Preliminary Study On The Regulation Of Pathogenic Fungi,Triterpenes Biosynthesis And Antioxidant Activity In Postharvest Ganoderma Lucidum

Ganoderma Lucidum,a kind of traditional and valuable Chinese herbal medicine,is rich in polysaccharide,triterpenoid,alkaloids and other active ingredients,and has been shown various bioactivities such as antioxidation,antitumor,antiviral,immune-modulating and protecting liver,etc.With the understanding of the health function,the consumption group of G.lucidum has expanded from China,Japan,Malaysia and other southeastern Asian countries to the West.Since the wild resource is rare,artificial cultivation is the main way to obtain G.lucidum products.High humidity environment is needed during the growth of the fruity body of G.lucidum.It is easy to be infected by pathogenic fungi if the management is poor.Furthermore,the G.lucidum fruiting body is also easy to be mildewed if it can't be dried in time after harvest.In order to control the pathogenic fungi of G.lucidum,the main pathogenic fungi were firstly studied and four strains of pathogenic fungi strains were isolated.The strain OTA was determined as Aspergillus flavus,strains OTB and OTD as Penicillium infrabuccalum,strain OTC as Trichoderma sp.by the morphology and rDNA ITS sequence analysis.Biological characteristics research shows that 4 strains of pathogenic bacteria in PDA medium grew well,and optimum temperature is 25 to 30?;The optimal carbon sources of OTA and OTB strains are xylose and glucose,respectively.The optimal carbon sources of OTC and OTD strains are fructose and sucrose.The optimal nitrogen sources of OTA and OTB strains were beef extract and urea,respectively.The optimal nitrogen sources of OTC and OTD strains were NaNO₃ and peptone.OTB,OTC and OTD strains grew well under acidic conditions,while pH has little effect on OTA growth.At the same time,the inhibitory effect of allyl isothiocyanate,a component of plant essential oil,on pathogenic bacteria is tested.The results showed that allyl isothiocyanate has a good inhibitory effect on the growth of OTA,OTB,OTC and OTD mycelia of bacterial strains.At 20?L/L dose,the inhibitory rate of allyl isothiocyanate on all four strains exceeds 97%.Triterpene is one of the main active ingredients in G.lucidum,its content directly affects the quality of G.lucidum fruiting body.To improve the content of triterpenes,the fruiting body of G.lucidum was treated by 21,40,60,80 and 100%oxygen at 1.5 mL/min for 6 days under 25oC,respectively.The effects of high oxygen treatment on the triterpenes biosynthesis,antioxidant activity and DNA damage protection of postharvest G.lucidum fruiting body were studied.The results showed that60%oxygen concentration can effectively slow weightlessness;The contents of total triterpenes,flavonoids and total phenols were increased by 50%to 80%compared with that of control group.The contents of 5triterpene monomers were also increased by high oxygen,and the highest content of triterpene monomer was ganoderic acid A,which was about 10times higher than that of ganoderic acid C1.High oxygen increase the gene expression levels of triterpene biosynthesis related enzymes:the most significant difference was observed in the expression of HMGR?3-hydroxy-3-methyl glutaryl coenzyme A reductase?;the expression level of HMGS?3-hydroxy-3-methyl glutaryl coenzyme A synthase?was the highest and that of OSC?Squalene epoxide cyclase?was the lowest.High oxygen could also enhance the antioxidant activity of G.lucidum.The scavenging rate on ABTS,superoxide anion and hydroxyl radical was significantly higher than that of the control group.The DNA damage protection rate of G.lucidum fruiting bodies treated with different concentration of oxygen ranged from 30%to 65%.The samples treated with 60%oxygen for 3 days had the highest activity,which was about 1.2times higher than that of the control group.In summary,the optimal conditions of high oxygen treatment were treating G.lucidum fruiting body by 60%oxygen for 3 days.Moreover,the spray drying method was used to produce microcapsule of G.lucidum triterpene to increase its water solubility and sustained release in the digestive juice.The conditions for microcapsule were:the ratio of core material and wall material was 1:2?m/m?;arabic gum and beta-cyclodextrin was used as wall materials at the ratio of 1:1?m/m?;the inlet temperature was 180;the flow rate was 30 ml/min;The embedding rate reached 88.9%under this condition.The release rate of microencapsulated G.lucidum tritepenes was:the simulated intestinal fluid>simulated gastric fluid>simulated oral fluid.The maximum release of microencapsulated triterpenoids in intestinal juice was 87.5%in 70 min.