Structural characterization, physicochemical properties and α-glucosidase inhibitory activity of polysaccharide from the fruits of wax apple

In this study, a novel water-soluble polysaccharide fraction (WAFP) was isolated from wax apple fruits. The structural characterization, physicochemical properties and alpha-glucosidase inhibitory activity of WAFP were investigated. The results indicated that WAFP had average molecular weight of 49.9 kDa, it was mainly composed of rhamnose, arabinose, xylose, mannose, glucose, and galactose with a molar ratio of 1.88: 2.20: 6.37: 1.48: 5.47: 2.82. Besides, the backbone of WAFP might consist of -> 4)-alpha-D-Glcp-(1 ->, -> 3,4)-beta-D-Xylp-(1 -> and -> 3)-beta-D-Galp-(1 ->, and the side chains might be composed of -> 3,5)-alpha-L-Araf-(1 ->, T-alpha-D-Glcp, -> 3)-beta-D-Manp-(1 ->, -> 4)-alpha-D-GalpA-(1 -> and -> 2)-alpha-L-Rhap-(1 ->. AFM images revealed that the height of WAFP molecules was about 12.8 nm. WAFP had no triple-helix structure, and it exhibited a shear-thinning behavior in the solution. SEM results showed that WAFP presented loose and incompact appearance and rough surface with many small irregular particles existed in the state of aggregation. Moreover, WAFP showed significant inhibitory effect on the activity of alpha-glucosidase.