Extraction, isolation, purification, and structural characterization of polysaccharides from Dioscorea opposita Thunb. Leaves, and their in vitro antioxidant and α-amylase/glucosidase inhibitory activities

To establish the optimal extraction process for polysaccharides from Dioscorea opposita Thunb. leaves using cellulase-aqueous extraction, and to investigate the structure and biological activity of these polysaccharides. The extraction process of polysaccharides from Dioscorea opposita Thunb. leaves was optimized through single-factor and response surface experiments, yielding two homogeneous polysaccharide fractions (DOLP-1 and DOLP-2) after separation and purification. Preliminary structural characterization of DOLP-1 and DOLP-2 was conducted using a combination of UV-Vis, FTIR, GC-MS, NMR, XRD, SEM, TG, periodate oxidation, and Smith degradation. Using in vitro experiments, we preliminarily evaluated the antioxidant and hypoglycemic potential of DOLP-1 and DOLP-2.. The results indicate that when the optimal extraction parameters were a solid-to-liquid ratio of 1:40 (g/mL), enzyme loading of 15 mg/g, extraction time of 72 min, and extraction temperature of 46 ℃ the extraction yield reached 10.46±0.13%. Two homogeneous polysaccharide fractions, DOLP-1 and DOLP-2, were obtained through separation and purification, with molecular weights of 19.11 kDa and 223.3 kDa, respectively. Both exhibit similar monosaccharide compositions (rhamnose, arabinose, mannose, glucose, galactose), but their molar percentages differ significantly, and both adopt a triple-helix configuration. Both possess a pyranose sugar structure and exhibit good thermal stability. DOLP-1 contains both α-glycosidic bonds and β-glycosidic bonds, while DOLP-2 contains only α-glycosidic bonds. In vitro experiments demonstrated that within the range of 0.25-8 mg/mL, DOLP-2 exhibited superior antioxidant and hypoglycemic activity. DOLP-2 showed strong scavenging capacity against DPPH, ABTS, and hydroxyl radicals, with half maximal inhibitory concentrations (IC50) of 1.552, 1.304, and 1.838 mg/mL, respectively. It also exhibited significant inhibitory effects against α-amylase and α-glucosidase, with IC50 values of 1.577 and 1.052 mg/mL, respectively.