Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Production of B-Galactosidase Using Lactic Acid Bacteria and Optimisation of Fermentation Parametters(Izmir Institute of Technology, 2007) Üstok, Fatma Işık; Tarı, Canan; Tari, Canan; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyFood grade thermostable B -galactosidase preparations are always in demand for a number of industrial applications. Thermostable -galactosidases from LAB having a neutral pH-optimum can be safely used to reduce the lactose content of milk for the lactose intolerant people. In this study, -galactosidase was produced with high productivities by novel Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus strains isolated from traditional Turkish yogurt samples in Toros mountain region. A full factorial statistical design was used separately for Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus strains in screening experiments. Among the strains, Lactobacillus delbrueckii subsp. bulgaricus 77 and Streptococcus thermophilus 95/2 were found to have high potential for B-galactosidase and lactic acid production, therefore these were used in the further optimisation studies.The efficiency of different cell disruption methods was investigated on the extraction of -galactosidase. Among these, lysozyme enzyme treatment was determined as the most effective method. Optimisation studies were carried out using response surface methodology to optimize fermentation conditions for pure strains as well as for mixed ones. Therefore, symbiotic relationship between St 95/2 and Lb 77 were investigated as well. Symbiotic relationship provided 39% and 6.1 % more -galactosidase activity and 44 % and 9.73 % more lactic acid production when compared to the optimisation results of pure strains Lb 77 and St 95/2, respectively.Overall, characterization studies showed that enzymes obtained from these strains can be considered as food grade and thermostable since they are obtained from thermophile, food originated novel LAB of local microflora.Master Thesis B-Galactosidase of Kluyveromyces Lactis: Immobilization, Characterization and Hydrolysis Behavior of Enzyme(Izmir Institute of Technology, 2008) Çabuk, Burcu; Harsa, Hayriye Şebnem; Harsa, Hayriye Şebnem; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyB-galactosidase (lactase) enzyme is of great industrial interest, since it can be used to solve problems associated with whey disposal and lactose crystallization in sweetened and frozen dairy products such as ice cream. All over the world, many people suffer from lactose intolerance and lactase preparations are used as supplements for these persons. B-galactosidase is also used to produce prebiotics since this enzyme hydrolyses lactose into galactooligosaccharides. Immobilized B-galactosidase preparations are preferred in many processes because they can be recycled and maintain their activities for a long time without loosing their chemical stability.Novel cross-linked chitosan-hydroxyapatite composite support has beenprepared, lactase from Kluyveromyces lactis was immobilized onto these beads. Lactase immobilization mechanism and effect of factors such as initial glutaraldehyde concentration, temperature, pH, initial lactase concentration, solid-liquid ratio on immobilzation mechanism were studied.Optimum cross-linking was obtained at the glutaraldehyde concentration of 100 mg/L. The optimum values of temperature, pH and solid/liquid ratio on lactase/HAChitosan were found to be 200C, pH 7.5 and 0.3g/ml Vg/Vl, respectively. The pH and thermal stabilities of free and immobilized enzymes were also investigated and it was observed that the relative activity remained above 83.2% within pH 6-7.5 and maximum activity yield was obtained at 370C for free and all immobilized enzymes. The Michaelis constant Km and Vmax of immobilized and free enzyme on chitosanhydroxyapatite composite beads were found to be 9.5 mM and Vm 454.5 .mol ONP min.1 mg.1 protein and 1.011 mM and 1098.9 .mol ONP min.1 mg.1 protein, respectively.