Isoliquiritigenin retards starch digestion by increasing resistant starch content and inhibiting the activities of α-amylase and α-glucosidase

The inhibition mechanism of starch digestion by a natural plant active ingredient isoliquiritigenin was studied. The results indicated that isoliquiritigenin effectively decreased the starch hydrolysis through increasing the content of resistant starch, and inhibiting the activities of α-amylase and α-glucosidase. The content of resistant starch increased by 18.85% with the addition of isoliquiritigenin at 8% content. Multispectral analyses showed isoliquiritigenin combined with α-amylase or α-glucosidase to form stable complexes by non-covalent bonds, leading to the enzyme's structure to be loose, which was supported by the results of unstable conformations and an increase in the freedom of amino acid residues of the enzymes in molecular dynamics simulation. Molecular docking demonstrated that isoliquiritigenin bound to the amino acid residues 304–310 nearby the active pocket of α-amylase, and inserted the active site of α-glucosidase competing with the substrate to bind the crucial amino acid residues (Asp215, Asp352 and Glu411), thereby inhibiting α-amylase and α-glucosidase activity. These findings highlight the development potential of isoliquiritigenin as a hypoglycaemic dietary supplement.