A comparative assessment of total phenolic content, ferric reducing-anti-oxidative power, free radical-scavenging activity, vitamin C and isoflavones content in soybean with varying seed coat colour

Reports concerning anti-oxidative properties of yellow, green and black soybean seeds available in the literature are insufficient and limiting. In the present investigation, mature seeds of 18 genotypes, 6 from each type of soybean i.e. yellow, green and black, were assessed for total phenolic content (TPC), ferric reducing-anti-oxidative power (FRAP), 2,2-diphenyl-1-picrylhydrazine (DPPH) free radical-scavenging activities (FRSA). Isoflavones and vitamin C, the antioxidants, were also determined in all the soybean genotypes. Significant genotypic variation was observed for TPC, FRAP, FRSA, isoflavones and vitamin C within each type of soybean. Maximum genotypic variation (7.27-fold) was observed for TPC in black soybean. Average FRAP value of yellow soybean was significantly (p < 0.05) lower than black and green soybeans. Average FRSA in black soybean was significantly higher than yellow and green soybean group. Average total phenolic content and isoflavones levels were not significant across different types of soybean. Correlation studies indicated significant (p < 0.05) positive correlation between FRSA and TPC in black soybean. Our results suggest that antioxidant constituents other than isoflavones contribute significantly to the FRSA in black soybean genotypes.