Study On Organic Acid Metabolism And Characteristic Flavor Of Tomato Sour Soup Fermented By Lactobacillus Casei H

Tomato sour soup(red sour soup)is a characteristic fermented food of ethnic minorities in Guizhou.Traditional red acid soup produces a large amount of organic acids and characteristic metabolites during the fermentation process,which together form a unique flavor.In order to further clarify the flavor characteristics of red sour soup,this experiment used the dominant strain Lactobacillus casei H1 screened from red sour soup as the fermentation strain to ferment red sour soup.Non target metabolomics(UHPLC-QTOF-MS)and Transcriptome methods were used to explore the differential metabolites of fermented tomato sour soup,analyze the differential metabolic pathways related to organic acid production,and the enzyme and gene expression related to the formation of organic acids and characteristic flavor substances,Analyze the enhanced fermentation of red acid soup by bacterial strains,with organic acids as the main characteristic metabolites,and provide support for the fermentation mechanism of forming the characteristic flavor of red acid soup.The main research findings and conclusions are as follows:(1)Using Lactobacillus casei H1 as a strain for enhanced fermentation of tomatoes to produce red acid soup,the p H value,total acid,and organic acid content of the fermented red acid soup were determined with different sugar ratios(0%,2%,5%,and10%)added.Finally,the optimal sugar content was determined to be 10%.By using the UHPLC-QTOF-MS non target metabolomics method to analyze the metabolites of A10 sample of red acid soup fermented with 10% sugar addition,the characteristic differential metabolites were screened.The results showed that compared with 0%sugar addition,R-lactic acid,acetoacetic acid,L-citric acid,succinic acid,pantothenic acid,vanillic acid and other differential metabolites were upregulated in the A10 group,and integrated with their differential metabolites through KEGG enrichment analysis,The metabolic pathways related to organic acid metabolism in A10 group include galactose metabolism,pyruvate metabolism,C5 branched chain dicarboxylic acid metabolism,butyric acid metabolism and other related metabolic pathways.(2)The differential gene expression was studied by transcriptome technology,and GO function significant enrichment analysis was carried out by differential expression genes.The results showed that the differential genes of Lactobacillus casei H1 were mainly enriched in the macromolecular metabolism process,protein metabolism process,redox coenzyme metabolism process in the biological process after being stressed by 10% sugar addition.The classification unit is cell composition,mainly including cytoplasm,ribosome and cell;The classification unit is the molecular functional component,which mainly includes ribosome structural components,nucleic acid binding genes and structural molecular activities.The KEGG significant enrichment analysis of differentially expressed genes showed that sugar stress significantly affected ribosome,galactose metabolism,nucleotide sugar biosynthesis and other metabolic pathways of Lactobacillus casei H1.(3)The characteristic flavor substances found by metabonomics technology include fatty acids such as arachidonic acid,4-hydroxy-3-methylbutyric acid;Lrhamnose 1,4-lactone,4-aminobutyrate and other ester substances;Alcohols such as cinnamyl alcohol,1-phosphate galactose alcohol,etc.,and combined with the literature to screen the corresponding lactate dehydrogenase,Galactokinase α-Glucosidase,glucose phosphate isomerase,mevalonate kinase β-21 related enzymes such as galactosidase.(4)Through the combination of non targeted metabolomics technology and transcriptome technology,KEGG enrichment analysis was carried out to find the same organic acid metabolism pathway,including galactose metabolism,starch and sucrose metabolism,fructose and mannose metabolism,carbon metabolism and pentose phosphate pathway.The corresponding organic acid metabolism related enzymes include 13 enzymes,including 2-oxo acid dehydrogenase acyltransferase,Transketolase,pyruvate oxidase,etc.