Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Isolation and Molecular Characterization of Lactic Acid Bacteria From Raw Milk(Izmir Institute of Technology, 2002) Çetin, Ali Emrah; Yenidünya, Ali Fazıl; Yenidünya, Ali Fazıl; 04.03. Department of Molecular Biology and Genetics; 04. Faculty of Science; 01. Izmir Institute of TechnologyLactic acid bacteria are industrially important because they are used as starter cultures in food production, they produce antimicrobial compounds and they are used in the formulation of probiotic products. Several dairy products such as raw milk, traditionally fermented cheese (produced without the use of commercial starter cultures), and kefir which are produced in country are good sources of novel lactic acid bacterial strains. These lactic acid bacterial strains may have potential for the production of new fermented dairy products with characteristic aroma and flavour. Therefore, the isolation of lactic acid bacteria from natural products and their identification are important. For many years, several phenotypic methods have been used to identify lactic acid bacteria, but they are not often capable of effectively differentiating subspecies and strains within a genus. New methods based on the genotypic properties have been developed and used for the proper classification of bacteria The aim of this research was the isolation of lactic acid bacteria from raw milk and the identification of the lactic acid bacterial isolates by biochemical tests, polymerase chain reaction (PCR)-based methods and pulsed field gel electrophoresis (PFGE). Lactic acid bacteria were isolated from cow.s raw milk and identified by biochemical reactions. Two PCR based methods, ITS-PCR (Internal Transcribed Spacer-PCR) and PCR-RFLP (PCR- Restriction Fragment Length Polymorphism) were then used for the differentiation of reference strains of lactic acid bacteria. PCR-RFLP method, based on the amplification and restriction digestion of 16S rRNA gene, was found to be useful for the identification. Thirteen raw milk isolates were identified as Lactococcus lactis, 24 as Enterococcus spp., and 2 as Lactococcus lactis subsp. cremoris by PCR-RFLP method. Pulsed field gel electrophoresis was also optimized for the identification of reference strains. Restriction profiles obtained by digesting the genomic DNA with Sma I enabled differentiation of the reference strains of Lactococcus, Enterococcus, and Streptococus thermophilus.Master Thesis Isolation and Molecular Characterization of Lactic Acid Bacteria From Cheese(Izmir Institute of Technology, 2003) Bulut, Çisem; Yenidünya, Ali Fazıl; Yenidünya, Ali Fazıl; 04.03. Department of Molecular Biology and Genetics; 04. Faculty of Science; 01. Izmir Institute of TechnologySpecially selected starter cultures are required for the industrial production of cheese. These starter cultures are mainly composed of lactic acid bacteria (LAB). StarterLAB have many functions in cheese production. They produce lactic acid during the fermentation process and provide formation of the curd. Futhermore, they show proteolytic activity and also they play a role in the production of aroma compounds and antimicrobial substances. In order to prevent loss of LAB biodiversity and loss of traditional cheese diversity, it is important to identify novel LAB from traditional cheese.The aim of this project was to isolate and identify natural LAB flora involved in traditional "Çömlek Peyniri" fermentation. In order to achive this goal, LAB were isolated and characterized by using phenotypic ( cell morphology, Gram staining, physiological and biochemical tests ) and genotypic methods (PCR- Restriction Fragment Length Polymorphism). Moreover, technological characterization was performed by monitoring the acid production profiles of the isolates.At the end of the study, a total of 113 coccal and 21 mesophilic lactobacilli were obtained and maintained for future use. It was found that cocci shaped isolates included 54 lactococci and 59 enterecocci. Further identification at the species level indicated that all of the lactococci isolates were L. lactis ssp. lactis. Thirty of the enterecocci were E. faecium, 8 of them were E. faecalis , 3 of them were E. avium, 2 of them were E. durans and 16 of them were other Enterococcus ssp. Lactobacilli isolates were identified as Lb. paracasei ssp. paracasei (3 isolate), Lb. casei ( 3 isolate ) and other Lactobacillus spp ( 15 isolate) . PCR-RFLP method which is based on the amplification of 16S rRNA- ITS genes and restriction digestion with HaeIII and TaqI endonucleases was found to be useful for further identification. Finally, acid production profiles of isolates indicated that 35 of the isolates could lower the pH of UHT skim milk below 5.3 for 6 h incubation at 30 °C and these isolates were therefore the best starter candidates for industrial applications.