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Cheese defects and possible causes of their origin
Mazal, Marek ; Legarová, Veronika (advisor) ; Vladimír, Vladimír (referee)
This bachelor thesis is dealed with cheese defects and possible causes of their origin, which are participated in their formation. The problems of cheese defects is not focused only on technical apects, but it is also focused on microbial risks of possible contamination, the work is directed there at microbial quality of milk, which is crucial at the cheese manufacture. Microbial quality of milk is very important for cheesemaking, but the milk can be contaminated during the manufacture and also during the transport or storage. It is obvious for the reason of milk contamination, that milk has to be heat-treat, in order not to be damaged the final product. However heat-treat is not complete solution, because some microorganisms tolerate higher temperatures or they survive by formation of spores. Another way of contamination is entering of microorganisms during the cheesemaking, maturing and due to unsuitable storage. The cheese is not damaged only by microorganisms, but there are also significant physical factors, which can influence the quality of cheese, these are water activity, pH, salt content and temperature. These factors influence the natural microflora, which is present in the final product. However it is important realize, that there are differencies of susceptibility to forming pathogens among the cheeses, long aged cheeses are low risk due to it´s low pH, which prevents forming of pathogens so the pathogens can not endanger the cheese quality.
It should be considered suitable methods for elimination of pontecial risks and relevant defects during the cheesemaking. The most important methods should be regular hygien procedures, appropriate manufacturing and agricultural processes. The system of risk analysis and Hazard Analysis and Critical Control Points (HACCP) should be certainly present. For the prevention of cheese defect it is necessary regular control of specific paramaters at important stages of manufacture.
Very important matter is cosumption of cheese contaminated by mycotoxins, because consumption of mycotoxins is relatively high risk for human health. Mycotoxins are able penetrate into the cheese primarly due to presence of microscopic fungus, furthermore they can occur also as derivatives of mycotoxins, which are eaten by animals with their feed.
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Foodborne Staphylococcus Aureus: Identification and Enterotoxin Production in Milk and Cheese.
Hrušková, Vendula ; Španová, Alena (referee) ; Kmet,, Vladimír (referee) ; Kaclíková, Eva (advisor)
Onemocnění z potravin (alimentární onemocnění) vyvolaná bakteriemi jsou stále aktuálním tématem v celosvětovém měřítku. Abychom zajistili výrobu zdravotně nezávadných potravin, je potřeba nových poznatků o virulenci patogenů, které by doplnily již známé skutečnosti o jejich růstu a přeživání v potravinách. Také potřebujeme vyvíjet rychlé a citlivé metody na detekci těchto patogenů. Dizertační práce popisuje metodu na detekci S. aureus v potravinách, která je založená na PCR v reálném čase ve spojení s namnožením v selektivním médium. Dále pojednává o vlivu environmentálních faktorů na růst S. aureus a tvorbu enterotoxinů v mléce a sýrech. Vyvinuli jsme rychlou a citlivou metodu na detekci S. aureus v potravinách s použitím selektivního namnožení a PCR v reálném čase. Nově vyvinutá metoda umožnila detekci S. aureus na druhý den od přijetí vzorku. Tato metoda může být použita jako rychlejší, citlivějsí a vysoce specifická alternativní metoda ke konvenční mikrobiologické metodě. Zkoumali jsme vliv tří různých teplot, 8°C, 12°C a 20°C na růst S. aureus a tvorbu enterotoxinu D v pasterizovaném mléce a na růst, expresi genu sed a tvorbu enterotoxinu D v tekutém médiu s extraktem z mozku a srdce (BHI). Experimenty byly prováděny v malých skleněných fermentorech po 6 dní. Genová exprese byla sledována pomocí qRT-PCR a tvorba enterotoxinu D byla měřena pomocí imunologické metody ELISA. Růstová křivka v BHI měla stejný průběh při 20°C a 12°C, ale v při 12°C začal růst se spožděním. Při 8°C nebyl pozorován žádný růst. Růst S. aureus v mléce byl ve srovnání s BHI menší. sed mRNA byla detekována při 20°C po 4 hodinách a při 12°C po 7 hodinách a produkce enterotoxinu se objevila v exponenciální fázi růstu. V mléce se produkce SED při 20°C a při 12°C objevila dříve, ale celkové množství vyprodukovaného SED bylo nižší než v BHI. Při 8°C nebyla pozorována žádná produkce SED stejně jako v BHI. Dále byl zkoumán společný vliv nízké teploty 12°C a přítomnosti kompetitivní doprovodné mikroflóry pocházející ze surového mléka na růst S. aureus a produkci enterotoxinu v pasterizovaném mléce. Byl pozorován inhibiční účinek na růst a produkci enterotoxinů a vliv kompetice byl výraznější než vliv nízké teploty. Produkce enterotoxinu byla nízká a odpovídala růstu. Snížením množství doprovodné mikroflóry a zvýšením inokula došlo pouze k nepatrnému zvýšení produkce enterotoxinu. V další fázi byly dva různé typy sýrů zaočkovány S. aureus za účelem simulace sekundární kontaminace při výrobě sýrů. Vzorky byly odebírány v průběhu 4 týdnů. Kritické faktory jako jsou kompetitivní mikrofóra nebo pH, které jsou zodpovědné za regulaci virulence S. aureus byly sledovány. Snažili jsem se rozlišit situace při kterých: (i) není pozorován růst, ale objevuje se produkce enterotoxinu a (ii) dochází k růstu ale bez produkce enterotoxinu.
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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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PCR identification of nonpathogenic bacteria strains in cheeses
Jurečková, Nela ; Doušková, Dagmar (referee) ; Španová, Alena (advisor)
Different species of genus Bifidobacterium are part of human and animal intestinal flora. These bacteria have benefit effects and therefore they are used in foods and pharmaceutical products as probiotics. Cheese is now suitable as a probiotic matrix except yoghurts and fermentated milks. This diploma thesis was focused on optimalization of DNA isolation from bacteria of genus Bifidobacterium. Magnetic microparticles (P(HEMA-co¬-GMA)) were used for DNA isolation in presence of 8% polyethyleneglycol PEG 6000 and 5 M sodium chloride. Phenol extraction weas also used as an isolation method. Isolated DNA was used for amplification in domain, genus and species specific PCRs. Optimized method was tested for detection of bacteria of genus Bifidobacterium in experimentaly prepared probiotic cheeses. These cheeses contained potential probiotic bacteria from Laktoflóra collection. Bacteria were identified into species using species specific PCR. Species Bifidobacterium animalis was identified in all samples of probiotic cheeses.
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DNA analysis of nonpathogenic clostridia isolated from cheeses
Chroboková, Maria ; Trachtová, Štěpánka (referee) ; Španová, Alena (advisor)
Polymerase chain reaction (PCR) is a molecular method which allows in vitro replication of nucleic acids. It allows the identification and quantification of microorganisms or to prove specific gene sequentions in different matrices of biological origin. Some nonpathogenic species of genus Clostridium cause damages of cheeses, so their identification and quantification is very important in cheesemaking. In this thesis, specific primers for genus Clostridium were tested. Bacterial DNA from culture collection strains and from strains isolated from damaged cheeses were used. Genus-specific region for Clostridium was amplified using specific primers. The PCR products (619 bp) were detected using electrophoresis in 1,8% agarose gel. Genus-specific character of primers was confirmed. DNA of Lactobacillus was used for negative control.
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Processed cheese analogues
Brabcová, Lenka ; Illková, Kateřina (referee) ; Vítová, Eva (advisor)
This bachelor thesis deals with the problem of cheese analogues with the focus on processed cheese analogues. The aim was to elaborate the literature background research focused on ingredients suitable for production of cheese analogues and their influence on physico-chemical and organoleptic properties. In the introductory part what the cheese analogues are, the reasons for their production and their use is explained. Special attention is dedicated to ingredients suitable for their production and their physico-chemical and organoleptic properties. Also technological process of manufacture, microstructure and their comparison with classic cheese are mentioned. These established theoretical informations will be a basis for following diploma thesis.
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Changes in acidity during round-eyed cheese ripening
RANDLOVÁ, Monika
This thesis focused on the factors influencing the ripening of cheese , especially the first phase. The literature review was prepared during maturation of cheese , which is a comprehensive summary of the changes caused syřidlovými enzymes and enzymatic activity of cultures in which the cheese gets the typical appearance, texture, flavor and composition
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Processing of fresh cheese depending on selected factors
KOŘÁN, Jakub
Bachelor thesis is focused on processing of fresh cheese depending on selected factors. The cheeses were made in laboratory for this purpose and some factors influencing cheese making were tested. The performed experiments show the effect on cheese yield, milk composition, good manufacturing process and different fermentation temperature. This influence is particularly evident in the overall yield of cheese curd, weight of curd, release rate of whey and pH of curd. The performed experiments can lead to conclusion that each of these factors affects the overall quality of the curd. From the perspective of producers of fresh cheeses is important to monitor these factors as compliance with proper procedure and avoiding the factors reducing yield, will have a positive economic impact.
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Cheeses and analogues products
LAFATOVÁ, Veronika
Bachelor thesis is focus on consumers? knowledge of analogues products with specialization in cheese. It was necessary created a questionnaire, which was fill in by randomly chosen respondents. This questionnaire survey shows preference in cheese consumption, consumers foreknowledge of analog product from points? of view marking of products, shopping behavior and about positives and negatives of cheese analogues. Main conclusion from questionnaire survey are, that consumers consume cheese often, main prefer cheese are semi-hard and fresh cheeses. Consumers have not enough information about product. This is caused by no precise information in label and very often is this product put between real cheese. Correct information in label and position in the shop could be significantly affect the purchasing behavior of consumers with bad benefit of analog products.
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Content of biogenic amines and polyamines in expired ripening cheeses
VODEHNALOVÁ, Klára
The aim of this thesis was to observe the occurrence of biogenic amines and polyamines in selected types of ripening cheeses and to assess the content of the materials since the expiration date. Content of biogenic amines and polyamines in chosen samples was monitored last day of the expiration date, a week after the expiration date, two weeks after the expiration date, and after four weeks from the end of the expiration date.
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