Quantitative Analysis of Daidzin, Daidzein, Genistin and Genistein in Various Foods by HPLC

A method was developed for the separation and analysis of isoflavone β-glycoside conjugates (daidzin, genistin) and aglucones (daidzein, genistein) in various foods.The isoflavones were extracted from dried samples with 80% aqueous methanol and from aqueous samples with methanol, and analyzed by reversed-phase HPLC using a gradient of methanol-water as the eluent.The recoveries of four kinds of isoflavones added to various foods were in the range of 84-104%. The limit of detection was 0.1μg/g in samples.Using the proposed method, 205 samples of commercial foods and other products were analyzed. Large amounts of isoflavones were detected mainly in soybeans and soy products. For example, in dry soybean seeds (n=12), daidzin was at the level of 270-1, 100μg/g, daidzein at 20-270μg/g, genistin at 370-1, 200μg/g and genistein at 21-350μg/g.