Effects of cooking on antinutrients and antioxidant properties of different accessions of winged bean (Psophocarpus tetragonolobus)

Asides from its robust nutritional profile, Psophocarpus tetragonolobus also possesses other health-promoting attributes. Hence, this study was designed to investigate the antinutrient content and antioxidant property of five different varieties of raw and cooked P. tetragonolobus. The varieties studied included, the indigenous variety (designated local) and four improved varieties (designated: T11, T31, T125, T154). Antinutrients like phenolic, tannin, glycoside and phytate concentrations were determined using standard methods while 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was carried out to ascertain the antioxidant activity. Phytate, cyanogenic glycosides and tannin levels were significantly (p<0.05) reduced due to cooking in T11 variety. In T125 variety, tannin was significantly lower in the cooked sample compared to the raw sample. However, the phenolic content in the T125 variety increased significantly (p<0.05) due to cooking. There was no significant difference in antioxidant activity between the raw and cooked samples across the five varieties. However, the improved varieties showed higher antioxidant activity compared to the local. Based on these results, the cooking process reduced the phytate, cyanogenic glycosides and tannin levels in the T11 variety while only the tannin level in T125 variety was significantly reduced. However, the antioxidant activity of P. tetragonolobus was not significantly impacted by cooking.