Improvement Of Saccharomyces Cerevisiae NX11424 By Mutagenesis And Cross Breeding

Saccharomyces cerevisiae is the predominant microorganism in the wine making process and has a significant impact on the quality of the wine.In recent years,we have selected the excellent yeast series strains with indigenous characteristics,which not only give a unique style of wine,but also produce less off-flavor.The indigenous yeast NX11424 has strong fermentation ability and unique flavor,which is an excellent strain in winemaking.However,this strain still produces a small amount of hydrogen sulfide and acetic acid,which has negative influence on wine flavor.Therefore,it is necessary to improve its characteristics by mutagenesis and crossbreeding methods.The native wild S.cerevisiae 112Y4 produces none hydrogen sulfide,which is an excellent characteristic that could be used to cross with NX11424 to obtain low hydrogen sulfide phenotype.Improve the volatile acid and ethanol properties of S.cerevisiae NX11424 by ARTP mutation.In this study,the main results are as followed:(1)The separation of haploid of NX11424 and 112Y4.Twenty-seven haploids were obtained from NX11424 and thirty-two haploids were obtained from 112Y4 by sporulating with two parents.Among them,twenty-five of haploid belonged to α type and two of haploid belonged to a type in NX11424;For 112Y4,twenty-nine of haploid belonged to α type and three of haploid belonged to a type.N17 and N9(from NX11424),Y35 and Y29(from 112Y4)were selected by BIGGY medium and Triple M medium with low hydrogen sulfide,which could produce 12.0,59.5,2.5,4.0 ppm,respectively.(2)The haploid N17 and N9 were crossed with haploid Y35 and Y29,respectively,to obtain the diploid strain by microscopic examination.According to the Interdelta typing analysis of the haploid and diploid strains,NY1735(N17×Y35)and NY929(N9×Y29)were obtained after the analysis.In addition,the hybrid strains NY1735 and NY929 were used for fermentation by simulated juice,producing hydrogen sulfide production of 9.5 ppm and30.8 ppm,respectively.The fermenting ability of hybrid NY1735 and NY919 were similar to NX11424 strain,which are two successfully improved strains with low hydrogen sulfide production.(3)The ARTP mutation of S.cerevisiae NX11424.260 strains were preliminary selected by TTC,2-DG and 2,4-DNP medium by ARTP mutation of NX11424.Further,260 strains were selected by 10 and 300 mL synthetic grape must fermentation and ice wine(800mL)by turns,and the mutant strain T2-5 was successfully obtained with low volatile acid activity,which was reduced by 26.4% in the Vidal fermentation.The mutant strain T2-62 was selected with low ethanol production,and ethanol yield was decreased by 21.3%.The sensory evaluation of the wine was carried out on the preferred mutant strain,and the scores were as followed: T2-5> F15> NX11424> T2-62.The persistence of aroma T2-5 enhancement,with a typical floral,honey,peaches,lemon,melon and other tropical fruit aroma.The aromas of wine samples were subjected to GC-MS chemical analyses.The concentration of higher alcohols,esters were slightly lower,but contained few fatty acids obviously.It had more varietal aroma-active compounds,especially 1-Octen-3-ol,2-phenylethanol,rose oxide,undecanal,which rich sweet kind of flowers.After the evaluation for the technological characteristics of wine,the T2-5 mutant strain exhibited low tolerance to high alcohol and high tolerance to high sugar compared with the original strain NX11424.In conclusion,we successfully selected the strain T2-5 with low volatile acid activity,it is a potential strain for ice wine fermentation.