Low-molecular-weight ferulic oligosaccharides derived from rice bran enhance the inhibitory effect on rice starch digestion by attenuating self-aggregation.

In this study, three different molecular weight ferulic oligosaccharides (RBFOs) were prepared from rice bran through graded precipitation with 50%, 70%, and 90% ethanol (named 50%RBFOs, 70%RBFOs, and 90%RBFOs). Their structure, aggregation behavior, and effects on rice starch digestion were systematically investigated. The results showed that with decreasing molecular weight, particle size reduced from 278.03 ± 12.71 nm to 170.77 ± 7.12 nm and Zeta potential absolute value decreased. Molecular weights of 50%RBFOs, 70%RBFOs, and 90%RBFOs were 35130 Da, 9185 Da, and 4698 Da, respectively, composed mainly of arabinose, xylose, galactose, and mannose. 90%RBFOs exhibited loose and fragmented structure, while 50%RBFOs presented a dense aggregated state. Thermal analysis showed that its thermal stability decreased with the reduced molecular weight. In vitro digestion experiments found that RBFOs can effectively inhibit rice starch digestion, reducing the starch hydrolysis rate from 79.54 ± 0.60% to 68.00 ± 0.42%, 62.19 ± 0.50%, and 44.04 ± 0.94%, respectively. Starch digestion kinetics further supported these findings. 90%RBFOs, due to the weaker self-aggregation and better dispersibility, can fully expose active sites to bind with starch, thereby effectively slowing down the digestion process. This provided a new theoretical basis for developing slow-digesting starch on rice bran.