Structural Characterization And Rheological Properties Of Polysaccharide From Huangshan Shier

Umbilicaria esculenta from Huangshan Mountain, commonly known as Huangshan Shier (HSSE) in China, is a type of edible and pharmaceutical lichens. Polysaccharides are the main bioactive compounds of HSSE which have shown pharmacological activities such as antineoplastic, antiviral and immunoregulatory activity. However, little attention was devoted to the polysaccharides from HSSE. In this study, we investigated the extraction conditions, chemical structure and rheological properties of polysaccharide from HSSE. The results were as following:(1) Optimal extraction conditions of polysaccharide from HSSE (HSSEP): Single-factor assays and Box Behnken design (with three factors and three levels) were first employed to study the effects of extraction temperature, extraction time and liquid solid ratio on the extraction yields of the HSSEP. The results indicated that the optimal extraction conditions were:extraction temperature 100.37℃, extraction time 0.98 h and liquid-solid ratio of 11.02 mL/g. Under these conditions, the maximum extraction yield of HSSEP was 27.68%.(2) Structural characterization of HSSEP:In preliminary experiments, two polysaccharide fractions named HSSEP1 and HSSEP2, were separated and purified from HSSE using a freeze thawing method. The structural characterization of HSSEP2 was investigated by a variety of chemical and instrumental methods. Monosaccharide compositions analysis indicated that the HSSEP2 was mainly composed of glucose. Methylation and GC-MS analysis indicated that HSSEP2 consisted of 1,6-Glcp glycosidic linkage, which was confirmed by NMR assay. The chain conformation and solution behavior were investigated by congo red test, viscosity test, electron microscopy observation and X-diffraction method, respectively. The results indicated that conformation of HSSEP2 fraction is spherical not helical, and there is a small amount of crystalline region in the polysaccharide.(3) Rheological properties of HSSEP2:The static and dynamic Theological properties were determined by a rheometer. The results showed that the HSSEP2 solution exhibited pseudoplastic flow behavior, the non-Newtonian flow behavior was more obviously with the shear rate increased. The effects of polysaccharide concentration, temperature, metal ion and alkali concentration on rheological properties of HSSEP2 also investigated. Rheological properties of HSSEP2 were influenced by species and concentrations of ions. A certain concentrations solution of HSSEP2 showed characteristic gel property under indoor temperature.(4) Immunomodulatory activities of HSSEP2 and HSSEP2D fractions:In vitro macrophage immunomodulatory assay showed that, all the polysaccharide fractions (20-500 μg/mL) could increase the cell proliferation, neutral red phagocytic activity and the yield of NO of RAW 264.7 cells in a dose-dependent manner, but the immunomodulatory activity of HSSEP2D was lower than HSSEP2.