Valorization of the pulp of Argania spinosa L. Processing and

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Valorization of the pulp of Argania
spinosa L. Processing and products
Towards an optimized valorization
of the Argan fruit
Pioch D1., Buland F-N1., Pingret de Sousa D1., Palu S1., Benismail MC².,
Mohktari M²., Larroque M3., Bastianelli D4., and Charrouf Z5.
1- CIRAD - UR 40 Génie des procédés - Bioraffinerie, TA-B40/16, 34398 Montpellier
Cedex 5, France. Email : [email protected]
2- IAV- Centre de recherché d’Agadir, Maroc ;
3- UMR QUALISUD, Faculté de Pharmacie, Université de Montpellier 1, 15 Av. Charles
Flahault 34000 Montpellier, France ;
4- CIRAD - UMR SELMET, Montpellier, France ;
5- Laboratoire de Chimie des Plantes et de Synthèse Organique et Bioorganique,
Faculté des Sciences, Université Mohammed V-Agdal, Rabat, Maroc.
Résumé
Ce travail est axé sur la pulpe du fruit de l’arganier : technologie et produits potentiellement utiles.
Un protocole a été développé afin de récolter des échantillons de fruits d’arbres sélectionnés, d’enregistrer
les données biométriques et d’effectuer des analyses sur la pulpe. L’étude montre l’effet de la forme des
fruits (fusiforme, apiculé, rond …) et de la maturation sur la composition chimique de la pulpe. Des
essais pilotes ont montré que les étapes clés (séchage, dépulpage mécanique, fractionnement-extraction)
peuvent être réalisées avec des équipements existants, malgré la variabilité de taille des fruits, dans le
but de préserver les composants naturels. Cette étude exploratoire, financée par l’ADS (RARGA2) Maroc,
laisse entrevoir plusieurs possibilités de valorisation de la pulpe : adaptation de la filière de production,
sélection variétale, stabilisation par séchage solaire, exploitation des produits nouveaux à haute valeur
ajoutée. Ces résultats montrent une voie pour le traitement et la valorisation optimisés de la totalité du
fruit de l’arganier parallèle à l’exploitation de l’huile et d’aliments pour bétail.
Mots clefs : mésocarpe argan, formes fruit, extraction, latex, huile pulpe, composition.
Abstract
This report focuses on Argan pulp: technical aspects and potentially useful products. A new
protocol was developed, to collect either all ripe fruits of a given tree under similar conditions in spite
of ripening lasting for weeks, or non-ripe fruits at different stages of maturity, recording biometric
data, chemical analysis. This study points out the effect of fruit shape (fusiform, pointed, round….)
and of ripening on the chemical composition of the pulp. Pilot trials showed that key steps (drying,
mechanical depulping, and fractionation-extraction) can be carried out efficiently with readily available
equipment, this in spite of large fruit variability, with the aim of preserving natural compounds. This
exploratory study, funded by ADS (RARGA2) Morocco, shows an alternative for adding value to pulp:
adapted organization of production chain, interest of varietal selection, stabilization by mild drying in
a solar oven, and new high value products in addition to usual kernel oil and fodder; thus opening the
way towards an optimized processing and valorization of the whole Argan fruit.
Key words : Argan mesocarp, fruit shape, extraction, latex, pulp oil, chemical composition.
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Introduction
The Argan tree is important from the environment standpoint. Its current decline, caused by climate
change, demography and overexploitation is expected to have drastic consequences on ecological,
economical and human sides. This is why it should be protected and even planted again1. Nowadays,
the Argan oil has become the principal product from economical point of view. The production chain
is based on a single market which is driven, by changing customer habits in industrialized countries
(cosmetics, health food).
Thus, under present situation, in addition to improving the current production chain centered
on kernel oil and fodder, it makes sense to expand our knowledge towards an alternative integrated
valorization of all products of the Argan tree. Here reported results deal with the pulp, owing to its
diversified chemical composition, although being much less investigated than Argan oil, [Charrouf
19902, 1991a3, 1991 b4, 20025, 20076 ; Chernane 19997; Fellat–ZarrouK 19878; Sandret 19579;
Tahrouch 199810];
The susceptibility of the pulp to degradation by biological and chemical agents (water, air,
Ceratite flies…) leds to pay attention to the whole production chain, from ripening and harvest. Thus
preserving the natural compounds during the production chain with the aim of accessing to quality
products has become a new challenge. The study focus (i) on technological aspects: key steps of
harvest, depulping (pericarp / mesocarp separation), fractionation, extraction, and (ii) on potentially
interesting products. It was necessary to improve our knowledge about the chemical composition of
the pulp ie its evolution with ripening and the influence of fruit shape.
1- Materials and methods
-2.1 Sample collection and preparation:
To achieve our goals, a procedure was set and applied, allowing the collection of fruits at the same
ripening stage for a given tree, in spite of the production period being spread over several weeks. In
fact fruits were considered ripe when falling on the ground and were collected daily for 2-3 weeks on
a polyethylene film placed under the tree in order to avoid contact with soil and limit degradation by
insects or micro-organisms. Daily harvested fresh fruits were then counted, and size and pulp / nut
ratio after manual depulping were measured on a representative sample. The pulp fraction was then
dried or frozen and stored until chemical analysis. This protocol was applied to trees selected on the
basis of fruit shape. For accessing to lots of fruits at various stages of maturity, all fruits of a given tree
were collected on the same day, either on the ground or in the tree, considering the following groups:
almost ripe, intermediate and unripe, as being respectively those close to falling but not yet fallen
(based on color), turning color green-yellow, still green. Above procedure was applied for analytical
purpose; for testing alternatives to current production chain which is based on sun drying prior to
manual depulping, and to allow fractionation of pulp as a fresh product, daily harvested lots of whole
fruits were stored at 4°C either as fresh fruits, or after stabilization. This last was achieved under
mild conditions through drying in a solar tunnel ventilated with a fan, and made of PE film to avoid
direct contact with sun light and subsequent degradation. Several tens of kilos were collected this way
for further technological investigation (influence of storage conditions, of drying stage, mechanical
depulping and fractionation).
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A total of 14 trees of the experimental conservatoire field at IAV Research Center in Agadir, free
of non statistical collection of fruits by goats and sheep, nor by harvesters, were selected, localized
with GPS and classified according to fruit shape. In all, this sample collection organized in late spring
gave access to a large number of typed samples, from 1kg for analytical purpose, up to 10kg for
technological trials, as summarized in table 1.
Table 1: Typed lots of Argan fruits obtained for analysis and technical trials
Processing trials
Ripening
Parameters
investigated
Oil extraction
depulping
Chemical
composition
Type of
samples
collected
Ripe fruits
Fresh
half dried
dried
Ripe
almost ripe
medium
unripe
Fruit shape
Pulp
contamination
Preservation
Chemical
composition
Environment
Storage
conditions
spherical
pointed
elongated
Harvest from
tree or ground
Ceratite infested
Goat-free field
close sheepfold
Fresh 4°C
Fresh -18°C
Half dried 4°C
Dried 4°C
2.2 Analytical procedures:
The water and volatile matter content were estimated by addition of different losses: exuded liquid
during travel, weight loss by stabilisation and determination of residual water and volatiles matters
content. The stabilization was made by drying with U.T.A. dryer at 40°C. The residual water content
was measured in accordance with ISO 665: 1997 Norm. 5 g of stabilized sample were grinded and put
in steam room at 103°C. The extraction of volatile compounds was performed in HeadSpace (SPME):
in Glass bottle corked by aluminum foil, with a fiber of Polydimethylsiloxane / Divinylbenzene (PDMS/
DVB) conditioned 30 min at 260°C before first use. 3 g of green, yellow or brown fruits’ pulp were taken.
The pulp was cut into small pieces. Several tests were conducted to optimize the protocol. Increasing
temperature of 70 to 90°C improves results, giving greater sensitivities. Finally, the extraction of
volatile compounds was made by heating samples at 90°C for one hour. It is important to note that
the temperature of the head space was 49°C and within the solid (pulp) was 57°C. In the end of volatile
compound’s adsorption on the fiber, desorption is thermally made (2 min at 260°C) in the injector of
GC coupled to a mass spectrometer.
Four types of solvents were used for extraction:
- Water: Aqueous extract was obtained in ebb at 90°C. It was used for sugar’s measurement
and identification. The separation and determination were performed by HPLC with Au electrochemical
detector.
- Hexane, dichloromethane and methanol: Extraction made in series by ebb solvent to
the previous extraction’s remnant (hexane, then dichloromethane, then methanol) with soxhlet’s
equipment. The samples were introduced in an extraction cartouche of cellulose and put into
the soxhlet. The solvent in the system was heated from the balloon and the vapor condensated
by distillation, dropping into the soxhlet and once the liquid reached the overflow level, a siphon
aspirated and unloaded it back to the distillation flask, carrying the extracted analytes into the bulk
liquid. This operation was repeated until complete extraction was achieved.
- Hexanic extract: The lipidic and polyisoropenic fractions (apolar fraction) were obtained by
precipitation with methanol. 2 ml of hexanic extract were filtered and 0,2 ml of methanol KOH 2M
were added for precipitation. The mixture was put in a vortex and filtered. The identification was
performed on 2 µl of extract by GC-MS.
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- The dichloromethanic extract was diluted in 50 ml of dichloromethane and 2 µl were used for
GC-MS analysis.
Non-extractibles matters measured were ash, cellulose and lignocellulose content of pulp.
Figure 1 gives the laboratory protocol for pulp fractionation.
Figure 1: Laboratory protocol for pulp fractionation
Results
3.1- Influence of fruit shape and ripening:
This study shows the effect of fruit shape (fusiform, pointed, round….), and of the degree of
ripening on the chemical composition of the pulp. The daily collection of fruits on the polyethylene film
was strongly dependent of the date (because of variation of weather conditions) as shown in Figure 2.
In fact the average fruit weight and the number of fruits fallen during one day, may vary similarly or
not depending also on the considered group (fruit shape). Regarding biometric data, the fruit shape
parameter -ratio length/diameter- 2.12 and 1.8 respectively for pointed and round shapes was very
close to those found by [Chernane et al. 2000; Zahidi 2004; Maallah 199211]. The standard deviation
of diameter and length over the collection time within fruits collected on a given is in the range of
1,8 mm for diameter and 2,8 mm for length. Regarding the composition, the percent of pulp in fruit
(dry pulp weight) varies according to the shape: pointed (apiculé) 23.8%; elongated (fusiforme) 18.8%;
round 16.7% with a relative variation within groups of trees producing fruits of same shape in the
range of 20%, but only 10% of relative variation during harvest period for a given tree (Fig. 3)
Figure 2 : Nbre of fallen fruits daily and average individual fruit weight for 3 selected trees
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Figure 3: Progress of pulp’s percentage in tree 04’s fruit
Several fractions were extracted from above pulp samples using a panel of methods and of solvents
according to procedure detailed in figure 1. The volatile fraction obtained by SPE showed lactones
(decanolactone), decenal, unsaturated hydrocarbons, all known as components of aromas.
Next fraction is the sugars in aqueous extract; during the ripening period total sugars vary from
3.0 to 16.7% for round fruits, while it may account for up to 23.8% vs fruit shape. Thus sugars
content could be taken as markers of ripening stage to determine harvesting date.
Then the non polar extract obtained with hexane (Table 2) makes up to 12% dry weight (dw),
as does Argan oil in the seed. Here this extract contains polyisoprene but also lipids. These lipids
account for 4.8 to 5.7% depending on fruit shape and may vary of 10-20% during ripening. The study
also confirmed the peculiar fatty acid composition of this pulp oil, being almost independent of fruit
shape (Table 3). The second fraction of the hexane extract, polyisoprene, also mentioned in literature
[Battino 192912; Fellat Zarrouck 198713], increases from 2 to 3.6% vs ripening, the maximum being
measured just before falling, but also strongly influenced by fruit shape (0.8 – 2.7%) maximum for
round fruit.
Table 2: Hexane fraction vs ripening and fruit shape
Pointed
ripe
Fusiform
ripe
Round
ripe
Round
almost
ripe
Round
medium
Round
almost
ripe
Lipids
(%p/dry pulp)
5,6
4,8
5,7
8,3
6,7
8,0
Polyisoprene
(%p /dry pulp)
0,81
0,66
2,7
3,6
2,0
2,6
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Table 3: Fatty acid composition of pulp lipids
4 shapes
Bibliography
Lauric C12 :0
0 – 1.6
-
Argan oil
(this work)
-
Palmitic C16 :0
23.7-25.7
18-31
10-15
Palmitoleic C16 :1
2.5- 3.4
1-3
-
Dioctyladipate
0.93
-
-
15-méthyl
hexadecanoic
0 – 2.7
-
-
4.2 – 5.6
2-7
-
Oleic C18 :1
13.1-15
3-42
43-50
Linoleic C18 :2
28.4 - 31.9
3-23
28-36
Linolénic C18 :3
12.5-12.8
0,4-5
-
Arachidic C20 :0
1.2 – 1.9
1
-
13-Docosenoic
C22 :1
0 – 1.0
-
-
2.4 - 3.3
-
-
StearicC18 :0
Lignoceric C23 :0
Last, the CH2Cl2 extract of pulp defatted with hexane contains bioactive compounds like amyrin,
lupenylacetate, pyrocatechol; 35 compounds were identified by GC-MS (6 previously reported) and
evolution vs ripening was noted, thus exemplifying the possibility of adapting the harvest time
depending on the goal.
Finally the cake after having extracted above fractions, still contains proteins (as N total), up to
10%, 25% variation vs ripening or shape and fibers with no influence of shape, but suffering 30%
variation during ripening, all these components giving a value to the solid as animal feed influenced,
by ripening and shape.
This should lead to select varieties based on morphological and chemical characters.
Pilot trials at 5 kg scale, showed that key steps -drying, mechanical depulping and fractionationextraction- can be carried out efficiently. These steps can afford the large biometric variability of
fruits, even without sophisticated equipments, while preserving product quality. It should be noted
that this new use of the pulp would require an adapted organization of the production chain, from
harvest, and would need appropriate varietal selection.
3.2 Processing trials at 10kg pilot scale
The use of a simple device comprising an horizontal cylinder serving as a mesh sized to retain
depulped nuts fitted with a rotating knifes at variable speed allowed a low ratio of broken nuts as
low as 0.2 and 0.7% fresh weight respectively with fresh and dried fruits (Table 3). This leaves open
both the options of processing fresh fruits or stabilized fruits that could afford a longer storage time
compared to the first option. This very low ratio of broken nuts should lead to high quality Argan oil
after subsequent breaking of separated nuts prior to extraction in screw press as currently done,
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221
although this was not tested because out of the scope of this explorative work. The yield of depulped
fruits in the range of 70% is only indicative here, because of the high dead volume of the equipment in
comparison to the relatively small size of fruits available for each trial; this yield could be augmented
by adjusting residence time of fruits and/or recycling of fruits if necessary.
The water content of fruits was found a key parameter, to be optimized in conjunction with
stabilisation option: partial drying in sun tunnel, complete drying in an electrical loop or fresh fruits
stored at 4°C. Worth noting that mechanical depulping did work in spite of fruit heterogeneity as
mentioned in the biometry section, although these few trials did not allow testing a very large panel of
fruits, including variable mechanical resistance of nuts known to be a key parameter when processing
palm kernels for example. Based on our expertise in this last field, it is reasonable to expect mechanical
processing of nuts be possible, although requiring a large, fully dedicated multidisciplinary study.
Table 3: Pilot trials for mechanical depulping at 10kg scale vs type of stored fruits
Type of fruit
Water content (%)
Fresh
75
Partly dried
66
Dry
16
Depulped (%)
70.5
71.3
69.2
Broken nuts (%)
0.2
3.7
0.7
Not depulped (%)
(to be recycled)
29
25
30
Conclusions
The peculiarity of Argan tree-sessile fruits and harvest period spread over several weeks- led to
set an adapted method, for collecting all fruits of a given tree at same ripening stage, while preventing
extensive degradation of pulp. This procedure for collecting representative samples is now available
for performing extensive research work, with the aim of characterizing the diversity of trees and fruits.
This study confirms the effect of fruit shape and degree of maturity on the chemical composition
of pulp, parameters rarely considered to date, although of prime importance in view of an improved
valorization of the whole fruit. This will lead to selecting trees, including characters linked to harvest
and processing aptitude of fruits, from chemical composition to mechanical properties, in addition to
resistance to Ceratite fly for example.
In view of achieving our goals, the processing trials have show the possibility of mechanizing
several steps, although much more work would be necessary to set successfully a new production
chain, achieving fractionation of pulp components while producing high quality Argan oil, as a
important product, among others addressing a wider panel of markets.
Complementing previous reports, a panel of potential derived products has been highlighted:
flavour; bioactive molecules; pulp oil; latex; all suitable for industrial applications. It should be
mentioned that these valuable extracts represent a portion at least equivalent to the kernel oil on a
weight basis (Argan oil) which can be still extracted by the usual processes. Then, other components
(cellulose, hemicellulose, sugars, proteins…), which make the main part of the pulp (on weight basis),
would still remain available for feeding local goats and sheep, owing to their high nutritional value.
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Applying above concepts would lead to a “biorefinery” devoted Argan tree, definitely strengthening
the production chain, which does not look to be sustainably implemented yet.
A. spinosa makes a specific agro-sylvo-pastoral system in Morocco, from both environmental and
social stand points. Domestication -adapted cropping system and production chain- would bring new
opportunities of sustainable development, while contributing to the preservation of this species.
Aknowledgement ADS–Morocco for funding in part of this research work (ARCADI project) under RARGA2, as well
as CIRAD, Agropolis-International and IAV-Agadir. Dr Jean-Claude Dumas, UMR QUALISUD and
Dr Frédéric Bonfils, UMR IATE both of CIRAD (Montpellier) and Dr Thierry Doco, INRA-Montpellier,
respectively for their help in processing trial, plyisoprene and sugar analysis; Dr Hicham Harhar,
Université Mohamed V, and Drs Miloudi Hilali and Badr, formerly students at IAV-Agadir for their
help in daily harvesting of fruits
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Actes du Premier Congrès International de l’ Arganier, Agadir 15 - 17 Décembre 2011