Isolation,Structural Characterization And Antioxidant Activity Of Two Polysaccharides From Bletilla Striata

Bletilla striata(Thunb.)Reichb.f.(Orchidaceae),whose underground part includes the tubers that are regarded as the main medicinal part and the fibrous roots that are often discarded in the processing,is a kind of herb with the medicine and food homology.To verify the potential application of fibrous roots,water-soluble crude polysaccharides cBSP and cFSP were isolated through a series of methods including hot water extraction,alcohol precipitation,petroleum ether degreasing and trichloroacetic acid deproteinization from the tubers and fibrous roots of Bletilla striata,respectively.The crude polysaccharides were further purified by column chromatography with DEAE-Sepharose Fast Flow gel and eluted against distilled water,after which the structure characterization and antioxidant activities comparison of the homogenized pBSP and pFSP were determined.The results of component analysis showed extremely low content of uronic acid in pBSP and pFSP,indicating that they could be regarded as neutral polysaccharides.The total sugar content was 107.7%and 97.82%,and the molecular weights were 3.28×105 DA and 9.11×104 Da,respectively.These two polysaccharides with uniform molecular distributions had few proteins and other impurities.The results of structural investigations showed that pFSP was composed of galactose,glucose and mannose(molar ratio 2.03:1.00:3.45),containing a main chain composed of(1?4)-?-D-Glcp,(1?4)-?-D-Manp and(1?3,6)-?-D-Manp residues,together with two branches composed of ?-D-Manp and(1?6)-?-D-Galp residues,while pBSP was only composed of glucose and mannose(molar ratio 1.00:1.34)?Although the main chain of pBSP only contained(1?4)-?-D-Manp,(1?4)-a-D-Glcp and(1?3)-?-D-Manp without branched chain,there were still some structure similarities with pFSP.In DPPH,ABTS and superoxide radical systems,due to the loose structure of pFSP with branches,it could exhibit more excellent free radical scavenging abilities than pBSP at the same doses.The scavenging rates of pFSP against DPPH·and superoxide anion were 64.47%and 72.27%at a concentration of 5 mg/mL,while those of pBSP were only 23.35%and 32.82%.The results of cytotoxic experiments revealed that Bletilla striata polysaccharides had no toxic effect on fibroblasts,but further promoted cell proliferation.The 24-hour-pretreatment on fibroblasts with Bletilla striata polysaccharides could significantly reduce the production of cellular ROS.These results confirmed the availability of Bletilla striata fibrous roots and showed that Bletilla striata polysaccharides had potential antioxidant capacity,which was expected to be exploited in the development of antioxidant functional food in the future.