Compound Enzyme Extraction of Platycodon grandiflorum Polysaccharides and Its Structure and Antioxidant Activity Characterization

Objective: Optimize the extraction process of Platycodon grandiflorum polysaccharides by compound enzyme method, and preliminarily analyze its structure and in vitro antioxidant activity. Methods: Response surface methodology was used to optimize the extraction conditions with the extraction rate of polysaccharides as the index and the addition amount of enzymes, solid-liquid ratio, enzymolysis time and enzymolysis temperature as the factors. The molecular weight and monosaccharide composition of purified polysaccharides were analyzed by high performance liquid chromatography (HPLC), the glycosidic bonds and surface morphology of purified polysaccharides were analyzed by nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), respectively, and the free radical scavenging ability and reducing power of purified polysaccharides were evaluated. Results: The optimum extraction conditions were as follows, the addition of cellulase, pectinase and papain was 2%, the enzymolysis time was 90 min, the solid-liquid ratio was 1:30 g/mL, the enzymolysis temperature was 50 ℃. Under these conditions, the actual extraction rate of polysaccharides was 9.01%±0.07%, and the purity of polysaccharides was 92%±0.76%. The purified polysaccharides component PGP-W-1 (6.2 kDa) was composed of mannose, rhamnose, glucose, galactose, xylose, and arabinose with a molar ratio of 4.9:4.3:7.9:7.8:4.8:18.6. NMR spectrum showed that PGP-W-1 was pyranose ring with α- and β-glycoside bond. The IC₅₀ values of the PGP-W-1 on DPPH free radicals, ABTS⁺ free radicals and hydroxyl free radicals were 2.14, 2.25, and 0.78 mg/mL, respectively. Conclusion: The optimized extraction process of Platycodon grandiflorum polysaccharide was feasible with high extraction efficiency and showed excellent antioxidant activity in vitro.