Probing molecular interactions of amylose-morin complex and their effect on antioxidant capacity by 2D solid-state NMR spectroscopy

Interaction of polyphenols and starch significantly governed the further applications on polyphenol-starchy foods. Elucidation of inter-molecular interaction is, however, a challenge because conventional characteriza-tions could not detect the change of micro-environment caused by weak interactions. Herein, a facile strategy for molecular detection of amylose-polyphenol interactions was reported using two-dimensional solid-state NMR spectroscopy. Amylose-morin complex was prepared and characterized using 1H NMR, FT-IR, DSC, XRD and SEM. Significantly, variation of chemical shifts, splitted peaks and peak width, monitored by 13C CP/MAS and 1H NMR spectra, identified the strong inter-molecular interaction and binding sites. Furthermore, correlated signals from 1H-13C HETCOR confirmed the binding sites of interactions. These findings confirmed the interaction was inter-molecular hydrogen bonds, which generated between hydroxy-3,5,7 of morin and hydroxy groups of amylose. Besides, DPPH radical scavenging and reducing power assay indicated inter-molecular hydrogen bonds are not strong enough to interfere antioxidant capacity of morin.

Automated summary

The interaction between polyphenols and starch plays a crucial role in the further applications of polyphenol-starchy foods. A facile strategy for detecting the amylose-polyphenol interactions was reported using two-dimensional solid-state NMR spectroscopy. Chemical shifts, peak splitting, and peak width changes observed in 13C CP/MAS and 1H NMR spectra confirmed the strong intermolecular interaction and binding sites. The findings revealed that the interaction was due to intermolecular hydrogen bonds formed between the hydroxy-3,5,7 of morin and the hydroxy groups of amylose. Moreover, the intermolecular hydrogen bonds did not significantly affect the antioxidant capacity of morin, as indicated by DPPH radical scavenging and reducing power assay.