Antioxidant properties, phytochemical composition, and antiproliferative activity of Maryland-grown soybeans with colored seed coats.

This study characterized and compared 18 colored seed coat soybeans for the isoflavone, total phenolic, and cyanidin-3-glucoside (Cy-3-glc) contents of their flour extracts and the fatty acid composition and carotenoid and alpha-tocopherol contents of their oils. Antioxidant assays also assessed activity of the flour extracts against peroxyl, hydroxyl, and ABTS(+) radicals. Black seed coat soybeans had the highest TPC, ORAC, HOSC, and ABTS(+) radical scavenging values, in addition to the highest isoflavone content, and were the only color to contain Cy-3-glc. Five soybeans (two black and one each brown, yellow, and green) were selected to test their effects on HT-29 human colorectal cancer cell growth. The effects of the hydrolyzed and unhydrolyzed extracts were compared to an aglycone isoflavone standard mixture of the same total molar concentration as the highest soybean concentration of 15 mg of seed flour equiv/mL of treatment media. All high doses of hydrolyzed soybean treatments except the green genotype significantly reduced cell number compared to control at 3 h of treatment time, whereas the high dose of isoflavone standard treatment took 72 h to show a significant reduction (P < 0.05).