Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Development of Fermented Vegan Food Formulations With Improved Angiotensin-I Converting Enzyme Inhibitory (ace-I) Activity(01. Izmir Institute of Technology, 2022) Esen, Berna; Harsa, Hayriye ŞebnemVeganism has become popular in recent years and the demand for vegan products is increasing, especially due to the positive effects of plant-based diets on health. Since veganism can be defined as a diet or lifestyle that does not support the consumption of any animal food, protein-rich legumes occupy a large place in the daily diet of vegans. The health-promoting potential of probiotics in various forms has been recognized for years, and one of these health-promoting properties is their antihypertensive effect. In this context, the aim of this thesis is to develop some vegan food formulations, such as vegan mayonnaise-based salad dressings prepared using chickpea aquafaba and plant-based milk alternative (PBMA) fermented using lactic acid bacteria (LAB), showing antihypertensive effect. Microbiological, and quality characteristics and antioxidant properties of the formulations were determined. In addition, proteolytic activity and angiotensin-I converting enzyme inhibitory (ACE-I) activity experiments were carried out to control the antihypertensive properties of salad dressings. As a result, there are 107 CFU/ml bacteria in the final products. The quality characteristics of the formulations were compared with the literature. Consequently, the ACE-I activity of PBMA was enhanced by LAB fermentation and vegan mayonnaise was enriched with these high-value ingredients.Master Thesis Molecular Evolution and Population Genetics of Acid Resistant Pathway Glutamate Decarboxylase in Lactic Acid Bacteria(Izmir Institute of Technology, 2022) Tekin, Burcu; Sezgin, EfeThe Glutamate Decarboxylase(GAD) Pathway (GDP) is a major acid resistance mechanism that allows Lactic acid bacteria (LABs) to survive in low pH food environments. In the thesis, we aimed to study the molecular evolution and population genetics of GDP genes in LABs to understand evolutionary processes shaping adaptation to high acid environments by contrasting species where the GDP genes are organized as an operon structure (Levilactobacillus brevis) versus lack of an operon structure (Lactiplantibacillus plantarum). Intraspecies molecular population genetic analyses with GDP genes of L. brevis and L. plantarum from various environments revealed that synonymous and non-synonymous nucleotide diversity is driven mainly by low-frequency changes. Neutrality tests revealed mostly negative values indicating negative selection against replacement changes. Similarly, molecular structure and amino acid characteristic analyses showed that none of the replacement changes on the GDP genes alter the important residues of the proteins supporting negative selection against non-conservative amino acid changes. Interspecies analyses were used to identify the closely related LABs. Moreover, phylogenetic analyses showed that the GDP gene tree topologies differed from the LAB species tree, indicating divergent evolutionary histories. The functionally preserved two gad copies of the L. brevis grouped separate phylogenetic clades, showing that the origin of the second gad gene might be via horizontal gene transfer from a phylogenetically distant LAB species rather than gene duplication. In conclusion, GDP in LABs exhibits a dynamic molecular evolutionary history that enables organisms to thrive in high acid environments.Master Thesis Modulating Akkermansia Muciniphila by Probiotics for Obesity Management(Izmir Institute of Technology, 2021) Kamber, Aslıhan; Harsa, Hayriye Şebnem; Bulut Albayrak, ÇisemThe aim of this thesis is to investigate the potential of lactic acid bacteria (LAB) having probiotic properties to trigger Akkermansia muciniphila as anti-obesity candidate. Artisanal strains of LAB were evaluated in terms of stability in gastrointestinal conditions, mucin/mucus non-utilization properties, growth in the presence of mucin, adhesion to the mucin/mucus layer, biofilm formation, lactate production abilities, antimicrobial properties, HT-29 cell binding and mucin/mucus thickness increment abilities. Among 40 strains, 17 of LAB including 6 olive isolates were selected for their tolerance to gastrointestinal conditions and analyzed for further abilities e.g., mucin promotion potential. Most of them (13 of the 17 bacteria) remained viable in the range of 106-108CFU/mL in the simulated gastric juice, and these bacteria continued their viability in the range of 105-107 CFU/mL in the simulated intestinal fluid. Besides, 6 reference and 7 L. bulgaricus isolates did not utilize the mucin and showed no or negligible growth in the presence of mucin. Additionally, 13 of the 17 bacteria adhered to mucin layer with variable degree of binding between 41.03-65.37%. Furthermore, variable degree biofilm formation efficiencies can also support their existence and adhesion to intestinal cells. Varying amounts of lactate by 7 LAB were produced (6.51-18.17 g/L) and this ability is another important criteria for supporting mucus pathway. All those strains adhered to HT-29 cell line and they showed significant increase in mucin thickness by comparing the control. L. plantarum C47 and Lactobacillus AK50 isolates were selected as the antiobesity prototype candidates for their desirable attributes.Master Thesis Isolation, Characterization, Determination of Probiotic Properties of Lactic Acid Bacteria From Human Milk(Izmir Institute of Technology, 2007) Yavuzdurmaz, Hatice; Harsa, ŞebnemProbiotics mean live microorganisms that have beneficial effects on their host.s health. Although probiotic strains can be isolated from many sources; for human applications the main criteria is being human origin.Breast milk is an important nutrient source for neonates. Lots of studies showed that this fluid has beneficial effects on the health of neonates. One reason of being beneficial is explaining by the microflora of human breast milk including beneficial lactic acid bacteria.In this study, isolates were identified by biochemical and molecular characterization and also probiotic properties of lactic acid bacteria, isolated from human milk were investigated.Three of the isolates were observed as potential probiotic. Two of them are bacilli and the other is cocci. These isolates showed resistance to stomach pH (pH 3,0), tolerance against 0,3% bile concentration and antimicrobial activity against Salmonella thyphimurium CCM 5445, Escherichia coli O157:H7 NCTC 129000 and Escherichia coli NRRL B-3008. After investigation the probiotic properties of these isolates, they were identified by biochemical characterization techniques and molecular identification by using amplification and restriction fragment length polymorphism (RFLP) of 16S ribosomal DNA (rDNA) and 16S sequencing. Two lactobacilli were identified as Lactobacillus oris and Lactobacillus fermentum. In the light of this study, it is observed that, human milk is a source of potential probiotic strains.Master Thesis Production of B-Galactosidase Using Lactic Acid Bacteria and Optimisation of Fermentation Parametters(Izmir Institute of Technology, 2007) Üstok, Fatma Işık; Tari, CananFood 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 Isolation and Molecular Characterization of Lactic Acid Bacteria From Raw Milk(Izmir Institute of Technology, 2002) Çetin, Ali Emrah; Yenidünya, Ali FazılLactic 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 Investigations on Aroma Profile of Artisanal Yoghurt Starter Cultyres(Izmir Institute of Technology, 2012) Baran, Ezgi; Harsa, Hayriye ŞebnemYoghurt is an important fermented milk product that is consumed widely around the world as a part of the diet. Yoghurt is produced by lactic acid fermentation using Streptococcus thermophilus, and Lactobacillus delbrueckii ssp. bulgaricus. The most important criteria in yoghurt production are the selection of artisanal yoghurt starter cultures to achieve the typical aroma and quality of the final product. The typical aroma of yoghurt is identified chiefly by acetaldehyde that is the most important for yoghurt aroma. The aim of this study is to determine artisanal yoghurt starter cultures that provide the most desirable aroma to yoghurt, in order to promote industrial production with such flavor. In the first part of this study, the influence of different aroma cultures addition on the aroma production properties in yoghurt products was investigated. Nine different aroma cultures were added into the starter culture combinations at two different inoculation ratios. Among all of the combinations, just one yoghurt combination was selected according to the highest acetaldehyde and also the highest sensory scores. According to the results, two batches of yoghurt were produced: Sample 1 containing only yoghurt starter cultures (Lactobacillus bulgaricus Y30 + Streptococcus thermophilus Y24), was used as control yoghurt; Sample 2 containing yoghurt starter cultures plus with selected aroma culture (P10), was used as yoghurt with aroma culture. Yoghurt samples were stored at 4 °C for 21 days. The pH, titratable acidity, total solids, fat, protein, syneresis, viscosity, aroma profile, lactic acid and lactose profile, proteolytic activity, microbiological characteristics and sensory characteristicsMaster 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.Master Thesis Structural Changes of Gliadins During Sourdough Fermentation as a Promissing Approach To Gluten-Free Diet(Izmir Institute of Technology, 2010) Kömen, Gökçen; Harsa, Hayriye ŞebnemGluten intolerance, celiac disease, is an autoimmune disease caused by the ingestion of gluten proteins and the only treatment is the strict gluten-free diet which results in a mucosal recovery. At this point, the variety, availability and low price of gluten-free products on the market are of great importance. Sourdough is a traditional fermented semi-product that contains lactic acid bacteria (LAB). LAB are capable of metabolizing proteins and peptides with their proteolytic enzymes. It is predicted that gluten proteins are able to be hydrolyzed with the help of this proteolytic mechanisms and also by the wheat proteolytic enzymes. the help of this proteolytic mechanisms and also by the wheat proteolytic enzymes. gliadins involved in gluten intolerance during sourdough fermentation with selected LAB. First, sourdough fermentation with selected Lactobacillus strains was accomplished. As a control, dough with no inoculation and chemically acidified dough were prepared. During 48 h of fermentation, changes in pH, acidity, LAB concentration and free amino nitrogen content were investigated. SDS-PAGE, 2-D electrophoresis and RP-HPLC were applied to prolamins extracted from each sourdough sample taken at definite time intervals. The results showed that the inoculated LAB adapted to the dough environment and as they grew, a decrease in pH, and an increase in acidity and free amino nitrogen were observed. According to SDS-PAGE, 2-D electrophoresis and RP-HPLC results, some modifications in the protein patterns were observed in the inoculated doughs. The same alterations occurred in control and chemically acidified doughs, but not as fast as inoculated ones.