The production of hydrolysates from industrially defatted rice bran and its surface image changes during extraction

Abstract BACKGROUND This research employed a mild subcritical alkaline water (mild‐SAW) extraction technique to overcome the difficulty of active compound extractability from industrially defatted rice bran (IDRB). Mild‐SAW (pH 9.5, 130 °C, 120 min) treatment followed by enzymatic hydrolysis (Protease G6) was applied to produce rice bran hydrolysate (RBH). Response surface methodology was used to identify proteolysis conditions for maximizing protein content and ABTS radical scavenging activity (ABTS‐RSA). Microstructural changes occurring in IDRB during extraction were monitored. The selected RBH was characterized for protein recovery, yield, antioxidant activities, phenolic profile and hydroxymethylfufural (HMF) content. RESULTS Optimal proteolysis conditions were 20 mL kg −1 IDRB (enzyme/substrate ratio) for 6 h. Under these conditions, the yield, ABTS‐RSA, ferric reducing antioxidant power and total phenolic content of the RBH were 46.1%, 294.22 µmol trolox g −1 , 57.72 µmol FeSO 4 g −1 and 22.73 mg gallic acid g −1 respectively, with relatively low HMF level (0.21 mg g −1 ). The protein recovery was 4.8 times greater than that by conventional alkaline extraction. Its major phenolic compounds were p ‐coumaric and ferulic acids. The microstructural changes of IDRB confirmed that the mild‐SAW/Protease G6 process enhanced the release of active compounds. CONCLUSION The process of mild‐SAW extraction followed by proteolysis promotes the release of active compounds from IDRB. © 2017 Society of Chemical Industry