Rice bran peptides with α-glucosidase inhibition activity delay the in vitro starch digestion of different rice foods

Rice bran peptides (RBPs) with α-glucosidase inhibition activity have shown great efficacy in reducing postprandial blood glucose levels. This study investigated the inhibitory mechanism of RBPs on amyloglucosidase (AMG) and their potential for modulating starch digestion in rice-based foods. The results demonstrated that RBPs significantly reduced the digestibility and estimated glycemic index (eGI) values of all rice foods in a dose-dependent manner. Fourier transform infrared (FTIR) spectroscopy revealed that interactions between RBPs and AMG resulted in significant alterations to AMG's secondary structure, characterized by a 20.31 ± 0.01 % decrease in α-helical content and a 59.33 ± 0.01 % increase in β-sheet content compared to the control. Moreover, the size exclusion chromatography (SEC) weight distribution curve further illustrated that RBPs delayed the hydrolysis of starch macromolecules, enabling them to remain in a higher molecular weight state during digestion. Molecular docking revealed that RBPs interact with critical catalytic residues via hydrogen bonding and electrostatic forces, directly obstructing substrate access to AMG's active site. In summary, RBPs altered the secondary structure of AMG, inhibited enzyme activity, and thereby delayed starch digestion. These findings further explain the possible mechanism of peptide effects on starch digestion and have important implications for the development of functional carbohydrate foods aimed at delaying starch digestion.