Correlation Between Microbial Diversity And Volatile Flavor Compounds In Kefir Fermentation Process

The growth,growth,phylum and growth status of microbes in Kefir are closely related to flavor substances and metabolites,which in turn affect the quality,taste and even safety of Kefir fermented milk.This paper intends to use sequencing technology combined with gas chromatography-mass spectrometry to analyze the volatile flavor components and physicochemical indexes in Kefir at different fermentation times handmade by the herdsmen’s families in Altay region,Xinjiang,and analyze the different fermentation times by high-throughput sequencing technology The composition and succession of the microbial community in the Kefir,the dominant microorganisms were identified.CCA canonical correlation analysis(Canonical correlation analysis)combined with Spearman correlation analysis was used to explore the relationship between the dominant bacterial species in Kefir and volatile components,revealing the correlation between the two.1.High-throughput sequencing results indicate that the types and composition of microorganisms in the fermentation process of Kefir alternate with each other.A total of 117 genus bacteria participate in fermentation,and the relative abundance is 45%.Of Lactobacillus.In addition,some relatively low-abundance bacteria include Bacillus Cohn,Lactococcus Schleifer et al.,1984,Haemophilus Winslow et a1,and Staphylococcus and Neisseriaceae are indispensable for fermentation.According to the changes of the bacterial community structure in different fermentation stages,the Kefir fermentation process can be divided into four stages,each of which has a significant comparison Statistical difference.Although the relative abundance of some genus fluctuates greatly during the fermentation process,it still exists throughout the fermentation process,indicating that the microbes in them are related to each other,resulting in a stable internal environment.2.There are 30 genera of fungi involved in the fermentation during the Kefir fermentation process.Aspergillus and Alternaria are the dominant bacteria in the Kefir fermentation process;followed by Mortierella,Cladosporium,Aspergillus,etc.During the fermentation process,the genus of fungi changes little,but it corresponds to the change of bacteria.3.The headspace sampling gas chromatography-mass spectrometry technology was used to detect and analyze volatile flavor substances in different fermentation stages of Kefir.A total of 174 substances were detected,including acids,esters,ketaldehydes,hydrocarbons,alcohols and Furan compounds are 6 major types of volatile flavor substances.Through analysis,the change trend of volatile flavor substances in the Kefir fermentation process is close to the change trend of microorganisms.4.Using CCA and Spearman to analyze the correlation between microorganisms and flavor substances in the fermentation samples.Among them,the correlation coefficient of Lactobacillus and acids is 0.7061,the correlation coefficient of esters is 0.3007,the correlation coefficient of hydrocarbons(HC)is 0.3979,the correlation coefficient of ketaldehydes(Carb)is 0.2389,The correlation coefficient of other substances(other)is-0.1098.Through analysis,it can be seen that the production of a flavor substance is produced by the fermentation and metabolism of multiple microorganisms.The relationship between microorganisms and flavor substances is not a simple relationship.It is necessary to further analyze the metabolic reaction,and the auxiliary metabolic pathways and metabolic conditions can be more clear and complex.Sex.5.Through morphological observation combined with sequence analysis,6 strains of lactic acid bacteria were identified including: 3 strains of Enterococcus faecalis,1 strain of Lactobacillus diolivorans,1 strain of saigon coli,1 strain of s..6.The optimal fermentation conditions for the identified strains are: fermentation strain inoculation amount 5%,fermentation time 24 h,fermentation temperature 30 ℃,sucrose addition amount 5%.In this study,the high-throughput sequencing analysis of Kefir microbes,the determination of Kefir volatile flavor substances,and the separation and identification of single Kefir strains used the same batch of Kefir.In the early stage of the experiment,a sufficient amount of Kefir was prepared to ensure sufficient parallel samples.