Community Struction And Function Of Lactic Acid Bacteria During Fermentation Process For Sesame-flavor Liquor Making

Liquor-making process is a spontaneous fermentation process which drived by microorganisms,including bacteria,yeasts and moulds.During liquor fermentation process,lactic acid bacteria account for a large proportion,the type and community dynamics of lactic acid bacteria are of great importance to liquor quality.However,there are few studies on lactic acid bacteria in sesame-flavor liquor fermentation process.In order to explore the structure and function of lactic acid bacteria during sesame-flavor fermentation process,the diversity and carbon source metabolic characteristics of lactic acid bacteria were analyzed by cultureindependent and culture-dependent methods.The community dynamic of lactic acid bacteria and influencing factors were analyzed by comparing craft liquor-making process and mechanized liquor-making process.The interaction between lactic acid bacteria and other microorganisms was studied by correlation analysis and co-culture experiments.The main results are as follows:(1)Lactic acid bacteria,accounted for 83.25% of the total bacteria,were the predominant bacteria during sesame-flavor liquor fermentation process.There were a rich variety of lactic acid bacteria in sesame-flavor liquor fermentation process.Lactic acid bacteria in sesame-flavor liquor fermentation process included Weissella,Pediococcus,Lactobacillus,Leuconostoc,and Lactococcus,which classified to 43 species.Ten species of lactic acid bacteria were observed higher than 0.5%,including Weissella paramesenteroides,Weissella cibaria,Weissella confuse,Pediococcus pentosaceus,Leuconostoc pseudomesenteroides,Lactobacillus fermentum,Lactobacillus plantarum,Lactobacillus paracasei,Lactobacillus acetotolerans and Lactobacillus sp..The similarity was only 92% between Lactobacillus sp.and Lactobacillus suebicus LC071852.1,and Lactobacillus sp.probably was a new specie of lactic acid bacteria.(2)Eighty five strains of lactic acid bacteria can be isolated from fermented grains,which classified to 12 species.The number of strains of Lactobacillus paracasei and Pediococcus acidilactici was 27 and 25,respectively.Several species,including Pediococcus pentosaceus,Lactobacillus fermentum,Lactobacillus plantarum,Lactobacillus acetotolerans,were also isolated.Culturable lactic acid bacteria had a better ability to use glucose,but there were differences in dextrin and other substances utilization.Lactobacillus had a better ability to utilize dextrin than Pediococcus.The dextrin utilization capacity of Lactobacillus was helpful for their growth in the later stage of pit-fermentation.(3)The community structure and quantity of lactic acid bacteria in liquor fermentation process were changing over time.In heap-fermentation stage,Weissella was more than half of the total bacteria.In pit-fermentation stage,Lactobacillus became the predominant bacteria,and the relative abundance of Lactobacillus sp.was up to 80% in the mid and later stage of pitfermentation.During heap-fermentation and the early stage of pit-fermentation,the biomass of lactic acid bacteria changed little.After 5 days of pit-fermentation,the biomass of lactic acid bacteria increased fast,and reached a maximum in the mid stage of pit-fermentation.In heap-fermentation stage,bacterial community structure in craft liquor-making process had a slight difference from mechanized liquor-making process.In pit-fementation,the bacterial community succession in mechanized liquor-making process was different from craft liquor-making process.Lactobacillus in mechanized liquor-making process became dominant earlier than craft liquor-making process.In mechanized liquor-making process,the bacterial community became dominated by Lactobacillus(93.31%)at 10 days of pit-fermentation.In craft liquor-making process,Lactobacillus(49.14%)increase slowly before 10 days.Lactobacillus dominated the bacterial community at 15 days(97.14%)of pit-fermentation in craft liquor-making process.The mechanized operation changed the structure and succession of lactic acid bacteria communities in liquor-making process,which caused the significant change of lactic acid,acetic acid and citric acid during the fermentation process.(4)Glucose consumption,dextrin consumption and ethanol production,not lactic acid,acetic acid and citric acid,correlated with bacterial communities.In the early stage of pitfermentation,with the consumption of carbohydrate,ethanol was constantly producing.Mechanized liquor-making process gave faster ethanol production in the first 5 days of pitfermentation.Higher ethanol production made faster rate of bacterial community succession,and made Lactobacillus become the dominant bacteria in advance.(5)According to the correlation between lactic acid bacteria and other bacteria during the fermentation process,lactic acid bacteria can be classified into Lactobacillus and nonLactobacillus(including Weissella,Pediococcus,and Leuconostoc).The non-Lactobacillus positively correlated with each other,and these lactic acid bacteria appeared mainly in the early stage of fermentation.Lactobacillus was negatively correlated with other bacteria,appearing mainly in the later stage of fermentation.Lactobacillus was positively correlated with Pichia and Saccharomyces,and negatively correlated with Wickerhamomyce and Aspergillus;while the lactic acid bacteria(Weissella,Pediococcus,Leuconostoc)negatively correlated with Saccharomyces.The lactic acid bacteria(Weissella,Pediococcus,Leuconostoc)may slow the growth of Saccharomyces,affecting the production rate of ethanol.The co-culture experiment results of lactic acid bacteria and yeasts showed three strains of Lactobacillus had no significant effect on the growth of Saccharomyces cerevisiae,while Pediococcus acidilactici inhibited the growth of Saccharomyces cerevisiae.