EFFECT OF A TYPICAL RURAL PROCESSING METHOD ON THE PROXIMATE COMPOSITION AND AMINO ACID PROFILE OF BUSH MANGO SEEDS (Irvingia gabonensis)

EFFECT OF A TYPICAL RURAL PROCESSING METHOD ON THE
PROXIMATE COMPOSITION AND AMINO ACID PROFILE OF BUSH
MANGO SEEDS
(Irvingia gabonensis)

Ekpe OO 1* , Umoh IB2 and OU Eka3





Ekpe Onot

















1*Corresponding author Email: onot_fni@email.com and/or :rooseh01@yahoo.com.
Co-ordinator, Food and Nutrition Programme, Ministry of Agriculture and Natural
Resources P.M.B. 1119, Calabar, Cross River State, Nigeria.

2Professor, Department of Biochemistry, College of Medical Sciences, University of
Calabar, Nigeia.

3Professor, Department of Biochemistry, College of Medical Sciences, University of
Calabar, Nigeria.

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ABSTRACT

Various researchers have confirmed the view that forest and wood lands, among other
natural boundaries in West Africa supply a massive amount of protein and
carbohydrates to the citizens; however industrialization and urbanization has threaten
many of the food species from these ecosystems. For instance Itugha known to be
highly prized and delicious indigenous food is getting extinct and the possibility of
it’s origin and composition being lost in antiquity is high, more so data on nutrient
composition of processed lrvingia products is limited.
Samples of Itugha were prepared as it is obtained in the local setting. These and fresh
seeds from the same source of fruits were subjected to proximate analysis and amino
acid profile determination.
The synergistic effect of pounding and fermentation (two rural processing methods)
on proximate composition and amino acid profile of Irvingia gabonensis seeds were
evaluated. Proximate analysis differed significantly (p > 0.05) between the processed
product and fresh Irvingia seeds in crude protein, fat, ash and dietary fiber contents.
Protein value was 19.4+ 0.4% dry matter (DM) for the product, 7.6 + 0.8 of (DM)
for fresh seed of var gabonensis, Crude fat 66.60+ 0.80% DM seed and 58.00+ 1.0%
product; ash 9.50+ 0.30% DM seed and 11.60 + 0.6% DM product. Dietary fibre was
18.20+ 1.80% DM seed and 12.30+2.00% DM product. Percent sucrose in starch was
2.10 + 3.50% DM seed and 9.60+ 3.10% DM product. There were significant losses
in fat, dietary fibre, moisture and carbohydrate due to processing. High moisture level
in seed 5.20 +0.6% DM compared with product 2.10+ 0.8% DM is indicative of the
presence of appreciable quantity of trapped water in the matrices of fresh Irvingia
seeds which was favourable for fermentation. Amino acid profile showed significant
differences (p < 0.05) in their levels in the seeds and the product. All the essential
amino acids (EAA) were quantified with Leucine recording the highest value. In all,
eighteen amino acids were quantified in both the fresh seed and processed product.
They are Leucine 8.30+ 0.11g/16g Nitrogen (N) product and 7.60 + 0.12g/16gN seed,
isoleucine 3.20+ 0.04g/16gN seed and 4.50+ 0.1g/16gN product; threonine 2.20+
0.30g/16gN seed and 3.10+ 0.1g/16gN product, glutamic acid 13.40+ 0.11g/16gN
seed and 15.20 + 0.10g/16gN product. These recorded increases. Serine 3.10+
0.04g/16gN seed and 2.80+ 0.01g/16gN product was the only amino acid that
recorded a decrease in level due to processing. Other amino acids were methionine,
tryptophan, valine, phenylalanine, histidine, aspartic acid, cystine, proline, glycerine,
alanine, tyrosine, lysine and arginine. Processing method resulted in slightly higher
levels of essential nutrients in the product than the seeds. Further investigation to
determine the micoflora involved in the fermentation is recommended. It would also
be necessary to isolate and identify the food enzymes in the endosperm of Irvingia
gabonensis. It has been observed that nutrient dense plant foodstuff are facing
extinction due to urbanization and increased patronage of fast foods, as such, there is
need to increase available information on their nutritive potentials to encourage
utilization.

Keywords: Pounding, Fermentation, Amino acids, Proximate, Irvingia .


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L'EFFET D'UNE METHODE DE TRAITEMENT TYPIQUEMENT RURALE
SUR LA COMPOSITION RAPPROCHÉE ET LE PROFIL DE L’ACIDE
AMINÉ DU NOYAU DE LA MANGUE SAUVAGE (Irvingia gabonensis)

Ekpe OO, Umoh IB et OU Eka


Résumé

Le effet synergétique du pilage et de la fermentation (deux méthodes rurales de
traitement) sur la composition rapprochée et le profil de l’acide aminé des graines
d’Irvingia gabonensis a été évalué. L’analyse rapprochée a différé considérablement
(p>0.05) entre le produit traité et les graines fraîches d’Irvingia dans les protéine
crues, les graisses, la cendre et les teneurs diététiques en fibre. La teneur en protéine
était 19,4+ 0.4% des matières sèches (m.s.) pour le produit, 7,6 + 0,8 de m.s pour la
graine fraîche de var gabonensis, les graisses crues 66,60+ 0,80% de m.s. pour la
semence et 58,00+ 1,0% pour le produit; la cendre 9,50+ 0,30% de m.s. pour la
semence et 11,60 + 0,6% de m.s pour le produit. La fibre diététique était 18,20+
1,80% de m.s pour la graine et 12,30+2,00% de m.s pour le produit. Le pourcentage
de la saccharose dans l'amidon était 2,10 + 3,50% de m.s pour les graines et 9,60+
3,10% de m.s pour le produit. Suite au traitement, il y a eu des pertes significatives
dans les grasses, les fibres diététiques, l’humidité et l’hydrate de carbone. Le niveau
élevé d'humidité dans les graines 5,20 +0.6% de m.s par rapport au m.s du produit
2,10+ 0,8% est une indication de la présence d’une quantité appréciable d'eau qui
stagne dans les matrices de graines fraîches d’Irvingia, et cette eau a été favorable à la
fermentation. Le profile de l’acide aminé a montré des différences significatives (p <
0,05) dans leurs niveaux dans les graines et dans le produit. Tous les acides aminés
essentiels (AAE) ont été quantifiés, la leucine enregistrant la valeur la plus élevée.
Dans l’ensemble, dix-huit acides aminés ont été quantifiés aussi bien dans la graine
fraîche que dans le produit traité. Ces acides sont comme suit : la leucine 8,30+
0,11g/16g, le produit azote (N) et la graine 7,60 +0,12g/16gN, l’isoleucine 3,20+
0,04g/16gN graine et 4,50+ 0,1g/16gN produit; thréonine 2,20+ 0,30g/16gN graine et
3,10+0,1g/16gN produit, acide glutamique 13,40+ 0,11g/16gN graine et 15,20 +
0.10g/16gN produit. Ces acides ont enregistré des accroissements. La sérine 3,10+
0,04g/16gN graine et 2,80+ 0,01g/16gN produit était le seul acide aminé qui a
enregistré une diminution de niveau à cause du traitement. Les autres acides aminés
étaient la méthionine, le tryptophane, la valine, la phénylalanine, l’histidine, l’acide
aspartique, la cystine, la proline, la glycérine, l’alanine, la tyrosine, la lysine et
l’arginine. La méthode de traitement a abouti à des niveaux légèrement plus élevés de
nutriments essentiels dans le produit par rapport aux graines. Une enquête plus
approfondie visant à déterminer les microflores impliquées dans la fermentation est
recommandée. Il serait aussi nécessaire d’isoler et d’identifier les enzymes
alimentaires dans l'endosperme de Irvingia gabonensis.

Mots-clés: Pilage, fermentation, acides aminés, rapproché, Irvingia.



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INTRODUCTION

Irvingia gabonensis is a non-timber forest product, made up of tree trunk (stem),
leaves, roots and fruits. The fruit comprises a fleshy part and the nut, which consists
of a hard shell and the kernel/seed. Its seeds have an outer brown testa (hull) and two
white cotyledons. It belongs to the genus Irvingia, species Irvingia gabonensis. Two
varieties have been identified in Nigeria; Var gabonensis and Var excelsa [1].
Irvingia gabonensis common names are bush mango, African mango, wild mango or
Dikanut plant and the local name is Kuwing (Agoi). Irvingia seeds constitutes an
important part of the rural diet in Nigeria. The sun-dried seeds are ground into flour
and used as soup thickeners. The white cotyledons are roasted and eaten in the
Bwemba community of Uganda; roasted seeds confer flavour and aroma on foods
especially vegetables [2]. It is the food gum component of the seeds that serves as a
thickening agent in water (especially hot water) [3].

Seeds are a prominent feature in the peasants dietary especially in the developing
countries and oilseeds are becoming valuable sources of nutrients for man, especially
in countries where the diet is plant-based. Ignorance of their food value has resulted
in their wastage in terms of economic returns or/and post harvest loses. Much work
has been done on some Nigerian seeds and legumes including Irvingia gabonensis
seeds. Solvent extraction of Var gabonensis seed yielded between 68% to 75% fat
[4]. Other reports on this seed nutrients content indicated that it contains 8.65%
protein, 14.1% carbohydrate, 2.1% moisture, 1.4% crude fibre, 16.8% ash and 38.9%
dietary fibre [5,6].

Reports on the nutrients composition of indigenous processed products from oilseeds
are limited. So far, melon (citrullus vulgaris) flour has been reported to have high
protein content 33.25 ± 0.9% compared to egg protein and 56.22 ± 0.8% fat [7].

This study was therefore aimed at increasing the body of available information on
nutrient composition, with particular reference to proximate composition and amino
acid profile of Irvingia gabonensis seed and a processed product called “Itugha” by
Agoi Ibami Community of Nigeria. Itugha is a very popular indigenous foodstuff
obtained using a typical traditional food processing technique involving pounding and
fermentation used together as a unit process.

MATERIALS AND METHODS

Sample Preparation
Fresh seeds were obtained from fruits collected from the Agoi Ibami forest in Cross
River State, Nigeria. The fruits collected and heaped to ferment, took between two to
three weeks at a temperature range from 26oC – 29oC. The fermented fruits were
depulped to obtain the seeds, which were then cracked to release the white
cotyledons. With the aid of a pestle and mortar, cotyledons (without the hull) were
pounded for about one hour on the first day. Pounding was repeated every day for
five days by which time the gummy component of the mashed Irvingia mass was lost.

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After each day’s pounding, the mash was stored away in a native gourd (Lagenaria
sicereria) container. At the end of six (6) days, when the “drawness” was completely
lost, the mash was molded manually into round or oblong shapes of convenient sizes.
These products were wrapped with Piper umbellantum (“Ansumsum’’) leaves and
placed over the fire place for two- three days to smoke dry. Samples of the processed
product from Irvingia gabonensis (Var gabonensis) seed and the fresh seeds were
then used for laboratory analysis.

Laboratory Analysis
Moisture, ash, crude protein, crude fat extract and crude fiber levels were analyzed in
the fresh seed and the processed food product using the AOAC methods [8]. Dietary
fiber and starch contents were determined using the method of Theander and
Westerland [9]. Amino acids were analyzed by the method of Basha et al [10] with a
slight modification.

Data Analyses
All analysis were done in triplicates. Data were analyzed by calculating mean and
standard deviation. Student t-test was used to test effect of pounding and
fermentation on the proximate and amino acid profile of Irvingia gabonensis seeds
and significance was accepted at p ? 0.05.

RESULTS

Data on proximate composition % DM , amino acid profile g/16g Nitrogen of lrvingia
gabonensis (bush mango) seeds and processed product are shown in Tables 1 and 2,
respectively. The values as presented in the tabulated results are mean of 3
determinations + standard deviation. P_values are also indicated.

Processing method increased some parameters of the proximate composition as in the
case of crude protein (7.60±0.80% DM seed to 19.40±0.4% DM product) and %
sucrose (2.10±3.5% DM seed to 9.60±3.10% DM product).

There was a decrease in crude fat content of seed from 66.60±0.80% DM to
58.00±1.00% DM processed product. Most of the crude fat was lost as “oil drip”
during drying Itugha at the fireplace and to the leaves used for wrapping products.
This increase “oil drip” was accompanied with development of spicy aroma and
flavour. Moisture level decreased due to processing. Dietary fiber and ash contents
also recorded decreases in values. Crude fibre content of Irvingia seed and ‘Itugha’
were 1.9±0.4g% DM and 1.8±0.2g% DM respectively. The values are comparative
showing that processing had not effect on crude fibre. Therefore the recorded
decrease in dietary fibre can then be attributed to microbiological metabolism of
lingo-polysaccharides.

The amino acid profile indicated the presence of eighteen amino acids and ‘Itugha’
had desirable pattern of essential amino acids. Some amino acids recorded increases
while others were low in their levels.


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DISCUSSION

Pounding is a size reduction unit operation in which impact forces were used in the
disruption of Irvingia seed matrices, rupturing cell walls thereby rendering the final
product porous in texture. This disruption of cells and the resulting increase in
surface area promoted oxidative degradation and higher rates of microbiological and
enzymatic activity [11]

High dietary fibre of the seeds (18.20 ± 1.0% DM) as shown in Table 1, indicated the
presence of reasonable quantity of trapped water. Water (bound) can be held by the
hydrophilic polysaccharides of the fibre. This water is unavailable and has very low
chemical activity [12]. The water in fresh Irvingia seed could possibly be bound
water, so crushing the seeds by repeated pounding dismembered the matrices,
disrupted the cells and made the water in the mash very much available for
biochemical reactions involved in fermentation process. Consequently, moisture level
as high as 5.20 ± 0.60% DM in the seed was favorable for the fermenting substrate, to
facilitate fermentation process more so as the porous texture of the mash made the
trapped water very mobile. Hook reported that moisture level of a food influenced the
texture and that the more ordered the endosperm structure the lower the rate of
moisture movement [13]. Stenvert and Kingswood suggested that for a soft porous
endosperm structure (as the mashed Irvingia seeds mass) water movement was very
rapid, and so pounding and fermentation increased the availability of bound water,
whether the water was held in fibre matrices and/or was trapped within cell wall
lumen (14). The porous texture of the final product (as a result of the processing
method) increased loss of water during drying thus resulting in a moisture content as
low as 2.10 ± 0.8% DM in the processed product. The pH of the mass of crushed
Irvingia seed also affected its water holding capacity. This is inferred, as pH affects
the swelling of polysaccharides. This lower moisture content of the product than the
seed could also be attributed to microbial biochemical reactions. The lower moisture
level is advantageous as it is known that, the lower the moisture content of a food the
longer the shelf-life as moisture content also determines the keeping qualities of
seeds, nuts, and fatty products.

Low carbohydrate content and moderately high dietary fibre content lend credence to
the presence of high pectic substances or complex carbohydrates. Consequently, the
increase in percent sucrose due to processing can be attributed to microbial enzyme
hydrolysis of these complex carbohydrates in the fresh Irvingia seed during
fermentation.

Irvingia gabonensis seed had ash content of 9.5 ± 0.3% DM and the product of
processing had 11.6 ± 0.6% DM as ash. Processing method resulted in higher ash
content and this high value predicts the presence of an array of mineral elements as
well as high molecular weight elements [15]. This requires investigation to ascertain
specific mineral elements, as they are very essential for tissue functioning and a
necessity in the dietary requirement for human nutrition. The result also indicated an
increased protein content as a result of the processing method. Fresh Irvingia

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gabonensis seed contained 7.60 ± 0.8% DM as protein and the processed product’s
value was 19.40 ± 0.4% DM as protein. The increase in protein level due to
processing was significant at (p < 0.5) and could be attributed to increased microbial
nitrogen during fermentation as a result of increased production of single cell
proteins. This typical rural processing method has enhanced the food value of
Irvingia seed, by increasing the protein content of the seed from 7.60 ± 0.8% DM to
19.40 ± 0.4% DM in the Irvingia based product. Thus indicating the importance of
this traditional food processing technique in food handling, which should be
encouraged and improved. Another possibility for the observed protein increase on
processing Irvingia gabonensis seed could be attributed to the presence of food yeast
in the final product. This requires microbiological investigation.

The seed contained 66.60 ± 0.8% DM crude fat and the processed product 58.00 ±
1.0% DM crude fat. Although a decrease in the fat content of the product was
observed, this was thought mainly to be due to the method of sample handling
employed during the analysis. The processed product was fairly oily/fatty. Oil drip
during drying for both sample production and preparation for analysis was significant,
as such much of it would have been lost.

Table 2 shows the amino acid profile of the seed and the processed product. All the
essential amino acids recorded increase in values due to processing effect. For the
amino acids that recorded increases due to processing, this could be attributed to their
microbial synthesis during fermentation. For instance, Leucine was the most
abundant essential amino acid in the product 8.30 ± 0.11g/16gN while the seed
recorded 7.60 ± 0.1g/16gN. This was followed by lysine 7.60 ± 0.1g/16gN in the
product and 5.80 ± 0.1g/16g N in the seed. This food product could effectively
complement grains/cereals as lysine is the limiting amino acid in this food group.
Valine, 3.0± 0.01g/16 N in the seed and 4.6 ± 0.01g/16g N in the product was
significant in its level. Of all the detected and quantified amino acids, Glutamic acid
was the most abundant in both the Irvingia seeds and the processed product, having
also recorded an increase due to processing. It seed content was 13.4 ± 0.11g/16g N
and the product 15.2 ± 0.1g/16g N. Serine was the only amino acid that recorded a
marginal decrease in value due to processing, 3.10 ± 0.04g/16g N in the seed and 2.80
± 0.01g/16g N in the product. The decrease was not significant (p < 0.05).The unit
process of drying Irvingia seed mash into “Itugha” was at temperatures above 100OC.
Thus, heating amino acids and sugar together which is known to produce furans,
pyrroles and pyrazines and the fact that some amino acids can also be converted non
enzymatically to carbonyl compounds used for formation of volatiles, can account for
the recorded decrease in levels of some amino acids. This observed decrease could be
attributed to degradation of ?-amino acids, by-products of which must have been used
for formation/production of volatiles [16]. There are other reports on amino acid
composition of some lesser known tree crops, chemical composition and functional
properties of raw, heat-treated and partially proteolysed wild mango (Irvingia
gabonensis) seed flour [17, 18]. There is need to improve upon methods of
processing and utilization of kernels of Irvingia gabonensis (Var. gabonensis and Var
excelsa) to lend credence to it’s domestication and commercialization drive [19, 20].


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CONCLUSION

The high nutritive quality of the Irvingia gabonensis (Var gabonensis) based product
as compared with its seeds implies that appropriate food processing technique is
another approach to improve plant foods’ quality. Since storage is one of the major
problems associated with handling fresh Irvingia seeds, processing these seeds fresh
using pounding and fermentation, not only arrest spoilage but also improves its
nutritive value. This should then encourage farmers to respond positively to
Agroforestry’s campaign for increased Irvingia gabonensis plantation establishment,
and value adding activities to obtain products of higher nutritional quality and longer
shelf-life [21, 22]. In the entire process, the seed cracking to extract the cotyledons
was most laborious and difficult. From Gabon to Cameroon and Nigeria, people
utilize different techniques to extract these Irvingia kernels. As was the case with this
work, fruits were allowed to ferment and the kernel extracted wet. Alternatively, they
can be extracted from fruits in the fresh state or fruits are fermented and sun-dried
before extracting. For the fresh fruits sharp knives are used to cut the fruit open while
in the fermented and/or dried state, heavy objects (especially stones) are used to crack
the nut. All these methods are hazardous and so the vegetative propagation of
Irvingia gabonensis should be directed towards varieties whose nuts slip open
naturally [23].


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Table 1: Proximate Composition of Fresh Bush Mango Seed and Processed Food
Product Samples (% Dry Matter)
Constituent Fresh
Irvingia
Seed
Processed product
Moisture
5.20 ± 0.60
2.10 ± 0.80
Dry Mater
94.80 ± 2.10
97.90 ± 1.10
Ash
9.50 ± 0.30
11.60 ± 0.60
Crude Protein
7.60 ± 0.80
19.40 ± 0.40
Crude Fat
66.60 ± 0.80
58.00 ± 1.00
Crude Fiber
1.90 ± 0.40
1.80 ± 1.00
Dietary Fiber
18.20 ± 1.80
12.30 ± 0.20
% Sucrose (starch)
2.10 ± 3.50
9.60 ± 3.10

Values are means of three independent determinations ± Standard deviation.
Significance was accepted at P < 0.05

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Table 2: Amino Acid Profile of Fresh Bush Mango Seeds and Processed Product
(g/16gN of Sample)
Amino Acid
Fresh Irvingia Seed
Processed Product
Leucine
7.60 ± 0.12
8.30 ± 0.11
Isoleucine
3.20 ± 0.04
4.50 ± 0.10
Methionine
1.30 ± 0.09
1.40 ± 0.03
Threonine
2.30 ± 0.30
3.10 ± 0.10
Tryptophan
1.50 ± 0.05
1.60 ± 0.05
Valine
3.00 ± 0.01
4.60 ± 0.01
Phenylalanin
2.10 ± 0.20
2.30 ± 0.20
Histidine
1.70 ± 0.11
1.90 ± 0.10
Lysine
Aspartic acid
5.80 ± 0.10
7.60 ± 0.10
Cystine
4.80 ± 0.10
5.10 ± 0.10
Serine
2.20 ± 0.10
2.40 ± 0.10
Glutamic acid
3.10 ± 0.04
2.80 ± 0.01
Proline
13.40 ± 0.11
15.20 ± 0.10
Glycine
2.40 ± 0.06
3.40 ± 0.10
Alanine
3.90 ± 0.11
5.40 ± 0.10
Tyrosine
3.20 ± 0.01
3.60 ± 0.01
Arginine
1.50 ± 0.16
1.70 ± 0.20

6.10 ± 0.13
6.70 ± 0.14

Mean of three determination ± standard deviation.
Significant difference was accepted at P< 0.05




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