Potent antioxidative o-dihydroxyisoflavones in soy sauces and their antioxidative activities
2002
"Esaki, H. (Sugiyama Jogakuen Univ., Nagoya (Japan)) | Osawa, T. | Kawakishi, S. "
"8-Hydroxydaidzein (8-OHD) and 8-hydroxygenistein (8-OHG) were isolated and chemically identified as main antioxidants in soy sauce (shoyu) called tamari. These o-dihydroxyisoflavone (ODI), which show significantly stronger antioxidative activities than those of daidzein and genistein, were considerably contained in the Kojis prepared for soy sauces of koikuchi and tamari type, which abundantly used soybeans for incubation with Aspergillus oryzae. 8-OHD and 8-OHG were also present in enough amounts to exhibit antioxidative activities in the koikuchi and tamari shoyu. In tamari, the ODI content was closely related to the additional water content in Moromi mashing. The ODI amounts in siro shoyu which made the wheat to be a main raw material were limited. The antioxidative activities of soy sauces with higher content of ODI were generally stronger than those of the others. There was a good correlation (r \0.959) between ODI contents and antioxidative activities. The amounts of 8-OHD and 8-OHG in soy sauce were not significantly decreased by heating in boiling water for 60 minutes. From these results, it was suggested that these ODI in soy sauce contribute to protect the oxidative deterioration during the brewing of shoyu and the storing of processed foods using it. (Received Dec. 21, 2001 ; Accepted Apr. 10, 2002)"
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