Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Isolation, Phenotypic and Genotypic Charecterization of Yoghurt Starter Bacteris(Izmir Institute of Technology, 2007) Erkuş, Oylum; Harsa, ŞebnemSpecific bacteria cultures, known as starters, are used for manufacturing of fermented milk products. Yoghurt is made from milk by the protocooperative action of well known starters, namely Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus. They lead to coagulation of milk by lactic acid fermentation and other products give the characteristic properties, such as acidity, aroma, and consistency. Traditional method, using part of a previous batch to inoculate a new batch, have been used for centuries. Such cultures lead to variable performance, however industrial production needs consistency. The method of choice is the use of bacterial strains with known physiological, biochemical and genotypic characters. The isolation and identification of natural starters is a need not only for the dairy industry, which still import starters abroad, but also for the preservation of natural lactic acid bacteria diversity of Anatolia. With this perspective, the aim of our study was the isolation of starters from artisanal yoghurts, and their biochemical and molecular characterization. At the end of the study, 66 cocci and 71 bacilli were isolated. According to biochemical identification, all the bacilli isolates were found to be L. delbrueckii ssp. bulgaricus, however cocci isolates showed highly variable sugar fermentation results and only 7 of them were characterized as S. thermophilus. The molecular characterization was based on the amplification and restriction fragment length polymorphism (RFLP) of 16S ribosomal DNA (rDNA) and internal transcribed spacer (ITS) region. Species-specific PCR amplification and 16S sequencing were also used for justification. All of the isolates were well identified with the help of molecular techniques.Master Thesis Determination of Aroma Compounds and Exopolysaccharides Formation by Lactic Acid Bacteri Isolated From Traditional Yogurts(Izmir Institute of Technology, 2007) Çelik, Elif Sinem; Korel, FigenYogurt, consumed widely around the world, is a fermented milk product as a result of the lactic acid fermentation by addition of starter cultures containing Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. The most important criteria for yogurt production is the selection of starter cultures since each culture affects the end-product quality differently. Our natural flora and traditional flavor have been continously changing due to the introduction of imported commercial starter cultures. Because of the necessity to preserve our natural starter cultures and to increase the availability of them for industrial use, these cultures must be isolated from artisanal yogurts, genetically characterized and investigated regarding their technological properties. Aims of our study were to determine the technological and organoleptic properties of starter cultures previously isolated and genetically characterized and to assess the feasibility of near-infrared (NIR) spectroscopy for determining the yogurt quality.Total of 20 different yogurt samples were produced using combinations of 5 Streptococcus thermophilus and 4 Lactobacillus delbrueckii ssp. bulgaricus strains. Yogurt samples were stored at 4 °C for 21 days. Chemical, physical, microbial and organoleptic analyses for samples were conducted at predetermined days.As a conclusion, it was found that 4 Streptococcus thermophilus and 4 Lactobacillus delbrueckii ssp. bulgaricus yogurt isolates have potential to be used in dairy industry regarding their high technological and organoleptic characteristics. In addition, NIR spectroscopy technique could be used successfully on yogurt samples to predict total solids, fat, pH, syneresis, and microbial counts of yogurts based on the calibration models (Genetic Algoritm).Master Thesis Determination of Whey-Based Medium Requirements and Growth Characteristics for the Production of Yoghurt Starter Cultures(Izmir Institute of Technology, 2008) Soydemir, Elçin; Harsa, Hayriye ŞebnemYoghurt is an important dairy product which is produced by thermophilic starter cultures including; Streptococcus thermophilus and Lactobacillus bulgaricus. They grow synergistically in milk by acidifying milk, produce specific aroma compounds and lactic acid which impact the quality of the yoghurt. Imported cultures are widely used in dairy industry to stabilize the technological properties which cause a change in our natural flora and flavour. Starters from traditional yoghurts have to be preserved. Under this perspective, the aim of this study was to determine the medium requirements of mixed starter cultures for production of starter bacteria which has been isolated and characterized before.Determination of medium requirements were done in a whey-based media. Since bacteriophages were one of the most important problem in dairy industry, to prevent cultures from phage adsorption, media was treated with different salts which can bind free calcium ions. Salts were examined for cell viability and phage infection effects.From these studies Na2HPO4 + KH2 PO4 with 2% of medium addition was chosen as the most effective. Mineral requirements of the mixed cultures were determined. The best combination; 10, 5, 50 ppm for Fe2+, Mn2+, Mg2+ ions with 0,939 desirability were used for initial mineral content of medium. Fermentation constants for mixed cultures were determined. Pure culture fermentations and mixed culture fermentations were performed. According to results mixed culture inoculations gave higher maximum specific growth rates; 0,9188h-1 and 0,7323h-1 for cocci and bacilli while 0,855h-1 and 0,659h-1 were obtained for cocci and bacilli from single strain fermentations.Master Thesis Isolation and Molecular Characterization of Lactic Acid Bacteria From Cheese(Izmir Institute of Technology, 2003) Bulut, Çisem; Yenidünya, Ali FazılSpecially 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.