Correlationship Between Microbiota And Volatile Compounds In Luzhou-flavour Daqu Of The Main Fermentation Stages

Daqu is a necessary saccharifying starter for Baijiu production in China.Recently,researches on microbiota and volatile compounds of Daqu have been more and more profound at home and abroad,however the understanding of the correlationship between microbiota and volatile compounds is not clear.Therefore in this study,based on the Luzhou-flavor Daqu fermentation process,the changes of fermentation parameters(temperature,moisture and acidity),volatile compounds by Headspace Solid-phase Microextraction coupled to Gas Chromatography-Mass Spectrometry and microbial communities by high-throughout technology of Illumina were detected.On the basis above,it focused on the characteristics of different stages and identified the significant species between different stages.Moreover,the core species highly related to volatile compounds were revealed by partial least squares regression analysis and correlation network analysis.The results were summaried as follows:1.The fermentation process was divided into three stages according to the temperature,including the heating period(0~5d),the holding period(5~13d)and the cooling period(13~29d).This study showed that the moisture content decreased from 40.56±0.31% to 11.13±1.10%.The acidity increased rapidly to 1.25±0.07 and then decreased slowly to 0.44±0.06.And through sensory evaluation it was found that moisture was utilized or evaporated with a small amount of colonies being appearing on the edge of section during the heating period,microbiota grew inward continuously during the holding period with the obvious "dressing" phenomena on the surface and section and the gray-white colonies tended to be full with obvious aroma of Daqu during the cooling period.Beside,a total of 68 kinds of volatile compounds were detected including 20 kinds of esters,14 kinds of alcohols,11 kinds of aldehydes and ketones,14 kinds of alkenes and 10 kinds of other compounds,among of which esters and alcohols dominated the fermentation process accounting for 45.41% and 29.03% respectively.The generation of volatile compounds was mainly concentrated on the holding period,and the content of compounds was stable in the cooling period to form a sense of “Nong-style”.That reflected the continuative and multistage of volatile compounds evolution in Daqu fermentation.2.Microbiota have reached a stable and balanced state for a period of fermentation time that the final "microbial collections" was formed.Among them,Weissella,Lactobacillus,Pantoea,Leuconostoc,C.Cyanobacteria,Thermomyces,Rhizopus are the dominant.The microbial community in Daqu had significant difference of three different fermentation stages(P<0.05)through diversity analysis and ANOSIM/Adonis analysis.And significant species between the heating period and the holding period were Cyanobacteria,Lactobacillus,Thermoascus,Dipodascus,Saccharomycetales,K.Fungi,Thermomyces,Rhizomucor,Candida;Significant species between the heating period and the cooling period were Weissella,Cyanobacteria,Saccharopolya,Bacillus,Staphylococcus,Aspergillus,Thermoascus,Thermomyces,Ipodascus,Saccharomycetales,K.Fungi,Rhizopus,Candida;Significant species between the holding period and the cooling period are Lactobacillus,Saccharopolyspora,Pediococcus,Bacillus,Pseudomonas,Aspergillus,Acetobacter,Thermomyces,Rhizopus,Saccharomycetales,Rhizomusor.3.Bacillus,Thermomyces,Thermoactinomyces,Acinetobacter,Thermoascus,Dipodascus and Hyphopichia were found to be the core microorganisms based on partial least squares regression analysis and correlation network analysis.And there were 15 volatile compounds highly related to these species,including ethyl acetate,isoamyl acetate,ethyl benzoate,ethyl tetradecanoate,ethyl pentadecanoate,isobutanol,n-butanol,phenylethanol,3-hydroxy-2-butanone,alpha-cypress,1-caryophyllene,roxene,3,4-dimethoxystyrene,2,3,5-trimethylpyrazine and 2,3,5,6-tetramethylpyrazine.At the same time,this study showed that moisture and acidity were positively correlated with some species in the early stage of fermentation,while temperature was strongly correlated with the others in the middle stage of fermentation by redundancy analysis.