Study On Microbial Diversity And Flavor Quality During Fermentation Of Corn Wine

Corn wine,also known as Baogu wine,is a kind of Guizhou special traditional wine,made from corn and brewed by traditional brewing techniques.The fermentation of corn wine is a traditional fermentation with the participation of multiple strains of bacteria in an open environment.In order to provide theoretical basis for the production and quality control of corn wine,the potential correlation between microorganisms and volatile and non-volatile metabolites in the fermentation process of corn wine was studied.At present,there are many studies on the correlation between microorganisms and flavor componds in fermented food,but there are few applications in corn wine.In this paper,the community composition and succession law of bacteria and fungi were studied in different fermentation stages(day 0,day 2,day 4,day 6,day 8 and day 12).The dynamic changes of physicochemical indexes,volatile flavor compounds,organic acids and non-volatile metabolites were analyzed.Multivariate statistical analysis was used to reveal the core functional microorganisms that contribute to the formation of flavor compounds.The main results are as follows:(1)The results showed that 819,612 effective sequences were obtained from bacteria and932,366 effective sequences were obtained from fungi.The microbial diversity and abundance index of bacteria were unstable,while the microbial diversity and abundance index of fungi showed a downward trend.6 bacterial phyla and 16 bacterial genera were identified in the bacterial community.6 bacterial phyla and 16 bacterial genera were identified in the bacterial community,among which Firmicutes,Proteobacteria and Bacteroidetes were the dominant phyla,Bacillus,Prevotella＿9,Acinetobacter and Gluconobacter were the dominant phyla.In the fungal community,3 fungal phyla and 5 fungal genera were identified,among which Ascomycota and Mucoromycota were the dominant fungal phyla,and Rhizopus and Saccharomyces were the dominant fungal genera.The network of microbial-microbial correlations showed 7 positive and16 negative correlations(| r |>0.5,p<0.05)between 14 bacterial and 5 fungal genera,indicating that the symbiotic effect between bacteria and fungi was greater than the antagonistic effect and that fungi had a greater influence on bacteria during the fermentation of corn wine.(2)The dynamic analysis of physicochemical indicators showed that there were significant differences(p<0.05)in temperature,pH,total sugar,total acid,alcohol,moisture content,starch content and amino acid nitrogen at different stages of the corn wine fermentation process.The growth and reproduction of microorganisms were faster in the early stage of fermentation,and as fermentation continued,the number of microorganisms decreased,so the temperature increased first and then decreased.The contents of total acid and amino acid nitrogen increased from0.68±0.05 g/L and 0.12±0.02 g/L to 1.71±0.02 g/L and 0.70±0.04 g/L,respectively.The pH value and total sugar content decreased from 6.59±0.02 g/L and 7.32±0.10 g/L to 3.73±0.004 g/L and0.64 ± 0.04 g/L,respectively.The results showed that 52 volatile flavor compounds,including 14 alcohols,8 esters,7 acids,6 aldehydes,6 alkanes,5 phenols,2 alkenes,and 4 other flavor compounds,were obtained during fermentation.Principal component analysis(PCA)of the volatile flavor compounds showed that significant separation occurred in the samples at six different stages of fermentation,and 24 volatile flavor compounds were identified as having a strong influence on the corn wine.A total of 9 kinds of organic acids were detected by high performance liquid chromatography(HPLC).Acetic acid and succinic acid were the main organic acids in the fermentation process of corn wine,and the others were pyruvic acid,oxalic acid,tartaric acid,malic acid,lactic acid,citric acid and fumaric acid.Malic acid,pyruvic acid,oxalic acid,tartaric acid,citric acid and fumaric acid showed an overall upward trend,while lactic acid showed an upward trend at first and then a downward trend.(3)The non-volatile metabolites in fermented grains of corn were studied by GC-TOF-MS.The results showed that 97 reliable metabolites were identified by quality control filtration(spectral similarity value >700).Unsupervised PCA analysis showed that metabolites moved from the fourth quadrant to the first quadrant,and there were significant differences between samples at different stages.A total of 25 different metabolites were screened based on OPLS-DA model,including 4 organic acids,3 amino acids,3 polyols,9 sugars and 6 other metabolites(VIP>1.0,p<0.05).Analyzing differences metabolites metabolic pathways and metabolism pathway enrichment analysis shows that received 35 metabolic pathways,including amino acetyl-tyrosine t RNA biosynthesis and metabolism,glycine,serine and threonine metabolism,valine,leucine and isoleucine biosynthesis,cysteine and methionine metabolism,phenylalanine metabolism,pyruvate metabolism and glycyrrhizic acid and dicarboxylic acid metabolism these 8 metabolic pathways for key metabolic pathways.(4)Redundant analysis(RDA)was used to analyze the correlation between microbial and physicochemical indicators.The results showed that Bacillus was affected by pH,total sugar and starch content,while Glucobacter was only positively correlated with total acid,water and amino acid nitrogen.In terms of fungi,Saccharomyces and Wickerhamomyces were affected by total acid,amino acid nitrogen and water,and Rhizopus was negatively correlated with water,total acid,starch,total sugar,water and amino acid nitrogen.Correlation analysis of microorganisms and volatile flavor compounds based on O2 PLS model showed that: A total of 9 microbial genera were associated with 52 kinds of volatile compounds(VIP>1.0,p<0.05),which were Gluconobacter,uncultured＿bacterium,Acetobacter,Aneurinibacillus,Sphingomonas,Saccharomyces,Rhizopus,respectively.The genus Wickerhamomyces and Aspergillus.Among them,Saccharomyces,Rhizopus,uncultured＿bacterium,Aneurinibacillus,Wickerhamomyces and Gluconobacter may be potential flavor contributing microorganisms in corn wine.The correlation analysis between microorganisms and non-volatile metabolites showed that there were 25 positive and 33 negative correlations between microorganisms and non-volatile significantly different metabolites(| r |<0.7,p<0.05).Saccharomyces,uncultured＿bacterium,Aneurinibacillus,Aspergillus,Pantoea and Rhizopus were the core microbial genera.In addition,the non-volatile metabolites(including organic acids)in corn wine fermentation were greatly affected by fungi.