Effect of Lauric Acid Concentration on the Formation and in Vitro Digestibility of Resistant Starch in Rice

Lauric acid (LRA), as a functional food additive, plays a crucial role in the preparation of V-type resistant starch (RS₅). To elucidate the mechanism by which LRA concentration influences the formation and in vitro digestibility of rice-derived RS₅—and to provide a theoretical basis for the development of low-glycemic index (GI) functional starch-based foods—this study utilized rice starch and varying concentrations of LRA (0%, 1%, 4%, and 7%) to construct rice starch–LRA complexes. A combination of analytical techniques, including complexation index (CI) determination, scanning electron microscopy (SEM), characterization of short-range molecular order, RS content measurement, molecular docking, and molecular dynamics (MD) simulations, was employed to systematically investigate the structural and digestive implications of LRA incorporation. The results demonstrated that LRA effectively formed stable complexes with rice starch, and the RS content increased progressively with higher LRA concentrations. While the addition of LRA did not significantly alter the surface microstructure of the RS, it notably reduced the short-range molecular order. MD simulations revealed that LRA molecules could be tightly embedded within the helical structure of amylose. Moreover, molecular docking indicated that LRA can target the active site of α-amylase, forming stable complexes with the enzyme through hydrophobic interactions and hydrogen bonding. This competitive binding inhibits the interaction between α-amylase and starch, thereby delaying starch hydrolysis. In summary, the incorporation of LRA significantly enhances RS formation in rice starch and effectively slows down its in vitro digestion rate. This is primarily achieved through the promotion of starch–lipid complex formation, disruption of short-range molecular order, and competitive inhibition of α-amylase activity.