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Four cultivars of brown cowpea (Vigna unguiculata. L. Walp) were analysed for their proximate composition, phytic acid, polyphenols and protein and starch digestibility (in vitro). Crude protein values ranged from 20.07 to 24.60%. Ether extract and crude fiber contents varied from 1.77 to 1.96% and 4.27 to 4.95%, respectively. All the four cowpea varieties differed significantly for their starch content which ranged from 46.84 to 53.63%. Antinutrients, phytic acid and polyphenols, showed significant variations among the varieties. In vitro digestibility of protein and starch of grains had a narrow variation. The variety CS-46 containing minimum amount of antinutritional factors had the highest protein digestibility.
Introduction
Cowpea (Vigna unguiculata L. Walp) is a legume consumed extensively in Africa and to a lesser extent in Asia. In India, it is mostly consumed as cooked whole seeds and immature seeds. Cowpeas are an important source of calories and vitamins as well as protein. The seed is 25% protein and 65% carbohydrate and contains thiamin, riboflavin and niacin (0.74, 0.42 and 2.81 mg/100 g, respectively) (Bressani, 1985). The nutritional quality of cowpea is poor due to the presence of several antinutritional factors such as trypsin inhibitors, flatulence causing oligosaccharides, phytic acid and polyphenols; low protein digestibility and deficiency of sulphur amino acids. Cowpeas have been shown to contain high levels of polyphenols, which play an important role in the reduction of protein digestibility (Elias et al., 1979) and starch digestibility (Thompson & Yoon, 1984). Phytic acid widely distributed in food grains lowers the bioavailability of minerals (Davies & Nightingale, 1975) and inhibits proteases and amylases (Singh & Krikorian, 1982).
In the recent past, several high-yielding cultivars of cowpea have been developed in India; however, the information on their nutritive value is lacking. The efforts put in by plant breeders in evolving a high-yielding variety may be of little significance unless it is evaluated nutritionally. The new varieties may not always be different in their nutritive value from the traditional varieties, there is a need for continuous monitoring of the changes in contents of both nutrients and antinutrients that accompany breeding. Therefore, the objective of the present study was to determine the proximate composition, level of antinutritional factors, phytic acid and polyphenols present in four brown cowpea varieties and...