Obtaining proteins and protein hydrolysate antioxidants from cold-pressed defatted rice Bran by ethanol-modified mild subcritical water extraction

This study aimed to elevate the recovery of bioactive compounds from a cold-pressed defatted rice bran using ethanol-enhanced mild subcritical alkaline water (m-SAWE tOH ) treatment. Optimal conditions of m-SAWE tOH to obtain extracts rich in protein were investigated. Three variables were assessed using a response surface methodology (RSM) in a Box-Behnken Design (BBD) with extraction temperature (x 1 , 110–120 °C), time (x 2 , 30–90 min), and ethanol level (x 3 , 0–70%). The protein-rich sediment (Prot-Sed) was precipitated by adjusting the extracted supernatant to 75% ethanol. The optimum m-SAWE tOH conditions for the Prot-Sed extraction were 120 °C, 38.9% ethanol, for 90 min. Ethanol enhanced the m-SAW, providing the Prot-Sed with higher protein, total phenolic content, and antioxidant activity (FRAP assay). Additionally, the 2-step process of m-SAWE tOH and protease hydrolysis increased the recovery of protein and phenolics by 1.93-fold and 10.42-fold, respectively, concomitant with an increase in antioxidant capacity. Amino acids (His, Leu, Met, Trp, and Val) and polyphenols (protocatechuic acid, p -coumaric acid, ferulic acid, and sinapic acid) possessing antioxidant capacity were presented in the Prot-Sed hydrolysate. The findings demonstrated that m-SAWE tOH is a green process that improves the release of bioactive components, adding value to biomaterials.