Isoflavone levels in soy foods consumed by multiethnic populations in Singapore and Hawaii

Concentrations and glucosidic conjugation patterns of isoflavones were determined in soy foods consumed by multiethnic populations in Singapore and Hawaii. Six raw and 11 cooked food groups traditionally consumed in Singapore and 8 food groups consumed in Hawaii were analyzed by reversed-phase high-pressure liquid chromatography with diode array detection. Mean total isoflavone levels varied between 35 and 7500 ppm, with the lowest values found in soy milk and burgers and the highest levels observed in soybean and its seeds and in supplements. Total isoflavone levels and conjugation patterns varied as a function of soybean variety, storage conditions, and food processing. A large contribution to the differences in total isoflavone content between food groups was due to the water content in foods and to leaching of polar analytes into the water phase during boiling. Soy protein drinks and traditional soy foods were found to possess very similar isoflavone amounts considering usual serving sizes.