Effect Of Environment Microbiota On The Characterized Flavor Compounds Of Light-flavor Baijiu

Baijiu is produced by traditional spontaneous solid-state fermentation under open condition,the microorganisms from environment such as air,floor,tool,equipment and surface of jar are also involved in the fermentation and the flavour of Baijiu is largely influenced by kinds of environmental factors.Especially in summer,there was a production break due to a decline in the productivity and quality of light-flavor Baijiu.The annual production was divided into three periods:(1)Lipai period(LP)refers to the beginning of a production cycle in September after the summer production break,(2)Tiaopai period(TP)refers to the last period of production before production break in the summer,(3)Yuanpai period(YP)refers to the production period between LP and TP.Throughout the annual production,it was found in common that the ester content in light-flavor Baijiu produced during LP was significantly lower than that produced during YP which was presumably due to the microbiota varied with different periods.In this study,the microbiota of the surrounding environment and starter in different periods were investigated.The flavor profile and microbiota during material processing and fermentation process in different periods were tracking monitored and analyzed by multivariate analysis to reveal the main different microorganisms in different periods.SourceTracker were used to analyze the main source of critical microorganisms during fermentation.Furthermore,the effects of critical microorganisms on flavor were investigated through correlation analysis and fortified fermentation.The main contents are as follows:1.Microbiota of air,surface of jar and Daqu in different periods:There was no significant difference between different periods in microbial counts of bacteria and fungi in Daqu and air.While the lactic acid bacteria counts on the surface of fermented jars in YP was significantly higher than that in LP.The surface of jar predominated by Pseudomonas in LP.In contrast,Lactobacillus dominated on the surface of the jar in YP.2.Dynamics of volatile flavors and microbiota during material processing of light-flavor Baijiu in different periods:Correlation analysis indicated that Lactobacillus,Pichia and Cyberlindnera showed positive correlation with various flavors during material p re treatment.Lactobacillus,Rhizopus,and Saccharomycopsis may get introduced from the environment with material pretreatment and would be an important source of microorganisms for alcoholic fermentation.3.Dynamics of volatile flavors and microbiota in different fermentation periods of light-flavor Baijiu:Volatile flavor dynamics during fermentation were investigated by HS-SPME-GC-MS.Multivariate analysis of volatile flavors revealed that the content of ethyl acetate and ethyl lactate during LP was significant lower than that during YP at the later stage.Furthermore,results indicated that the differences of microbial community occurred at later stages,mainly due to different structures of Lactobacillus.At the later stage in YP,Lactobacillus acetotolerans predominated in the fermented grains while was in a very low abundance in LP.Correlation analysis indicated that Lactobacillus and Saccharomyces positively correlated with most esters,acids and alcohols,etc.Species-level analysis showed that L.acetotolerans had a positive correlation with short chain carbon esters.The different lactic acid bacteria counts and structure may be the important factors which caused difference in flavor profile between LP and YP.4.Sources of bacterial communities during fermentation:SourceTracker analysis revealed that bacteria in fermented grains of LP were mainly from Daqu.While,bacteria in fermented grains of YP were mainly from sorghum after cooling,Daqu and surface of jar.The dominant bacteria Lactobacillus plantarum and Lactobacillus brevis mainly derived from Daqu.L.acetotolerans and Lactobacillus hilgardii predominant in YP mainly derived from sorghum after cooling and surface of jars.5.Effect of fortified fermentation with different strains on the flavor of Baijiu:Indigenous lactic acid bacteria with high alcohol tolerance and esterase activity were selected for fortified fermentation.The selected strains could significantly promote the forming of ethyl acetate.Higher harmony and ester content in the samples fermented with L.hilgardii and L.acetotolerans were found than control.Pichia anomala could also promote the forming of ester although the effect is weak than the selected lactic acid bacteria,but it could avoid rancidity as only a little acid accumulate in the samples.