The effect of ultrasound irradiation on the physicochemical properties and α-glucosidase inhibitory effect of blackberry fruit polysaccharide

In this study, the influence of ultrasound irradiation on the characterization and alpha-glucosidase inhibitory effect of polysaccharide from blackberry fruit (BBP, molecular weight of 591.39 kDa) was investigated. After degraded, BBP-8, BBP-16 and BBP-24 three fractions were obtained with molecular weight of 363.93, 249.51 and 177.42 KDa, respectively. Moreover, compared with the particle size of BBP (1070.5 nm), that of BBP-8, BBP-16 and BBP-24 were decreased to 679.9, 548.8 and 395.4 nm, respectively. However, the monosaccharide composition test, FT-IR, and tertiary structure analysis all indicated that the ultrasound did not destroy the primary structure of the original polysaccharide. In addition, the degraded polysaccharide (BBP-24) exhibited the stronger alpha-glucosidase inhibitory activity than that of BBP. By fluorescence spectrum and circular dichroism spectrum analysis, we found that the polysaccharide could induce the structure change like rigidity structure (alpha-helixe) and loop structure (random coil) of alpha-glucosidase to inhibit its activity by binding to the alpha-glucosidase. The polysaccharide with different molecular weight showed different binding capacity which was related to its inhibitory effect on the alpha-glucosidase. In general, the results suggested that appropriate degradation was benefit for the enhancement of the inhibitory effect on alpha-glucosidase of blackberry polysaccharide, and ultrasound irradiation was a green and efficient method to produce bioactivity-added polysaccharide for use in the functional food.