Green extraction of non-starch polysaccharides from millet using a deep eutectic solvent: structural elucidation and structure-activity relationship of their inhibition of α-glucosidase.

Millet has a low Glycemic Index and help to control the concentration of Fasting and Postprandial Blood Glucose. This study employed a deep eutectic solvent method to extract non-starch polysaccharides from millet, optimizing the extraction process to achieve a polysaccharide yield of 5.92%. The polysaccharide fraction NSPM-DES-2 was obtained through separation and purification. Structural analysis revealed this polysaccharide fraction to be a relatively uniform glucan with a molecular weight of 4.978 kDa. Its backbone consists of interlinked →4)-α-D-Glcp-(1→ and →4,6)-α-D-Glcp-(1→ units, exhibiting a triple-helix structure. The inhibitory effect of NSPM-DES-2 on α-glucosidase was investigated using methods including enzyme kinetics, fluorescence quenching, and molecular docking. The findings revealed that this polysaccharide component inhibits α-glucosidase through reversible mixed-type inhibition (IC50 = 6.39 mg/mL). Furthermore, it alters the enzyme's secondary structure and binds stably to α-glucosidase via intermolecular forces such as hydrogen bonding. These results indicate that NSPM-DES-2 from millet holds promise as a natural hypoglycemic resource.