Studies On The Separation, Purification, Structure Identification, Solution Conformation And Rheological Properties Of Polysaccharides From Tremella Fructus Fruit Body

Tremella fuciformis Berk,also known as white fungus,is a precious edible medicinal fungus.Polysaccharides are one of the main active components of T.fuciformis.It has important biological activity such as immune regulation,antitumar,hypoglycemic lipid,anti-oxidation,anti-aging and so on.This thesis focused on the polysaccharides extracted from the fruiting bodies of T.fuciformis from the following parts:crude polysaccharides obtained by hot water extraction and ethanol precipitation;separation and purification of homogeneous fraction;structure elucidation and conformation in solution of the homogeneous fraction;rheological properties of TFP60solution.Three crude polysaccharide fractions(TFP30,TFP60 and TFP80)were extrated by fractional precipitation with adding alcohol successively to bring final alcohol concentration to 30,60,80 vol.%.And given the polysaccharide content,TFP60 was selected to futher purification.DEAE-Sepharose Fast Flow and Sephacryl S500 gel column chromatography were then carried out to purify the crude fraction TFP60.After purification,the homogeneous fraction TFP60-2a was acquired,which was no nucleic acids and proteins,the average molecular weight was 6.180×10~5 Da.Afterwards the primary structure of TFP60-2a was determined by IR and GC.These results revealed that TFP60-2a was an acidic polysaccharide composed of L-Rhamnose,L-Fucose,D-Xylose,D-Mannose and D-Glucose,the molar ratio of 0.34:1.07:1.00:1.47:0.46.To study the advanced structure of TFP60-2a,differential scanning calorimeter(DSC),congo red test,SEC-MALS-RI-Vis,atom force microscopy(AFM)and scanning electron microscope(SEM)were used.The result of DSC analysis revealed that TFP60-2a has good thermal stability between 30-200℃.The congo red test suggested that TFP60-2a didn’t exist in triple-helix conformation.From the result of SEC-MALS-RI-Vis,the molecular parameters of TFP60-2a were determined as:weight-average molecular weight(M_w)of 1.071×10~6 Da,number-average molecular weight(M_n)of 8.110×10~5 Da,z-average molecular weight(M_z)of 1.324×10~6 Da.The low polydispersity index(PDI)was calculated as 1.321 from the ratio of M_w to M_n,suggesting the narrow molecular mass distribution for TFP60-2a.Meanwhile,a v value of 0.531 around indicated a random string conformation in solution for TFP60-2a.In addition,the rheological behavior of TFP60 polysaccharide solution was also investigated at the same time.The results showed that:TFP solution is a pseudoplastic fluid.In the low angular frequency,TFP solution was failed to form gel,in the high angular frequency,G’was dominant,guessing that TFP may form a weak gel.And with the increase of the concentration of TFP solution,these would help the formation of gel structure,but the temperature has little effect on it.