Analysis on the Isoflavone Profile and Antioxidant Activity in Vitro of Different Soybean Varieties

In order to study the components and content of soybean isoflavones and antioxidant activity of different varieties of soybeans, hundred kernel weight and seed coat color of 50 soybean varieties were measured. High performance liquid chromatography (HPLC) was used to determine the components of isoflavone. DPPH and ABTS radical scavenging activities were used as indicators to evaluate the antioxidative activity of soybean methanol extract. Samples were analyzed by correlation analysis, principal component and cluster analysis methods. The results showed that the hundred kernel weight ranged from 7.05~47.46 g. L^*, a^* and b^* of soybeans with different seed coat color showed significant differences (P<0.05). Results of HPLC revealed that the glycosidic isoflavone was the main isoflavone component in soybean, accounting for more than 90% of the total isoflavone. The content of genistin was the highest. The Andou 115 variety exhibited the highest isoflavone content, which was 2500.78 µg/g. Meanwhile, the Jingjiang loofah green variety has the lowest content of soy isoflavones at 888.86 µg/g. The DPPH and ABTS radical scavenging activities values of Andou 115 varieties were relatively high, which reached (16.11±0.25) and (8.12±0.04) µmol V_C/g, respectively. The content of glycosidic isoflavone had a high linear correlation with DPPH and ABTS radical scavenging activities (R² was 0.903 and 0.867 respectively). Principal component analysis showed that 6 indicators could be represented by 2 principal components (cumulative contribution rate reaches 66.3%). Cluster analysis divides 50 kinds of soybeans into 4 categories: The first category gathered higher content of glycitein and glycitin. The second category gathered high content of daidzin, daidzein, genistin and genistein. The third and fourth categories gathered varieties with medium level isoflavone and low isoflavone content respectively. The isoflavone composition and content and antioxidant activity of different soybean varieties are significant different. The results can provide a theoretical basis for the comprehensive development and utilization of soybeans.