ANTIOXIDANT PROPERTIES OF CONDIMENT PRODUCED FROM FERMENTED BAMBARA GROUNDNUT (VIGNA SUBTERRANEA L. VERDC)

Abstract

ABSTRACT This present study sought to investigate the effect of fermentation on the phenolic content and antioxidant properties of condiment produced from Bambara groundnut seed (Vigna subterranea L. verdc). The seeds were manually dehulled, washed and boiled until adequately softened. The water was later drained off and the seeds were spread in flat calabashes, covered with banana leaves and then wrapped in jute sacks and left to ferment at 37C for 4 days to produce the condiment. Aqueous extracts of fermented and unfermented Bambara groundnut seeds were obtained by homogenizing the seed in distilled water (1:10 w/v) and then centrifuged to give clear supernatants that were subsequently used for the analysis. The total phenol, total flavonoid and the antioxidant properties (reducing power, Fe2+chelating ability, 1,1-diphenyl-2-picrylhydrazyl [DPPH] free radical-scavenging ability, 2,2-azinobis(3-ethylbenzo-thiazoline-6-sulfonate) [ABTS]• radical scavenging ability and OH• radical-scavenging ability) of the extracts were determined. The result of the study revealed that fermented Bambara groundnut seed had significantly higher (P < 0.05) total phenol content (550 mg/100 g), total flavonoid (64 mg/100 g) and nonflavonoid content (486 mg/100 g) than the unfermented Bambara groundnut seed (total phenol [211 mg/100 g], total flavonoid [44 mg/100 g] and nonflavonoid [167 mg/100 g]). The fermented Bambara groundnut seed also had significantly higher (P < 0.05) reducing power, free radical-scavenging ability (DPPH, ABTS• and OH• radicals) and Fe2+ chelating ability than the unfermented seed. Fermentation increases the phenolic content and antioxidant capacity of fermented Bambara groundnut, and condiment produced from fermented Bambara groundnut seed could serve as a cheap functional food. PRACTICAL APPLICATION Bambara groundnut is a highly nutritious legume seed indigenous to Africa, but its consumption is limited due to the presence of antinutritional factors and its hard-to-cook nature. Traditionally, legumes and oil seeds are usually fermented into local condiments which serve as soup thickeners and flavor enhancers in food preparation. Fermentation is being shown not only to improve the nutritional quality of legume seeds but also to increase their antioxidant properties by increasing the polyphenolic constituents, thereby increasing their potentials as functional food (improvement of conventional foods with added health benefits) and nutraceutical sources. However, to encourage the consumption of the underutilized Bambara groundnut, the beans fermented into condiment could be produced on a large scale as a cheap functional food which will encourage the overall consumption of the food crop.