Research On Chemical Structural Identification And In Vitro Antioxidative Activity Evaluation Of Polysaccharides From Dendrobium Fimbriatum Hook

Dendrobium fimbriatum Hook is one of the main varieties of medicinal Dendrobium in China.It can diminish inflammation,clear the sight and improve the immunity of human body.In this paper,a homogeneous polysaccharide cDFP-W1 was isolated and purified from the stem of D.fimbriatum by a new method.The physical and chemical properties,structure features and in vitro antioxidative activity of the polysaccharide were first studied.Furthermore,a more comprehensive understanding of chemical structure of the polysaccharides was obtained,which laid a theoretical foundation for studying the structure-activity relationships.The dry stem powder of D.fimbriatum was treated by the water extracting-alcohol precipitating,Sevag deproteinization,freeze-drying to prepare polysaccharide(cDFP).The cDFP was successfully fractionated by anion exchange resin DE-52 and gel filtration chromatography Sephadex G-75 to obtain a homogeneous polysaccharide(cDFP-W1).The relative molecular mass and monosaccharide composition were determined by high-performancegelpermeationchromatography(HPGPC)andprecolumn derivatization of PMP.The structure features of cDFP-W1 were elucidated by means of UV spectroscopy,infrared spectroscopy and methylation analysis.The results showed that the carbohydrate and glucuronic acid content of cDFP-W1 were 96.85%and0.29%.The UV analysis showed a single characteristic absorption peak of polysaccharides at 190 nm,indicating no nucleic acid,protein or other impurities.The infrared spectroscopy illustrated that the cDFP-W1 was a typical carbohydrate compound.The high performance gel permeation chromatogram had a single symmetrical peak at 38.707 min,indicating that the cDFP-W1 was a homogeneous polysaccharide with a molecular weight of 4.0×10~4 Da,which was mainly consisted of D-mannose and D-glucose in a molar ratio of 1:3.84.Methylation and nuclear magnetic resonance spectrum analysis showed that the cDFP-W1 was linked by the sugar residues of 1,4-linked Glcp,1,4-linked Manp,1,4,6-linked Glcp and the branch chain of T-linked Manp.Based on the above results,the possible repeating units were speculated.(?)In this study,the in vitro antioxidative activity of cDFP-W1 was evaluated by determining the scavenging capacity of ABTS,DPPH and hydroxyl radical.The results showed that the cDFP-W1 had a certain scavenging ability against all three free radicals,and the scavenging ability was positively correlated with the concentration.When the concentration of polysaccharide was 4 mg/mL,the free radical scavenging rates were46.72%,40.96%and 58.64%,respectively.