A Study On Medium Composition Optimization,Primary Structural Characterizations,and Antioxidant Activities Of The Exopolysaccharides From Ganoderma Lingzhi

Ganoderma lingzhi Sheng H.Wu,Y.Cao&Y.C.Dai,a new species discovered from nothern China in 2012,belongs to the family Ganodermataceae in the order of Polyporales.Polysaccharide,which are among the important active components of mushrooms,have been reported to possess wide-ranging and potentially significant pharmacological properties in biochemical and medicinal areas.Therefore,the present study has carried out the following researches:(1)On the basis of many physicological indexes,the in vitro antioxidant activities of G.lingzhi were evaluated in the condition of liquid cultivation:Based on the tested indicators,the results showed that G.lingzhi had higher antioxidant activities,accelerating vigorous growth and metabolism of the fungus.Under the condition of liquid cultivation,large amounts of polysaccharide,polyphenol,flavonoid,and AA content and SOD activities were detected.The fungus exhibited remarkable scavenging activities against hydroxyl radicals,superoxide anions,DPPH radicals,and ABTS radicals.Stronger FRAP and higher ferrous ion chelating activity were also notable.It was suggested that the antioxidant activity of the fungus was closely related to mycelial growth,secondary metabolism secretion,and reduction capacity.Certain environmental stress can also stimulate the fungus to activate its antioxidant system to protect itself from oxidative damage.(2)The medium composition for production of exopolysaccharide from G.lingzhi was optimized by employing response surface methodology to sep up experiments and mathematical model:To improve the production of exopolysaccharide from G.lingzhi,PBD,path of steepest ascent,and BBD in response surface methodology were employed to set up mathematical model and exopolysaccharide yield was taken as the response.The optimal composition for production of exopolysaccharide from G.lingzhi was obtained as follows:glucose 59.62 g/L,yeast extract 10.03 g/L,CaCO3 0.2 g/L,vitamin B145.13 mg/L,KH2PO4 1.0 g/L,peptone 1.5 g/L,Tween 80 10.26 mL/L,ZnSO4 0.3 g/L,mannitol 1.5 g/L,MgS04 0.5 g/L,and aspartate 8.86 g/L.Under the optimized conditions,the exopolysaccharide yield was 3.57±0.21 g/L,which corresponded well to the theoretical result of 3.53 g/L predicted by the developed model,and this yield was 3.16-fold higher than that produced in basal medium alone.It was concluded that the response surface methodology could be indeed used for optimizing medium composition for improving exopolysaccharide yield.(3)The exopolysaccharide from G.lingzhi was extracted and isolated by ethanol precipitation,and its structural features including total carhydrate content,protein content,uronic acid content,molecular weight,monosaccharide composition,and spectrometric properties were characterized:Cell-free culture medium was harvested after cultivating G.lingzhi according to the up-mentioned optimized medium compostion.Its exopolysaccharides(denoted as GLEPS)were extracted and isolated from the culture medium by concentration,ethanol precipitation,Sevag method,dialysis,and lyophilization,with an extraction yield of 35.37%.GLEPS contained 87.97%carbohydrates and 21.74%uronic acids.No adsorption was observed at 280 nm on the UV spectrum,indicating possible absence of protein in GLEPS.The molecular weight of GLEPS was estimated to 475000 and 21.6 kDa by HPGPC.HPAEC results demonstrated that GLEPS was a heteropolysaccharide composed of L-Ara,D-Gal,p-Glc,D-Man,L-Rha,D-Xyl,galacturonic acid and glucuronic acid with the contents of 0.67%,0.91%,12.47%,50.75%,21.24%,3.21%,1.57%,and 9.17%,respectively.FT-IR analysis confirmed that GLEPS possessed ?-glucosidic bond in its structure.(4)The in vitro antioxidant activities of the exopolysaccharide from G.lingzhi was assessed systematically:In vitro antioxidant activities of the exopolysaccharide GLEPS from G.lingzhi were assessed systematically.The antioxidant indexes reached their peaks when the concentration of GLEPS was 2.0 mg/mL.GLEPS also exhibited a dose-dependent manner and possessed higher antioxidant capacity than that of the positive control.It was indicated that GLEPS had higher antioxidant activity,which could be explored as a novel natural antioxidant in functional food or medicine.The results facilitate further studies,development,and utilization of the medicinal fungus G.lingzhi.