Study On Structure,Synthesis Related Enymes And Hypoglycemic Activity Of Exopolysaccharide From Cordyceps Militaris Mycelium

As one of the traditional Chinese medicines in China,Cordyceps militaris is widely used as a medicinal and folk nourishing food.Polysaccharide is an important active ingredient of Cordyceps militaris,which is rich in biological activity.In recent years,the hypoglycemic activity of polysaccharides has received much attention.In this paper,the structure of the exopolysaccharide of Cordyceps militaris was characterized;the effects of culture conditions on the yield of exopolysaccharides and polysaccharide synthase were analyzed;the hypoglycemic activity of exopolysaccharides was also studied.The results are as follows.Cordyceps militaris was liquid fermented to obtain fermentation broth.The crude exopolysaccharide was obtained by ethanol precipitation,protein and pigment removement.The carbohydrate content was determined by phenol sulfuric acid method to be 33.59%.The pure polysaccharide was purified by Sephadex G-200,named as EPS,and its carbohydrate content was 65.32%.The molecular weight was measured to be 1.556×103 kDa by high performance liquid chromatography with dextran as a standard.The structure of EPS was analyzed by specific optical rotation,infrared spectrum,nuclear magnetic resonance,monosaccharide composition and methylation.ete.The results showed that the specific optical rotation of EPS was-85°.The monosaccharide of EPS was composed of mannose,glucose and galactose,whose molar ratio was 1.68:1:1.83.The main chain of EPS was mainly composed of(1?4)linked galactose,(1?3)linked galactose and glucose,(1?3,6)linked mannose,(1?4)linked mannose present in the main chain or branch.The Congo red test showed that there was a triple helix structure when the concentration of the NaOH solution was 0.25-0.30 mol L-1.Scanning electron microscopy results showed that the morphology of EPS had crossed fibroid structure with irregularporous structures at the surface.The effects of fermentation conditions on the production of exopolysaccharides and the activity of polysaccharide synthase in Cordyceps militaris were investigated.Studies had shown that the production of exopolysaccharides and the enzyme activity of phosphoglucose mutase(PGM),UDP-glucose pyrophosphorylase(UGP),phosphogluco-se isomerase(PGI)were all higher in the fermented conditions of glucose 4%,beef cream 1%,CaCOa3 0.05%,pH 7 for five days.In addition,PGM and UGP were the most relevant to the production of exopolysaccharides.The hypoglycemic activity of the exopolysaccharide of Cordyceps militaris was studied.The results of antioxidant capacity of EPS in vitro showed that the scavenging ability of EPS to DPPH free radicals,·OH radicals,O2-·free radicals and ABTS was 53.7±1.63%,45.4 ± 1.56%,23.7±1.02%and 46.7±1.41%at the concentration of 3 mg mL-1.It indicated that EPS had antioxidant capacity,and it was possible to treat diabetes by affecting oxidative stress.The results of a-glucosidase inhibition experiments in vitro showed that the inhibition rate of ?-glucosidase increased as the purity and concentration of polysaccharides increased.The results of the hypoglycemic model in mice indicated that both medium and high dose of EPS could reduce mouse's blood sugar content,restore glucose tolerance,improve fat metabolism disorder,and repair and protect damaged liver and kidney tissues.