Study On Extraction,Structure Characterization And Biological Activity Of Lycium Barbarum Polysaccharides

Plant polysaccharides are a kind of natural product with significant biological activities,and it is also one of the current research hotspots.Polysaccharides in the same plant are usually composed of carbohydrates with relative molecular mass ranging from hundreds to tens of thousands or even hundreds of thousands and millions,which belong to a mixture with a very large span of relative molecular mass.Therefore,there are potential and significant differences in the composition and structural characteristics of polysaccharides obtained by different extraction methods for the same plant,and further affect their bioactivities.However,at present,research workers are mostly adopted in extracting polysaccharides from plants by simplex extraction method.After purification,carrying out these studies of structure features and bioactivities.Although these studies have confirmed that the discovery of effective substances with specific bioactivities has a positive significance.However,the chemical constituent of extractions is closely linked with biological activities.Therefore,there is improvement space in the current research thoughts on polysaccharides.Relevant research can be carried out on the accuracy of the correlation between the chemical constituents and biological activities of the extractions,which is more conducive to the further development and utilization of plant polysaccharides.In the present study,Lycium barbarum L.was used as the research object,and the five polysaccharide fragments（LBP-1～LBP-5）were selectively extracted by different extraction methods（cold water extraction,boiling water extraction of filter residue after cold water extraction,50%ethanol solution ultrasonic-assisted extraction,25%ethanol solution ultrasonic-assisted extraction of filter residue after 50%ethanol solution ultrasonic-assisted extraction,and hot water extraction）.Moreover,the chemical composition,structural characteristics,and bioactivities of the LBPs were explored.The aim is to establish the relationship between extraction methods,physicochemical properties,and bioactivities.The main research contents and conclusions are as follows:1.Preparation and chemical composition of Lycium barbarum polysaccharides by different extraction methodsIn this paper,five polysaccharides from Lycium barbarum L.（LBPs）（LBP-1～LBP-5）were selectively extracted by different extraction methods.The yield was 20.7～100.1 g,and the yield rate was 2.1%～10.1%.The results of the chemical composition analysis showed that alkaloids were not detected in the five LBPs.The total polysaccharide content was（81.95%±1.6%）～（92.96%±0.76%）,the uronic acid content was（8.26%±0.46%）～（24.81%±0.46%）,and the protein content was（0.06%±0.03%）～（1.35%±0.13%）.All five LBPs were acidic polysaccharides.There was no significant difference in the species of chemical composition.2.Differences in structural characteristics of Lycium barbarum polysaccharides by different extraction methodsThe results of high-performance liquid chromatography showed that the monosaccharide compositions of the five LBPs were basically the same,mainly including glucose,xylose,and galactose,the sum of the three monosaccharides is about 85%of all known monosaccharide components.However,there was a significant difference in the content ratio of different monosaccharides.The results of ultraviolet spectrum analysis indicated that contained only a little protein with carbohydrate conjugated in the five LBPs and no other impurities.The results of infrared spectra analysis indicated that the five LBPs had typical infrared spectral characteristics of polysaccharides,but there were differences in peak intensity.The results of the nuclear magnetic resonance characteristic spectrum analysis revealed that the five LBPs had two configurations ofαandβ.The results of scanning electron microscopy showed that the five LBPs have different apparent morphologies.Among them,the surface of LBP-1 and LBP-3 was slightly smooth and distributed with holes of different sizes.LBP-2 showed irregular small particles,and the surface became more irregular and rough.The surface of LBP-4 is relatively smooth and uniform,slightly wrinkled,with a dense structure and almost no pores.LBP-5 showed a more compact structure and a thicker sheet structure.Further,the results of the thermogravimetric analysis showed differences in the mass loss of five LBPs,and its pyrolysis process was mainly divided into three stages.LBP-1 and LBP-5 had better thermal stability than other components,while LBP-2 had poor thermal stability.Meanwhile,there were triple helix structures in LBP-2,LBP-3,and LBP-4,which enhanced the activities of polysaccharides.There was no difference in glycosidic bonds and main functional groups of Lycium barbarum polysaccharides by different extraction methods.However,there was significantly difference in monosaccharide compositions,triple helix conformation,stability,and appearance morphology.3.Differences in biological activities of Lycium barbarum polysaccharides by different extraction methodsThe results of the activities screening suggested that the biological activities of the five LBPs were significantly different.LBP-3 showed the highest antioxidant capacity,and the IC₅₀ values for the clearance rates of lipid oxidation,DPPH,and ABTS were 0.46,0.45,and 0.50 mg·m L^-1,respectively.The inhibitory rate of LBP-3 on pancreatic lipase and binding sodium cholate,sodium glycocholate,and sodium taurocholate were better than those of other fractions,and the IC₅₀ values were 5.14,0.065,0.052,and 0.63 mg·m L^-1,respectively,which was slightly inferior to the positive control group.In the meantime,LBP-3 also showed stronger inhibitory effects on acetylcholinesterase and nitrosation reaction,and the IC₅₀ values for the inhibitory rate of acetylcholinesterase,nitrite scavenging,and blocking nitrosamine formation ability were 4.12,1.43 and 0.03 mg·m L^-1,respectively.But unlike the other sections,the inhibitory rate of LBP-4 onα-amylase and its activation rate of alcohol dehydrogenase were better than those of other ingredients,and the IC₅₀ values were 0.62 and 8.53 mg·m L^-1,respectively.Meanwhile,LBP-2 showed stronger inhibitory activity againstα-glucosidase,hyaluronidase,and tyrosinase,and the IC₅₀ values were 2.37,1.56,and 3.15 mg·m L^-1,respectively.Based on the systematic extraction method,this study explored the effects of different extraction methods on the physicochemical properties and in vitro bioactivities of LBPs,and established the relationship between extraction method and the type of polysaccharide,expecting to provide references for the precise development and utilization of LBPs.