Isolation And Cultivation Of Bacterial Resources In Kefir And Research Of Some Functional Strains

Kefir is a kind of fermented dairy with a long history,which is composed of lactic acid bacteria,yeast and acetic acid bacteria.Kefir contains abundant physiological active components.It was found that the bacteriocins produced by lactic acid bacteria could kill spoilage microorganisms,so it has a great potential to become a new food preservative.A large number of experiments show that some lactic acid bacteria strains have the function of cholesterol- lowering efficacy.The preliminary analysis of the Kefir strains is equivalent to establish a repository of probiotics,which could lay a foundation for the probiotics function research.The main content of this paper contains the screening and identification the strains of Kefir,metagenome sequencing analysis,primary screening the lactic acid bacteria strains of production bacteriocin in Kefir,primary screening the lactic acid bacteria strains of cholesterol- lowering efficacy in Kefir.(1) Screening Kefir strains and identification of bacterial 16 Sr DNA and yeast26 Sr DNA:Kefir strains were isolated with MRS,AC,YEPD culture medium,then the bacterial 16 Sr DNA and yeast 26 Sr DNA sequences were amplified by PCR,comparing them in BLAST.Six kinds of lactic acid bacteria were obtained,the results are as follow:Leuconostoc mesenteroides,Leuconostoc mesenteroides subsp. mesenteroides,Lactococcus lactis,Lactococcus lactis subsp. lactic,Lactobacillus plantarum,Lactobacillus plantarum subsp. plantarum,a total of 47 strains;Three kinds of acetic acid bacteria were obtained,the results are as follow: Acetobacter orientalis,Acetobacter okinawensis,Acetobacter ghanensis strain,a total of 19 strains;one kind of yeast was obtained,the results are as follow :Kazachstania unispora,a total of 7 strains;In addition,there is a strain of Streptococcus thermophilus and 4 strains of Enterococcus faecalis.(2)Kefir metagenomic sequencing: Kefir composition is complex,Kefir is dominated by lactic acid bacteria and acetic acid bacteria.The lactic acid bacteria are dominant species.At the same time,it was found that although the source of Kefir was different,the compositionof the strains and the type of bacteria have high similarity.From the level of phylum,Kefir is mainly composed of Firmicutes and Proteobacteria.From the level of genus,Kefir is mainly consisted of Lactobacillus and Acetobacter,The second is Streptococcus and Bacillus,then Propionibacterium, Rhodospirillaceae, Novosphingobium are only a tiny percentage.(3)Primary screening the lactic acid bacteria strains of production bacteriocin in Kefir :the lactic acid bacteria strains that can product bacteriocin in Kefir were screened by using Oxford cup,then observing the zone of inhibition,screening two times.Results showed that the barteriocins had no effect on yeast,but take effect on the four types bacteria indicators and four L lactis subsp. lactis strains had obvious the zone of inhibition.(4)Primary screening the lactic acid bacteria strains of cholesterol-lowering efficacy in Kefir:the lactic acid bacteria strains of cholesterol – lowering were screened two times.Results showed that the 17 strains had effect on cholesterol-lowering.Then r12 and r20 had a relatively obvious cholesterol-lowering ability.They are Lc mesenteulides subsp.mesenteulides and L lactis subsp.lactis.