| At present,the production technology of fruit vinegar is mainly liquid-state fermentation(LSF)by use single strain,and its fermentation products are simple in composition,and solid-state fermentation(SSF)fruit vinegar is better than LSF fruit vinegar in flavor,taste and nutrition.Therefore,it is urgent to improve the fermentation technology of fruit vinegar or to develop special mixed bacteria to improve the quality and flavor of fruit vinegar,while SSF of fruit vinegar as one of the ways to improve the quality of fruit vinegar has not been systematically studied.Based on this,in this study,jujube vinegar(JV)was produced using the solid-state fermentation(SSF)technology,referring to the SSF process of Shanxi aged vinegar,and adopted multi-omics technology to clarify the fermentation rules,explore the fermentation mechanism,and finally anchored the core functional microorganisms in the SSF process of JV.The purpose of this study are to improve the fruit vinegar brewing methods to produce high quality and good taste JV,at the same time parsing the dynamic change of microbiota and metabolites and their correlation during the SSF process,excavation microorganisms resources which suitable for fruit vinegar brewing.It also provides directional target for artificial assembly of mixed bacteria suitable for SSF of fruit vinegar in the future.Main results of this study were summarized as follows:(1)11 physical and chemical characteristics of JV during SSF were monitored.Pearson correlation analysis showed that there was a highly significant correlation between the main consumption and the main products,while the correlation of temperature and the moisture content with other indicators was not high;The contents of non-volatile acids,total esters,proteins,amino acids,reducing sugars and flavonoids in solid-state fermentation jujube vinegar(SSFJV)were higher than those in liquid-state fermentation jujube vinegar(LSFJV)(P<0.01);HS-SPME-GC-MS was used to analyze the aroma components of those two types JV,and the results showed that contents of aroma components in SSFJV were higher then those in LSFJV.The sensory evaluation method of fuzzy mathematics was used to evaluate the two kinds of JV,the results showed that the sensory quality of SSFJV was "excellent" while LSFJV was "medium".(2)The results of high-throughput sequencing analysis showed that the richness and diversity of bacterial communities were constantly changing during the SSF process of JV,forming a relatively stable community structure in each period.By HCA and PCA analysis,the fermentation process could be divided into four stages: S1(d0),S2(d1-d5),S3(d6-d7)and S4(d8-d14).ANOSIM analysis showed significant difference between the four stages(P<0.01);Lefse analysis showed that the dominant bacterial community changed and succeeded significantly during the fermentation process,which promoted the fermentation process smoothly.The function of different bacteria in four stages was analyzed,and it was found that S1,S2 and S3 had little difference in function.Compared with S3,S4 significantly increased the abundance of many secondary metabolic functions.RDA and LR analysis of bacterial community and physicochemical indexes showed that acidity was the main driving force of bacterial community structure change.There was no significant difference in the bacterial community structure and changes among the three batches,indicating that the fermentation process was stable.(3)High-throughput sequencing analysis showed that the fungal community gradually tended to be balanced and stable during constant adjustment.Different kinds of yeasts were dominant,and almost all of them came from Daqu.They were metabolically active at the liquor stage,and then their abundance decreased.According to fungal community succession,the fermentation process can be divided into three stages: S1(d0),S2(d2-d6)and S3(d8-d14).ANOSIM analysis shows that segmentation is reasonable;Lefse analysis and differential function prediction showed that the differential fungal communities changed significantly in S1 and S2.Compared with S2,the abundance of the differential pathway was lower in S3 and had little effect on the metabolic profile of the whole substance.RDA and LR analysis showed that sugar content was the main driving force of fungal community structure change.(4)The non-volatile substances(NVSs)in SSF and fumigation stage(FS)of JV were analyzed by using UPLC-MS /MS metabolomics technique.A total of 357 compounds in 12 categories were detected.Carbohydrate was higher in early fermentation stage,organic acids and amino acids were higher in late fermentation stage,and the content of aldehydes increased significantly in FS.The whole brewing process could be divided into four stages:S1(d0),S2(d2-d6),S3(d8-d14)and S4(d17)by HCA and PCA analysis combined with ANOSIM verification.The PLS-DA model was established to screen the differential metabolites in adjacent stages.It was found that there were 89 differential metabolites between S2 and S1,47 of which were significantly decreased mainly in sugars,and 42 of which were significantly increased mainly in alcohols,organic acids,esters and amino acids.There were 26 kinds of different metabolites between S3 and S2,7 of which were significantly decreased,and 19 of which were significantly increased,mainly amino acids.Compared with S3,94 different metabolites were found in S4,and 60 of them were significantly decreased,mainly amino acids,34 species were significantly increased,covering all categories,which might be caused by the concentration effect of FS.KEGG enrichment analysis showed that the metabolic pathway(KO01100)accounted for the largest proportion,which was also the pathway with significant differences and obvious enrichment among different stages.AMOVA analysis of NVSs from 3 batches showed no significant difference between any two batchs(P>0.05),indicating that the changes of metabolites were relatively stable.(5)The metabolomics technique of SPME-GC-MS was used to analyze the volatile substances(NVSs)in SSF and FS of JV.A total of 206 substances were detected in 9categories.The relative contents of each substance changed during SSF and FS,but the total number of substances increased.Alcohols are prolific during the alcoholic fermentation(AF)stage;The most ester species,prolific in the middle and late stage;The number of acids increased significantly in the acetic acid feimentation(AAF)stage.Ketones,aldehydes,heterocyclic compounds and hydrocarbons were mainly produced and detected in AAF and FS.The whole brewing process could be divided into three stages: S1(d0-d8),S2(d9-d14)and S3(d15-d17);43 ingredients existed in the three stages contributed significantly to the core flavor composition of JV.A total of 28 different substances were screened,which could be used as markers to reveal the fermentation mechanism.(6)O2-PLS model was used to analyze the correlation between microbial and metabolites during the SSF.After the model was successfully constructed,analysis results showed that there are 10 bacteria genera and 4 fungi genera with VIPpred>1,and a total of 95 microbial is highly correlated with more than 100 kinds of metabolic substances(|ρ|>0.7),including 63 of bacteria genera and 32 fungi genera;Analysis of microbial genera with high correlation of metabolites in each category showed that the correlation were different,however,most of the changes were mainly attributed to bacteria,which further indicated that bacterial community played a more important role in the SSF process of JV.(7)Considering the relative abundance of each microbial genus and its importance to metabolic changes,11 core functional microbial genera,including 8 bacterial genera and 3fungal genera,were anchored in the SSF process of JV.They were Lactobacillus 、Acetobacter、Pediococcus、Staphylococcus、Saccharopolyspora、Streptomyces、Weissella、Bacillus、Saccharomyces、Pichia and Aspergillus,they were highly correlated with the84.26% of all metabolites(|ρ|>0.8);PICRUSt2 function prediction analysis showed that 8core bacterial genera performed 88.52% of the bacterial community function,and 3 core fungal genera performed 84.53% of the fungal community function,indicating that core functional microorganisms contributed major functions in the SSF process of JV.Mixed functional bacteria can be constructed in the future based on this,which is dedicated to brewing fruit vinegar and improving the quality of fruit vinegar. |
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