Rice bran valorization: Oil extraction via extrusion-SCCO2 processing and development of protein hydrolysates from its residue

This study presents a comprehensive approach to rice bran valorization, focusing on enhancing oil extraction and utilizing the residual bran for protein hydrolysate production. Extrusion-stabilized rice bran underwent supercritical CO2 (SCCO2) extraction at 60 °C, 20 kg/hr flow rate, and 40 MPa for 80 min. This process yielded over 70 % oil recovery, with reduced free fatty acids and increased retention of beneficial compounds like tocopherols and γ-oryzanol compared to fresh bran. Fatty acid profiles remained unaltered throughout the extraction process. The residual bran from SCCO2 extraction was then used to produce protein hydrolysates using two enzymatic treatments: 1 % Alcalase with 3 % Flavourzyme (RHF) and 3 % Protamex (RHP) for 30–150 min. Both hydrolysates exhibited significantly enhanced antioxidant activities compared to unhydrolyzed protein. RHF treatment produced higher DPPH radical scavenging activity (up to 60.80 %) than RHP, while both treatments improved Fe²⁺ chelating ability (up to 82.55 %) and ferric reducing antioxidant power (up to 11.90 mmol/mg). Functionally, both hydrolysates demonstrated dramatically improved water solubility (>82 % vs. 6.35 % for unhydrolyzed protein) and foaming properties. Foam capacity increased from 17.38 % to 39.61 % (RHF) and 53.69 % (RHP), with improved stability. However, emulsion capacity decreased for both hydrolysates, though RHF treatment showed slightly improved emulsion stability. This integrated approach demonstrates the potential for maximizing rice bran utilization, producing high-quality oil through extrusion-SCCO2 processing, and developing functional protein hydrolysates with enhanced antioxidant and functional properties, suitable for applications in functional foods and nutraceuticals.