Daily intake of isoflavones based on the market basket method

Daily intake of isoflavones (daidzin, glycitin, genistin, daidzein, glycitein, and genistein) was determined quantitatively, based on the market basket method. Acid hydrolysis during extraction of foods was chosen to convert phytoestrogenes into the respective aglycons, facilitating HPLC analysis and allowing quantitation of total isoflavones as aglycones including both originally present glycosides and "free" aglycones. The isoflavones were extracted from samples with methanol and determined by reversed-phase HPLC analysis using a linear gradient of methanol-water as the eluent. From the results of hydrolysis, the daily intake of total isoflavon was 38.1 mg/adult Japanese. The values obtained by the market basket method and the National Nutrition Survey method were similar.