Screening And Identification Of Cholestrol-Lowering Lactic Acid Bacteria And High Cell Density Cultivation

In this thesis, lactic acid bacterias were firstly isolated from traditional fermentativefood products. Secondly lactic acid bacterias with the bile salt hydrolase gene werescreened by PCR with the reasonable primer. Thirdly the strains with highcholesterol-lowering ability were selected and the properties of acid-tolerance, resistanceto bile, prebiotic utilization, antibiotic senbility were studied, one good strain was acquired.Next the strain was identifid by morphology, physiological and biochemical reaction and16S rDNA orthology. Growth performance and high density cultivation of the strain werelastly studied. The results were as follows.(1)22lactobacillus strains were isolated from traditional fermentative vegetables andfermentative dairy products. They were coded with SC1, SC2, SC3, SC4, SC5, SC6, SC7,SC8, SC9, SC10, SC11,SC12,SC13,SC15,SC18,N2,N3,L18,L19,L21,L22. Next thecholesterol–lowering strains were screened by PCR based on the BSH gene.The resultsshowed that11strains had the cholesterol-lowering ability, they were SC3,SC5,SC6,SC13,SC15,SC18,N19,L18,L19,L21,L22.(2) The cholesterol-lowering abilities of the11strains were again screened by ferricammonium method. The results showed that three strains of11strains had higherdegradation ability, they were SC18, L22, L21. The cholesterol-lowering abilities of thethree strains were separately46.37%,41.99%,35.99%. Next acid-tolerance, resistance tobile, antibiotic senbility, prebiotic utilization of the three strains were studied. The resultsshowed that the strain SC18had preferably acid-tolerance, bile--tolerance, prebioticutilization, antibiotic senbility.(3) According to the results of morphological features, physiological and biochemicaltest and16S rDNA sequences analysis, the SC18strain was identified as Lactobacillusplantarum.(4) The SC18had the quicker growth rate and better acid-producing ability.(5) The best carbon source was glucose, the best nitrogen source was peptone, thebest buffer salt was K2HPO4,the optimal culture conditions were the pH6.5, temperature35℃, culture time25h.The best feeding culture ways was feeding carbon and nitrogensources(C/N ratio was5:1), feeding number was three times.