Changes in Isoflavone Level and Antioxidant Capacity of Black Soybean (Glycine max (L.) Merr.) Cultivar 'Kou-Iso-Kuro 65 gou' by Processing Methods

摘要

High isoflavone containing black soybean 'Kou-Iso-Kuro 65 gou' is a new breed of 'Shin-Tanbaguro', and enjoys a good reputation in the market. We prepared boiled beans, tofu, and other processed products of `Kou-Iso-Kuro 65 gou', and investigated each for isoflavone and anthocyanin contents. Additional investigations on the antioxidant capacity of both raw beans and products were also conducted. The isoflavone content of `Kou-Iso-Kuro 65 gou' was 532.4 mg/100g-DW, more than twice that of the original 'Shin-Tanbaguro'. The isoflavone content of 'Kou-Iso-Kuro 65 gou' processed products was more than twice that of 'Shin-Tanbaguro', a significant increase. Malonyl glycoside was decreased and glycoside was increased by cooking. Isoflavone content and composition varied according to the processing method. For example, in steamed beans, isoflavone loss was suppressed, while in tofu, the aglycone level was promoted. Anthocyanin content was the same or higher than `Shin-Tanbaguro' both in raw beans and products. In additional investigations of functionality, 'Kou-Iso-Kuro 65 gou' showed a higher H-ORAC score than 'Shin-Tanbaguro' both in raw beans and processed products. Thus, `Kou-Iso-Kuro 65 gou' possesses higher isoflavone and anthocyanin contents, significant functionality, and is larger in size compared to other black soybeans. Steamed beans and tofu are functional processed products that utilize the advantageous character of this cultivar.