Analysis On The Flavor Characteristics And Mechanisms Of Zygosaccharomyces Bailii In Maotai-flavor Liquor Making

Chinese Maotai-flavor liquor is produced by a relative high temperature fermentation that resulted in the specific physiological characteristics and mechanisms of brewing microbes to contribute to the unique flavor of this liquor.Zygosaccharomyces bailii is a dominant species in Chinese Maotai-flavor liquor fermenation,but its function and mechanism are still unclear.Therefore,it is important to study the fermentation characteristics and mechanisms of Z.bailii under the Maotai-flavor liquor fermentation environments,which is significant to better understanding the function of Z.bailii and to improving the theoretical system of Maotai-flavor liquor fermentation.This study focused on the Z.bailii 15 strain which was isolated from Maotai-flavor liquor fermentation process and had an excellent phemotype.Its physiological characteristics were studied under different fermentation environments and its fermentation mechanisms were further revealed based on the genome and transcriptome analysis.The main contents and results are as follows:(1)The fermentation characteristics of Z.bailii 15 were studied by comparing with those of Saccharomyces cerevisiae MT1.Results showed that the biomass of Z.bailii 15 was 54%of that of S.cerevisiae MT1 and its highest ethanol yield(4.02 g·L-1)was about 36% of that of S.cerevisiae MT1.Meanwhile,the alcohols and ketones productions of Z.bailii 15 were less than those of S.cerevisiae MT1,but its acids,esters and aldehydes productions were 1.75 times,2.28 times and 3.45 times of those of S.cerevisiae MT1,respectively.Moreover,compared with S.cerevisiae MT1,it was able to generate 19 specific flavor compounds including 2-heptanol,2-nonanol,1-nonanol,1-hexanol,geraniol,2-heptanone,propionic acid,butyric acid and etc.,which might significantly contribute to the flavor of Maotai-flavor liquor.The genome analysis showed that key genes involved in the Harris pathway and Ehrlich pathway for the flavor compounds production could be found in the Z.bailii 15 genome,including at least 14 amino acid transferases,3 ?-keto acid decarboxylases,4 alcohol dehydrogenases and 3 aldehydes dehydrogenases genes.In addition,the specific genes ARO9,ARO8 and ALDH2 were found in the Z.bailii 15 genome,which might be associated with its unique metabolism of flavor compounds.(2)The fermentation characteristics and mechanisms of Z.bailii 15 at 30°C and 37°C were analyzed.Compared with at 30°C,the biomass of Z.bailii 15 at the end of fermentation decreased by 32% and its highest ethanol yield(2.23 g·L-1)decreased by 45% at 37°C.Meanwhile,the flavor compounds production of Z.bailii 15 per unit cell was also significantly changed.Among them,the alcohols and esters productions had no significant change,the ketones production decreased by 28.30%,but the acids and aldehydes productions were respectively 110% and 41% higher than those at 30°C.The transcriptome analysis showed that 126 and 131 genes in the Z.bailii 15 genome were significantly up-regulated and down-regulated(?2-fold,P<0.05),respectively,at 37°C compared with at 30°C.Among them,genes related to the amino acids transport were significantly up-regulated.Amino acids were one of the main sources of flavor compounds,therefore,those up-regulation genes might bebeneficial to increasing the flavor compounds production of Z.bailii 15.In addition,genes involved in the MAPK signaling pathway,yeast cell proliferation and cell wall formation of Z.bailii 15 were also significantly changed,which might have a certain effect on the survival of Z.bailii 15 in high temperature environment.(3)Z.bailii 15 was separately cultured with S.cerevisiae MT1,Lactobacillus buchneri XJ-L2 and Bacillus licheniformis MT6,respectively.In mixed cultures,the growth and ethanol production of Z.bailii 15 were inhibited by S.cerevisiae MT1,while were not affected by L.buchneri XJ-L2 and B.licheniformis MT6.Meanwhile,the flavor compounds production of Z.bailii 15 was reduced by S.cerevisiae MT1 and L.buchneri XJ-L2,but was promoted by B.licheniformis MT6 and among them,the alcohols,acids,esters and aldehydes productions increased by 41%,36%,44% and 73%,respectively,compared with those in Z.bailii 15 single culture.Transcriptome analysis of Z.bailii 15 showed that genes,related to the carbohydrate metabolism,amino acids metabolism and energy metabolism,were significantly up-regulated(?2-fold,P<0.05)in mixed culture with B.licheniformis MT6.Flavor compounds mainly derived from the metabolism of carbohydrates and amino acids;therefore,those up-regulated genes might be beneficial to increasing the flavor compounds production of Z.bailii 15.