Preparation, Structural Characterization, and Synergistic Hypoglycemic Effect of Jujube Polysaccharide–Polyphenol Complex

Type 2 diabetes mellitus (T2DM) is a globally prevalent chronic metabolic disorder that poses severe public health risks. Synthetic hypoglycemic agents are susceptible to inducing adverse reactions, thus driving the development of natural, safe and highly effective plant-derived hypoglycemic active compounds as a research hotspot. Inhibiting the activity of α-glucosidase and α-amylase represents an effective strategy to regulate postprandial blood glucose levels. This study investigated the synergistic hypoglycemic activity of a composite (PS-PP) formed by polysaccharide (PS) and polyphenols (PP) from Ziziphus jujuba Mill. cv. Muzao and elucidated the structural basis underlying this synergistic effect. First, MPS and MPP were isolated and purified, followed by the in vitro assembly to prepare PS-PP. The hypoglycemic activities of MPS, MPP and MPS-PP were evaluated via in vitro enzyme inhibition assays, while structural characterization was conducted using GPC-MALLS, FT-IR and SEM techniques. Results demonstrated that PS-PP exerted the strongest activity under optimal conditions (0.75 mg/mL concentration, pH 4.0, 1:2 mass ratio), with IC₅₀ values of 1.14 μg/mL and 0.82 μg/mL against the two enzymes, which were superior to those of polysaccharides (15.10 and 36.06 μg/mL) and polyphenols (1.18 and 46.24 μg/mL). Structural analysis revealed that the interaction between PS and PP was primarily mediated by hydrogen bonds. PS-PP exhibited significant differences from single-component compounds in molecular weight distribution, functional group binding and surface morphology. These structural alterations were identified as the key factors contributing to its enhanced hypoglycemic efficacy. This study clarifies the synergistic hypoglycemic mechanism of MPP-PS and lays a scientific foundation for the development of natural hypoglycemic preparations and functional foods.