Correlation Between Microbial Diversity And Short Chain Fatty Acids In Kefir Fermentation Process

Microorganism in Kefir has a clear influence on the metabolites in its fermentation process.This experiment aims to utilize the Single Molecule Real Time(SMRT)and Gas chromatography-mass spectrometry(GC-MS)to analyze the hand-made kefir of herdsmen in Kashgar,Xinjiang.Microbial community analysis was carried out on Kefir with different fermentation time to determine the dominant bacteria genus.Through Canonical Correlation Analysis(CCA)and Pearson Correlation Coefficient analysis,Correlation analysis technology was used to explore the correlation between the dominant bacteria genus and the corresponding short-chain fatty acids in the fermentation process of kefir,and to reveal the degree of correlation between the two.The new technology was used to better analyze the microorganisms in the process of Kefir fermentation,and the relationship between microorganisms and short-chain fatty acids in the process of fermentation was clarified,which provided a research basis for the further analysis of the metabolic pathways and gene expression of microorganisms in the process of Kefir fermentation.The main research results are as follows:Using SMRT sequencing analysis,it was found that the microbial community composition and microbial diversity changed greatly during the fermentation process of kefir.In the process of fermentation,30 genera of prokaryotes were identified.In the process of fermentation,the dominant genera were: Enterobacter,Bdellovibrio,Methylophilus,Sphingomonas,Ralstonia.A total of 36 genera have been identified in the eukaryotic microbiota of Kefer,and the dominant genera are: Galactomyces,Vanderwaltozyma,Mortierella,Alloteropsis,Rhizopus,Nicotiana.The abundance of the same genus varied greatly in the fermentation process.Classifying and analyzing the flavor substances(short chain fatty acid test)at different fermentation time points of Kefir by means of GC-MS,the contents of acetic acid and propionic acid in the fermentation samples were low in the early stage of fermentation,but increased gradually with fermentation.The content of acetic acid increased from 11.871?g/mL in the early stage of fermentation to 1520.56 ?g/mL.The content of propionic acid increased from 1.17 ?g/mL at the beginning of fermentation to1.82 ?g/mL.The content of butyric acid decreased with the increase of fermentation time(8.57?g/mL-5.80?g/mL).CCA combined with Pearson Correlation Coefficient was used to analyze the correlation between microorganisms and short chain fatty acids in fermentation samples.Among them,Bacillus was positively correlated with acetic acid and propionic acid.Enterobacter was positively correlated with acetic acid and butyric acid,and with caproic acid.Streptococcus is positively correlated with isobutyric acid,iso-valeric acid and butyric acid.A significant positive correlation was found between Aeromonas and acetic acid.Methylophilus was positively correlated with isobutyric acid and caproic acid.Sphingomonas was positively correlated with propionic acid and butyric acid.The genus Ralstonia was positively correlated with caproic acid.There was a positive correlation between isovaleric acid and Campylobacter.Galactomyces was positively correlated with acetic acid and propionic acid.There was a significant positive correlation between the genus Vanderwaltozyma and butyric acid.Mortierella had a significant positive correlation with caproic acid.Nicotiana was positively correlated with butyric acid.There was a significant positive correlation between Alloteropsis and isobutyric acid.Through this study,it is confirmed that there is a significant correlation between microorganisms and short-chain fatty acids in the process of Kefir fermentation,and the internal relationship between microbial community succession and the formation of short chain fatty acids in the process of Kefir fermentation is preliminaries revealed.The factors affecting Kefir fermented milk were determined from large to small:fermentation time was greater than fermentation temperature and yeast inoculation amount,and sucrose added amount had the least influence.The optimum production conditions were as follows: fermentation time 14 h,fermentation temperature 25 ?,yeast inoculation amount 1%,sucrose addition amount 5%.Controlling fermentation temperature and inoculating proper amount of yeast are beneficial to improve the quality of Kefir fermentation products,and the products with stable state,good coagulant effect and good taste can be obtained.