The Impact Of Different Saccharomyces Cerevisiae Strains On Microbial Diversity And Wine Quality In Chinese Rice Wine Fermentations

Chinese rice wine(CRW),with thousands of years of history in China,is one of the largest fermented wines in the world.Its unique flavor,low alcoholicity and high nutritional value make it popular in China.In the process of CRW fermentation,the microbial communities are composed of the microbes in the wheat Qu and the yeast in the starter.Through the coordinated fermentation of multiple microorganisms,the microbial community structure and flavor composition of rice wine are complex.Saccharomyces cerevisiae dominates ethanol fermentation and produces a variety of flavor substances,but the influence of S.cerevisiae on the fermentation microbial community is still unclear.The influence of yeast strains on gene function and flavor substances needs to be studied.The study is aimed at these problems,and uses advanced metagenomic methods to study the impact of S.cerevisiae strains on the composition of microbial communities and flavor metabolites.The main research contents are listed as following:(1)The extraction method of microbial total DNA in the wheat Qu and in the fermentation broth of CRW complex system was optimized.Finally,the optimized SDS-CTAB method improved the total DNA extraction efficiency.It can reduce the interference of non-microbial components in the system and provide a good basis for high-throughput sequencing(HTS)of subsequent CRW fermentation microbes.(2)Based on the high-throughput sequencing analysis of the fungal internal transcriptional spacer(ITS1)and the 16 S rRNA gene of bacteria,the abundance of fungi in the fermentation process of the three CRW(YJSH1,N85,XZ11)have the similar change trend.The fungi in the saccharification fermentation stage was mainly from Aspergillus in the wheat Qu,and the S.cerevisiae in the middle and late stages of fermentation.There are many kinds of bacteria,which are mainly from the wheat Qu,but its community structure is quite different from that of the wheat Qu.The most abundant six bacterial genera are Leuconostoc,Pantoea,Enterococcus,Lactobacillus,Saccharopolyspora and Staphylococcus.S.cerevisiae mainly affects the bacterial community structure,of which Lactobacillus is the most significant different bacterial genus among different CRW,especially in the late stage of CRW fermentation.The relative abundance of Lactobacillus in CRW sample fermented by XZ11 yeast strain was 16.1%,which was about 5 times that of N85 wine sample and 9.6% for YJSH1 wine sample.The abundance of each KEGG metabolic pathway in the three fermentation stages showed a similar trend: The change was highest in the saccharification fermentation,the primary fermentation was the lowest stage,and the Secondary fermentation was the median stage?(3)Volatile compounds were extracted by a headspace solid phase microextraction(HSSPME)and gas chromatography-mass spectrometry(GC-MS)was employed for separation and quantitative analysis.A total of 57 volatile compounds were detected in volatile flavor compounds,of which alcohols and esters account for more than 90%.The esters are the most type of components,and the content of alcohol is the highest.The lactic acid content of organic acids is the most and its difference is significant between CRW samples.After multivariate statistical analysis,the CRW fermented by the same S.cerevisiae strain was clustered into one type,among which phenylethyl acetate,caprylic acid,caproic acid,propanol lactone,acetic acid,ethyl heptanoate,ethyl pentadecanoate are the most important distinguishing substances among the CRW.The results showed that the S.cerevisiae strains or the changes of microbial community structure of CRW had significant effects on flavor substances.(4)At the end of secondary fermentation,the composition and abundance of bacterial and fungal species were compared by means of metagenomics.Bacteria are the most important microbe at this stage and the strain with the largest difference in microbial composition among the three wines is Lactobacillus brevis.Through the eggNOG database analysis,it is found that the highest functional abundance in the microbial system is metabolism,of which carbohydrate metabolism is an important metabolism of CRW fermentation.Subsequently,the gene set was compared with the CAZy database,which indicated that the strain with the most significant functional difference between CRW was Lactobacillus brevis.Through the analysis of KEGG pathway and species correlation,it was found that Lactobacillus brevis contributed significantly to the metabolism difference between the CRW.Therefore,the three strains of S.cerevisiae mainly affected the structural changes of Lactobacillus brevis in the fermenting microbial community,and also changed the gene function of the microbial system.Our results indicated that Lactobacillus brevis is a characteristic strain causing the change of flavors of different CRW.Taken together,this work provided some new research ideas for the study of CRW microbes,with important guiding value for rational utilization of the interaction of CRW fermentation microbes and precise control of microbial flora metabolism.