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Analysis of drinks sweetened with stevia extracts
Procházka, Václav ; Hrstka, Miroslav (referee) ; Vespalcová, Milena (advisor)
The steviolglycosides are the natural, sweet substances from Stevia rebaudiana Bertoni. It affect human health positively and its sweetness is 300x stronger than the sweetness of sucrose. That's why it's used to sweetening the commercial products. Because of its potential properties it's good to have an appropriate method to isolate it. High performance liquid chromatography ( HPLC) is based on the separation of analyte between two immiscible phases with high pressure pump and appropriately chosen stationary phase in the column. Than the analytes come out from the column in different retention times. This master´s thesis follows up selection of the best HPLC system for isolation of the main steviolglycosides and its analysis in commercial products. In the theoretical part of the thesis is described the origin, basic characteristics, botanical description, cultivation and affect to the human health of Stevia rebaudiana Bertoni and its use in food industry. There are also concisely characterized the sweet substances contained in the plant, so called steviolglycosides. Than there are given the theoretical basics of high performance liquid chromatography, HPLC instrumentation and its specific applications at sleviolglycosides with the basic chromatographic parameters. The object of the first experimental part was to research the optimum conditions for time and separation effective chromatographic analysis and select the best chromatographic system for isolation of steviolglycosides. In the second experimental part, I have compared and defined the main steviolglycosides (stevioside, rebaudioside A) in nine selected products, commercially available in Czech republic, with the best chromatographic method. In these products was the contain of the stevioside or rebaudioside A confirmed or refused.
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Chemical composition of berries juices from some cultivars of European elder
Šafránková, Petra ; Vespalcová, Milena (referee) ; Hrstka, Miroslav (advisor)
This thesis deals with chemical composition of the juice from selected species of elderberry (Sambucus nigra L.). The theoretical part is dedicated to botanical characteristic of elderberry including the origin and the extension. There are also mentioned the medical effects of elderberry with the description of the cultivation of this herb with the examples of particular cultivated species. In the experimental section were laid down the particular chemical parameters (yield, pH, relative density, titrable acidity, formol number, content of instant dry mass and reducing sugar) in the juice from the fruits of these cultivated species of elderberry: Albida, Allesö, Aurea, Bohatka, Dana, Heidegg 13, Haschberg, Körsör, Mammut, Pregarten, Riese aus Voßloch, Sambo, Sambu, Samdal, Sampo, Samyl a Weihenstephan. The median of the yield has been 700,0 ml/kg, the median for the pH assessment has been 4,03. The median of relative density of all species was 1,0361, the median of titrable acidity was 141,83 mmol l -1. The median of the overall content of amino acids was 30,5 ml 0,1 mol l-1 NaOH/100ml, the median of the content of the dry mass was 9,5 weight %. The median of the assessment of the reducing sugar was 5,02%.
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Dietary fiber in food and possibilities of its determination
Piškulová, Lenka ; Hrstka, Miroslav (referee) ; Vránová, Dana (advisor)
The work deals with the definition of dietary fiber, its division and basic describtion of building dietary fiber components. Finally, it focuses on basic methods and ways of determining of dietary fiber. The practical part compares the obtained amount of insoluble dietary fibre in different kinds of gluten-free and gluten bread. The results were obtained by using the method according to Henneberg and Stohmann.
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Basic chemical characteristics of juices of selected white currant varieties
Zlámalová, Petra ; Hrstka, Miroslav (referee) ; Vespalcová, Milena (advisor)
The bachelor thesis deals with determination of basic chemical charcteristics of juices of selected white currant varieties. The theoretical part focuses on botanical description of the plant, history of cultivation, important chemical substances contained in the fruits and their effects on human body. There is also described use of white currant in the food industry and the basic principals of determination of the juice parameters, there. The experimental part focuses on determination of juice yield, soluble solids, pH, dry matter content, titrable acidity and formol number. Based on resultes, the individual cultivars were compared. The determination showes that cultivar Olin has the highest titrable acidity and the most of soluble solids at all. Cultivar Orion has the biggest juice yield, cultivar Primus has the biggest dry matter content and cultivar Jantar has the highest formol number and pH.
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An aplication of the mathematical dislocation theory to the problem of the crack in the vicinity of the bi-material interface
Padělek, Petr ; Hrstka, Miroslav (referee) ; Profant, Tomáš (advisor)
The presented diploma thesis deals with a problem of the determination of the stress intensity factor of the finite length crack in the vicinity of the bi-material interface solved by the distributed dislocation technique. The work is divided into several parts. The first part is theoretical and includes basic concepts of the fracture mechanics, the crack behaviour at the bi-material interface, the formulation of the singular integral equation by virtue of the distributed dislocation technique, the Bueckner's principle, complex potentials and consequently the determination of the stress intensity factor. The second part is the theory application to the specific configuration of the crack of the finite length with respect to the bi-material interface and in the third part, there is carried out the solution of this problem for various configurations of the bi-material solved by the distributed dislocation technique and its comparison with the results obtained from the FE analysis.
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The addition of carbon dioxide to milk for cheese production
Králová, Petra ; Hrstka, Miroslav (referee) ; Kvasnička, Miloš (advisor)
This work deals with the addition of carbon dioxide to milk for cheese production. The first aim was to elaborate a literary search focused on chemical composition of milk and its changes after addition of carbon dioxide and to describe production processes, with or without addition of carbon dioxide. The opening part was in particular focused on production of cheese with carbon dioxide and what all this gas causes during production. Carbon dioxide significantly decreases pH, thereby preventing from multiplication of undesirable microorganisms, it is also very important for shortening of production time, because it shortens the coagulation time. The main aim of experimental part was to determine the optimum addition of carbon dioxide to milk for production of Balkan cheese and using several analytical methods to compare cheese produced with and without addition of carbon dioxide. The sensory methods suitable for following of sensory differences of produced cheeses were also chosen and applied. By request of Dairy in Polná Ltd., the operation economy was calculated, which revealed that production with carbon dioxide is very useful and can reduce production costs of Balkan cheese, which would certainly be positive. The advantages and disadvantages of cheese production with carbon dioxide for consumers as well as for producer are evaluated as conclusion of this work.
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The influence of the autochthonous yeasts and technological process on the chemical parameters the wine
Chmelová, Petra ; Hrstka, Miroslav (referee) ; Vránová, Dana (advisor)
This bachelor´s thesis deals with influence of the autochthonous yeasts and technological process on the chemical parameters of the wine. The theoretical part describes the history of viticulture in the world and in Bohemia and Moravia, characteristics of grapevine, morphological structure and chemical structure of grapes. There are also analyzed the individual proces steps in the production of wine and consequently the most commonly used of analytical methods for the examination of the must samples. The experimental section presents the results obtained by monitoring chemical changes in the examined musts during fermentation. Experimentally measured parameters in this work are reducing sugars, pH, titratable acids and ethanol content in the samples must. The samples used for analysis were from variety of the Grüner Veltliner from village Kobylí.
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Crack in prismatic bars
Meňhert, Samuel ; Hrstka, Miroslav (referee) ; Profant, Tomáš (advisor)
This thesis deals with summarization of information about fracture mechanics mainly with methods which estimate stress intensity factors. They play an important role in determination of behavior of cracks in engineering process. The main goal of this thesis will be familiarization with Kienzler hypothesis which deals with strain energy release rate and internal effects in a point of disrupted cross section and comparison with classic K-concept, when the stress intensity factors are determined by infinite series.
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Impact of elevated carbon dioxide concentration on protein content of gliadin fraction in winter wheat
Hamříková, Dominika ; Omelková, Jiřina (referee) ; Hrstka, Miroslav (advisor)
In this diploma thesis protein content of gliadin fractions in winter wheat (Triticum aestivum) var. Bohemia was studied. The crop was cultivated in conditions with ambient (AC) and elevated (EC; 700 mol•mol-1) carbon dioxide concentration. Moreover, half of the samples was fertilized with nitrogen in an amount of 200 kg•ha-1. Other observed environmental factors were drought and UV radiation. The gliadin proteins were separated by A PAGE method and quantified by computer densitometry. Generally the protein content within , and gliadin fractions varied, while the protein content of gliadins remained unchanged or almost unchanged. Clearly the nitrogen fertilization had the most pronounced impact on the gliadin protein content and it significantly increased the protein content in wheat grain. Most subfractions reacted in conditions of AC, drought and without UV radiation and in conditions of EC with natural rainfall and UV radiation. The interaction of nitrogen fertilization with UV radiation (AC, drought) was significant and so was the interaction of nitrogen fertilization excluding UV radiation (EC, drought). The interaction of nitrogen fertilization and natural rainfall significantly increased the protein content in conditions of AC without UV radiation and in conditions of EC with UV radiation. EC alone and the interaction of EC with other factors had only a small impact. The impact was the most pronounced in interaction with nitrogen fertilization. EC with nitrogen fertilization (drought without UV radiation) increased the gliadin protein content and EC excluding nitrogen fertilization (drought and natural rainfall with UV radiation) decreased the protein content.
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Accuracy of the method for assessment of allergenic aroma compounds
Rychetský, Matěj ; Hrstka, Miroslav (referee) ; Vítová, Eva (advisor)
This bachelor thesis deals with the verification of the accurancy of the method for determination of potentially allergenic substances in confectionery. In the theoretical part the synthetic and natural fragrances, which are present in foodstuffs are described. Furthermore, the method of solid phase microextraction in connection with gas chromatography with mass spectrometry, which was used in the measurement, is briefly characterized. Finally, the basic criteria measured in the validation of the analytical method are described. In the experimental part, the repeatability and reproducibility of the HS-SPME-GC-MS method for the determination of potentially allergenic substances in candy samples was verified. It was found by the measurement that the used method is suitable for qualitative determination (based on retention times), but the method shows minor inaccurancies in quantitative determination (determination based on peaks area) and it will be improved in following experiments.
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