NUTRITIONAL AND IN VITRO ANTIOXIDANT INVESTIGATIONS OF SELECTED FERMENTED UNDERUTILIZED LEGUMES

Abstract

The effect of fermentation on the antioxidant properties of four selected underutilized legumes; Cajanus cajan L. Millsp (Pigeon pea), Vigna subterranea L. Verde (Barnbara groundnut), Sphenostylis stenocarpa Harms (African yam bean) and Phaseolus vulgaris L. (Kidney bean) was investigated. The beans were cooked for 8 hr, soaked in boiled water [or another 12 hr, .dehuled, and then boiled again for another 4 hr. The cotyledons were drained and later wrapped in jute sacks and left to ferment naturally for 3 - 4 days at 37°C to produce local condiments. The nutrient, antinutrient and mineral content of both the fermented and unfermented legumes were analyzed. Antioxidant properties as typified by phenolic content, reducing property, free radical scavenging ability and inhibition of lipid peroxidation in the liver of an adult male cow was also investigated. The results revealed fermented legumes to have higher nutritional , qualities. The phenol content (mg TA/g) ranged from 7.5 (V subterranea) to 3.8 (C cajan) in the fermented legumes and 5.8 (V subterranea) to 2.5 (C cajan) in the unfermented legumes. The ability of the polyphenol content of the legumes to reduce Fe3 + to Fe2 + as a measure of their antioxidant activities revealed that the fermented legumes exhibited higher reducing power (00 700) 0.78 (V subterraneai to 0.33 (C cajan) than the unfermented legumes 0.74 (I/. subterraneai - 0.20 (C cajan). Polyphenols of the fermented legume were better scavengers of stable I,I-diphenyl 2-picryhydrazyl radicals (%) [91. 3 (S stenocarpai (056.5 (C cc!j((n)l than the unfermented ones [84.9 (V subterraneai to 40.2 (C cajan)); they inhibited lipid peroxidation more as seen by measuring the reduction in the thiobarbituric acid reactive species TBARS in vitro in the liver of an adult male cow with a dose-dependent response than the ., unfermented legumes. Hence, it was concluded that, fermentation process improved the nutritional quality, increased phenolic distribution and also the overall antioxidant activities or the legumes; Vigna subterranea was found to be the most promising.