The contents and distributions of major isoflavones in commercial soy products

This study investigated the isoflavone content and the in vitro antioxidant ability of various traditional soybean products sold in supermarkets. The distribution and content of four major isoflavones, daidzin plus genistin, daidzein, and genistein were analyzed by HPLC, while the in vitro antioxidant ability was evaluated by measuring the percentage inhibition of the oxidation of linoleic acid. It was found that the distribution and content of isoflavones varied in different traditional soy products. Glycosidic isoflavones (genistin and daidzin) seemed to be the major isoflavones in unfermented products, while genistien was dominant in fermented bean curd but not in miso. Unfermented soy products had better antioxidant abilities according to the results from the in vitro test. However, further investigations are necessary to determine the in vivo antioxidant effects.