Fractionation, Structural Characterization and In Vitro α-Amylase and α-Glucosidase Inhibitory Activities of Polysaccharides Derived from Lycium barbarum L.

Polysaccharides have attracted extensive attention due to their pharmacological activities, such as regulating depression, antitumor, hypoglycemic and lipid-lowering effects, and regulating intestinal flora. In this study, four crude polysaccharide fractions, designated LICP007, LICP008, LICP009 and LICP010, were prepared from Lycium barbarum L. Based on the in vitro α-amylase and α-glucosidase inhibitory assays, LICP007, which showed the strongest activity among the four crude polysaccharides (inhibition rates of 61.42 ± 0.29% against α-amylase and 40.69 ± 0.35% against α-glucosidase at 50 mg/mL), was selected for further separation and purification, and one neutral polysaccharide (LICP007-N1) and two acidic polysaccharides (LICP007-S2 and LICP007-S5) were obtained by DEAE-52 cellulose anion-exchange and Sephadex G-200 gel permeation chromatography. Among them, LICP007-S5 showed the best inhibitory activity against α-amylase and α-glucosidase, with inhibition rates of 98.38% and 43.45% at 20 mg/mL, respectively. Physicochemical characterization showed that LICP007-S5 differed markedly from LICP007-N1 and LICP007-S2 in molecular weight distribution, monosaccharide composition and morphology. Structural analysis indicated that LICP007-S5 is an acidic heteropolysaccharide rich in galacturonic acid (27.5 mol%); atomic force microscopy (AFM) and Congo red test results suggest that it may adopt an ordered, possibly triple-helical conformation, although this requires further verification. These findings provide comparative information on the structure and biological activity of different Lycium barbarum polysaccharides and highlight their potential as natural α-amylase and α-glucosidase inhibitors for the dietary management of type 2 diabetes in functional foods.