Study on the Effects of Polyphenols on the Properties, Microstructure, and Digestibility of Rice Protein Gel and the...

Rice protein has limited gelation properties, restricting its food applications. This study added four polyphenols-catechin (C), epicatechin (EC), tannic acid (TA), and proanthocyanidins (PC)-to rice protein to investigate their effects on gel rheology, in vitro digestibility, and microstructure. Multi-spectroscopy and molecular docking were used to explore interaction mechanisms. During the temperature sweep (95 °C), PC- and TA-composite gels (GRP-PC, GRP-TA) showed storage moduli slightly higher than the pure rice protein gel (GRP), while GRP-C and GRP-EC (C- and EC-composite gels) were similar to GRP. In frequency sweep (25 °C), GRP had the highest modulus, followed by GRP-PC > GRP-TA > GRP-EC > GRP-C. Polyphenols reduced total digestibility (from 77.4% to 67.6-75.2%). All polyphenol-complexed gels showed markedly improved ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) and DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activities. C and EC induced loosely crosslinked microstructures, whereas TA and PC formed sheet-like aggregates. Fluorescence quenching was predominantly static, with quenching rates TA > PC > EC > C. Binding constants followed the same order. Thermodynamic parameters (ΔH > 0, ΔS > 0, ΔG < 0) indicated hydrophobic interactions as the driving force. Molecular docking revealed that PC formed the most hydrogen bonds (8) with rice glutelin, followed by TA (4), C (5), and EC (3). These findings provide data support for designing rice protein-based functional foods.