Microbial Community Succession And Its Drivers During Roasted Sesame-flavor Liquor Fermentation

The assembly and succession of microbial community play an important role in food fermentation process and quality of final products.However,it's not clear how the microbial community assembled and which factors affected this process now.Therefore it's critical for revealing brewing mechanism of food microbe to explore microbial community succession and its drivers during food fermentation process.This study revealed microbial community succession and dominant genera during roastedsesame flavor liquor fermentation through high throughput sequencing.Then environmental drivers and microbial interactions during community succession process were revealed through multivariate statistical analysis.After comparing microbial community of different brewing systems,strengthening microbe were selected based on abundance and distribution and applied to fermented grains to reveal effects of strengthen on community composition and succession trajectories.This study provided a basis for revealing brewing mechanism of liquor microbe and improving the controllabilityduring fermentation.The main results of this study are as follows:(1)Lactobacillus,Bacillus,Pichia,Saccharomyces,Aspergillus,Wickerhamomyces,and Geotrichum were identified as dominant genera during roasted sesame-flavor liquor(QT)fermentation based on average relative abundance(> 1.0%)and distribution frequency(> 50%)through high throughput sequencing.The fermentation process was divided into two stages according to changes of physicochemical properties.At stage ?(0~5 d),the temperature increased from 22.0 ? to 35.0±2.0 ?.The curves of ethanol and reducing sugar had maximum slope.Bacillus(54.12%±7.12%)and Pichia(64.86%±10.30%)were the genus of prokaryotic and eukaryotic microorganisms with the highest average abundance,respectively.At stage ?(5~30 d),the temperature decreased to 26.0±1.0 ?.The curve of acidity had maximum slope at 5~10 d.Lactobacillus(91.07%±16.96%)replaced Bacillus and became the most dominant microorganism in prokaryotic microflora until the end of fermentation;Saccharomyces(41.66%±6.31%)became the most dominant microorganism in eukaryotic microflora followed by Pichia(29.26%±7.58%)and Aspergillus(16.52%±3.96%).The average abundance of Wickerhamomyces(1.96%±0.76%)and Geotrichum(1.68%±0.77%)during roasted sesameflavor liquor fermentation was relatively stable.(2)The enviroemntal forces and biological forces of driving community succession during fermentation(QT)were revealed by multivariate statistical analysis.The interpretation rate of environmental forces on microbe distribution was 68.27% during roasted sesame-flavor liquor fermentation.Acidity and ethanol were the highest explanatory variables at stage ?(0-5 d)and stage ?(5-30 d)respectively.The interpretation rates of ethanol,acidity and its combination were 13.76%,4.43% and 23.17%,which indicated ethanol and acidity had synergetic effect on community succession.The Sperman correlation analysis showed complex microbial interactions during fermentation that there were 49 and 37 significant associations of microbial genus(> 1% abundance more than 1 sample)at stage I(0-5 d)and stage II(5-30 d)respectively.(3)Microbial community of different roasted sesame-flavor liquor systems(numbered as QT and JZ)were compared for selection of strengthening microbe.?-diversity showed that Chao 1 index(F=91.856,p<0.001)and Shannon Index(F=8.026,p=0.008)of the eukaryotic microflora were significantly lower in QT sesame-solid state fermentation system and there was no significant difference in Chao 1 index and Shannon index of prokaryotic microflora in two brewing systems according to ? diversity index.The principal component analysis(PCA)the LEfSe analysis showed differences in the community composition and succession trajectories.The abundance and distribution of Lactobacillus,Bacillus,Pichia,Geotrichum,Saccharomyces,Trichosporon,Clavispora,Wickerhamomyces,Aspergillus and Candida in different brewing systems showed significant differences,which were main basis for selection of strengthening microbe.(4)Microbe belonging to 8 genera except mould were selected and applied to fermented grains(QT)to explore effects of strengthening on liquor microbial community.There was no significant difference in overall microbial community composition through the average abundance of Lactobacillus significantly decreased from 17.91%±6.32% to 2.47%±0.77%(p= 0.014)while the average abundance of Bacillus significantly increased from 54.12%±7.23% to 81.97%±5.5%(p=0.006)at 0 d after strengthening.Samples of 0 d and 2 samples of 5 d and 10 d respectively showed obviouely different succession trajectory after strengehing,but the succession trajectories coincided with each other in the anaphase of fermentation.Contents of 10 volatile compounds(OAV> 1)increased after strengthening and the overall flavor profile was not damaged.The flavor and texture of the upper distilled liquor before and after strengthening were similarly.Those results showed that the liquor community succession during fermentation was a dynamic process with certain stability.