National Repository of Grey Literature 147 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Monitoring process contaminants in coffee roasting using LC-MS
Ilyushchenkova, Alexandra ; Juglová, Zuzana (referee) ; Diviš, Pavel (advisor)
The bachelor thesis focuses on monitoring changes in the concentration of process contaminants during coffee roasting using liquid chromatography with mass detection. Green coffee was roasted at 220 °C for 14 minutes with two-minute intervals. Samples for analysis were taken from 10. by 24. minutes of roasting. Practical monitoring of the acrylamide’s formation during coffee roasting was not carried out, since it was not possible to detect acrylamide in coffee using a mass detector, even after its derivatization with thiosalicylic acid. The relevant data were taken from other scientific articles, which reported a linear increase in concentration with the roasting time up to the maximum value and a subsequent exponential decrease at the end of roasting. By monitoring 5-hydroxymethylfurfural, it was found that during roasting, this substance is gradually formed in coffee due to the decomposition of carbohydrates, however, with increasing roasting time, the degradation of this substance occurs quite quickly. The concentration of 5-hydroxymethylfurfural was also determined in coffee samples purchased in the trade network. Concentrations of 5-hydroxymethylfurfural in these samples ranged from 0,3 to 0,38 mg/kg, which are corresponded to those reported in other expert studies.
Content of risk elements in food for dogs and cats
Hrabalová, Karolína ; Slavíková, Zuzana (referee) ; Diviš, Pavel (advisor)
This bachelor's thesis deals with the determination of risk elements, namely mercury, arsenic, cadmium and lead in dog and cat food. The concentration of mercury was determined using the AAS technique, and the concentration of arsenic, cadmium and lead was determined by the ICP-MS method after microwave decomposition of the samples using mineral acids. A total of 30 feed samples were analyzed. In most samples, the concentrations of monitored elements were lower than the maximum permissible values given by the EU Commission Regulation, two samples did not meet the requirements of the regulation. The concentration of risk elements in the feed, except for arsenic, did not depend on the type of meat used in the feed. Feeds containing fish meat showed demonstrably higher concentrations of arsenic than feeds with other meats. Due to the relatively low proportion of meat in feed and due to the overall lower concentrations of risk elements in meat, it can be assumed that the vegetable or other component of the feed, or the technology of feed production, is responsible for the increased concentration of risk elements in feed.
Pepper quality in terms of piperine content
Lamplot, Marek ; Vítová, Eva (referee) ; Diviš, Pavel (advisor)
The aim of this bachelor's thesis was to determine the quality of pepper available in the commercial network of the Czech Republic. The quality of the pepper samples was determined based on the piperine content. Piperine was extracted from pepper samples using acetone and the extracts were subsequently analyzed using high-performance liquid chromatography with a mass detector. In all samples, the water content was determined by Karl-Fisher titration, and the piperine content in the samples was subsequently converted to dry matter. The content of piperine in pepper varied from 49 to 90 mg/g and met the requirements of the current legislation, which specifies a minimum piperine content of 4 % in pepper. Statistical analysis showed that there is a statistically significant difference between individual pepper samples in terms of piperine content, which points to the fact that pepper from different producers comes from different sources.
Effect of added carbohydrates on the quality of cereal kvass and kvass bread
Stoklásková, Olga ; Vítová, Eva (referee) ; Diviš, Pavel (advisor)
The aim of this bachelor thesis was to characterize selected chemical, senzoric and rheologic properties of sourdough breads with added particular saccharides in the dough. In the theoretical part, processes during mixing, proofing and scaling of the sourdough in fixed conditions are analysed; researched sugars are characterized and their influence on the sourdough product, resulting from present research, is discussed. The experimental part focuses on particular analyses, that influence the quality of sourdough product and determine so its market demand. According to the analysis, sourdough fortification of low honey concentration tends to the maximal volume of the loaf and the most tender crumb at the same time. Higher additions of white table sugar increase the total acidity of the dough the most significantly; unlike, a malt flour provides a smooth, sweetish aroma to the bread. This is because of inhibition of acetic acid production by maltose during sourdough fermentation. Unfortunately, lower concentration of acetate and higher content of remaining sugars in the same time is a factor of shortening the microbial shelf-life of the bread after its baking.
The influence of coffee bean grinding and brewing method on the content of selected substances in a coffee cup
Dvořáčková, Sabina ; Vítová, Eva (referee) ; Diviš, Pavel (advisor)
This thesis deals with the influence of barista methods on the content of selected aromatic substances and caffeine in variously ground coffee. In the theoretical part, general information about the coffee plant, the chemical composition of the coffee bean, cultivation, post-harvest processing technology, including individually discussed barista preparation methods are presented. Furthermore, this part is devoted to the description of 10 selected volatile compounds that are part of the aromatic coffee profile, together with the characterisation of the xanthine alkaloid caffeine. The experimental part was filled with the analysis of 100% Arabica coffee samples that were prepared through a lever coffee machine, moka pot and Vacuum pot. These methods were used to prepare coffee samples that were ground to the finest, medium and coarse grinding grades as the effect of relative coffee particle size on the extraction efficiency of the studied compounds was investigated. Based on the results obtained, it was found that the highest caffeine concentrations were measured in espresso samples of medium ground coffee, which were extracted using a lever coffee machine and contained up to 110 mg of caffeine in 30 ml. Similar results were obtained for coffee samples made from the coarsest ground beans prepared using a moka pot, with caffeine concentrations averaging 176 mg per 50 ml of beverage. The most abundant volatile flavouring substance was furfuryl acetate. Its highest concentrations were recorded in the coarsest coffee samples from the vacuum pot, which proved to be the method with the best repeatability. Calculated values based on 1 kg of coffee identified 2-methylpyrazine as the most abundant volatile, which, like furfuryl acetate, was followed by high furfuryl alcohol.
Use of wheat bran for fertilizer production
Maňáková, Helena ; Štursa,, Václav (referee) ; Diviš, Pavel (advisor)
This diploma thesis deals with the production of fertilizer from wheat bran and spent coffee grounds, which are produced in large quantities in the food industry. The efficiency of the removal of caffeine and phenolic substances from coffee grounds using the oxidation reason and the possibility of recycling the usable oxidizing effect were tested. We managed to oxidize almost all phenolic substances and a significant amount of caffeine from coffee grounds, even through the recycled oxidizing effect. Fertilizer in the form of pellets was subsequently formed from coffee grounds and bran. During pelleting, the optimal degree of wetting of the material was studied to achieve optimal yield of pellets and sufficiently strong pellets. Different ratios of substrates for pelletization were also studied and the quality of produced pellets was assessed. The content of macro and microelements in the prepared pellets was determined. Pellets have been shown to be a good source of elements important for plant growth.
Bioavailability of magnesium and zinc from food supplements
Lindovský, Patrik ; Křikala, Jakub (referee) ; Diviš, Pavel (advisor)
This bachelor's thesis deals with the analysis of dietary supplements containing magnesium and zinc. The analysis examined the content of active substance and solubility in simulated gastric acid. The method used to analyze the active substance content was inductively coupled plasma optical emission spectrometry. This method was also used to determine the degree of solubility of the active substances. A total of thirteen different samples of dietary supplements were examined, all of which contained magnesium as the active ingredient and four of these samples additionally contained zinc. All samples contained the declared amount of magnesium. The zinc amount in food supplements was in accordance with the content stated on the label. In some samples the amount of zinc was determined to be lower, but the deviation from the declared amount did not exceed 14 %. Solubility tests have shown that some products do not contain a suitable type of coating to protect the active substance, which may cause a deterioration in bioavailability.
Control of careless heating of honeys using HPLC and MAS techniques
Radvanová, Tereza ; Punčochářová, Lenka (referee) ; Diviš, Pavel (advisor)
Honey is a popular natural food. Liquid honey without any trace of crystalization is much more desirable. Therefore, honey undergoes heat treatment to dissolve formed crystals. Exposure to high temperetures can cause chemical changes of honey components and formation of undesirable reaction products. When honey is heated 5-hydroxymethylfurfural can be formed and activity of enzyme diastase lowers. In this bachelor thesis, 5-hydroxymethylfurfural content was analyzed by HPLC-MS and activity of enzyme diastase was determined with commercial Phadebas method followed by MAS in 11 honey samples. Analysis determined 5 honey samples with above the limit content of 5-hydroxymethylfurfural and 1 sample with insufficient diastase activity. 5-hydroxymethylfurfural content in honey correlated well with diastase activity values (r = 0,612).
Determination of the risk elements and other elements concentration in animal feed
Křehlíková, Jana ; Juglová, Zuzana (referee) ; Diviš, Pavel (advisor)
This thesis deals with the determination of selected microelements and macroelements and risk elements in dog and cat food. The theoretical part describes the nutrition of dogs and cats and focuses on the safety of the food in the context of contamination with risk elements. Another topic discussed is the chemical analysis of feeds, specifically the determination of nutritionally important substances, beneficial elements, and contaminants. The experimental part deals with the preparation and digestion of feed samples and the subsequent analysis of these samples using ICP-OES and AAS methods. The detected concentrations of the elements of interest in the feeds were compared with the feed standards issued by the Department of Veterinary Medicine and the decree issued by the Ministry of Agriculture. The analysed feeds were found to be deficient in some elements. The content of the risk elements in the feed met the legal limits and did not pose a health risk to the animal. Elements for which the legislation does not provide a maximum permissible limit were present in the feed-in in high concentrations that could already harm the animal's health.

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See also: similar author names
4 Diviš, Patrick
3 Diviš, Petr
2 Diviš, Přemysl
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