Optimization of Fermentation and in Vitro Digestion of Fermented Mixed-Bean Milk by Response Surface Methodology

In this study, red beans, black beans and soybeans were utilized to produce fermented mixed-bean milk. The changes of total phenols, total flavonoid and antioxidant capacity of the product were investigated by single factor experiment and response surface methodology. The results showed that the optimum fermentation process of fermented mixed-bean milk was sucrose addition of 7.2%, transglutaminase addition of 0.63 g/L and fermentation for 10 h accompanying the sensory score of 88.1 points. After digested with gastric juice and intestinal juice, the total phenols content in fermented mixed-bean milk were increased by 25% and 61%, while total flavonoid were increased by 51% and 22%. Before digestion, DPPH, ABTS, hydroxyl radical clearance and reducing power were 47.71%, 20.53%, 41.45% and 0.22 respectively. After gastrointestinal juice digestion, the antioxidant indexes were increased by 35.0%, 48.1%, 43.1% and 27.3% respectively. After intestinal juice digestion, the reducing power of fermented mixed-bean milk was 10% lower than that of gastric juice digestion, but still higher than that of undigested sample. The total phenols content after digestion was positively correlated with DPPH radical scavenging rate, ABTS and hydroxyl radical scavenging rate (P < 0.05) and there was a positive correlation between total flavonoid and reducing power (P < 0.05). Consequently, the results could provide a reference for the future research and development of fermented mixed-bean milk.