Rice bran extract with α-glucosidase inhibitory activity: Preparation, in vitro evaluation and molecular mechanism

Rice bran peptides, effective against type 2 diabetes via α-glucosidase inhibition, face scalability challenges due to complex, costly preparation processes. Rice bran extract (RBE) with enhanced protein yield and α-glucosidase inhibitory activity was prepared by directly hydrolyzing defatted rice bran. The optimized conditions achieved a protein extraction yield of 53.52 ± 0.65 % and an IC₅₀ value of 3.45 ± 0.17 mg/mL. RBE exhibited competitive inhibition of α-glucosidase, with binding to the enzyme's active site. Fluorescence spectroscopy and infrared spectral analysis revealed that RBE induced static fluorescence quenching and altered the secondary structure of α-glucosidase, decreasing α-helix (9.684 %) and increasing β-sheet (45.377 %) content. Peptides GK-6 and KK-8 with low binding energy (-10.249 and -9.277 kcal/mol). Molecular docking revealed that GK-6 and KK-8 interacted with the active site of α-glucosidase through hydrogen bonding, inhibiting the glycosylation process between the enzyme and its substrate complexes. These findings highlight the potential of RBE as a natural α-glucosidase inhibitor, providing a theoretical basis for the development of RBE-based functional foods for regulating carbohydrate metabolism.