Exploring inhibition mechanisms of molecular weight-regulated feruloylated oligosaccharides from rice bran on α-glucosidase.

The digestion rate of starch is closely associated with postprandial blood glucose fluctuations. Delaying starch digestion through the inhibition of α-glucosidase activity represents an effective strategy for glycemic regulation. Although numerous studies have demonstrated that various polysaccharides have enzyme inhibitory activity, the mechanism of rice bran feruloylated oligosaccharides (RBFOs) in inhibiting α-glucosidase remains poorly understood. In view of this, this study systematically investigated the inhibitory effects and underlying molecular mechanisms of RBFOs with different molecular weights (50%RBFOs, 70%RBFOs, 90%RBFOs) against α-glucosidase. Enzyme kinetic was used to evaluate the inhibitory activities and patterns, and multi-spectral techniques with microscopic imaging were used to elucidate the interaction mechanisms between RBFOs and α-glucosidase. The results showed that RBFOs effectively inhibited α-glucosidase through a mixed inhibition mode. Among the tested fractions, 90%RBFOs exhibited inhibitory activity comparable to that of acarbose. Spectroscopic and isothermal titration calorimetry analyses jointly confirmed that RBFOs bound to α-glucosidase spontaneously with negative enthalpy, driven by a combination of hydrogen bonds or hydrophobic effects, accompanied by significant enzyme conformational rearrangements. In addition, microscopic observations showed that RBFOs formed stable complexes with α-glucosidase by encapsulating enzyme molecules. Notably, 90%RBFOs exhibited a greater ability to penetrate the enzyme active site. Overall, this study attempted to clarify the structure-activity relationship of RBFOs in inhibiting α-glucosidase activity, providing important insights into the molecular mechanism of RBFOs' inhibition on α-glucosidase.