DISTRIBUTION OF ISOFLAVONES AND ANTIOXIDANT ACTIVITIES OF SOYBEAN COTYLEDON, COAT AND GERM

Abstract

ABSTRACT Soy isoflavones in the cotyledon, coat and germ of four soybean varieties from the southern U.S.A. were determined and compared. Isoflavones with aglycone, daidzein, genistein, glycitein and aglycone, withβ-glucoside, genistin, daidzin and glycitin, were found in the four varieties. The range of total soy isoflavones in cotyledon, coat and germ extracts from the varieties was 2.73–9.71, 5.56–16.94 and 27.76–81.43 mg/g, respectively. Soy germ was the richest source of isoflavones among the three soybean parts. Distribution of the isoflavones in soy cotyledon was different from that in soy coat or germ. Daidzin and glycitin were the major isoflavones in the germ and coat, while daidzin and genistin led in the cotyledon. Compared with theβ-glucoside forms isoflavones, the aglycone isoflavones were at a much lower level in all three soy parts. The difference of the distribution profiles may reflect different isoflavone biosynthesis preference between soy cotyledon and coat or germ. Total phenolic content of the three soy part extracts from high to low was germ, cotyledon and coat. Antioxidant activity of the three part extracts from each variety was measured using 2,2′-diphenyl-1-picrylhydrazyl free radical scavenging method. The order of the antioxidant activity was germ = cotyledon > coat. This study demonstrated that soy germ could be a good source rather than whole soy flour for preparing highly concentrated soy isoflavones extract. It provided useful information for effectively utilizing each part of soybean based on their different compositions, and maximizing the economic value of soybean. PRACTICAL APPLICATIONS This study presented the distribution of isoflavones and their antioxidant activity in soybean cotyledon, coat and germ. The information would be useful in preparing soy products with higher level of isoflavones and antioxidant activity retained. It could also be used in developing soy isoflavone concentrate for food antioxidants or nutritional supplements. These value-added post-harvest applications will increase the economic value and potential utilization of soybean.