Changes in Phenolic Compounds (Isoflavones and Phenolic acids) and Antioxidant Properties in High-Protein Soybean (Glycine max L., cv. Saedanbaek) for Different Roasting Conditions

Abstract

Contents of phenolic compound including isoflavones and phenolic acids as well as antioxidant effects in high-protein soybean cultivar "Saedanbaek" were evaluated under different roasting conditions. The roasted soybean exhibited significantly higher antioxidant activity than unroasted soybean in the three antioxidant methods including 2,2-diphenyl-1-picrylhydrazyl, 2,2-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid), and Ferric reducing antioxidant power. In particular, the roasted soybean at 200 degrees C for 15 min showed the highest antioxidant activity in comparison with other conditions. The contents of phenolic compounds, isoflavone aglycones (genistein, daidzein, and glycitein), isoflavone beta-glucosides (genistin, daidzin, and glycitin), and phenolic acids increased, whereas isoflavone malonyl-beta-glucosides decreased during roasting process. Moreover, total phenolic and flavonoid contents as well as those of isoflavone aglycones, isoflavone-beta-glucosides, and phenolic acids increased, leading to a general increase in antioxidant activity after roasting. These results suggest that the roasting soybean extracts could contribute to obtaining natural antioxidants in certain food applications.