Identification Of A Lactone-producing Fungus And Preliminary Study On Its Fermentation Condition

Nowadays most of the flavors used for the preparation of perfume compounds are produced by chemical synthesis and these compounds are racemic mixtures,which differ much in the flavor quality from natural compounds.People find that the residual chemical compounds in the flavors may be toxic to human health,as a result,customers regard flavors with "nature"label as safe and reliable addition agent.More and more researchers put their eyes on the production of natural flavors by biotechnology,so the development and utilisation of natural products is the current in flavor industry.Lactones are widely distributed in fruits,beverages and daily products.They have been utilized as flavor and fragrance compounds in many products,the most well known lactone is gamma-decalactone which has strong peach and cream odour.Natural gamma-decalactone can be extracted from fruits,however,due to the limit of production region and seasons,it is hard to provide large amount of natural products.Gamma-decalactone can be produced by biotransformation and most of the microorganisms used for the biotransformation are yeast and some filamentous fungi,such as Yarrowia lipolytic,on which many patents have been applied for,Sporidiobolus salmonicolor and Sporidiobolus ruinenii.The strain used in this paper is a basidiomycete,polyporales sp.It can automatically synthesize gamma-decalactone and gamma-octalactone without any oil or fatty acid as substrate.When adding castor oil,the yield of gamma-decalactone increases much.The thesis consists of the purification and identification of the strain,identification of partial metabolites,the optimization of medium for fermentation of gamma-decalactone and preliminary study on the fermentation conditions.Specific studies are as follows:1?Morphological characters and identification of the strainThe basidiocarp is in semicircular shape,sessile,imbricate on the tree trunk.Fruiting body is straw yellow and color turns to apricot yellow at the edge.The back is white,covered with fungus holes.Hyphae can be divided into two kinds,one is reproductive hyphae,which is hyaline,with many lock-like joints and at the same time some septates.The other is skeleton hyphae with thick walls and spiral.We amplified the 18srRNA gene and ITS with the primers NS1,NS8 and ITS1,ITS4 respectively,and then a phylogenetic tree was built.But we can not identify the strain,so for the time being,we call it polyporales sp.LH-1.2?Identification of partial metabolitespolyporales sp.LH-1 can produce severval natural flavors with castor oil as substrate,the main flavor is gamma-decalactone,at the same time,with some gamma-octalactone and 8-decalactone,still there are some unidentified compounds which belong to enols or esters.Gamma-decalactone,gamma-octalactone and?-decalactone are all in pleasant aroma which can be used as safe food additives.polyporales sp.LH-1 can synthesize large amount of extracellular polysaccharide,in the supernatant the yield reaches 0.8g/l,and the mycelia,35mg/g.It can synthesize lots of organic acid which low the pH of the medium to 2,so that it can prevent interference of other microorganisms.3?optimization of the fermentation conditionThe composition of medium in the flask is:soluble starch 10g/l,soymeal 10g/l,castor oil 100ml/l,MgSO4 0.5g/l,KH2PO4 0.46g/l,Na2HPO4.12H2O 1.2g/l,tween 200.05%,pH5.The yield of GDL can reach 3.2g/l at the 6th" day.5L and 3Lauto-controlled fermenter were used in the amplified experiment.It was found that dissolved oxygen influences the fermentation very much,the fermentation conditions remain further studying.