Isoflavone, a group of phytoestrogen, reduces postmenopausal symptoms and the risk of osteoporosis of women. Glycosidic forms of isoflavones are presented in non-fermented soyfoods such as tofu and they are less bioavailable than the aglycone isoflavones. Aglycone forms of isoflavones or more bioavailable forms can be increased by acid hydrolysis during tofu processing. The present study investigated the possibility of increasing the aglycone forms of isoflavones by acid hydrolysis. We used five types of tofu in this study: soybean tofu with hydrolysis, soybean meal tofu with hydrolysis, soybean tofu in general process, soybean meal tofu in general process, and commercial tofu. Defatted soybean meal was used as the major ingredient in the tofu which was made by using the new method—acid hydrolysis. To identify the isoflavone quantities in all five types of tofu, high performance liquid chromatography with diode array detection (HPLC-DAD) analysis was employed. The genistein ratio between hydrolyzed tofu and standard tofu was 1:1-8, and the daidzein ratio between hydrolyzed tofu and standard tofu was 1:6-12. The five types of tofu were analyzed for the crude protein and micronutrients such as calcium (Ca), magnesium (Mg), potassium (K), iron (Fe), zinc (Zn), and selenium (Se) by the modified Kjeldahl method and inductively coupled plasma emission spectroscopy (ICP-ES), respectively. The mean crude protein concentration of hydrolyzed tofu from soybean meal was 40.8%. In addition, especially the hydrolyzed soybean meal tofu showed the higher concentration of Ca (27,307 mg/kg) and K (25,553 mg/kg). By and large, soybean meal tofu with acid hydrolysis is a rich source of isoflavone aglycone compared with other types of tofu.
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