| Traditional fermented sourdough,as one of the traditional fermented foods,is formed by fermentation under the combined action of various microorganisms.During the process of fermentation of sourdough,lactic acid bacteria(LAB)and yeasts endow the sourdough with unique flavor through their own metabolism.It is necessary to study and discuss them in depth.Therefore,this study first used Illumina high-throughput sequencing technology to analyze the microbial diversity in sourdough during different fermentation periods,which more intuitively reflects the microbial community composition and dynamic changes in sourdough.On this basis,the traditional separation and culture method was further used to separate the lactic acid bacteria and yeasts in the traditional fermented sourdough,and the first-generation sequencing was used for species identification.Finally,the characteristics of the isolated lactic acid bacteria and yeast were screened.The research results can provide technical support and theoretical basis for improving the quality of sourdough and industrial production of related fermented products.The main findings are as follows:1.Microbial community structure and succession law of sourdoughSequencing results showed that in terms of bacteria,Cyanobacteria were detected in large numbers in the early stage of fermentation(12h).As the fermentation progressed,LAB such as Lactococcus,Leuconostoc,Weissella and Enterococcus gradually became dominant bacteria and remained relatively stable.In terms of fungi,yeast genera,including Hanseniaspora and Pichia,were the absolute dominant flora in sourdough.At the same time,the results of PICRUSt function prediction analysis showed that the community structure change of sourdough is an important reason for the change of its overall metabolic function.2.Isolation and identification of lactic acid bacteria in acid dough samplesThere are 42 LAB-like strains were separated by traditional pure culture method,according to gram staining and hydrogen peroxide enzyme reaction,the 39 strains were Gram-positive and catalase-negative,and the 39 strains were preliminary identified as LAB.LABs were identified further by 16 S r DNA gene sequences,the result showed that 39 strains of LAB were belonged to 2 genera and 6 species,including 16 strains of E.faecalis which accounted for 41.03% in the total isolates,1 strain of E.pseudoavium which accounted for 3.00% in the total isolates,1 strain of E.faecalis which accounted for 3.00%in the total isolates,18 stains of L.plantarum which accounted for 46.15% in the total isolates and 3 strains of L.casei which accounted for 7.69% in the total isolates.3.Isolation and identification of yeast in acid dough samplesThen the yeasts were isolated from traditional fermentation sour dough using traditional pure culture method in the study,and there are 10 strains of like-yeast were preliminary separated based on morphological characters of yeast.After that,10 strains of yeast were identified further by 26 S r DNA D1/D2 area gene sequences,the results showed that 10 strains of yeast were belonged to 4 genera such as Saccharomyces,Pichia,Wickerhamomyces and Torulaspora,and 6 species including 5 strains of Saccharomyces castellii,2 strains of Pichia fermentans,2 strains of Wickerhamomyces anomalus and 1strains of Torulaspora delbrueckii.4.Preliminary screening of functional bacteria with potential probioticsFinally,the isolated LAB and yeast strains were screened for their functions and probiotic properties.Among them,the tolerance of Lactobacillus casei HR3-1 under the environmental conditions of p H 3 and 10% salt concentration exceeded 80%;S.castellii HR-1 can survive under 20% salt concentration,and it also has bile salt tolerance and certain inhibitory properties of Staphylococcus aureus.It can be seen that the community structure of LAB and yeast in traditional sour dough fermentation is relatively abundant,which can further excavate the excellent and analyze their metabolic mechanism in the fermentation process So that it can be better applied to the fermentation process of sour dough,improve the quality of the sour dough and accelerate its industrial production. |
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