et al 1982, Crouse et al 1989). L'origine de cette dureté est due à une plus forte activité de la
calpastatine, un inhibiteur du système protéolytique des calpaïnes (Whipple et al 1990b, Shackelford
et al 1991). A la suite de ces études, une mesure de l'activité de la calpastatine a été mise au point et
des paramètres génétiques estimés. Trois études ont calculé des héritabilités élevées (h2=0,53 en
moyenne) et des corrélations génétiques élevées avec la force de cisaillement: rg=0,76 en moyenne
(Shackelford et al 1994, Wulf et al 1996, Kim et al 1998), alors qu'une quatrième étude a conclu
qu'une telle mesure ne serait pas utile (O'Connor et al 1997). Quoiqu'il en soit, une telle mesure n'a pas
dépassé le stade expérimental et n'a pas été intégrée dans les programmes d'évaluation des
reproducteurs.
En Amérique du Nord, la grille de paiement des carcasses intègre une note de persillé (marbling); les
catégories de prix les plus élevées (choice et prime) correspondent aux teneurs en lipides
intramusculaires les plus élevées: 5-8% et 8-11% respectivement. Cette valorisation du gras
intramusculaire a comme finalité déclarée l'amélioration de la tendreté. En fait, il apparaît que, si elles
sont effectivement positives, les relations phénotypiques sont peu élevées entre la teneur en lipides
intramusculaires ou la note de persillé, d'une part, et la tendreté et la force de cisaillement de la viande,
d'autre part (corrélations moyennes respectives de 0,17 et -0,19 citées par Renand et al 2001). En
Australie, une étude à grande échelle sur les préférences des consommateurs a montré que le degré de
satisfaction du consommateur augmente avec le persillé et que la note de tendreté bénéficie de
l'appréciation favorable de la flaveur et de la jutosité lorsque le persillé est plus élevé (Egan et al
2001). Alors que les corrélations phénotypiques sont faibles, les corrélations génétiques sont assez
élevées entre la note de persillé d'une part et la note de tendreté ou la force de cisaillement d'autre part:
0,40 et -0,55 respectivement en moyenne (Bertrand et al 2001). A l'heure actuelle dans ces pays,
l'amélioration de la tendreté se base quasi exclusivement, faute de critère de sélection plus direct, sur
une sélection indirecte visant à accroître la note de persillé. Le gras intramusculaire constitue en fait
une garantie contre les excès de cuisson qui induisent une forte contraction des fibres musculaires et
une perte d'eau élevée, d'où une moindre tendreté. Dans ces conditions, plus il y a de lipides
intramusculaires, moins dure et moins sèche sera perçue la viande. Des recherches sont néanmoins
menées pour trouver d'autres caractères plus directement impliqués dans les phénomènes de
maturation et donc dans la tendreté de la viande. Il faut noter que les tests de dégustation dans les
études nord-américaines ou australiennes se font avec des viande cuites à 70°C à cœur à la différence
de l'étude française citée plus haut pour laquelle cette température était de 55°C. De ce fait il est
difficile d'envisager une amélioration de la tendreté dans nos races à viande à travers une sélection
pour accroître la teneur en lipides intramusculaires comme cela est préconisé dans ces pays.
4.3 / Sélectionner pour accroître les lipides intramusculaires?
Les bouvillons ou bœufs des études nord-américaines ou australiennes sont nettement plus gras que
nos taurillons. La relation entre flaveur et lipides intramusculaires sur ces animaux est plus faible en
moyenne que dans l'étude française citée plus haut: r=0,16 (valeur citée par Renand et al 2001). Cette
différence peut s'expliquer par le fait que la relation entre flaveur et teneur en lipides intramusculaires
est curvilinéaire. Elle n'est significativement positive que pour de faibles teneurs en lipides (Denoyelle
1995).
361
Les carcasses étant systématiquement notées sur le persillé, les taureaux nord-américains et australiens
font l'objet d'une évaluation génétique sur ce caractère simultanément à l'évaluation sur la carcasse.
Les estimations de l'héritabilité sont plutôt élevées: h2=0,46 en moyenne (Bertrand et al 2001).
L'amélioration conjointe de la composition des carcasses et du persillé est possible si la sélection porte
sur un index combiné qui tient compte de la corrélation génétique entre ces deux caractères. Les
estimées de cette dernière couvrent un large spectre de valeurs avec une moyenne relativement faible
en définitive: -0,28 (Bertrand et al 2001). Ces auteurs rapportent par exemple qu'en race Angus des
progrès génétiques positifs sont observés sur la croissance et le persillé sans modification de
l'épaisseur de gras sous-cutané, ni du rendement en viande maigre. Une telle note n'existe pas en
France. Il faudrait donc mettre en place un dosage des lipides intramusculaires pour sélectionner les
taureaux lors de leur testage sur descendance. Une alternative au dosage chimique pourrait être
l'utilisation de la spectrophotométrie dans l'infrarouge comme c'est le cas en Australie (Perry et al
2001). Afin de s'affranchir de l'étape de sélection sur descendance et d'accroître le nombre de taureaux
évalués, une méthode d'estimation du persillé in vivo à partir d'une échographie du muscle long dorsal
a été mise au point (Herring et al 1998, Hassen et al 1999 et 2001). Reverter et al (2000) ont montré
que cette mesure réalisée sur des mâles de 16 mois présentait une corrélation génétique assez élevée
avec la teneur en lipides intramusculaires de bœufs apparentés abattus à 16 ou 23 mois: 0,54. Sapp et
al (2002) ont montré qu'une sélection phénotypique divergente sur cette mesure réalisée chez de
jeunes taureaux de un an de race Angus (3,8 % vs 1,7 %) avait permis d'obtenir une réponse corrélée
significative sur la note de persillé des descendants sans que le poids et l'épaisseur de gras sous-cutané
de ceux-ci diffèrent. Toutefois ces méthodes de sélection du gras intramusculaire sont appliquées sur
des populations qui ont déjà des niveaux de persillé assez élevés. Comparativement, en France les
animaux des races à viande spécialisées sont plus maigres. A titre de comparaison, les taurillons des
études rapportées plus haut (Renand et al 2001 et 2002) ne contiennent que de 1,6 % à 1,8 % de
lipides intramusculaires en moyenne en fin d'engraissement entre 16 et 23 mois. La teneur de
candidats à la sélection à 13-15 mois est certainement encore plus faible et sa mesure in vivo sera
d'autant moins précise pour discriminer les animaux. Cette précision serait pourtant d'autant plus
nécessaire qu'une sélection pour accroître les dépôts adipeux intramusculaires simultanément à la
croissance musculaire devrait tenir compte d'une corrélation génétique assez élevée entre les premiers
et l'adiposité de la carcasse (0,66), telle que celle trouvée en race Charolaise (Renand et al 1994).
4.4 / Recherche de marqueurs moléculaires
En l'absence de critères de sélection effectivement utilisables dans les programmes d'amélioration
génétique, on peut espérer pratiquer quelque sélection sur les qualités de la viande si des gènes sont
mis en évidence pour avoir un effet significatif sur ces qualités dans nos races à viande. Un premier
gène connu concerne l'hypertrophie musculaire (mh ou gène culard) qui a un effet marqué sur les
qualités des carcasses et de la viande: rendement musculaire accru, réduction des dépôts adipeux et du
squelette, viande plus claire avec du collagène plus soluble et un plus grand nombre de fibres
musculaires (Ménissier 1982). Des mutations au sein du gène de la myostatine sur le chromosome 2
sont à l'origine de ces phénomènes (Grobet et al 1998). La sélection directe sur ce gène est désormais
possible et sa gestion au sein des races dépend de la politique des organismes raciaux.
Le développement de la carte génétique des bovins avec l'identification de plus de 2000 marqueurs a
permis la mise en place de plusieurs programmes de détection de QTL. A ce jour, l'USDA de Clay
Center (Keele et al 1999, Stone et al 1999, Casas et al 2000, MacNeil et Grosz 2002), l'AgResearch de
Nouvelle-Zélande (Morris et al 2002) ou l'Université de Saskatchewan au Canada (Buchanan et al
2000, Schimpf et al 2000) ont publié des résultats sur l'existence de possibles QTL. Des QTL relatifs
aux performances de croissance, d'abattage, de persillé et éventuellement de force de cisaillement ont
ainsi été détectés un peu partout sur le génome, sans que des zones ne ressortent avec évidence si ce
n'est le chromosome 5 qui apparaît impliqué dans plusieurs QTL ségréguant dans plusieurs familles de
référence. Les résultats des expériences menées par le CSIRO en Australie et l'A&M University au
Texas n'ont été que très partiellement publiés. La première équipe a par exemple mis en évidence cinq
possibles QTL affectant le poids à la naissance (Davis et al 1998).
Le stade suivant est la recherche de marqueurs suffisamment proches (en déséquilibre de liaison) du
gène d'intérêt ou, si possible, de celui-ci même avec la mutation causale afin de s'affranchir du risque
362
de recombinaison entre les marqueurs et le gène impliqué lorsqu'on veut sélectionner pour l'allèle
favorable chez des reproducteurs de race pure. Cette recherche met en œuvre le clonage positionnel
pour cibler la région du génome contenant un QTL et l'approche 'gène candidat' pour tester
l'implication de gènes potentiels dans la variabilité génétique détectée. C'est ainsi qu'à la suite des
travaux de Moody et al (1996) qui ont trouvé une association entre IGF1 et croissance, Stone et al
(1999) notent qu'un QTL sur la croissance est localisé sensiblement dans la même région du
chromosome 5 que le gène de l'IGF1 (Kappes et al 1997), ce qui en fait un gène candidat potentiel. De
même, Casas et al (2000) ont mis en évidence un QTL affectant la force de cisaillement dans la même
région du chromosome 29 où Smith et al (2000) ont positionné le gène de la m-calpaïne (CAPN1),
protéase impliquée dans les mécanisme de maturation de la viande (Koohmaraie 1994). Récemment,
Page et al (2002) ont effectivement trouvé que ce gène possédait un polymorphisme significativement
corrélé à la tendreté dans deux familles informatives constituées à l'USDA et à l'AgResearch.
A la suite des travaux cités plus haut montrant que l'activité de la calpastatine présentait une variabilité
génétique en relation avec la tendreté, Lonergan et al (1995) et Chung et al (2001) n'ont pas pu mettre
en évidence de relation entre tendreté et divers polymorphismes détectés dans le gène de la
calpastatine. En revanche, l'équipe australienne du CSIRO a breveté un test génétique à partir de la
mise en évidence d'une association entre un nouveau polymorphisme dans ce gène et la force de
cisaillement (Barendse 2002a). Cette même équipe, en adoptant une approche candidat positionnel, a
également breveté un test génétique suite à une étude d'association entre un polymorphisme de la
thyroglobuline, hormone dont le gène a été localisé sur le chromosome 14 par Daskalchuk et Schmutz
(1997), et la note de persillé de la viande (Barendse 2002b). Buchanan et al (2002), quant à eux, ont
mis en œuvre une démarche 'gène candidat', sans tenir compte du QTL affectant le persillé mis en
évidence sur le chromosome 2 (Schimpf et al 2000). Ils affirment, par une étude d'association, que le
gène codant pour la leptine, sur le chromosome 4, présente un polymorphisme en relation significative
avec l'adiposité des carcasses, sans mention du persillé toutefois.
L'étape finale est de valider le polymorphisme et l'effet de ces gènes et/ou marqueurs dans les races
pures. Cette validation est indispensable préalablement à l'exploitation directe et unique du
déséquilibre de liaison. C'est ce qui a été mis en place en Australie avec la seconde phase du
programme 'Cooperative Research Centre for Cattle and Beef Industry' (Bindon 2001) et aux EtatsUnis avec le programme 'National Carcass Genetic Merit Project' (Bertrand et al 2001). Dans les deux
cas, ces programmes sont issus d'une collaboration entre la recherche et la filière (organismes raciaux
et industrie). Dans le programme américain, 14 races sont concernées et testées sur un seul type de
production. Dans le programme australien, 6 races sont concernées, mais plusieurs systèmes de
production sont pris en compte. Dans les deux cas le nombre d'animaux contrôlés est particulièrement
important, entre 7 et 8000.
Conclusions
L'amélioration génétique des qualités de la viande doit se raisonner en fonction du système de
production. Il est clair que les problèmes auxquels sont confrontés les filières ne sont pas du tout les
mêmes lorsqu'il s'agit de porcs ou de volailles d'une part et de bovins d'autre part. Les premiers sont
essentiellement concernés par les qualités technologiques du fait de la part prépondérante de la
transformation. Des réponses génétiques à des défauts majeurs ont été apportées et le maintien d'une
pression de sélection sur les qualités technologiques est possible grâce à l'enregistrement en routine de
prédicteurs de celle-ci en abattoir, la mesure du pH par exemple. Pour les qualités organoleptiques de
la viande de ces deux espèces, les études portent actuellement sur la compréhension des mécanismes
mis en jeu, en particulier le rôle des lipides intramusculaires et la recherches de critères prédictifs.
Dans le cas de la volaille, une première solution, non génétique, a consisté à mettre en place des
systèmes de production drastiquement différents avec un abattage plus tardif.
Même si la qualité de la viande des lapins ne semble pas poser de problèmes suite à la sélection des
caractères de production, une étude des qualités organoleptiques est engagée pour une meilleure
connaissance de celles-ci et l'estimation des paramètres génétiques associés. Le cas de la viande
d'agneau n'a pas été traité ici car elle ne présente pas de problème non plus. Le gène à effet majeur sur
363
la croissance musculaire (callipyge) n'est pas exploité dans nos races ovines bouchères car il a des
effets trop détériorateurs sur la tendreté (Koohmaraie et al 1995).
Chez les bovins, la commercialisation de la viande en frais et le stade de maturité nettement plus
avancé que dans les autres espèces placent la tendreté comme qualité prioritaire à améliorer. Ce
caractère ne pouvant être mesuré en routine, l'espoir réside dans la recherche de gènes marqueurs
utilisables pour une sélection directe. Il est donc nécessaire de trouver un ou des gènes responsables ou
des marqueurs très proches pour exploiter le déséquilibre de liaison au sein des populations élevées en
France. Toutefois, cette démarche se heurte à la pauvreté des résultats publiés dans le domaine public
et à la difficulté d'obtenir des données phénotypiques pertinentes pour étudier finement des régions du
génome ou tester d'éventuels gènes candidats mis en évidence dans d'autres études.
Cet article est issu d'une communication présentée lors des 9èmes Journées des Sciences du Muscle et
Technologies de la Viandes (15 et 16 octobre 2002 à Clermont-Ferrand) et publiée dans un numéro
hors série de la revue Viandes et Produits carnés.
Références
Baas T.J., Newcom D.W., 2002. Use of real-time ultrasound to predict intramuscular fat percentage in
live swine. Proc. 7th World Congr. Genet. Applied Livest. Prod., CD-ROM, communication n 03-10.
Barendse W., 2002a. DNA markers for meat tenderness. Patent WO02064820, http://ep.espacenet.com
(septembre 2002).
Barendse W., 2002b. Assessing lipid metabolism. Patent WO9923248, http://ep.espacenet.com
(septembre 2002).
Berri C., Wacrenier N., Millet N., Le Bihan-Duval E., 2001. Effect of selection for improved body
composition on muscle and meat characteristics of broilers from experimental and commercial lines.
Poultry Sci., 80, 833-838.
Bertrand J.K., Green R.D., Herring W.O., Moser D.W., 2001. Genetic evaluation for beef carcass
traits. J. Anim. Sci., 79 E. Suppl., E190-E200.
Bidanel J.P., Rothschild M.F., 2002. Current status of quantitative trait locus mapping in pigs. Pig
News and Information, 23, 39N-53N.
Bidanel J.P., Milan D., Renard C., Gruand J., Mourot J., 2002. Detection of quantitative trait loci for
intramuscular fat content and lipogenic enzyme activities in Meishan x Large White F2 pigs. Proc. 7th
World Congr. Genet. Appl. Livest. Prod., CD-ROM, communication n°03-13.
Bindon B.M., 2001. Genesis of the Cooperative Research Centre for the Cattle and Beef Industry:
integration of resources for beef quality research (1993-2000). Austr. J. Exp. Agric., 41, 843-853.
Bouffaud M., Desautes-Sawadogo C., Tribout T., Boulard J., Lagant H., Coudurier B., Sellier P.,
2002. Etude de quelques facteurs de variation du défaut “viande destructurée” sur le jambon frais.
Journées Rech. Porcine en France, 34, 1-6.
Buchanan F.C., Thue T.D., Winkelman-Sim D.C., Plante Y., Schmutz S.M., 2000. Two QTLs for
growth map to bovine chromosome 14. Proc. 27th Intern. Conf. Anim.Genet., July 22-26, 2000, Univ.
Minnesota, 53, B122.
Buchanan F.C., Fitzsimmons C.J., Van Kessel A.G., Thue T.D., Winkelman-Sim D.C., Schmutz S.M.,
2002. Association of a missense mutation in the bovine leptin gene with carcass fat content and leptin
mRNA levels. Genet. Sel. Evol., 34, 105-116.
Burrow H.M., Moore S.S, Johnston D.J., Barendse W., Bindon B.M., 2001. Quantitative and
molecular genetic influences on properties of beef: a review. Austr. J. Exp. Agric., 41, 893-919.
Casas E., Shackelford S.D., Keele J.W., Stone R.T., Kappes S.M., Koohmaraie M., 2000. Quantitative
trait loci affecting growth and carcass composition of cattle segregating alternate forms of myostatin.
J. Anim. Sci., 78, 560-569.
Christian L.L., 1972. A review of the role of genetics in animal stress susceptibility and meat quality.
In: Proceedings of the pork quality symposium. Cassens R.G., Giesler F., Kolb Q. (Eds), Univ.
Wisconsin, Madison, USA, 91-115.
Chung H.Y., Davis M.E., Hines H.C., 2001. Relationship of two PCR-RFLP in the bovine calpastatin
gene with calpastatin activity, meat tenderness and carcass traits. Pecial Circular- Ohio Agric.
Research and Development Center, 181, 27-34.
364
Crouse J.D., Cundiff L.V., Koch R.M., Koohmaraie M., Seideman S.C., 1989. Comparisons of Bos
indicus and Bos taurus inheritance for carcass beef characteristics and meat palatability. J. Anim. Sci.,
67, 2661-2668.
Daskalchuk T.E., Schmutz S.M., 1997. Genetic mapping of Thyroglobulin on bovine chromosome 14.
Mamm. Genome, 8, 74-76.
Davis G.P., Hetzel D.J.S., Corbet N.J., Scacheri S., Lowden S., Renaud J., Mayne C., Stvenson R.,
Moore S.S., Byrne K., 1998. The mapping of quantitative trait loci for birth weight in a tropical beef
herd. Proc. 6th World Congr. Genet. Appl. Livest. Prod., 26, 441-444.
Denoyelle C., 1995. Evolution de la flaveur de la viande bovine en fonction de la teneur en lipides
intra-musculaires. Viandes et Produits Carnés, 16, 89-92.
Dikeman M.E., Reddy G.B., Arthaud V.H., Tuma H.J., Koch R.M., Mandigo R.W., Axe J.B., 1986.
Longissimus muscle quality, palatability and connective tissue histological characteristics of bulls and
steers fed different energy levels and slaughtered at four ages. J. Anim. Sci., 63, 92-101.
Ducos A., Garreau H., Bidanel J.P., Le Tiran M.H., Breton T., Flého T., Runavot J.P., 1995.
Utilisation du Blup modèle animal pour l'évaluation génétique des porcs contrôlés dans les stations
publiques françaises. Principes et premiers résultats. Journées Rech. Porcine en France, 27, 135-142.
Egan A.F., Ferguson D.M., Thompson J.M., 2001. Consumer sensory requirements for beef and their
implications for the Australian beef industry. Austr. J. Exp. Agric., 41, 855-859.
Eikelenboom G., Minkema D., 1974. Prediction of pale, soft, exudative muscle with a non-lethal test
for the halothane-induced porcine malignant hyperthermia syndrome. Tijdschr. Diergeneesk., 99, 421426.
Estany J., Camacho J., Baselga M., Blasco A., 1992. Selection response of growth rate in rabbits for
meat production. Genet. Sel. Evol., 24, 527-537.
Estrade M., Vignon X., Rock E., Monin G., 1993. Glycogen hyperaccumulation in white muscle fibres
of RN- carrier pigs. A biochemical and ultrastructural study. Comp. Biochem. Physiol., 104B, 321326.
Fernandez X., Monin G., Talmant A., Mourot J., Lebret B., Bernard P., Gilbert S., Sirami J., Malter
D., 1996. Influence de la teneur en lipides intramusculaires sur l'acceptabilité, par les consommateurs,
de la viande de porc et du jambon cuit. Journées Rech. Porcine en France, 28, 163-170.
Fernandez X., Monin G., Talmant A., Mourot J., Lebret B., 1999. Influence of intramuscular fat
content on the quality of pig meat. 1. Composition of the lipid fraction and sensory characteristics of
m. longissimus lumborum. Meat Sci., 53, 59-65.
Fernandez X., Santé V., Baeza E., Le Bihan-Duval E., Berri C., Rémignon H., Babilé R., Le Pottier
G., Astruc T., 2002. Effect of the rate of muscle post mortem pH fall on the technological quality of
turkey meat. British Poultry Sci., 43, 245-252.
Fouilloux M.N., Le Roy P., Gruand J., Renard C., Sellier P., Bonneau M., 1997. Support for single
major genes influencing fat androsterone level and develoment of bulbo-urethral glands in young
boars. Genet. Sel. Evol., 29, 357-366.
Fouilloux M.N., Renand G., Laloë D., 2001. Utilisation de performances contrôlées en abattoir et
évaluation génétique en races bovines allaitantes en France. Renc. Rech. Ruminants, 8, 341-344.
Franck M., Monin G., Legault C., 2000. Observations complémentaires sur le jambon destructuré:
caractérisation du phénomène par le pH et la couleur du muscle semi membraneux. Journées Rech.
Porcine en France, 32, 345-349.
Fujii J., Otsu K., Zorzato F, De Leon S., Khanna V.K., Weiler J.E., O'Brien P.J., Mac Lennan D.H.,
1991. Identification of a mutation in porcine ryanodine receptor associated with malignant
hyperthermia. Science, 253, 448-451.
Gamand R., 1998. Paramètres génétiques et phénotypiques de la qualité de la viande dans deux
expériences de sélection de bovins Charolais, Aubracs, Salers et Gascons. Mémoire de fin d'études
d'Ingénieur, ENSA Rennes.
Gondret F., Combes S., Larzul C., de Rochambeau H., 2002. The effects of divergent selection for
body weight at a fixed age on histological, chemical and rheological characteristics of rabbit muscles.
Livest. Prod. Sci., 76, 81-89.
Grobet L., Poncelet D., Royo L.J., Brouwers B., Pirottin D., Michaux C., Ménissier F., Zanotti M,
Dunner S., Georges M., 1998. Molecular definition of an allelic series of mutations disrupting the
myostatin function and causing double-muscling in cattle. Mamm. Genome, 9, 210-213.
365
Guéblez R., Le Maitre C., Jacquet B., Zert P., 1990. Nouvelles équations de prédiction du rendement
technologique de la fabrication du “jambon de Paris”. Journées Rech. Porcine en France, 22, 89-96.
Harris J.J., Miller R.K., Savell J.W., Cross H.R., Ringer L.J., 1992. Evaluation of the tenderness of
beef top sirloin steaks. J. Food Sci., 57, 6-9.
Hassen A., Wilson D.E., Amin V.R., Rouse G.H., 1999. Repeatability of ultrasound-predicted
percentage of intramuscular fat in feedlot cattle. J. Anim. Sci., 77, 1335-1340.
Hassen A., Wilson D.E., Amin V.R., Rouse G.H., Hays, C.L., 2001. Predicting percentage of
intramuscular fat using two types of real-time ultrasound equipment. J. Anim. Sci., 79, 11-18.
Herring H.O., Kriese L.A., Bertrand J.K., Crouch J., 1998. Comparison of four real-time ultrasound
systems that predict intramuscular fat in beef cattle. J. Anim. Sci., 76, 364-370.
Jacquet B., Sellier P., Runavot J.P., Brault D., Houix Y., Perrocheau C., Gogué J., Boulard J., 1984.
Prédiction du rendement technologique de la fabrication du “jambon de Paris” à l'aide de mesures
prises à l'abattoir. Journées Rech. Porcine en France, 16, 49-58.
Janss L.L.G., Van Arendonk J.A.M., Brascamp E.W., 1997. Bayesian statistical analyses for presence
of single genes affecting meat quality traits in a crossbred pig population. Genetics, 145, 395-408.
Johnston D.J., Reverter A., Robinson D.L., Ferguson D.M., 2001. Sources of variation in mechanical
shear force measures of tenderness in beef from tropically adapted genotypes, effects of data editing
and their implications for genetic parameter estimation. Austr. J. Exp. Agric., 41, 991-996.
Kappes S.M., Keele J.W., Stone R.T., MacGraw R.A., Sonstegard T.S., Smith T.P.L., Lopez-Corrales
N.L., Beattie C.W., 1997. A second generation linkage map of the bovine genome. Genome Res., 7,
235-249.
Karlsson A.H., Klont R.E., Fernandez X., 1999. Skeletal muscle fibres as factors for pork quality.
Livest. Prod. Sci., 60, 255-269.
Keele J.W., Shackelford S.D., Kappes S.M., Koohmaraie M., Stone R.T., 1999. A region on bovine
chromosome 15 influences beef longissimus tenderness in steers. J. Anim. Sci., 77, 1364-1371.
Khalil M.H., Owen J.B., Afifi E.A., 1986. A review of phenotypic and genetic parameters associated
with meat production traits in rabbits. Anim. Breed. Abst., 54, 725-749.
Kim J.J., Davis S.K., Sanders J.O., Turner J.W., Miller R.K., Savell J.W., Smith S.B., Taylor J.F.,
1998. Estimation of genetic parameters for carcass and palatability traits in Bos indicus/Bos taurus
cattle. Proc. 6th World Congr. Genet. Appl. Livest. Prod., 25, 173-176.
Koch R.M., Dikeman M.E., Crouse J.D., 1982. Characterization of biological types of cattle (cycle
III). III. Carcass composition, quality and palatability. J. Anim. Sci., 54, 35-45.
Koohmaraie M., 1994. Muscle proteinases and meat aging. Meat Sci., 36, 93-104.
Koohmaraie M., Shackelford S.D., Wheeler T.L., Lonergan S.M., Doumit M.E., 1995. A muscle
hypertrophy condition in lamb (Callipyge): characterization of effects on muscle growth and meat
quality traits. J. Anim. Sci., 73, 3596-3607.
Larzul C., Le Roy P., Guéblez R., Talmant A., Gogué J., Sellier P., Monin G., 1997a. Effect of
halothane genotype (NN, Nn, nn) on growth, carcass and meat quality traits of pigs slaughtered at 95
kg or 125 kg live weight. J. Anim. Breed. Genet., 114, 309-320.
Larzul C., Lefaucheur L., Ecolan P., Gogué J., Talmant A., Sellier P., Le Roy P., Monin G., 1997b.
Phenotypic and genetic parameters for Longissimus muscle fiber characteristics in relation to growth,
carcass and meat quality traits in Large White pigs. J. Anim. Sci., 75, 3126-3137.
Larzul C., Le Roy P., Sellier P., Jacquet B., Gogué J., Talmant A., Vernin P., Monin G., 1998. Le
potentiel glycolitique du muscle mesuré sur le porc vivant : un nouveau critère de sélection pour la
qualité de la viande? Journées Rech. Porcine en France, 30, 81-85.
Larzul C., Le Roy P., Gogué J., Talmant A., Jacquet B., Lefaucheur L., Ecolan P., Sellier P., Monin P.,
1999. Selection for reduced muscle glycolytic potential in Large White pigs. II. Correlated responses
in meat quality and muscle compositional traits. Genet. Sel. Evol., 31, 61-76.
Le Bihan-Duval E., Mignon-Grasteau S., Millet N., Beaumont C., 1998. Genetic analysis of a
selection experiment on increased body weight and breast muscle weight as well as on limited
abdominal fat weight. British Poultry Sci., 39, 346-353.
Le Bihan-Duval E., Berri C., Baeza E., Millet N., Beaumont C., 2001. Estimation of the genetic
parameters of meat characteristics and of their genetic correlations with growth and body composition
in an experimental broiler line. Poultry Sci., 80, 839-843.
366
Le Bihan-Duval E., Berri C., Baeza E., Duclos M., Santé V., Rémignon H., Le Pottier G., Bentley J.,
Fernandez X., 2002. Selection on the technological quality of the meat in poultry. Proc. 7th World
Congr. Genet. Appl. Livest. Prod., CD-ROM, communication n°11-14.
Le Roy P., Naveau J., Elsen J.M., Sellier P., 1990. Evidence for a new major gene influencing meat
quality in pigs. Genet. Res., 55, 33-40.
Le Roy P., Juin H., Caritez J.C., Billon Y., Lagant H., Elsen J.M., Sellier P., 1996. Effet du génotype
RN sur les qualités sensorielles de la viande de porc. Journées Rech. Porcine en France, 28, 53-56.
Le Roy P., Larzul C., Gogué J., Talmant A., Monin G., Sellier P., 1998. Selection for reduced muscle
glycolytic potential in Large White pigs. I. Direct responses. Genet. Sel. Evol., 30, 469-480.
Le Roy P., Monin G., Kerisit R., Jeanot G., Caritez J.C., Amigues Y., Lagant H., Boulard J., Billon Y.,
Elsen J. M., Sellier P., 2001. Effets interactifs des gènes RN et HAL sur la qualité de la viande:
résultats obtenus lors de la fabrication du jambon cuit prétranché. Journées Rech. Porcine en France,
33, 103-110.
Lonergan S.M., Ernst C.W., Bishop M.D., Calkins C.R., Koohmaraie M., 1995. Relationship of
restriction fragment length polymorphisms (RFLP) at the bovine Calpastatin locus to calpastatin
activity and meat tenderness. J. Anim. Sci., 73, 3608-3612.
MacNeil M.D., Grosz M.D., 2002. Genome-wide scans for QTL affecting carcass traits in Hereford x
composite double backcross populations. J. Anim. Sci., 80, 2316-2324.
Maignel L., Guéblez R., Bardinal M., Garreau H., Bidanel J.P., Sellier P., 1998. Paramètres génétiques
de la composition chimique de deux dépôts adipeux (bardière et panne) et du muscle Long dorsal chez
le porc. Journées Rech. Porcine en France, 30, 73-80.
Ménissier F., 1982. General survey of the effect of double muscling on cattle performance. Current
Topics Vet. Med. Anim. Sci., 16, 23-53.
Milan D., Le Roy P., Woloszyn N., Caritez J.C., Elsen J.M., Sellier P., Gellin J., 1995. The RN locus
for meat quality maps to pig chromosome 15. Genet. Sel. Evol., 27, 195-199.
Milan D., Jeon J.T., Looft C., Amarger V., Robic A., Thelander M., Rogel-Gaillard C., Paul S.,
Iannucelli N., Rask L., Ronne H., Lundström K., Reinsch N., Gellin J., Kalm E., Le Roy P., Chardon
P., Andersson L., 2000. A mutation in PRKAG3 associated with excess content in pig skeletal muscle.
Science, 288, 12481251.
Monin G., Sellier P., 1985. Pork of low technological quality with a normal rate of pH fall in the
immediate post-mortem period: the case of the Hampshire breed. Meat Sci., 13, 49-63.
Monin G., Larzul C., Le Roy P., Culioli J., Mourot J., Rousset-Akrim S., Talmant A., Touraille C.,
Sellier P., 1999. Effects of the Halothane genotype and slaughter weight on texture of pork. J. Anim.
Sci., 77, 408-415.
Moody D.E., Pomp D., Newman S., MacNeil M.D., 1996. Characterization of DNA polymorphisms in
three populations of Hereford cattle and their association with growth and maternal EPD in line 1
Herefords. J. Anim. Sci., 74, 1784-1793.
Morris C.A., Pitchford W.S., Cullen N.G., Hickey S.M., Hyndman D.L., Crawford A.M., Bottema
C.D.K., 2002. Additive effects of two growth QTL on cattle chromosome 14. Proc. 7th World Congr.
Genet. Appl. Livest. Prod., CD-ROM, communication n°11-43.
Naveau J., 1986. Contribution à l'étude du déterminisme génétique de la qualité de la viande porcine.
Héritabilité du rendement technologique Napole. Journées Rech. Porcine en France, 18, 265-276.
O'Connor S.F., Tatum J.D., Wulf D.M., Green R.D., Smith G.C., 1997. Genetic effects on beef
tenderness in Bos indicus composite and Bos taurus cattle. J. Anim. Sci., 75, 1822-1830.
Ollivier L., Sellier P, Monin G., 1975. Déterminisme génétique du syndrome d'hyperthermie maligne
chez le porc de Piétrain. Ann. Génét. Sél. Anim., 7, 159-166.
Page B.T., Casas E., Heaton M.P., Cullen N.G., Hyndman D.L., Morris C.A., Crawford A.M.,
Wheeler T.L., Koohmaraie M., Keele J.W., Smith T.P.L., 2002. Evaluation of single-nucleotide
polymorphisms in CAPN1 for association with meat tenderness in cattle. J. Anim. Sci., 80, 3077-3085.
Perry D., Shorthose W.R., Ferguson D.M., Thompson J.M., 2001. Methods used in the CRC program
for the determination of carcass yield and beef quality. Austr. J. Exp. Agric., 41, 953-957.
Piles M., Blasco A., Pla M., 2000. The effect of selection for growth rate on carcass composition and
meat characteristics of rabbits. Meat Sci., 54, 347-355.
367
Pla M., Guerrero L., Guardia D., Oliver M.A., Blasco A., 1998. Carcass characteristics and meat
quality of rabbit lines selected for different objectives : I. Between lines comparison. Livest. Prod.
Sci., 54, 115-123.
Pollock D.L., 1997. Maximising yield. Poultry Sci., 76, 1131-1133.
Rabot C., Rousseau F., Dumont J.P., Rémignon H., Gandemer G., 1996. Poulets de chair: effets
respectifs de l'âge et du poids d'abattage sur les caractéristiques lipidiques et sensorielles des muscles.
Viandes Prod. Carnés, 17, 17-22.
Rémignon H., Gardahaut M.F., Marche G., Ricard F.H., 1995. Selection for rapid growth increases the
number and the size of muscle fibres without changing their typing in chickens. J. Muscle Res. Cell
Motil., 16, 95-102.
Renand G., 1985. Genetic parameters of French beef breeds used in crossbreeding for young bull
production. II. Slaughter performance. Genet. Sel. Evol., 17, 265-282.
Renand G., Fisher A.V., 1997. Comparison of methods for estimating carcass fat content of young
Charolais bulls in performance testing station. Livest. Prod. Sci., 51, 205-213.
Renand G., Berge P., Picard B., Robelin J., Geay Y., Krauss D., Ménissier F., 1994. Genetic
parameters of beef production and meat quality traits of young Charolais bulls progeny of divergently
selected sires. Proc. 5th World Congr. Genet. Appl. Livest. Prod., 19, 446-449.
Renand G., Fouilloux M.N., Ménissier F., 1998. Genetic improvement of beef production traits by
performance testing beef bulls in France. Proc. 6th World Congr. Genet. Appl. Livest. Prod., 23, 7780.
Renand G., Picard B., Touraille C., Berge P., Lepetit J., 2001. Relationships between muscle
characteristics and meat quality traits of young Charolais bulls. Meat Sci., 59, 49-60.
Renand G., Havy A., Turin F., 2002. Caractérisation des aptitudes bouchères et qualités de la viande
de trois systèmes de production de viande bovine à partir des races rustiques françaises Salers, Aubrac
et Gasconne. INRA Prod. Anim., 15, 171-183.
Reverter A., Johnston D.J., Graser H.U., Wolcott M.L., Upton W.H., 2000. Genetic analysis of liveanimal ultrasound and abattoir carcass traits in Australian Angus and Hereford cattle. J. Anim. Sci.,
78, 1786-1795.
Ricard F.H., 1975. Essai de sélection sur la forme de la courbe de croisance chez le poulet. Dispositif
expérimental et premiers résultats. Ann. Génét. Sél. Anim., 7, 427-444.
Ricard F.H., Touraille C., 1988. Selection for leanness and carcass quality. In: Leanness in domestic
birds. Leclercq B., Whitehead C.C. (Eds), Butterworth, London, UK, 377-386.
Sanchez M.P., Le Roy P., Griffon H., Caritez J.C., Fernandez X., Legault C., Gandemer G., 2002.
Déterminisme génétique de la teneur en lipides intramusculaires dans une population F2 Duroc x
Large White. Journées Rech. Porcine en France, 34, 39-43.
Sapp R.L., Bertrand J.K., Pringle T.D., Wilson D.E., 2002. Effects of selection for ultrasound
intramuscular fat percentage in Angus bulls on carcass traits of progeny. J. Anim. Sci., 80, 2017-2022.
Saugère D., Runavot J.P., Sellier P., 1989. Un premier bilan du programme de sélection contre le gène
de la sensibilité à l'halothane chez le porc Landrace Français. Journées Rech. Porcine en France, 21,
335-344.
Sauveur B., 1997. Les critères et facteurs de qualité des poulets Label Rouge. INRA Prod. Anim., 10,
219-226.
Schimpf R.J., Winkelman-Sim D.C., Buchanan F.C., Aalhus J.L., Plante Y., Schmutz S.M., 2000.
QTL for marbling maps to cattle chromosome 2. Proc. 27th Intern. Conf. Anim.Genet., July 22-26,
2000, Univ. Minnesota, 48, B103.
Schwörer D., Hofer A., Lorenz D., Rebsamen A., 2000. Selection progress of intramuscular fat in
Swiss pig production. EAAP Publ., 100, 69-72.
Seideman S.C, Koohmaraie M., Crouse J.D., 1987. Factors associated with tenderness in young beef.
Meat Sci., 20, 281-291.
Sellier P., 1998. Genetics of meat and carcass traits. In: The Genetics of the Pig. Rothschild M.F.,
Ruvinsky A. (Eds), CAB International, Oxon, U.K., 463-510.
Sellier P., Le Roy P., Fouilloux M.N., Gruand J., Bonneau M., 2000. Responses to restricted index
selection and genetic parameters for fat androstenone level and sexual maturity status of young boars.
Livest. Prod. Sci., 63, 265-274.
368
Shackelford S.D., Koohmaraie M., Whipple G., Wheeler T.L., Miller M.F., Crouse J.D., Reagan J.O.,
1991. Predictors of beef tenderness: development and verification. J. Food Sci., 56, 1130-1140.
Shackelford S.D.,Savell J.W., Crouse J.D., Cross H.R., Schanbacher B.D., Johnson D.D., Anderson
M.L., 1992. Palatability of beef from bulls administered exogenous hormones. Meat Sci., 32, 397-405.
Shackelford S.D., Koohmaraie M., Cundiff L.V., Gregory K.E., Rohrer G.A., Savell J.W., 1994.
Heritabilities and phenotypic and genetic correlations for bovine postrigor calpastatin activity,
intramuscular fat content, Warner-Bratzler shear force, retail product yield, and growth rate. J. Anim
Sci., 72, 857-863.
Shackelford S.D., Wheeler T.L., Koohmaraie M., 1995. Relationship between shear force and trained
sensory panel tenderness ratings of 10 major muscles from Bos indicus and Bos taurus cattle. J. Anim.
Sci., 73, 3333-3340.
Smith T.P.L., Casas E., Rexroad III C.E., Kappes S.M., Keele J.W., 2000. Bovine CAPN1 maps to a
region of BTA29 containing a quantitative trait locus for meat tenderness. J. Anim. Sci., 78, 25892594.
Stone R.T., Keele J.W., Shackelford S.D., Kappes S.M., Koohmaraie M., 1999. A primary screen of
the bovine genome for quantitative trait loci affecting carcass and growth traits. J. Anim. Sci., 77,
1379-1384.
Touraille C., Kopp J., Valin C., Ricard F.H., 1981. Broiler fowl meat quality. 1. The effect of age and
growth rate on meat physico-chemical and organoleptic traits. Arch. Geflügelk., 45, 69-76.
Tribout T., Garreau H., Bidanel J.P., 1996. Paramètres génétiques de quelques caractères de qualité de
la viande dans les races porcines Large White et Landrace Français. Journées Rech. Porcine en France,
28, 31-38.
Tribout T., Lagant H., Caritez J.C., Gogué J., Gruand J., Guéblez R., Labroue F., Bidanel J.P., 2001.
Estimation, par utilisation de semence congelée, du progrès génétique réalisé en France entre 1977 et
1998 dans la race porcine Large White. Dispositif expérimental et premiers résultats. Journées Rech.
Porcine en France, 33, 119-125.
Van Laack R.L.J.M., Stevens S.G., Stalder K.J., 2001. The influence of ultimate pH and intramuscular
fat content on pork tenderness and tenderization. J. Anim. Sci., 79, 392-397.
Whipple G., Koohmaraie M., Dikeman R.D., Crouse J.D., Hunt M.C., Klemm R.D., 1990a. Evaluation
of the attributes that affect longissimus muscle tenderness in Bos taurus and Bos indicus cattle. J.
Anim. Sci., 68, 2716-2728.
Whipple G., Koohmaraie M., Dikeman R.D., Crouse J.D., 1990b. Predicting beef-longissimus
tenderness from various biochemical and histological muscle traits. J. Anim. Sci., 68, 4193-4199.
Wulf D.M., Tatum J.D., Green R.D., Morgan J.B., Golden B.L., Smith G.C., 1996. Genetic influence
on beef longissimus palatability in Charolais- and Limousin-sired steers and heifers. J. Anim. Sci., 74,
2394-2405.
369