Effects of Chinese yam and its peel polysaccharides on blood glucose and lipids in type 2 diabetic mice.

Chinese yam (Dioscorea opposita Thunb.) is a traditional medicinal and edible homologous material, with polysaccharides being its primary bioactive components. In this study, two polysaccharides (CYP and CYPP) were isolated and purified from Chinese yam (cv. Tiegun) and its peel, and their anti-diabetic activities were investigated. Structural characterization revealed that the weight-average molecular weights of CYP and CYPP were 74,746 Da and 118,083 Da, respectively. Monosaccharide composition analysis showed that both polysaccharides had similar compositions, primarily consisting of mannose, galactose, and galacturonic acid. Further nuclear magnetic resonance (NMR) spectroscopy analysis demonstrated that CYP mainly contained β-type glycosidic bonds, while CYPP possessed both α- and β-type glycosidic bonds. In a type 2 diabetes mellitus (T2DM) mouse model induced by high-fat diet (HFD) combined with streptozotocin (STZ), both polysaccharides exhibited significant hypoglycemic and hypolipidemic activities. Further investigations revealed that CYP and CYPP could effectively improve metabolic profiles in diabetic mice, significantly regulating two key metabolites, UDP-N-acetylglucosamine and uridine diphosphate glucose (UDP-glucose) while influencing pentose and glucuronate interconversions and starch and sucrose metabolism pathways. Additionally, 16S rRNA sequencing results demonstrated that CYP and CYPP significantly ameliorated gut microbiota dysbiosis in T2DM mice. Notably, compared with CYP, CYPP exhibited superior hypoglycemic and hypolipidemic efficacy, and this functional discrepancy may be closely associated with its higher molecular weight characteristics and distinctive viscoelastic properties. In conclusion, this study demonstrates that CYPP is a promising prebiotic agent for managing T2DM by modulating metabolic pathways and gut microbiota, offering new insights for the valorization of agricultural by-products.