Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Subject: search.filters.subject.Yogurt

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Now showing 1 - 5 of 5
  • Master Thesis
    Development of Strained Yogurt Ice Cream With Aronia and Hydrolyzed Collagen
    (01. Izmir Institute of Technology, 2024) Korel, Figen; Korel, Figen; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Yogurt ice cream, made using yogurt cultures Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, is integrated with freezing technology, and it is a healthy food that creates cooling effect on consumers. In this study, it was aimed to obtain strained yogurt ice cream that would allow consumption of hydrolyzed collagen and aronia together. Different concentrations of collagen were added to samples with and without aronia. Different amounts of stevia were also added to selected sample due to its antioxidant activity. The quality of the ice creams in the study were evaluated by analyses as follows; dry matter, protein, fat, ash, carbohydrates, pH, color, viscosity, overrun, melting rate, antioxidant activity, coliform and lactic acid bacteria counts, and sensory analyses. While aronia decreased pH, collagen increased pH; adding stevia did not cause any significant change on pH. A correct proportion was observed between the viscosity and fat content of formulations. Samples were examined for antioxidant activity by DPPH and total phenolic content analyses. According to DPPH analysis results, sample B containing 20g of aronia had highest antioxidant activity. According to total phenolic content analysis, sample F containing 20g of aronia and 2.5g of hydrolyzed collagen had the highest total phenolic content. After the antioxidant activity was evaluated, stevia was added as a sweetener to sample E, which contained 1g of hydrolyzed collagen. According to sensory analysis results, sample E1 containing 20g of aronia, 1g of collagen and 0.006g of stevia was the most liked yogurt ice cream in terms of taste.
  • Master Thesis
    Isolation, Phenotypic and Genotypic Charecterization of Yoghurt Starter Bacteris
    (Izmir Institute of Technology, 2007) Erkuş, Oylum; Harsa, Hayriye Şebnem; Harsa, Şebnem; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Specific 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, Figen; Korel, Figen; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Yogurt, 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 Şebnem; Harsa, Hayriye Şebnem; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Yoghurt 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
    Investigations on Aroma Profile of Artisanal Yoghurt Starter Cultyres
    (Izmir Institute of Technology, 2012) Baran, Ezgi; Harsa, Hayriye Şebnem; Harsa, Hayriye Şebnem; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Yoghurt 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 characteristics