Utility of isoflavone preparations from soy sauce cake as antioxidant materials

Abstract

The aged mash (fermented moromi) in soy sauce brewing was pressed to separate into liquid soy sauce and soy cake (soy sauce lee). The major quantity of free isoflavones in the mash remained in the soy cake. The remaining rate of 8-hydroxydaidzein (8-OHD), 8-hydroxygenistein (8-OHG), daidzein and genistein in the soy cake were 65.2%, 82.9%, 88.5% and 95.0%, respectively. These potent antioxidative o-dihydroxyisoflavones (ODI) in various soy cakes, which were obtained from the brewing makers, were also present in rich enough amounts to utilize these cakes as antioxidant materials. The extracted preparations with ethanol and ethyl acetate, in addition to a highly concentrated ODI fraction separated by Amberlite XAD-2 column chromatography, showed strong antioxidative effects against fish oil in both oil and lipid/ aqueous systems. In particular, the ODI fraction exhibited higher antioxidative activity than α-tocopherol in these model systems. It also showed higher DPPH radical scavenging activity and stronger inhibition of lipid peroxidation in a liposome system. From these results, it was suggested that the soy cake dealt with as industrial waste could be well used as antioxidant materials.