Studies On Physicochemical Properties And Antioxidant Activity Of Exopolysaccharides From Pholiota Dinghuensis Bi

Pholiota dinghuensis Bi is a new species in Pholiota family,and is only found in Guangdong Province of China.Modern medical research shows that the fungi polysaccharides possess many biological functions,such as immunomodulatory,anti-tumor,antioxidation,cholesterol-lowering,hypoglycemic,anti-bacterial,anti-virus,anti-allergic and anti-inflammatory,hepatoprotectivity and intestinal prebiotics.Recently,major studies for Pholiota dinghuensis Bi mainly forcus on the optimization of mycelium polysaccharide fermentation conditions,purification and evaluation of antitumor activity,while on the investigation of exopolysaccharides has not yet been reported.Therefore,this study was aim to separate and purify exopolysaccharides from Pholiota dinghuensis Bi?PDP?,determine their physical and chemical properties,structures and antioxidant activities.The results were shown as following:1 Separation,purification and physicochemical properties of PDPThe yield for PDP production was 930 mg/L under the conditions of 28 ? and 120 rpm with the amount of 15%inoculation cultivation.Firstly,crude PDP was separated with DEAE fast flow anion exchange column chromatography,and each fractions of crude PDP was purified with the use of Sephadex G-100 gel filtration column chromatography.Finally,three fractions?PDP-1?PDP-2 and PDP-3?were obtained.The contents of total sugar,uronic acid,protein and sulfuric acid were determined by the method of sulfuric acid-phenol coloration,the m-hydroxy diphenyl coloration procedure,coomassie brilliant blue coloration and barium chloride-gelatin,respectively.The results showed that total sugar contents of crude PDP,PDP-1,PDP-2 and PDP-3 were 66.93%,63.20%,68.95%and 37.81%,respectively;Uronic acid contents were 0.61%,0.58%,0.94%and 0.58%,respectively;Protein contents were 0.88%,0.01%,0.24%and 0.01%,respectively;Sulfuric acid contents were 4.67%,10.45%,2.98%and 12.11%,respectively;PDP-3 showed relatively higher contents of protein,uronic acid and sulfuric acid among the polysaccharide fractions.The digestion of exopolysaccharides of PDP-1,PDP-2 and PDP-3 was studied in vitro by employing a simulated gastric juice and upper gastrointestinal model and analyzing molecular weight variation of digested products at different digestion times.The results indicated that PDP-1 was not digested in artificial gastric juice until 6 h.While PDP-2 and PDP-3 was stable in the degradation of artificial gastric,and digested in the intestinal juice after 4 h.ARSE rheometer was used to study PDP static rheological properties of exopolysaccharides,the results showed that the apparent viscosity increased with increase of the concentration,and temperature had no significant effect on PDP apparent viscosity.PDP apparent viscosity was higher in acidic condition than in in alkaline condition.NaCl and CaCl2,especially CaCl2,can increase the apparent viscosity of PDP.Sucrose can significantly increase PDP apparent viscosity.2 Structure of PDPThe relative molecular weight was determined by HPGPC.The results showed that the peaks of PDP-1 and PDP-2 were uniform,which demonstrated that the two components were separated well with high purity.Molecular weights of PDP-1,PDP-2,PDP-3 were 2.67×104,1.25×106 and 1.39×106 Da,respectively.PDP-1 was composed of mannose,ribose,rhamnose,galacturonic acid,glucose,galactose and fucose,and themolar ratio was 5.58:0.46:0.13:2.50:0.81:0.65:16.06;PDP-2 was composed of mannose,ribose,rhamnose,galacturonic acid,glucosamine and fucose,the molar ratio was 5.90:0.44:0.14:2.16:0.42:13.29;PDP-3 was composed of mannose,ribose,glucuronic acid,galacturonic acid,fucose,the molar ratio was 69.92:3.66:1.60:3.81:18.47.Galactose was found in PDP-1,but not in PDP-2 and PDP-3;glucuronic acid was found in PDP-3,while not in PDP-1 and PDP-2.Infrared spectrum of PDP showed that all samples posessed the characteristics peaks of polysaccharides.The spectrum absorption peak showed that the PDP-2 and PDP-3 were acidic polysaccharides.And PDP-3 might be complex of polysaccharide with protein or peptide.UV spectrum results indicated that certain protein or peptide exsisted in all samples,and higher protein absorption of PDP-3 in 280 nm was obvious,which demonstrated that PDP-3 contained higher amount of protein than other components of PDP.3 Antioxidant activities in vitro of PDPThe antioxidant activities in vitro of PDP were evaluated by measuring DPPH,hydroxyl and superoxide anion free radicals scavenging activity,metal ion chelating activity and Fe²⁺ reducing power.PDP-3 exhibited relative stronger scavenging activity than the others in most cases.The differences in antioxidant activities in vitro might be due to their differences in molecular weight,monosaccharide composition and uronic acid content.