Optimization of Extraction Technology, Structure Characterization and Antioxidant Activity of Polysaccharide from Hibiseus manihot L.

To optimize the extraction technology of polysaccharides from Hibiseus manihot L. the dried flower buds, and study its structure and antioxidant activity. In this study, on the basis of single factor experiments, the orthogonal experimental design methodology the optimization of extraction process of polysaccharide of the dried flower buds was carried out by water extraction and alcoholic precipitation method. The crude polysaccharides composition was analyzed by high performance liquid chromatography (HPLC), the functional groups and external structure of the polysaccharide were analyzed by Fourier infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), and the free radical scavenging ability and reducing power of the polysaccharides were also tested. The results showed that the optimal extraction conditions were as follows: Extraction temperature of 100 ℃, extraction duration of 3 h, solid-liquid ratio of 1:50 g/mL. Under this condition, the yield of polysaccharide was 17.23%±0.19% and the polysaccharide content was 27.87%±0.60%. The polysaccharide from the dried flower buds was composed of arabinose, galactose, rhamnose, mannose and glucose in molar ratios of 0.97:1:0.23:0.05:0.43. The obtained polysaccharide extract was found to be mainly composed of irregular lamellar structures with the functional groups of uronic acid and pyranose ring. The polysaccharides have certain ability of scavenging DPPH free radical, ABTS⁺ free radical, the corresponding half-inhibitory concentrations (IC₅₀) of polysaccharides against DPPH radicals and ABTS⁺ radicals were 1.22 and 4.43 mg/mL, respectively, it would prove that the polysaccharide had good antioxidant activity. The results would provide a theoretical basis for structural determination research of polysaccharides of Hibiseus manihot L..