Study On Sulfated Carboxymethylation Modification And Antioxidant Activity Of Jujube Polysaccharides

As the main biological active component of red jujube,has the functions of anti-fatigue,immune regulation,anti-oxidation,anti-tumor,liver protection,hypoglycemia and gastrointestinal protection,the biological activity of polysaccharides is closely related to its molecular structure,while some natural plant polysaccharides have weak biological activity,so molecular modification of polysaccharides has gradually become a research hotspot in recent years.Jujube polysaccharides as raw materials in this thesis,the initial impurity removal process was carried out by deproteinization and decolorization.The modification polysaccharides were further purified by DEAE-52 cellulose column chromatography and Glucan G-100column chromatography.The structure characterization and in vitro antioxidant detection were tested after the purification,confirming that both sulfated and carboxymethylated modification can improve the antioxidant activity of jujube polysaccharides.The specific results were as follows:1.Sulfated modification and structural characterization of Jujube polysaccharidesTaking jujube polysaccharide as raw material,Deproteinization by Sevage method,the protein removal rate was 74.5%,the polysaccharide retention rate was 70.8%.The decolorization rate was 87.4%,the retention rate was 72.8%by using AB-8 macroporous resin.The best modification process of jujube polysaccharide by sulfation is time 2 h,temperature 60℃,dosage of esterifying agent 1.0 g,and the highest degree of substitution was 0.955.The structure of polysaccharide was analyzed by AFM,HPLC,SEM,Congo red test and HPGPC.The results showed that unmodified and sulfated jujube polysaccharides were mainly composed of glucose,glucuronic acid and arabinose,and the relative molecular weights were 4.865×10³ Da and 7.426×10³ Da,respectively.Congo red test showed that jujube polysaccharides did not have triple helix structure,and sulfated modification did not affect the triple helix structure of jujube polysaccharides.2.Carboxymethylation modification and structural characterization of Jujube polysaccharidesDeproteinized and decolorized jujube polysaccharides as raw materials,the modification conditions of carboxymethylation were optimized by single factor and response surface test.The results of carboxymethylation modification of Jujube polysaccharide showed that the optimal conditions were as follows:3.5%monochloroacetic acid,3 mol/L Na OH concentration,70℃.The characteristic absorption peaks of carboxymethylation were 1592.89cm^-1 and 1421.26cm^-1,indicating that the polysaccharides were successfully modified by carboxymethylation.Scanning electron microscopy results showed that the surface of carboxymethylated jujube polysaccharides was smooth,and the particles were small and flaked.Gel chromatography analysis showed that the relative molecular weight of unmodified and carboxymethylated jujube polysaccharides were 4.865×10³ Da and 8.314×10³ Da respectively.3.Determination of antioxidant activity of jujube polysaccharide and its derivatives in vitroThe reducing power of red jujube polysaccharides,the scavenging rate of DPPH,hydroxyl,ABTS,superoxide anion radical and Fe²⁺chelating ability were measured.The effects of sulfated and carboxymethylated modification on the antioxidant activity of ziziphus jujube polysaccharides in vitro were investigated.For sulfated,carboxymethylated and unmodified jujube polysaccharides,ABTS free radical and DPPH free radical scavenging rate were 99.02%,99.59%,53.95%and 84.70%,93.83%,53.85%,respectively,when the concentration was 5 mg/m L.hydroxyl radical and superoxide anion radical scavenging rate were38.75%,44.7%,29.25%and 46.57%,47.73%,44.89%,respectively.The results showed that both sulfate modification and carboxymethylation modification could improve the antioxidant activity,and the antioxidant activity effect of carboxymethylated jujube polysaccharides was more obvious.