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Reologické vlastnosti bílých jogurtů
Fabianová, Jana
Diploma thesis in its theoretical part solves the problems of the milk assortment of dairy products, especially yogurt. It splits yogurt to the different types describing their production and chemical and physical properties. It is followed by a chapter devoted to the physical characteristics of foods, as well as their rheological properties, specifically viscosity. The practical part deals with the rheological properties of specific samples of commercially available yogurt. For these seven samples was determined by the density and the viscosity and shear stress versus shear rate. To assemble the flow and viscosity curves were used Ostwald-de Waeleho model, thanks to him, it was subsequently decided what kind of fluid as, Newton viscosity law, in the case of yogurt is. For the samples was determined as well as the time and temperature dependence of viscosity. Selected samples were analyzed fat content, which can be compared with data on the packaging of the sample.
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Reologické vlastnosti kečupu
Mejzlíková, Vendula
In theoretical part of this thesis is writing about tomatoes as a raw material for production of ketchups. There is also disclosed the production of tomato puree, which is the main raw material for production of ketchup. In the next part are theoretically recorded rheological properties of foodstuffs. The practical part of the thesis delas with rheological properties of ketchup. There were selected samples of commercial ketchup and one sample of homemade ketchup. At these samples, there were determinated their viscosity, density and shear stress depending on shear rate. The Ostwald-de Waele model were used for compiled flow and viscosity curves formating of each sample. With a help of this model was determined, what type of fluid is the particular ketchup. Also was monitored the time depedence of the viskosity of ketchup. Then there is compared the relationship between viscosity and densit of ketchups on the content tomatoes in each sample.
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Vliv teploty na tokové chování čokolády
Bureš, Václav
A large part of this bachelor thesis is focused on cocoa beans and chocolate as well. Acquisition, evaluation and treatment of cocoa beans. Then also for industrial chocolate production, finally adjustment before being packaged, storage before it reaches commercial networks for sale to the final consumer as well as their effect on the human body and health. I chose three varieties of chocolate from the same commercial chocolate manufacturer with at least 50%, 78% and 99% cocoa content. For these chocolate samples I have described their characteristics and chemical composition. The second part is practical and deals directly with shear stress change at increasing shear strain rate and temperature change. Flow properties were measured using RST rheometer (Brookfield, USA) with a cone-plate spindle arrangement (RCT-50-2) incl. duplicator for tempering samples. The measured values were evaluated and processed into graphs and tables. Measured values were modeled using suitable mathematical models. Casson model, Bingham model and Herschel-Bulkley model. The most suitable models are Casson's model and Herschel-Bulkley's model.
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Gelation of waterglasses depending on their composition
Otřísalová, Pavlína ; Kalina, Lukáš (referee) ; Bílek, Vlastimil (advisor)
This bachelor thesis studies how are gelation of sodium and potassium silicates (water glass) influenced by their composition. The main goal of the thesis was to investigate the effect of silicate concentration, molar ratio, and alkaline ions on the gelation time. Qualitative analysis of obtained gels was also performed. The thesis includes literature research in the field of chemistry of silicate sols and gels. In the experimental part were prepared samples of both sodium and potassium silicates with silicate concentrations of 15 M and molar ratios of 0,53,0. Gelation was induced by adding calcium ions. Gelation time was measured using rheological oscillation tests (time sweep) and visual method. Qualitative analysis of the gels was performed using rheological oscillation tests (amplitude and frequency sweep) and visual method. Three significant trends were observed: 1) NaVS samples always had shorter gelation time than KVS samples 2) the higher the silicate concentration the higher the gelation time 3) gelation time of samples with molar ration of 2 was most influenced by silicate concentration. It was also observed that the formation of gel network was promoted in systems with 1) higher molar ratios 2) higher silicate concentrations 3) presence of K+ ions. Gels with molar ratios 2 were significantly weaker than those with ratio of 2,5 or 3,0.
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Preparation and characterisation of polysaccharide hydrogels
Kulíšková, Kateřina ; Kadlec, Martin (referee) ; Smilek, Jiří (advisor)
This bachelor thesis deals with the study of preparation and characterization of alginate hydrogels. It focuses mainly on the ionic crosslinking of alginate using divalent metal cations Ca2+, Cu2+, Zn2+, Ba2+, Fe2+ together with the trivalent cation Fe3+ in order to compare the crosslinking abilities of different oxidation states. The exogenous method was used for the preparation of alginate hydrogels and the prepared hydrogels were thus studied in the form of millimetre spheres. In the experimental part, optimization was performed to find out the optimum gelation time, which resulted in the crosslinking of the hydrogels throughout their volume. Ca2+ ions were used as a reference due to their wide application and the extensive experience with these ions at the faculty. The knowledge from the optimization was applied to the preparation of the other ions samples. The viscoelastic properties of the hydrogels were investigated by rheological measurements in the form of amplitude and squeeze tests. All ions, except Fe2+, were found to crosslink the hydrogels throughout the volume. Based on the complex modulus, the order of ions was determined according to the degree of crosslinking, The degree of crosslinking also has major impact on the degree of syneresis.
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Polyvinyl alcohol hydrogels with gradient structure in crosslinking density
Ščotková, Romana ; Kalina, Michal (referee) ; Smilek, Jiří (advisor)
The presented thesis introduce one of the many possibilities for the physical preparation of PVA hydrogels with a gradient in the crosslinking density. Based on the research conducted, the main focus of which was the preparation methods of gradient hydrogels and the characterization of their properties, a cyclic freezing and thawing method was selected and optimized with a focus on the selected preparation parameters. The next step was to perform pilot experiments leading to the confirmation and characterization of the resulting gradient structure by selected instrumental techniques such as rheology, scanning electron microscopy or a method based on monitoring the loss of dispersion during drying of the samples. In addition to the confirmation of the gradient structure, one of the parameters studied was the effect of the addition of polysaccharide on the resulting mechanical properties. Gradient hydrogels with different molecular weights or biopolymer additions were compared in the second part of the experimental work based on diffusion experiments using methylene blue. At the end of the work, all the results obtained were discussed and additional measurements were proposed for a deeper understanding of the subject.
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