Changes of astringent sensation of soy milk during tofu curd formation.

The effect of isoflavone on soy milk and tofu astringency was investigated, and no consistency was found between an undesirable astringent taste and isoflavone contents. Isoflavone-enriched extract (approximately 39% isoflavones) showed no astringency. Soybean foods having high amounts of isoflavones showed less astringency. About 80% of isoflavones exist freely in both soy milk and tofu, but 55% of phytates (which play an important role in the formation of the tofu curd network) exist freely in the soy milk, and 6-13%, on the basis of coagulation, existed freely in the tofu curds. A 1% potassium phytate solution at pH 7 showed the very same astringency as soy milk; however, calcium phytate at the same concentration and pH showed no undesirable sensation. Thus, it is assumed that the astringent characteristics caused by phytic ions in soy milk are lost upon conversion of phytic ions to their insoluble salt forms during soy milk coagulation.