Separation, Purification, Structural Characterization and Hypoglycemic Effect Study of Homogeneous Mori fructus Polysaccharide

Background/Objectives: Mori fructus polysaccharides are key bioactive components with diverse activities, but structural characterization of homogeneous fractions remains limited, hindering insights into structure–activity relationships. This study addresses this gap by isolating and characterizing a homogeneous polysaccharide (MFP-III) from M. fructus. Methods: MFP-III, representing the final gel-filtration homogeneous fraction, was purified using defined procedures: DEAE-52 cellulose chromatography followed by Sephadex G-100 gel filtration. Purity and homogeneity were validated by high-performance liquid chromatography (HPLC). Structural characteristics were analyzed via HPLC, GC-MS, FTIR, and NMR spectroscopy. Meanwhile, hypoglycemic activity of MFP-III was evaluated. Results: MFP-III (94.2 ± 2.6%) has a molecular weight of approximately 6.83 kDa, primarily composed of rhamnose, arabinose, galactose, glucose, mannose, and galacturonic acid. Its backbone structure is presumed to be →2,4)-α-L-Rhap-(1 → 4)-α-D-GalpA-(1→, with branching units potentially attached to O-4. MFP-III demonstrated significant inhibitory activity against α-glucosidase (IC50 = 1.56 mg/mL) and α-amylase (IC50 = 2.07 mg/mL), stronger than acarbose at equivalent concentrations. Conclusions: The findings provide preliminary insights into the hypoglycemic structure–activity relationship of MFP-III, providing data support for the development of blood glucose-lowering natural inhibitors, and offering a theoretical foundation for advancing the application of polysaccharides from other sources.