Influence of roasting on the antioxidant activity of small black soybean (Glycine max L. Merrill)

Small black soybean (SBS), a kind of Glycine max L. Merrill, has various biological actions such as osteoblastic cell proliferating, anticancer, and antioxidant activity. Many studies have shown that thermal processing preserves the health benefits by enhancing antioxidant activity. In this study, we compared the antioxidant effects of SBS based on roast processing conditions using DPPH and ABTS assays. Additionally, we measured phenolic contents and Maillard reaction products (MRPs) to identify the factors that changed SBS antioxidant activity due to roasting. Furthermore, we performed MTT and ROS assays in PC12 cells stressed by H₂O₂ to investigate how roast processing increases SBS antioxidant activity in a cell culture system. The roasted SBS exhibited significantly higher antioxidant activity than unroasted SBS in the ABTS and DPPH assays. In particular, the roasted SBS at 250 °C for 30 min showed the highest antioxidant activity, compared to any other condition. Antioxidant compounds such as phenolic acid and MRPs increased in the SBS following roast processing. Moreover, the roasted SBS protected the PC12 cells from H₂O₂ toxicity by reducing ROS generation better than unroasted SBS. These results demonstrated that the antioxidant effects of SBS can be maximized by roast processing.