Study On The Synthesis Mechanism And Antioxidant Activities Of Truffle Exo-polysaccharides Adjusted By Dioscorea Saponin

Truffle is an edible fungus with extremely high nutritional value and biological activity.As the main bioactive substance of truffle,truffle polysaccharides can be good at lowering blood sugar,anting tumor,anting oxidation and regulating immunity.However,the scare natural truffle resources can't meet the market requirements.The long growth period and environmental factors including climates,diseases and insect pests cause unstable truffle production.The liquid fermentation can overcome the above drawbacks and some natural compounds can be used to increase the production of bioactive substance.For this purpose,we optimized the culture condition and investigated the mechanism that the Dioscorea saponins?DS?increased exo-polysaccharides?EPS?of Tuber melanosporum.In addition,EPS structure and antioxidant activity change caused by DS was studied during the fermentation process.The results included the following:?1?Dioscorea provided the best EPS production compared to ginger,balsam pear,licorice,ginseng,Bupleurum,Ophiopogon,Platycodon grandiflorum and Akebia trifoliata.The functional ingredient DS significantly increased the truffle EPS production.The optimal medium contained sucrose 3%,frucose 4%,yeast extract0.7%,corn flour 1.1%,KNO₃ 0.5%,peptone 0.9%,KH₂PO₄ 0.18%,MnSO₄ 0.24%and DS 0.5%.The optimal culture conditions were 7%inoculum,culture temperature of 20?,rotary speed of 139 rpm,and culture time of 5-5.21 days.The EPS production could reach 9.85±0.643 g/L in the optimized medium by the liquid fermentation process under the optimal culture conditions.?2?The isolation and purification of EPS exhibited that only one polysaccharide TP1 was isolated from the EPS without DS,and two EPSs STP1 and STP2 were purified from the EPS with DS.It was proveb by HPLC analysis that the TP1 was composed of mannose,rhamnose and glucose,that STP1 was composed of glucose,galactose and arabinose,and that STP2 was composed of rhamnose,glucose,galactose and arabinose.FTIR analysis had proven that their main component was glucose,which was?-D-glucopyranose.?3?The antioxidant activity analysis of TP and STP indicated that the antioxidant activities of the EPS depended on EPS concentration.The DPPH free radical scavenging capability and total antioxidant activities of the STP were 61.37%,50.02%higher than those of the TP.The kinetics model analysis exhibited that the increase of scavenging DPPH free radical and total anti-oxidant capability depended on the maximum reaction velocity not the affinity for the substrate.Compared with TP,STP could not improve the capacity to inhibit hydroxyl radical synthesis.The inhibition of hydroxyl radical by STP was a mixed type.Among them,anti-competitive suppression was the main type.?4?The scanning electron microscopy?SEM?showed that the morphology of the truffle mycelium significantly changed after the addition of DS in the medium.The truffle mycelium became finer and more mycelia surface folds were observed.The reason can be the thinner cell wall and the increase of cell membrane permeability caused by DS.DPH probe studies,conductivity and macromolecular determination showed that DS increased the cell membrane fluidity and permeability,which could facilitate the exchange of intracellular and extracellular substance,accelerate the cell metabolish and facilitate the synthesis of EPS.The proteomics analysis exhibited that DS induced 23 proteins synthesis and terminated 1 protein synthesis.