Physicochemical properties and in vitro hypoglycemic activities of hsian-tsao polysaccharide fractions by gradient ethanol precipitation method

Hsian-tsao polysaccharides fractions (HPs), including HP20, HP40, HP60, and HP80, were fractioned by gradient precipitation of 20 %, 40 %, 60 %, and 80 % (v/v) ethanol, respectively. Their physicochemical properties and in vitro hypoglycemic activities (inhibitory activities on α-amylase and α-glucosidase, glucose adsorption capacity, and glucose diffusion retardation) were determined. The results showed that, with ethanol upward, the average particle size, molecular weight, and apparent viscosity of HPs were decreased while carbohydrate and uronic acid contents, absolute zeta potential, and thermal stability were increased. Each of the HPs contained Rha, Ara, Gal, Xyl, Man, and GalA with different molar ratios, indicative of anionic heteropolysaccharides with uronic acid. HPs, with diverse structures and surface morphologies as proved by FTIR and SEM, whose solutions were pseudoplastic fluids, exhibited elastic behavior of weak gel networks at concentrations of >1 %. Moreover, HPs showed inhibitory activities on α-amylase and α-glucosidase, of which HP80 was the strongest. For α-amylase, HP20 and HP60 behaved as mixed inhibitors, while HP40 and HP80 were non-competitive. For α-glucosidase, HPs acted as mixed inhibitors. Additionally, HPs possessed glucose adsorption capacity and glucose diffusion retardation, with the best for HP20. These results suggested that HPs possessed hypoglycemic activities, which could be developed as functional food or hypoglycemic drugs.