Soy Isoflavone Transformation during Grey Sufu Fermentation
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Abstract:
Soy isoflavone composition and content were compared between grey, red, white, and low-salt sufu (or fermented tofu). Changes in soy isoflavone content during the fermentation of grey sufu were also investigated. The results showed that soy isoflavone glucosides were almost completely converted to aglycones in all four types of sufu. Isoflavone content in grey sufu was significantly lower than that in the other types of sufu, in addition to being only 33.01% of the content in red sufu. Additionally, daidzein and genistein content was significantly higher than that of glycitein in all four types of sufu. Monitoring soy isoflavone conversion in grey sufu during the fermentation process showed that glucosides were the main forms of soy isoflavone in pizi, among which, genistein content was higher than daidzein and glycitin content. Soy isoflavone glucosides were converted to soybean isoflavone aglycone during the pre-fermentation process. There was a slight decrease in soy isoflavone glucoside content during the salting process. The total amount of soybean isoflavone aglycone decreased significantly at 30 d post-fermentation. Among soybean isoflavone aglycones, daidzein might be partially converted to equol, which resulted in the lower content of soy isoflavones in grey sufu than in other types of sufu. It remains to be seen if the transformed substance was equivalent in the four types of sufu.
