Application of response surface methodology to acidified water extraction of black soybeans for improving anthocyanin content, total phenols content and antioxidant activity

Acidified water extraction of total anthocyanin content, total phenol content and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) scavenging activity from black soybeans (Glycine max [L.] Merr. Cheongja4ho) was optimized using response surface methodology (RSM). A five-level, three-factor central composite design was employed to optimize the conditions for the maximum yields of these three components using19 different experiments. The HCl concentration (0.3-0.5%), solid-liquid ratio (1/30-1/50 g/mL) and extraction temperature (30-50 °C) significantly affected three components. The optimized conditions were HCl concentration of 0.359%, solid-liquid ratio of 1/54.2 g/mL and extraction temperature of 56.8 °C for total anthocyanin content (136.68 mg/100 g), total phenol content (1197.09 mg/100 g) and ABTS+ scavenging activity (211.65 mg/100 g). These experimental values fit well with the predicted values. Among three anthocyanins found in the black soybean extracts, cyanidin-3-O-glucoside was the major one (65-73% of the total), followed by petunidin-3-O-glucoside (17-23%) and delphinidin-3-O-glucoside (10-12%).