Changes Of Flavoring Substances And Microbial Community In Fermentation Of Vinegar

Shanxi vinegar has a long history and is one of our traditional vinegar,which not only has a unique mark flavor,but also has various functions such as lowering blood pressure and lowering blood lipid.This paper studied the main physicochemical parameters,microbial community structure,and the rule of succession of flavor substances in Cuqu and vinegar fermented grains at different stages of fermentation.This paper also explored the correlation between microorganisms and indexes in Cuqu and vinegar fermented grains at different stages of fermentation.The main research results were as follows:1.Analysis of physical and chemical parameters: The moisture content of alcohol fermentation stage was 55.72±2.17%～62.11±1.98%,and that of acetic acid fermentation stage was 56.93±2.57%～60.89±2.21%.During the fermentation process,p H and total acid showed different change rules.The p H value kept decreasing,reaching the lowest of3.78±0.08,while the total acid kept rising,from the initial 1.04±0.12g/100 g to5.31±0.20g/100 g.The contents of amino acid nitrogen and soluble salt-free solid increased with fermentation.The reducing sugar showed a tendency of rising first and then decreasing in the fermentation process of vinegar.2.Analysis of community structure: High-throughput sequencing was used to study the microbial community composition during the fermentation of Shanxi vinegar.The results showed that,Firmicutes,Proteobacteria and Ascomycota were the main bacteria and fungi in the fermentation stage of Cuqu,alcohol fermentation stage and acetic acid fermentation stage,respectively.The dominant bacterial genera in Cuqu were Bacillus,Lactobacillus and Weissella,while the dominant fungal genera were Aspergilus and Issatchenkia.In alcohol fermentation stage,the Lactobacillus and Weissella showed a trend of change,and Lactobacillus gradually becomed the dominant bacterial genus in late fermentation,while Issatchenkia was on the rise at this stage.It eventually became the dominant genus of fungi.The dominant bacteria genus in acetic acid fermentation stage changed from the initial Lactobacillus to Acetobacter,Issatchenkia was the main bacteria genus in the middle and late stages of acetic acid fermentation stage,and Aspergilus was the main bacteria genus at the end of fermentation.There were 23 significant differences between alcohol fermentation stage and acetic acid fermentation stage,including 15 bacterial genera and 8 fungal genera.3.Analysis of main flavor substances: the organic acids in Cuqu were mainly succinic acid,lactic acid and citric acid,leucine and glutamic acid were the main essential amino acids and non-essential amino acids,respectively.A total of 30 volatile substances were detected in Cuqu,and the relative content of alkane was the highest,47.7±1.73%.In the process of fermentation,the total amount of organic acids showed an increasing trend,and the final content was about twice of the initial content.The contents of lactic acid and acetic acid in acetic acid fermentation stage were higher than that in alcohol fermentation stage.Glutamic acid,proline,leucine and aspartic acid were the main amino acids in the fermentation process,and the highest amino acid content is in the alcohol fermentation stage.A total of 111 kinds of volatile substances were detected in the whole fermentation process,including 92 kinds in alcohol fermentation stage and 103 kinds in acetic acid fermentation stage.There were 8 kinds of unique volatile substances in alcohol fermentation stage and 19 kinds in acetic acid fermentation stage,respectively,and 84 kinds of volatile substances in the two fermentation stages.There are 39 kinds of volatile substances with VIP>1,including 7 kinds of acids,4 kinds of alcohols,21 kinds of esters,4 kinds of alkanes,1 kind of ketones,1 kind of furans and 1 kind of aldehydes.4.Correlation analysis: Bacillus,Acetobacter and Paenibacillus showed significant positive correlation with amino acids in Cuqu,while Saccharomyces showed significant positive correlation with volatile substances in Cuqu.During the fermentation process,11 bacterial genera and 11 fungal genera were significantly correlated with the physicochemical parameters of vinegar grains,Lactobacillus was the main bacterial genus with significant positive correlation with amino acid during the fermentation process,and Acetobacter was positively correlated with 18 volatile substances.The main fungi genera that were positively correlated with volatile substances during fermentation were Phaeosphaeria,Alternaria,Saitozyma,Cladosporium,Malassezia and Acremonium,etc.