Hydrolysates of rice vs. glutinous rice proteins via sequential pepsin-trypsin hydrolysis: Simulating in vitro digestion.

Low water solubility strictly limits the potential applications of rice (Oryza sativa) protein isolate and glutinous rice (Oryz asatin L. var. glutinosa Matsu) protein. This study aimed to enhance the solubility of rice protein isolate (RPI) and glutinous rice protein (GRP) through enzymatic hydrolysis using pepsin and trypsin. It evaluated the impact of hydrolysis time (30, 60, and 120 min) and enzyme types (pepsin and trypsin) on their physicochemical characteristics and functional properties. The solubility of GRP hydrolyzed by pepsin for 60 min reached 46.86 %, whereas that of RPI hydrolyzed under the same conditions for 120 min stood at 35.16 %. Microstructural analysis indicated that enzymatic hydrolysis destroyed the dense protein structure, leading to the formation of loose small particles. Surface hydrophobicity significantly decreased, and the emulsifying activity index (EAI) of GRP hydrolysates reached a maximum of 0.28 m2/g. Antioxidant assays confirmed that the DPPH (2,2-Diphenyl-1-picrylhydrazyl) radical scavenging rate of pepsin-hydrolyzed protein hydrolysate (60 min) reached 80 %, and the ABTS (2,2'-Azobis-3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging rate of pepsin-trypsin-hydrolyzed products (30 min) was 70 %. This study provides quantitative data supporting the application of RPI and GRP in functional foods.