Theses supervised by Prof. Dr. Sevim Kaya
10 theses · Gaziantep University
Effect of milk type on thermal properties of Gaziantep cheese
Because of its importance in terms of nutrition, cheese is included in the daily nutrition lists. Besides the nutritional value of cheese, information such as which source and which methods used in production is important both in terms of nutritional value and economy of processes. Such reasons cause problems in cheese production such as imitation/adulteration and the product needs to be analyzed. Thermal analysis, which is one of the analysis methods, is used in the characterization of foods. Thermal analysis; provides valuable information on many thermo-physical properties of food products. The resulting data can be used to understand the differences, especially if there is one, about the product structure. In this study, it was aimed to analyze possible differences in thermal properties of Gaziantep cheeses resulted from different animal milks and thus to determine the source of milk used in cheese. While there is no statistical difference between Cp values of Gaziantep cheese produced from cow and goat milk (p>0.05), Cp of cheese produced from sheep milk is statistically significantly different from cheese produced from cow and goat milk (p<0.01). There was no statistical difference between the Tg values of cheese produced from cow's and sheep's milk (p>0.05). The Tg value of cheese produced from goat's milk and the Tg value of cheese produced from cow's milk were statistically different (p<0.01), and the difference between the Tg value of cheese produced from sheep's milk is significant (p<0.05). Key words: Thermal properties, Gaziantep Cheese, Milk, Glass Transition Temperature
Kahramanmaraş bölgesı̇nde bulgur ve bulgur ürünlerı̇ne yönelı̇k tüketı̇cı̇ tercı̇hlerı̇nin araştırılması
Bulgur and bulgur products may be sold and stored in bags composed of cloth or polymer, which exhibit disparate permeability and physical characteristics that could potentially impact the product. The products can be sold in bulk without individual packaging, directly from sacks or specific bulk storage, in accordance with customer requirements. Aim of the study was to evaluate preferred storage-packaging systems for bulgur and bulgur products by consumers in Kahramanmaraş region. In the region, some of the consumers produce their own bulgur at their home, instead of buying them from market. Accordingly, an investigation of bulgur and its derivatives has been undertaken to ascertain consumer preferences with regard to home production, direct purchases from sacks, bulk purchases, and purchase of those already packed. These factors are important for the purpose of revealing bulgur consumption habits. The recommendations that can be drawn from the results obtained in this study are expected to contribute to the consumption and marketing of the bulgur. This survey was applied to 350 households in order to interview face-to-face with households living in the urban area of Kahramanmaraş province. Statistical analysis of the data showed that consumers do not have sufficient knowledge about the nutritional value of these products and that the impact of packaging materials used for bulgur and bulgur products on product characteristics, including shelf life, is not widely understood by consumers.
Wangashi peynirinin standardizasyonu ve üretiminin karakterizasyonu
Wangashi cheese processing based on the use of Calotropis procera plant stems as a coagulant was characterized and standardized. Crude extract obtained from Calotropis plant stems was used to set solution of milk powder at various pH (4-8) and temperature (35-80oC) in order to examine effect of pH and temperature on milk clotting and proteolytic activities. The pH 5.5 and temperature of 70oC were recorded as optimum pH and temperature. After that concentration of the crude extract enzyme was assayed to purify using ammonium sulfate precipitation at various percentage of saturation (20%-80%) at determined optimum pH and temperature, whereby the saturation of 70% was detected to be the best because of its high specific activity, yield and purification fold. Two different of Wangashi cheese were produced in laboratory, one using directly the crude extract and the other the purified crude extract from Calotropis procera at optimum condition. Their chemical, textural and thermal properties were determined using standard methods. A significant difference between parameters tested was observed (p < 0.05). A decreasing in moisture content, increasing in protein content and also an improvement of color and textural parameters were recorded in cheese obtained using purified crude extract Calotropis procera stems. Key Words: Wangashi cheese, Calotropis procera, milk clotting activity, proteolytic activity, Standardization.
Aktif ambalaj polimer filmlerinin difüzyon özelliklerinin incelenmesi ve kaşar peynir uygulamaları
The thesis was started up to present the diffusion kinetic of antimicrobials from active polymer films. The barrier, thermal and mechanical and, the antimicrobial properties, and application of the antimicrobial active films were also analyzed. Nisin, potassium sorbate, silver substituted zeolite and chitosan were the antimicrobials used in the active films to form N-, PS-, AgZeo- and CTS-films, respectively. It was seen that diffusivity constants of nisin and potassium sorbate (Dn and Dps) were affected by the pH, aw and temperature. Diffusivity of silver substituted zeolite (DAg) was the lowest of all and depended on pH and temperature; however diffusion of chitosan from antimicrobial films was not detected. Temperature dependence of diffusivity of antimicrobials was evaluated using the Arrhenius type model showed the activation energy of DAg was the highest with a value of 34.16 kJ/mol, indicating the highest temperature sensitivity. Diffusion of antimicrobials to the surface of the Kaşar cheese was checked, and the lowest detection belonged to AgZeo-film. Incorporation of antimicrobials into polymer film was not ended with adverse effects on the properties of the films. The study was completed by applying antimicrobial films to pack Kaşar cheese, and they were stored at 5, 15 and 25°C. Usage of antimicrobial films improved the shelf life of Kaşar cheese twice. Hence, it was possible to state that all active films studied could be used as a food packaging material.
Determination of quality parameters and shelf-life of hen egg
The quality parameters (changes in the weight, pH, area and height of albumen and yolk) of shell egg were determined. Weight and color change of shell egg was determined at 10, 16, 20 and 30oC. Area and height change of albumen and yolk and pH change of whole egg were determined at 10, 20 and 30oC. Haugh unit which is accepted as the most important parameter for shelf-life determination of egg was calculated using weight and height change. The order of the quality loses of egg was evaluated as zero order because a linear relation was observed for all quality changes with respect to storage time at studied temperature ranges.It was determined that quality of egg is strictly temperature dependent and especially Haugh unit and pH were affected more than weight changes. The highest quality loss observed at 30oC. Arrhenius-type equation was used for calculation of activation energies for each quality parameter. The effect of temperature and storage time were found as significant for weight and pH change and Haugh unit (P<0.05). The most temperature dependent quality parameter was determined as Haugh unit and the second one is pH and the least temperature dependent parameter weight due to activation energies. Shelf life of the shell egg was calculated as 50 ± 2, 33± 2 and 20 ± 2 days at 10, 20 and 30oC according to pH changes, respectively.
Properties and application of whey protein isolatebased edible films containing clove and apricot essential oils
The targets of the study were to examine the effect of clove and apricot essential oils on the mechanical, antimicrobial and barrier properties of whey protein (WPI) based edible films and to investigate the applicability of the films to a food system. Clove and apricot essential oils were added to WPI solutions were coded as C-WPI and A-WPI, respectively. Kaşar cheese were selected as the food system. Cheese sample were sliced and dipped into WPI, C-WPI, A-WPI solutions and uncoated samples were prepared as control, then they were stored at 4° C for 28 day. Texture profile and microbiological analysis of the samples were evaluated to determine changes in structural properties of the cheese and antimicrobial properties of the films during storage.As it was aimed, both essential oils were bring in films antimicrobial property, further clove has more pronounced effect than apricot. It was determined that addition of essential oils to edible films decreased tensile strength and elastic modulus but increase percent elongation at break. But more pronounced effect of addition of the oils was observed for elastic modulus values than tensile strength. The elastic modulus value of C-WPI decreased to one-fifth of the WPI value. According to the results of texture profile analysis and rheological analysis essential oils incorporated edible films did not show a distinct differences with respect to WPI based film coated and uncoated cheese samples.
The drinking-milk consumption habits in Gaziantep
The use of various nutrients in the survival of human beings is important. Milk and milk products contain essential protein and fat for a balanced diet rich in lactose, vitamins and minerals. Aim of the study was to analyze consumer expectations and which factors affecting their milk and milk products consumption trends. After evaluation of milk consumption and the effective factors, it would be possible to adjust the production of drinking-milk with caring consumer needs, and develop some marketing plans encouraging the people. The factors examined were organized to evaluate effect of different processes applied on drinking milk, which factors might affect purchasing decision. The results were assessed using reliability analysis, frequency analysis and chi-square test. A survey was performed with 383 participants living in Gaziantep. The obtained data was evaluated using IBM SPSS Statistics 25 software. It was concluded that 88.7% of the participants consumed the drinking-milk and 42.3% of the participants drank one cup a day. 37.5% of the consumers preferred pasteurized milk, 35.4% UHT milk, and 27.1% open milk. The analysis results showed that 69.1% of the consumers give an importance to the brand when making the purchase decision, at the same time, 89.4% read the expired date. Further, for 71% of the participants the fat quantity referred to the quality of milk.
Aktif paketleme filmlerinden su ve antimikrobiyal madde difüzyonu
The release of antimicrobial agents (potassium sorbate, nisin, and chitosan) which the activity of them depends on the migration from the packaging films to the food surface and the apparent diffusivity constants (D) were examined. Moisture sorption isotherms of the active packaging films were an important parameter for the migration of the agents. In the study moisture sorption isotherms of the films were investigated and D of the films was evaluated. The release kinetics of potassium sorbate (1, 3, and 5%) and nisin (1, 2, and 3%) from polyethylene films were described using Fick?s second law of diffusion and D were found to be 4.21×10-21, 1.75×10-20 and 2.73×10-20 cm2/s at 25°C; 1.55×10-19, 2.69×10-19 and 2.82×10-19 cm2/s at 35°C, respectively. The release of chitosan from polyethylene films could not be detected. The moisture equilibrium isotherms of the films containing potassium sorbate, nisin and chitosan were determined by the Dynamic Vapor Sorption (DVS) method using the instrument, the DVS Intrinsic. Guggenheim, Anderson and De Boer (GAB) model was chosen the most suitable equation to define the adsorption isotherms of the films. The monolayer moisture content (Mo) of the films containing potassium sorbate 2%, nisin 3%, and chitosan 3% were 1.89, 0.29 and 0.09 at 20°C, respectively. D of the films between water activities of 70% to 80% RH were found as 4.12x10-20, 8.35x10-19 and 3.23x10-21 cm2/s at 20°C, respectively for potassium sorbate (2%), nisin (3%) and chitosan (3%) containing films. Keywords: Active packaging, antimicrobial agent, diffusion, moisture sorption
Storage stability of lokum
The storage stability of lokum is related with textural and thermal properties as a function of storage conditions (temperature and percentage relative humidity (RH)). Lokum is a high sugar containing food and it is generally stored at ambient conditions changed from region to region. In this study, the effect of these conditions (32, 53, 75%RH and 15, 25, 35°C) on textural and thermal properties of lokum was determined. Since the major deterioration factor affecting the textural property of lokum is moisture gain or loss, moisture sorption isotherms (MSI) of lokum were determined at 25°C. Glass transition temperature (Tg) of lokum stored at different RH at 25°C were determined to estimate thermal property. Oswin and Kwei Equations were the best fitting mathematical models for MSI and the relationship between Tg and water activity (aw) of lokum, respectively. Textural Profile Analyzer was used to evaluate the effect of storage conditions on textural properties. Weight changes of samples were also monitored. It was found that lokum became softer when the temperature and RH were increased besides it became harder at low temperature and RH. It was possible to state that the highest quality problem was getting softer structure which was observed in lokum samples stored at 35°C and 75%RH. The activation energies of lokum samples stored at 32%RH and 53%RH were calculated as 22.55 kJ/mol and 39.5 kJ/mol and it was determined that there was not regular changing trend in textural parameters of samples stored at 75%RH with temperature change.
Development and characterization of some composite (WPI, SPI and CMC based) edible films
Edible films based on different proteins, polysaccharides and/or lipid were developed with their optimal proportions. Whey protein isolate (WPI), soy protein isolate (SPI) and carboxymethyl cellulose (CMC) were used as protein and polysaccharide resources, respectively. Besides, sunflower oil (SO) was added into the films. Moisture absorption, mechanical, barrier, physical and thermal properties of the composite films were investigated. Moisture absorption of the films containing single component was tested at three different relative humidity (30, 50 and 80%) conditions at room temperature using dynamic vapor sorption instrument. Water vapor permeability (WVP) and oxygen permeability (OP) of the films were determined using analytical and instrumental techniques, respectively. Significant reduction in WVP and OP of the WPI films was obtained upon addition of SO. Mechanical properties also affected by addition of SO that percent elongation (%E) was increased by four times. It was determined that glass transition temperature was increased proportionally with SO amount for WPI films but SPI-SO blend film had less value than that of SPI. CMC addition improved the WVP but it caused negative effect on OP. WS1 (0.05% SO added WPI) and SPI-CMC were assumed to be the best two combinations among all studied films. Key words: Composite edible film, whey protein isolate, soy protein isolate, carboxymethyl cellulose, sunflower oil