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Research Article
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Proximate Analysis and Physico-Chemical Properties of Groundnut (Arachis hypogaea L.) |
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V.N. Atasie,
T.F. Akinhanmi
and
C.C. Ojiodu
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ABSTRACT
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Proximate, physico-chemical and elemental analysis of groundnut were determined. The results showed that the groundnut oil contained 47.00% fat, 38.61% protein, 5.80% moisture, 1.81% carbohydrate, 3.70% crude fibre and 3.08% ash. Minerals (mg/100g) included: Na (42.00±0.71), K (705.11±0.86), Mg (3.98±0.04), Ca (2.28±1.94), Fe (6.97±1.62), Zn (3.20±0.11), P (10.55±0.68). The physico-chemical characteristics showed; saponification value, 193.20mgKOH/g, iodine value 38.71 (g/100g), acid value 5.99 (mgKOH/g), free fatty acid (mgKOH/g) 3.01 peroxide value 1.50 (meq/kg) and refractive index 1.449. The predominant fatty acid was found to be oleic acid (41.11%). The groundnut can thus be considered as a good source of protein with high nutritional value.
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Introduction
Good nutrition is a basic human right. In order to have a healthy population
that can promote development, the relation between food, nutrition and
health should be reinforced. In developing countries, one of the ways
of achieving this is through the exploitation of available local resources,
in order to satisfy the needs of the increasing population (Achu et
al., 2005). Knowledge of the nutrition value of local dishes, soup
ingredients and local foodstuffs is necessary in order to encourage the
increase cultivation and consumption of this highly nutritive nut. The
consumption will help to supplement the nutrients of the staple carbohydrate
foods of the poor who cannot afford enough proteins foods of animal origin
(Achu et al., 2005). Several studies have been carried out on the
chemical and functional properties of kernels and defatted cakes of groundnut
(Arachis hypogaea L.), an under exploited nut, largely consumed
by the western and most populations in Africa. (Weiss, 1983; Bansal et
al., 1993; Pancholly et al., 1978; Ahmed and Young, 1982).
They showed these nuts as good source of lipid and protein and the defatted
cakes could be used as protein supplement in human nutrition. Groundnuts
(Arachis hypogaea L.) have various uses:- adds to good nutritional
value, as soup thickener and when cooked, roasted, dried or fried serve
as snacks. Sometimes, paste used as margarine or butter. Moreso, there
are less expensive, widely distributed easily cultivated, consumed and
sold by the masses.
Groundnut, Arachis hypogaea L. also known as peanut or earthnut
is a native to a region in eastern south America (Weiss, 1983). It is
grown as an annual crop principally for its edible oil and protein rich
kernels seeds, borne in pods which develop and mature below the soil surface.
The groundnut, a herbaceous plant of which there are varieties, common
in the united states, grow up to 30-46 cm high do not spread. Runner varieties,
the most common in the West Africa are shorter and run along the ground
for 30-60 cm (Asiedu, 1992). Peanut (Arachis hypogaea L.) is now
grown world wide in the tropic and temperature zones primarily as an oilseed
crop (Bansal et al., 1993). Peanut seeds make important contribution
to the diet in many countries. The fatty acids composition of the endogenous
fats ranges from 22 to 30% (5). and the average oil content may reach
50% (Pancholly et al., 1978; Derise et al., 1974). These
play an important role in determining shelf life, nutrition and flavour
of peanuts seeds. Chemical composition of Aboriginal peanut seeds were
analyzed (Nelson and Carlos, 1995) among six cultivars, the result showed
presence of oil, protein. The fatty acid composition in (g/100g of total
fatty acids) showed indicators of oil stability and shelf life (Ahmed
and Young, 1982; Branch et al., 1990). These two fatty acids can
account for up to 80% of the totalfatty acids (Young and Walter, 1972;
Abdel Rahman, 1982ab; Woodroof, 1983). (Sekhon et al., 1972) have
shown that the high linoleic acid content, with its two unsaturated bonds,
is undesirable because it decreases the shelf life of the product. Studies
have also indicated high carbohydrates in newly germinated groundnut kernels,
but the levels begins to fall at an average of 46%, 5 weeks as the seeds
starts to store oil (Abdel Rahman, 1982ab).
Before the oil boom in Nigeria, there was the groundnut pyramid in Jos,
Northern Nigeria. The nutritive value of food was rich as
the nut is affordable and use in diverse ways, with the oil boom, all
focus is on the petroleum and little attention is given to the cultivation
of the nut, which serve as good source of oil, protein, employment and
export to the country.
The purpose of this study is aimed at evaluating the nutritional value
of the seeds grown in Nigeria. This will aid promotion of the use of the
nuts in the management of the nutrition-related problems in Nigeria in
particular and in Africa in general. It consists of analyzing the moisture,
crude protein, total lipids, ash and soluble nitrogen and total protein
content in the defatted seeds elemental analysis of the mineral content.
The physico-chemical characteristics of groundnut by extracting the oil
from the groundnut seeds.
Materials and Methods
Sample collection and treatment: Shelled groundnut was collected
from groundnut processing industries, transported in polythene bags to
the laboratory, then sun dried for about two hours, later dried in an
oven at 100-107°C, the red skins were removed squeezed with hand,
craked into small pieces, placed in an airtight bottle and stored in the
desiccator for analysis.
Assays: The moisture content was determined by drying in an oven
at 100-107°C to constant weight (AOAC, 1980). The crude fat was determined
by continuous extraction in a Soxhlet apparatus for 18h using hexane as
solvent, ash by incinerating in a furnace at 550°C, crude fibre by
sequential hot digestion of the defatted samples with dilute acid and
alkaline solutions and total carbohydrate by difference according to (AOAC,
1980). The crude protein content was evaluated by digestion of the sample
using Kjeldahl’s method (Devani et al., 1989) nitrogen determination
by a spectrophotometric method described by (Devani et al., 1989).
All analysis were done in triplicate.
Elemental analysis: Atomic absorption spectrophoto-meter Buck
210 VGP, with computer readout was used, the elements of interest were
Na, Mg, Zn, Fe, Ca, K and P. For phosphorus the Vanadate colorimetric
by modified phosphomolybdate method was used.
Procedure: The phosphorus was determined as phosphate by the vanadium
phosphomolybdate (vanadate) colorimetric method in which the phosphorus
present as the orthophosphate reacted with the vanadate-molybdate reagent
and produced a yellow orange complex, at absorbance of 420 nm. This modified
colorimetric procedure was employ using 5% solution of molybdic acid in
10N sulfuric acid in a medium of 26% acetone by volume. The yellow complex
formed by phosphate with vanadate and molybdate in acid has a high precision
in the quantitative colorimetric determination of phosphorus. The mixed
reagent of vanadate and molybdate was allowed to stay a few days before
use, as it tends to precipitate. Only one molybdate was used in acid solution
and acetone-water solution as the solvent. The former eliminates the need
to age the reagent. The solvent, intensified the phosphomolybdate color
and allowed complete solution of the organic phosphates. The extraction
process was simplified by the use of water-soluble solvent (acetone).
For complete color development, the final volume solution was as low as
30% and as high as 90% acetone by volume with very little change in color
intensity which took place between the concentration. The color formed
immediately and was stable for some hours and the phosphorus pentoxide
was detected using the Klett-Summersion photoelectric colorimeter at 430
mμ.
Physico-chemical characteristics
Fatty acid determination using gas chromatography: Gas chromatography
was used in which nonvolatile fatty acids were chemically converted to
the corresponding volatile methyl esters. The resulting volatile mixture
was analyzed by gas chromatography.
Procedure: About 2 grams of the oil was weighed, in a small beaker
and dissolved in 50 mL of chloroform, transferred into a hundred volumetric
flask and diluted to the mark with chloroform. 1 mL of the unknown sample
was transferred into a 10 mL screw top culture tube with a Teflon liner.
Exactly 1.00 mL of a standard solution of 0.814mg/ml pentadecanoic acid
was then added. The glycerides in the oil sample was esterified as well
as the pentadecanoicacid standard, the efficiency for esterification of
the standards is the same as that of the glycerides, the response of the
detector to each of the fatty acid methyl ester with the internal standard
was the same, with this we were able to qualify the amount of each ester
in the fat by comparing the integrated areas with the known concentration
of the standard. Most of the chloroform was evaporated under a stream
of nitrogen until-100 μL of the solution remained. 1 mL of interesterification
reagent {25vol% of a 12% BF3-methanol solution, 20vol% benzene
and 55vol%methanol} was added. The tube was flushed with nitrogen, sealed
and heated in a 100°C water bath for 30 minutes-after which the methyl
esters was extracted with hexane and H2O, the final mixture
of the reagent, hexane and water were in the ratio 1:1:1 (adding 1 mL
each of hexane and water to the reaction mixture). The mixture was shaken
thoroughly for 2 minutes. A stable emulsion was formed which was broken
by centrifugation. Half of the top hexane phase was transferred into a
small text tube for injection.
The iodine value was determined by the WIJ’s method already described
by (Bansal et al., 1993).
Table 1: |
Proximate composition %.and Fatty acid profile of
groundnut |
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Table 2: |
Physico-chemical characteristics of Groundnut oil |
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Table 3: |
Mineral content (mg/100g) of groundnut oil |
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Results and Discussion
Results of the proximate composition of the groundnut investigated is
shown in Table 1. The moisture content is 5.80%, ash
content 3.08%, crude fibre 3.70%, crude protein 38.61%, fat content 47%
and carbohydrate (by difference) 1.81%. The fat, protein and ash contents
are similar to the reports of Nelson and Carlos (1995) which indicated
the fat content among 29 cultivars between 47.0%-50.1%, protein 26.3%-30.9%,
ash 2.4-2.7%. The moisture content and crude fibre agreed with that of
NAS (1980) of 5.0% and 3.0% respectively. The fat content is important
in diets as it promotes fat soluble vitamin absorption. It is a high energy
nutrient and does not add to the bulk of the diet. The crude fibre in
this result indicates the ability of groundnut to maintain internal distention
for a normal peristaltic movement of the intestinal tract; a physiological
role which crude fibre plays. Diets low in crude fibre is undesirable
as it could cause constipation and that such diets have been associated
with diseases of colon like piles, appendicitis and cancer. The carbohydrate
value by difference in this work is very low which shows that groundnut
is more of a body building food.
Table 2 shows the physico-chemical properties of groundnut.
The saponification value, of 193.20mgKOH/g agreed with Pearson’s
(1981), 187-196mgKOH/g. This property makes it useful in soap making.
Iodine value 38.71g/100g indicates low degree of unsaturation and classified
the oil as non-drying oil (80-100g/100g) as recorded for most edible oil,
Pearson (1981). Acid value of 5.99mgKOH/g was close to Arachis (4.0mgKOH/g)
by Pearson (1981) and Soyabean 4.279mgKOH/g (Akanni et al., 2005).
The free fatty acid is 3.0mgKOH/g, this indicate some percentage of fatty
acid present in the oil and that the oil may likely undergo oxidation.
The peroxide value 1.50meq/kg is not far from cotton seed oil of 2.5meq/kg
(Popoola and Yangomodou, 2006). The low value indicates that the oil can
resist lipolytic hydrolysis and oxidative deterioration. The refractive
index, 1.449 showed that the oil contained some double bonds in its fatty
acid composition as reported by Eromosele and Pascal (2003), that refractive
index increases as the double bond increases.
Table 3, is the elemental composition in which the
predominant elements are potassium, sodium and phosphorus, contrary to
Wen-Hesin et al. (1997) which gave the most predominant elements
as potassium, phosphorus, magnesium and calcium. The most abundant mineral
K is expected because it is the most prominent mineral in Nigerian Agricultural
products. The presence of calcium, magnesium, phosphorus is good indication
that the groundnut is rich in the minerals for bone formation calcium
is very essential in blood clothing muscles contraction and in certain
enzymes in metabolic processes. Low Ca/P ratio facilitates calcinations
of calcium in the bone while the Ca/P ratio above two helps to increase
absorption of calcium in the small intestine. Also Na/K ratio is very
important in the body for prevention of high blood pressure. Na/K ratio
less than one is recommended. The Na/K ratio in this work is about 0.06,
which is indicative that the groundnut is very good for human health and
would probably prevent high blood pressure. The fatty acid profile in
Table 1 showed the percentage of oleic acid 41.11% and
palmitic acid 8.17% in good agreement with Nelson and Carlos’31.8%-46.6%
oleic and 9.3%-13.35% palmitic. Presence of oleic acid showed double bond
in the fatty acid.
Conclusion: Groundnut characteristically contained high level
of oil and protein with low level of moisture, ash and carbohydrate, this
makes it a potential source of edible oil. The high protein 38.61% of
the defatted groundnut makes it good as cake for human consumption and
useful as animal feeds. The low moisture content is an advantage when
the shelf life is considered. The low ash content is indicative of low
level of inorganic impurities and qualifies the oil as good source of
mineral element. Though the saponification value is high, a property adequate
for soap making industry, it is not attractive as a raw material because
of its economic and nutritive implications. Low iodine value in the nut
is the suitability for cooking while the peroxide values are indicators
of the ability to resist lipolytic and oxidative deterioration when stored.
Elemental abundance speeds up metabolic process and improve growth and
development (Akanni, 2005).
This work has enabled us to conclude that the nutritive value of groundnut
seeds from Nigeria can be considered a good source of protein. The defatted
seeds can be used to prepare food, as snacks, pastes and used in diets
to prevent against some mineral deficiencies. This will aid to fight against
malnutrition, especially protein-calorie, malnutrition, leading to better
nutrition and health in Nigeria and Africa as a whole. Further research
is being conducted to study the detailed physico-chemical composition
of other kernel nuts and oils in Nigeria, the nutritional quality of the
proteins and lipids.
Acknowledgement
We thank our various universities for assistance, especially the university
of Agriculture Abeokuta, Ogun state, for using the laboratory and equipments.
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