Dough grain rice bran hydrolysate characterization and stability of biofunctional peptides; antioxidants and ACE/DPP-IV inhibitory activities during in-vitro gastrointestinal digestion

Abstract

Dough grain rice bran is a byproduct obtained from the rice milling process of dough grain stage, representing a potential protein source of bioactive peptides. This work aimed to optimize the Neutrase hydrolysis time to produce rice bran hydrolysate (RBH) with antioxidant activities at semi-pilot scale reactor. In addition, the effect of spray drying inlet temperatures on physicochemical and antioxidant properties of RBH powder was determined. RBH hydrolyzed for 2 h exhibiting the highest antioxidant activity, was spray-dried at 140 °C (RBH140), 150 °C (RBH150), and 160 °C (RBH160). The highest yield was observed in RBH150 (61.32 %). SEM images of RBH showed spherical, irregular, concave, and wrinkled particles. FTIR analysis revealed significant structural changes, with RBH160 exhibiting the highest β-turn but the lowest β-sheet and random coil content. RBH160 had higher molecular weight distribution peptides of 1000-3000 Da, total phenolic content, ABTS antiradical activity, and FRAP values, but RBH160 displayed a darker color and lower α-amino content than RBH140 and RBH150, although metal chelating activity was not significantly different among the samples. After in vitro gastrointestinal digestion, the digested RBH150 exhibited a higher low molecular weight peptides <500 Da, increased antioxidant activities, and stronger dipeptidyl peptidase IV (DPP-IV)/angiotensin converting enzyme (ACE) inhibitory activities compared to undigested samples. RBH150 also protected Caco-2 cells from H<inf>2</inf>O<inf>2</inf>-induced oxidative damage. This suggests that RBH from dough grain can serve as multi-target functional ingredients in metabolic disorder management such as, diabetes, hypertension, and illnesses linked to oxidative stress.