Chemical Composition and Physicochemical Characteristics of Two Varieties of Bambara Groundnut (Vigna subterrenea) Flours
Proximate, mineral composition and physicochemical characteristics of two varieties of bambara groundnut (Vigna subterranean) flours were determined using standard techniques. The two varieties (cream coat and dark red coat) of bambara groundnut have comparable mean values of total ash, crude protein and carbohydrate. (by difference) of 4.28 and 3.89%; 11.56 and 11.05% and 73.30 and 73.87%, respectively. But there are little variations in the values of moisture, crude fat and crude fibre. The two varieties were found to be good sources of essential minerals such as Fe, Na, K, Mg and Ca but Cu, Mn and Zn contents were low. Pb, Cd and Cr were not detectable. The results of physicochemical characteristics of bambara groundnut oils showed that they have similar mean values of the following parameters: Free fatty acid.85 and 4.80 mg g-1; Acid value, 0.92 and 0.98; Saponification value24.9 and 140.5 mg KOH g-1; Iodine value21 and 120 mg iodine g-1; peroxide value86 and 290 and specific gravity 0.88 and 0.85 for cream coat and dark red coat, respectively indicating that they are drying oils and edible.
Bambara groundnut (Vigna subterranean (L.) Verdc.) belongs to the legumiosae, subfamily papilionoideae. It is commonly known as Gujiya among the Hausa tribes of Nigeria. Bambara groundnut was once said to be the third most important grain legume after groundnut (Arachis hypogaea L.) and cowpea (Vigna unguiculata (L.) Walp) in Sub-Saharan Africa (Rachie and Silvestre, 1977; Johnson, 1968). It is a major source of cheap dietary phytoprotein for both humans and livestock in the Sudano-Sahelian parts of tropical Africa and Asia where animal protein is expensive (Linnemann, 1994). This legume which was formally popular in the northern part of Nigeria because it is well favoured by dry lands and environmental climatic conditions has been gradually replaced over the course of decades by the groundnut particularly in more productive areas.
The reported works on the Bambara groundnut (BBG) seeds included the evaluation of chemical composition of BBG (Enwere and Hung, 1996; Temple and Aliyu, 1994; Poulter, 1981) investigation of fatty acids composition of BBG seed oils (Gaydolel et al., 1983; Ferrao et al., 1987) and determinations of functional properties of BBG seed flour (Adebowale and Lawal, 2004; Onimawo et al., 1998). Processing treatment which has improved the utilization of BBG has been reported by Akpapunam et al. (1996).
This research was undertaken to determine the proximate and mineral compositions and physicochemical characteristics of two common varieties of BBG seed flours producing in Nasarawa state, Nigeria in order to supplement, contradict and/or add to existing data in literature. Such data will be considerable values to dieticians, food scientists and manufacturers, medical personnel, nutritionists and also in the preparation of a much needed food composition table for Nigeria.
MATERIALS AND METHODS
Bambara groundnut seeds were collected from the farm located at Keffi, Nasarawa State, Nigeria during the period of harvesting in December 2004. Two different colour varieties of cream coat (A1) and dark red coat (B1) were identified, sorted and screened to remove the bad seeds. Their corresponding dehulled samples labelled A2 and B2 were then processed for analysis. The dehulled seeds were dry-milled into fine flours. The removal of the hull and the preparation of the dehulled samples were done according to the method of Oshodi and Ekperigin (1989).
The proximate analyses of the samples for moisture, total ash and crude fibre
were carried out in triplicate using the methods described in AOAC (1990). The
nitrogen was determined by the micro-Kjeldahl method described by Pearson (1976)
and the nitrogen content was converted to protein by multiplying by 6.25. Carbohydrate
was determined by difference. All the proximate values were reported in %.
The oil sample was extracted from the seed flours by soxhlet extraction using petroleum ether of Analar grade (British Drug Houses, London), boiling range 60-80°C for 8 h (James, 1996).
The minerals were analysed by dry-ashing the samples at 550°C to constant weight and dissolving the ash in volumetric flasks using distilled, deionised water with a few drops of concentrated hydrochloric acid. Sodium and potassium were determined by using a flame photometer (Model 405, Corning, UK) using NaCl and KCl to prepare the standards. All other metals were determined by atomic absorption spectrophotometer (Perkin-Elmer Model 403, Norwalk CT, USA). All determinations were done in triplicate. All chemicals used were of analytical grade (BDH, London). Earlier, the detection limits of the metals had been determined according to Techtron (1975). The optimum analytical grade was 0.1 to 0.5 absorbance units with a coefficient of variation of 0.87-2.20%. The minerals were reported as mg/100 g.
The physicochemical analysis of the seed oil for acid value, iodine value, saponification value, peroxide value, free fatty acid and specific gravity, were carried out according to the methods of AOAC (1990).
The research study was conducted between February and October 2005 in the Chemistry and Industrial Chemistry Laboratories of Nasarawa State University, Keffi and Federal University of Technology, Akure respectively.
RESULTS AND DISCUSSION
The data on the proximate composition, energy and fatty acid values of the cream coat (A2) and dark red coat (B2) of Bambara groundnut seed flowers are shown in Table 1.
The percentages of moisture content, total ash, crude protein and carbohydrate (by difference) of the two varieties (A2 and B2) are comparable with a difference of less than 1.0 while difference of about 2.0% are observed in the percentages of crude fat and crude fibre.
The moisture content values were generally low but are within the range expected of most legumes (Olaofe and Sanni, 1988; Oyenuga, 1968). The low moisture content will afford a long shelf-life for BBG dehulled seeds. B2 seed flour with higher moisture content would imply higher susceptibility to microorganism attack than the A2 seed flour.
The crude fat content value of A2 compares favourably with the value
of 6.0% of bambara groundnut as reported by Elegbede (1998).
|| Proximate composition of two varieties of BBG seed flours
|Values are mean±standard deviation of triplicate determinations,
a Calculated fatty acids (0.8 x Crude fat), b Calculated
metabolisable energy (KJ/100 g) (Protein x 17+Fat x 37+Carbohydrate x 17)
But this crude fat content does not qualify BBG as oil-rich legume when compared
with soybean (22.8 and 23.5%) reported by Salunkhe et al. (1985) and
Paul and Southgate (1980); pumpkin seed (49.2 and 47.0%) by Aisegbu (1987) and
Fagbemi and Oshodi (1991) and C. vulgaris (47.9-51.1%) by Ige et al.
The crude protein values of the two varieties which are nearly the same are not comparable with 24% for BBG reported by Poulter (1981); 175-21.1% by Onimawo et al. (1998); 22.2% by Ferao et al. (1987) and 16.6-18.2 g/100 g by Amarteifio and Moichubedi (1997). The reason for the differences may be due to the genotype and the environment conditions under which they are grown (Salunkhe et al., 1985; Aremu et al., 2005). The crude fibre, total ash and carbohydrate content values are comparable with some reported works in the literature (Poulter, 1981; Amarteifio and Moichubed, 1997; Shils and Young, 1988).
The calculated free fatty acids for the two varieties is moderate enough which suggest that BBG seeds oil is suitable for edible purposes and can also be utilized for industrial purposes. The calculated metabolisable energy values of 1691.26 KJ/100 g and 1595.34 KJ/100 g for A2 and B2, respectively showed BBG seeds have energy concentrations favourably comparable to cereals.
Table 2 represents mineral content of two varieties of BBG seed flours. The values recorded for the two varieties are comparable with little variations in some minerals.
Lead (Pb), cadmiun (Cd) and chromium (Cr) were not detected in any of the varieties
indicating that BBG seeds are free from toxic and undesirable minerals which
are harmful to the body. The least and abundant minerals in the two varieties
of BBG seed flours were Cu and Ca, respectively. Calcium is important in blood
clotting, muscle contraction and in certain enzymes in metabolic processes.
Magnesium is the next highest mineral composition in both varieties. It has
been reported that Magnesium is an activator of many enzyme systems and maintains
the electrical potential in nerves (Ferrao et al., 1987). The values
obtained for Na and K are reasonably high in both varieties and may satisfy
the nutritional needs of the consumers.
||Mineral content of two varieties of BBG seed flours (mg/100
g of sample)
|Values are Mean±Standard deviation of triplicate determinations,
ND = Not Detected
|| Physicochemical characteristics of two varieties of BBG Seed
|a Values are mean±standard deviation of
Sodium and potassium are required to maintain the osmotic balance of the blood
fluids, pH of the body, regulate muscle and nerve irritability and control of
glucose absorption (Fleck, 1976; Pike and Brown, 1967). The ratio of sodium
to potassium, Na/K, in the body is of great concern for prevention of high blood
pressure. Na/K ratio less than one is recommended. Table 2
further shows the Na/K ratios for the two varieties of BBG seed flours. The
values obtained which were < 1 show that the food under consideration would
probably reduce high blood pressure (Nieman et al., 1992).
The values of Fe, Mn and Zn which are also shown in Table 2 are evenly distributed between the two varieties. Iron is reported to be very important for normal functioning of the central nervous system (Vyas and Chandra, 1999; Adeyeye and Fagbohun, 2005). Iron also facilitates the oxidation of carbohydrates, proteins and fats. Zinc is present in all tissues of the body and it is a component of more than fifty enzymes. Consumption of meat (or other animal products) with vegetable enhances the absorption of both Iron and Zinc (Bender, 1992; NAS, 1971). Generally the values for most of the minerals in this present study are less than that of some oil seeds reported by Olaofe et al. (1994).
The results of the physicochemical characteristics of two varieties of BBG
seed flours are shown in Table 3. A2(cream coat)
seed oil is yellow in colour while B2 (dark red coat) is light yellow.
The values obtained for all the physicochemical parameters are comparable between the two varieties. The free fatty acids values for A2 and B2 seed oils respectively are comparable with the value of 4.20 mg g-1 reported by Ferrao et al. (1987). Free fatty acids can stimulate oxidative determination of oils by enzymatic and/or chemical oxidation to form off-flavour components (Akintayo and Bayer, 2002). The specific gravity for BBG oils (A2 and B2) are less that one (<1) indicating that it is less dense than water. The iodine values obtained for the two varieties of BBG oils place them in the drying group oil since drying oils have an iodine value above 100 (Duel, 1951). The acid values for A2 and B2 which compare favourably with adenopus brevilorus seed oils (Akintayo and Bayer, 2002) and Hausa melon seed oil (Oladimeji et al., 2001) showed that BBG oil is an edible oil. Both oils showed high saponification values suggesting their utilization in production of liquid soaps and shampoos. The unsaponifiable matter values of 2.35±0.15 (A2) and 2.25±0.3% (B2) are favourably compared with 2.44% reported by Gaydolel et al. (1983).
The present study indicates that the chemical composition of bambara groundnut is independent of the variety. The crude protein and fat were very low incomparable with soybean and groundnut but they were good sources of essential mineral. The suitability of the oils for domestic use and utilization in production of liquid soap and shampoos are also revealed.
The authors are very grateful to Prof. L. Lajide of Chemistry Department, Federal University of Technology, Akure, Nigeria for assisting in getting some of the facilities used and Mr. Bernard Ashkaa of Nasaraw State University Keffi for Technical Assistance.
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