Preparation, structure and α-glucosidase inhibitory of oligosaccharides by enzymatic hydrolysis from Annona squamosa polysaccharide

Annona squamosa (AS) has relatively high content of polysaccharides which had effective hypoglycemic activity. The oligosaccharides have advantages in the digestion and absorption. However, there were few reports on oligosaccharides from AS. In the manuscript, pectinase was utilized to degrade Annona squamosa polysaccharide (ASP). The product was acetylated, purified by silica gel column and deacetylated to obtain a novel oligosaccharide Z. The structure of Z was identified with NMR, mass spectrometry and monosaccharide composition analysis. The results demonstrated that the oligosaccharide Z was a trisaccharide with molecular weight of 518 Da. The structure of oligosaccharide Z was linear skeleton composed of β-D-Glc-(1→2)-β-D-Glc-(1→3)-α-D-GalA. The oligosaccharide Z can effectively inhibit the activity of α-glucosidase with reversible type and mixed-type inhibition. The oligosaccharide Z had effective binding effect with α-glucosidase from molecular docking experiments. The results revealed that the oligosaccharide Z has the potential to be utilized as α-glucosidase inhibitor. The manuscript provided theoretical basis for the new applications of AS in food industry and pharmaceutical industry. It also provided valuable clues for finding new potential hypoglycemic drugs from natural sources.