DPPH Radical-Scavenging Compounds from Dou-Chi, a Soybean Fermented Food

Dou-chi, a traditional soybean food fermented with Aspergillus sp., is usually used as a seasoning in Chinese food, and has also been used as a folk medicine in China and Taiwan. As 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavengers, four phenol compounds, one isoflavanone, eight isoflavones and one 4-pyrone have been isolated from dou-chi. Among these fourteen compounds, 3′-hydroxydaidzein, dihydrodaidzein and a 4-pyrone compound have not yet been isolated from soybean miso. The structure of the novel 4-pyrone compound, 3-((E)-2-carboxyethenyl)-5-(4-hydroxyphenyl)-4-pyrone-2-carboxylic acid was elucidated by using the same compound as that obtained from the biotransformation of daidzein. 3′-Hydroxydaidzein showed as high DPPH radical-scavenging activity as that of α-tocopherol, and 6-hydroxydaidzein had mushroom tyrosinase inhibitory activity with an IC50 value of 10 μM. The order of estrogenic activity is as follows: genistein > daidzein >> 3′-hydroxydaidzein > 8-hydroxygenistein, using a green fluorescent protein expression system. Furthermore, the contents of isoflavones in the fermentation process of dou-chi were measured.