Extraction, characterization and antioxidant activities of an acidic polysaccharide from Dendrobium devonianum

Dendrobium devonianum Paxt (D. devonianum) is widely used as a healthy food and traditional Chinese medicine. It is rich in bioactive polysaccharides, but the acidic polysaccharide have not been reported. In this research, the enzyme-assisted extraction and structure characterizations of an acid polysaccharide (DDPp2) and its antioxidant activities were studied. The results showed the optimum extraction conditions were at enzyme concentration of 0.94% at 51.06 °C and pH 4.94. The molecular weight of DDPp2 was 306 kDa and composed of four monosaccharides in the molar ratio of mannose:glucose:galactose:glucuronic acid = 6.37:4.99:1.71:2.39 with α-configuration sugar. SEM and TEM analysis showed that the surface of the polysaccharide was smooth and holes in the sheet and multiple molecular chains were intertwined with each other. Free radical scavenging tests in vitro showed DDPp2 had very strong scavenging abilities for hydroxyl radical, ABTS radical and superoxide anion free radicals. Cell experiment showed DDPp2 had no cytotoxicity and could significantly increase the activities of CAT, SOD and GPX, reduce the content of MDA in RAW264.7 cells. The investigation showed that DDPp2 is a potential antioxidant.