Dendrobium hancockii polysaccharides, structure characterization, modification, antioxidant and antibacterial activity

Three novel water-soluble polysaccharides (PDH-1, −2, −3) were obtained from Dendrobium hancockii Rolfe. Their structures were studied using physicochemical and spectroscopic analysis. The crude polysaccharide (PDH) was further modified by degradation (DGPDH), deacetylation (DAPDH), and carboxymethylation (CPDH). The natural polysaccharides consisted of D-Man and D-Gal in different molar ratio. The main glycosidic bonds were β-D-1, 4-Manp, which were substituted with O-Ac groups at O-2 or O-3 position. Small amount of →4)-α-D-Manp, →4)-α-D-Glcp-(1→, and →4)− 3, 6-di-O-Ac-β-D-Manp-(1→ residues were also identified. The in vitro antioxidant and antibacterial activities were also evaluated. The polysaccharides show different antioxidant activity, among which DAPDH has the best effect. DAPDH, DGPDH, and PDH-3 showed antibacterial activity against four strains (B. cereus, B. subtilis E. coli, and S. pullorum) with the MICs < 10.0 mg/mL. These data provided useful information for further study on the application on food or pharmaceutical industries of D. hancockii polysaccharides.