Preparation, structure analysis and ACE inhibitory activity of konjac oligosaccharide

Abstract

Konjac contains a large amount of glucan, which is a new functional sugar. Konjac oligosaccharides have high medicinal value, and it is of certain significance to prepare konjac oligosaccharides with konjac as raw material. In this study, the crude polysaccharide was extracted from konjac and then isolated by 95% alcohol-precipitation. The crude polysaccharide was degraded with β-mannanase to obtain the degradation product, named KPD. Then the KPD was acetylated by the pyridine acetic anhydride method in order to be purified by silica gel column to obtain the acetylated product named AC-P3. The structure of AC-P3 was analysed by physicochemical and instrumental analyses. The results indicated that the molecular weight of the AC-P3 was 1254 Da, and that the specific rotation was −20°. And then the AC-P3 was deacetylated with CH3ONa-CH3OH solution to obtain the final product, named P3. The structure of P3 was also analysed by physicochemical and instrumental analyses. The molecular weight of the P3 was 666 Da, and the specific rotation was +45°. The result of monosaccharide composition revealed that P3 was consisted of mannose (Man), glucose (Glc), and galactose (Gal) with a molar ratio of 2:1:1. Moreover, the NMR characteristic spectras of P3 was compared with that of AC-P3 to conduct the structural characterization of P3. The results indicated that P3 was a kind of tetrasccharide with a linear backbone of Glc-(1→4) Man (1→4) Man and glycosyl residues of P3 was Man (3→1) branched-Gal. The Angiotensin I-Converting Enzyme (ACE) inhibitory activity assay showed that P3 had a certain inhibition on ACE activity.