Optimizing protein hydrolysates of rice bran: Physicochemical, antioxidant, antibacterial properties, and chemometric analysis for functional food potential

Abstract

Rice bran is one of the major by-products of the rice milling process. This study examined the physicochemical alterations and potential functions of protein hydrolysates of rice bran. After removal of fats, rice bran protein was hydrolyzed by using bromelain (Br), trypsin (Tr), papain (Pa), and pepsin (Pe) for different durations (1–5 h). The dry yield of the hydrolysates (3.43–6.30%), the peptide (34.87–85.68 mg/g), and the total phenolic contents (TPC) (21.94–74.59 mg GAE/g) displayed a weak correlation with the duration of the hydrolysis. Hydrolysates Br5h, Tr1h, Pa1h, and Pe4h exhibited the most potent ferric reducing antioxidant power (FRAP) and strong 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical scavenging abilities among all samples. Following exposure to elevated temperatures (65–100°C), the antioxidant properties of Br5h (ABTS 136.67 mg TE/g; FRAP 35.83 mg Fe(II)/g) and Pe4h (ABTS 44.78 mg TE/g; FRAP 49.77 mg Fe(II)/g) remained potent. Furthermore, it is worth noting that Br5h and Pe4h exhibited the most robust antibacterial effects, particularly against Staphylococcus aureus and Escherichia coli. Additionally, principal component analysis revealed comprehensive physicochemical and antioxidant properties within the hydrolysates. Notably, strong associations were identified between FRAP and peptide content, as well as TPC in Br4h, Pe3h, Pe4h, and Pe5h. Overall, the hydrolysates Br5h and Pe4h, which demonstrate exceptional thermal stability, show significant potential as components for the future development of functional food products with antioxidant and antibacterial properties.