ACE-inhibitory activity and antioxidant properties of a low MW rice bran protein hydrolysate

Rice bran (RB), a widely available protein-rich waste derived from the rice production chain, represents a potential source of bioactive peptides. In this study a two-step, easily scalable enzymatic hydrolysis protocol to obtain RB protein hydrolysates (RBPH) is described. Firstly, a pre-treatment with commercial carbohydrase mixtures was performed to selectively remove polysaccharides of RB cell wall. The resulting protein-enriched fraction was then hydrolyzed with a combination of two different proteases, i.e., Alcalase® 2.4L and Flavourzyme®. RBPH was separated by membrane ultrafiltration and the fraction with low MW peptides (RBPH U < 1 kDa) was subjected to ACE-inhibitory and antioxidant assays, the latter both in vitro and at cellular level. RBPH U < 1 maintains the same ACE-inhibitory activity (68.7 %) before and after simulated gastrointestinal digestion. Moreover, RBPH U < 1 shows the ability to effectively scavenge ABTS and DPPH radicals, besides reducing ferric ions, and it can significantly mitigate oxidative stress-induced damage on human intestinal Caco-2 cells. Interestingly, its antioxidant capacity is maintained also after simulated gastrointestinal digestion. Results obtained suggest that peptides from RB proteins have the potential to be used in the development of functional foods that support intestinal health and alleviate illnesses linked to oxidative stress.