Molecular interactions between apigenin and starch with different amylose/amylopectin ratios revealed by X-ray diffraction, FT-IR and solid-state NMR

Starch can readily form complexes with polyphenols. However, its two components, namely amylose and amylopectin, differ significantly in their ability to complex with phenolic compounds. Given that the mechanism of their interaction is still poorly studied, this work investigated intermolecular interactions between apigenin and starch with different amylose/amylopectin ratios using 1H NMR, FT-IR, XRD, DSC and solid-state NMR. Results showed that corn starch with high amylose/amylopectin ratios had a better complexing ability and higher complexing index with apigenin than amylopectin. Besides, solid-state NMR suggested that the molecular mechanism behind the strong intermolecular interactions between corn starch and apigenin involved hydrogen bonds. Furthermore, the detailed binding sites of hydrogen bonds, that linked by hydroxyl-starch and phenylapigenin were also confirmed by 1H-13C heteronuclear correlation (HETCOR) spectra. This study revealed the molecular mechanism on amylose/amylopectin complexing with apigenin and provides a theoretical basis for further developing polyphenols in starchy food.