A correlation between the level of phenolic compounds and the antioxidant capacity in cooked-with-rice and vegetable soybean (Glycine max L.) varieties

This study was undertaken to determine the content of phenolic compounds contained in embryo, cotyledon and seed coat of nine soybean (Glycine max L.) varieties. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity was also measured to determine the correlation between the level of phenolic compounds and antioxidant capacity. A total of 10 anthocyanin constituents and 21 phenolic compounds was detected and quantified. In all nine varieties, the seed coat and cotyledon had the highest and lowest levels of phenolic compounds and anthocyanins, respectively despite the fact that all of them showed a wide variation in total amounts of phenolic compounds and anthocyanins in seed coat, embryo, and cotyledon. The seed coat tissue, but not other seed parts, showed a strong correlation between the seed coat color and the content of both phenolic compounds and anthocyanins. The brown and black soybean seed coat contained much higher levels of phenolic compounds and anthocyanins in seed coat tissue than the yellow or green coat soybean. Among the individual phenolic compounds, syringic acid (214 mu g g(-1) ) and chlorogenic acid (31 mu g g(-1)) were highest in seed coat and embryo, respectively. Myricetin was highest both in whole seed (16.7 mu g g(-1) ) and cotyledon (16.0 mu g g(-1)), being equivalent to 20 and 30% of total phenolic compounds, respectively. Among the 10 anthocyanins, cyanidin-3-glucoside was found to accumulate at the highest level in the seed coat (1783 mu g g(-1) ), whole seed (106 mu g g(-1)) and embryo (0.35 mu g g(-1)), which correspond to 95, 96, and 40% of the total anthocyanin contents, respectively. The cotyledon accumulated pelargonidin-3-glucoside (0.39 mu g g(-1)) at the highest level that is equivalent to 62% of total anthocyanin contents. DPPH activity was found to have a strong correlation ((***)Probability < 0.001) with phenolic compounds (0.67(***)) and anthocyanins (0.70(***)).