| Guizhou traditional Tomato sour soup has distinct characteristics and a long history of consumption and production,but the relationship between microbial community changes and the formation of organic acids and volatile flavor substances during the fermentation process of Tomato sour soup and the volatility of Tomato sour soup fermented by inoculated dominant bacteria Few studies have been conducted on flavor compounds.In this study,the structure system of microbial flora,organic acids and volatile flavor substances in the fermentation process of traditional Tomato sour soup were analyzed,and the change rules of dominant microorganisms,organic acids and key volatile flavor substances in the fermentation process of traditional Tomato sour soup were clarified.and correlation,and using the dominant strain Lactobacillus casei H1 isolated from the traditional Tomato sour soup as the strain to ferment the Tomato sour soup,to monitor the dynamic changes of the physicochemical properties and volatile flavor substances during the enhanced fermentation process of the Tomato sour soup,and to establish the advantages The composite fermentation of Tomato sour soup by strains revealed the advantages of multi-bacteria fermented Tomato sour soup,and provided a theoretical basis for the industrial production and quality control of Tomato sour soup.The main findings and conclusions are as follows:（1）High-throughput sequencing analysis of the microbial diversity of traditional Tomato sour soup showed that:at the bacterial genus level,Lactobacillus（28.67%）、Enterobacter（12.37%）、Providence（12.37%）、Providencia（12.19%）was the dominant genus in the first round of fermentation,and the abundance of the dominant bacteria in the second round of fermentation changed,which were Lactobacillus（50.11%）、Enterobacter（13.86%）and Providencia（8.61%）,and In the traditional old sour soup（B）,Lactobacillus（99.01%）was the absolute dominant genus.At the level of fungal genus,the dominant fungal genera in the first round of fermentation of traditional Tomato sour soup were Pichia（65.89%）and Geotrichum（30.56%）.They were Pichia（73.68%）、Geotrichum（13.99%）and Brettanomyces（5.15%）.Brettanomyces is a fungal genus unique to the second round of fermentation,and The traditional old sour soup（B）was dominated by Pichia（60.06%）and Brettanomyces（36.59%）.The traditional fermentation of Tomato sour soup is a co-fermentation of lactobacillus and yeast.Lactobacillus is the main dominant bacteria in the fermented Tomato sour soup.（2）The analysis results of organic acids and volatile flavor substances in traditional Tomato sour soup showed that the content of lactic acid(28.72±0.12mg·m L-1)was the highest during the fermentation process.44 substances were detected from the traditional Tomato sour soup fermentation process by GC-IMS;O2PLS-DA and heat map cluster analysis found that ethyl 2-methylpropionate、butyraldehyde、2-octanol、6-methylpropionate-5-hepten-2-one、linalool and2-butanone run through the fermentation process of traditional Tomato sour soup and are the main characteristic flavor substances.In addition,sample A（the end of one round of fermentation）has more characteristic flavor substances,while sample B（traditional old sour soup）has the least characteristic flavor substances,indicating that the types of characteristic flavor substances in traditional Tomato sour soup gradually decrease and concentrate with the prolongation of storage time,and finally becomes the traditional Tomato sour soup with obvious flavor characteristics.The abundance of flavor substances in sample F（the end of the second round of fermentation）was the highest,and the characteristic flavor substances were also the most prominent,achieving the best flavor state.（3）The results of correlation analysis between microorganisms,organic acids and key volatile flavor substances during the fermentation process of traditional Tomato sour soup showed that the microorganisms that were significantly positively correlated with key organic acids and lactic acids in traditional Tomato sour soup included Lactobacillus、Brettanomyces、Serratia、Kosakonia、Psychrobacter、Rozellomycota、Basidiomycota、Ceratobasidium、Basidiomycota;O2PLS-DA analysis identified 11 bacterial genera and 18 fungal genera,Lactobacillus as the most important bacterial genus in traditional Tomato sour soup,with 11 species Volatile flavor compounds were significantly positively correlated,and significantly negatively correlated with volatile flavor compounds with strong pungent odors such as methyl mercaptan、3-pentanone and benzaldehyde;the dominant fungal genera Pichia and Geotrichum were associated with 14 flavor compounds.There was a significant positive correlation,and the dominant fungus genus Brettanomyces was significantly positively correlated with the four flavor substances,which further verified the importance of dominant bacteria in the formation of volatile flavor substances,and also indicated that the fermentation of Tomato sour soup was a joint fermentation of lactobacillus and yeast.（4）The dominant strain Lactobacillus casei H1 was used as the strain to strengthen the fermented Tomato sour soup,and the analysis of physical and chemical indicators showed that the acid production rate of the Tomato sour soup in the enhanced fermentation group was higher than that of the traditional naturally fermented Tomato sour soup.16.44±0.032g·kg-1),the acidity of the second-round fermentation of traditional natural fermentation Tomato sour soup for 19 days(14.35±0.040 g·kg-1)can be reached,and the nitrite content is significantly lower than that of the natural fermentation group,indicating that the cheese Lactobacillus H1 not only increased the rate of acid production,but also had a strong ability to degrade nitrite,which improved the safety of sour soup.A total of 43 qualitative substances were detected in the fermentation process of enhanced fermentation Tomato sour soup by GC-IMS technology;most of the volatile flavor substances in enhanced fermentation group Tomato sour soup were similar to traditional natural fermentation Tomato sour soup,mainly esters,alcohols However,the relative contents of esters and alcohols in the enhanced fermentation group were 1.26 times and 1.8 times higher than those of traditional Tomato sour soup,respectively;cluster difference analysis of heat map found that the main characteristics of the fermentation process of enhanced fermentation Tomato sour soup were The abundance of flavor substances and the amount of esters were greater than those of traditional natural fermentation,among which ethyl 2-methylpropionate and 6-methyl-5-hepten-2-one were the main characteristic flavor substances shared by the two groups of Tomato sour soups.In addition,a unique pyrazine（2-ethylpyrazine）was also detected at the end of the intensive fermentation.Therefore,the use of the dominant lactic acid bacteria to strengthen the fermentation significantly shortened the fermentation period on the basis of ensuring product quality,and improved the flavor of the Tomato sour soup.quality.（5）Using Lactobacillus casei H1,Lactobacillus rhamnosus H3,and yeast（Saccharomyces cerevisiae）according to the ratio of 1%:2%:1%to carry out compound fermentation of Tomato sour soup（including pepper）with dominant strains.The results showed that compared with the natural fermentation group,the two groups of Tomato sour soup fermented with single bacteria and compound strains could significantly improve the fermentation speed and shorten the fermentation period.Among them,the mixed bacteria fermentation group had the best effect,and the fermentation time was 5 days.From 3 groups（mixed bacteria group,H1 group,natural fermentation group）,72 kinds of volatile flavor substances（mixed bacteria group）,64 kinds（H1 group）and 57 kinds（natural fermentation group）were detected in the fermentation process of Tomato sour soup.Sexual flavor compounds.Through O2PLS-DA and heat map clustering difference analysis,it was found that 31 flavor substances（the most）contributed more to the mixed fermentation group（VIP>1）,including 14 kinds of esters;There are 17 kinds of flavor substances with>1),including 6 kinds of esters;11 kinds of flavor substances that contribute more to the natural fermentation group（VIP>1）,including 5 kinds of esters.In addition,one unique pyrazine compounds with greater contribution was identified in the mixed bacteria fermented Tomato sour soup（2,6-dimethylpyrazine）.In conclusion,the mixed fermentation not only increased the richness of the characteristic flavor substances in the Tomato sour soup,but also significantly increased the amount of esters that contributed more.Therefore,the mixed fermentation made the aroma of the Tomato sour soup more pure and thick. |
