Effect of Boiling and Fermentation on the Anti-Nutritional Factors of Cowpea (Vigna unguiculata) in Oyo State

Cowpea is a major protein source in Oyo State and across Nigeria, but its nutritional value is substantially limited by anti-nutritional factors including phytates, tannins, and trypsin inhibitors that reduce protein and mineral bioavailability. This study evaluates the effects of boiling and fermentation on the anti-nutritional factor content of cowpea varieties marketed in Ibadan, Oyo State. Three varieties of cowpea, white-eye, black-eye, and brown-eye, were subjected to boiling for thirty and sixty minutes, and to natural fermentation for twenty-four and forty-eight hours separately. Anti-nutritional factors quantified include phytic acid by the Wade reagent colorimetric method, tannins by the Folin-Denis method, oxalic acid by the permanganate titration method, and trypsin inhibitor activity by the BAPA substrate method. Hemagglutinin (lectin) activity was assessed by the blood agglutination method. Results show that both boiling and fermentation significantly reduced all measured anti-nutritional factors compared to raw cowpea. Extended boiling at sixty minutes produced greater reductions in trypsin inhibitor activity and phytic acid than thirty-minute boiling. Fermentation for forty-eight hours was more effective at reducing tannins and phytates than twenty-four-hour fermentation. Combined boiling followed by fermentation showed additive reductive effects in preliminary tests. Lectin activity was completely abolished after sixty-minute boiling in all three varieties. These findings support the nutritional value of longer cooking and fermentation processing of cowpea and have implications for dietary recommendations in Oyo State. Keywords: cowpea, anti-nutritional factors, phytate, fermentation, Oyo State.