Protein quality and antioxidant properties of soymilk derived from black soybean after in vitro simulated gastrointestinal digestion

Summary Protein quality and antioxidant properties of soymilk derived from black soybean (eight varieties) in China were analysed following in vitro simulated gastrointestinal digestion (including dialysis). Soymilk from black soybean possessed high okara weight but low yield, protein content and sensory scores. The in vitro digestibility of protein in all black soymilk samples was higher than 60%, and the Shenmu black soybean exhibited the highest digestibility. Non‐digested milk from the black soybean exhibited significantly high total phenolic content ( TPC ) (127.15–173.04 mg/100 mL ), ferric‐reducing antioxidant power ( FRAP ) (272.18–366.27 μmol L −1 ) and DPPH free radical‐scavenging activity (61.20–83.81%). These parameters were significantly lower in the non‐digested soymilk than those in soymilk after gastric digestion but higher than those of soymilk in the dialysed fraction. Gastric digestion significantly increased bioactive compound levels released from black soymilk, and the bioaccessibility of phenolic compounds was 24.37–36.05%. Hence, black soymilk was sufficiently available for human absorption.