Enhanced functional and antioxidant properties of rice bran protein through solid-state fermentation

• SSF method yielded 64.70% protein from defatted rice bran. • RBPC showed superior functional and antioxidant properties. • RBPC exhibited high solubility, foam stability, and emulsion stability. • Fermentation significantly enhanced the RBPC antioxidant activity. • RBPC is a promising, versatile food ingredient. This study successfully extracted protein from defatted rice bran, a by-product of the rice bran oil industry, using solid-state fermentation (SSF) with a mixed Koji starter, composed of a mixed microbial culture. The fermentation process significantly produced cellulase, amylase, and both neutral and alkaline protease activity, resulting in a high protein extraction yield of 64.70 % after 48 h of fermentation. The resulting rice bran protein concentrate (RBPC), obtained by spray-drying the extract, contained approximately 50 % protein, with dietary fiber as the second most abundant component. Compared to both rice protein (RP) and alkaline-extracted defatted rice bran protein (A-DRBP), RBPC demonstrated significantly improved functional and antioxidant properties. RBPC exhibited superior solubility (69.32 % at pH 9), foam stability (121.67-136.67 %), and emulsion stability (38.64 min). These improvements are attributed to its peptide rich composition and increased soluble dietary fiber. While its water absorption was lower, its oil absorption was comparable to the other samples. Furthermore, RBPC showed notably higher antioxidant activity. Its DPPH and ABTS radical scavenging capacities were 17.25 and 32.46 mg eq Trolox / g dry sample, respectively, and it had a high total phenolic content (34.30 mg GAE / g dry sample). The amino acid profile of the RBPC was consistent with those reported for rice bran protein in the literatures. The composition of RBPC primarily consisted of short peptides, ranging from 8-46 amino acids. These findings demonstrate that RBPC is a highly versatile and promising ingredient for the food industry.