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Influence of aroma active compounds on flavour of yogurts
Malina, Jiří ; Babák, Libor (referee) ; Vítová, Eva (advisor)
This diploma thesis deals with the questions of determination of aroma active compounds present in yoghurts. These compounds are crucial for flavour of these fermented dairy products. Four types of yoghurts were analyzed, creamy (10 % of fat), medium-fat and medium-fat Bio (3 % of fat) and light (0,1 % of fat), produced by Mlékárna Valašské Meziříčí, spol. s r.o. Analysis was carried out by gas chromatography with extraction of analytes by SPME - solid phase microextraction. Five groups of different aroma active compounds such as ketones, aldehydes, organic acids and their esters and alcohols in different amounts were determined. These compounds are mostly metabolic products of Streptococcus salivarius subsp. thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, dairy yoghurt cultures usually used for yoghurt production. Less amounts are present in cow's milk or in dairy additives. Yoghurts were simultaneously sensorially evaluated using ranking test and scale test for determination of acceptability and flavour. The assessors were students and staffs of faculty of chemistry BUT.
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Influence of aroma active compounds on flavour of fruit yogurts
Malina, Lukáš ; Babák, Libor (referee) ; Vítová, Eva (advisor)
This diploma thesis deals with the determination of aroma compounds in fruit yoghurts. These compounds are crucial for flavour of these dairy products. Two types of fruit yoghurts were analyzed, creamy (8 % of fat) and light (less than 0,1 % of fat), with various fruit ingredients, produced in dairy Mlékárna Valašské Meziříčí, spol. s r.o. Analysis was carried out by gas chromatography with extraction of analytes by SPME - solid phase microextraction. Six groups of different aromatic compounds such as ketones, aldehydes, organic acids and their salts, alcohols and sulfides in different amounts were determined. These compounds have mostly microbiological origin (Streptococcus salivarius subsp. thermophilus, Lactobacillus delbrueckii subsp. bulgaricus are dairy yoghurt cultures usually used for yoghurt production), less amounts are present in cow's milk or in dairy additives. Yoghurts were simultaneously sensory evaluated using ranking test, scale test and pair test for determination of acceptability and flavour. The assessors were students and staffs faculty of chemistry VUT.
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Microbial characterization of yoghurts and probiotic foods.
Kocourková, Hana ; Burdychová, Radka (referee) ; Španová, Alena (advisor)
Zvýšená konzumace fermentovaných mléčných výrobků v posledních letech vede k zavádění nových výrobků na trh. Funkční a probiotické produkty jsou v dnešní době také hojně rozšířeny. Cílem diplomové práce bylo posoudit mikrobiální kvalitu komerčních jogurtů a nefarmakologických probiotických výrobků. Bylo zkoumáno 24 vzorků jogurtů a 8 vzorků probiotických mléčných výrobků. Pozornornost byla zaměřena zvláště na kvantifikaci mikroorganismů v jednotlivých výrobcích a na sledování viability buněk. Většina mléčných produktů obsahovala počty odpovídající minimální požadované hodnotě 1x107cfu/ml. Nicméně byly objeveny produkty, které neobsahovaly živé bakterie nebo obsahovaly jen jejich menší množství. To platí zejména pro běžné jogurty. Probiotické mléčné výrobky v zásadě obsahovaly větší množství bakterií než jogurty, protože je u nich navíc požadováno 1x106cfu/ml minimálního množství specifických bakterií jiných než jogurtových startovacích kultur. Isoláty z fermentovaných mléčných výrobků byly identifikovány jako Streptococcus thermophilus and Lactobacillus spp. Isoláty byly poté rozlišeny na jednotlivé kmeny pomocí RAPD použitím tří různých primerů. Byla zjištěna velká různorodost mezi kmeny rodu Lactobacillus spp. používaných různými podniky.
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Viscosity and acidity of selected type of natural yoghur
BÁRTOVÁ, Zuzana
The aim of the thesis was to evaluate the acidity and viscosity of natural yoghurt depending on the different addition of skimmed milk powder and using of the methods of sensory analysis to evaluate the perception of these properties by young consumers. Part of this work was to analyse acidity and viscozity in selected kinds of natural yoghurts purchased in the market network of the Czech Republic (CR). The literature search mentions basic characteristic of yoghurts and their classification, acidity and rheological properities of yoghurts including the factors, which affect them and sensory analysis. In the experimental part of the study the acidity value, total solids and viscosity measurements were detected by physico-chemical analyses of samples of natural yoghurts. At samples of yoghurts with different content of skimmed milk powder the sensory evaluation was also subjected and the graphs of sensory profile were compiled. The observed results showed, that from the samples of yoghurts made in the laboratory was the most satisfactory sample containing 10 % of skimmed milk powder. At samples purchased in the market network of CR were detected very low leveles of titratable acidity.
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Consumer preferences of selected milk products
ČÁSENSKÁ, Julie
The aim of this thesis was to evaluate the offer of fermented dairy products in the market network, and evaluate the favourite flavours of yogurts among university students. Market research of fermented dairy products was conducted in 3 hypermarkets, all the products in the offer were recorded. A simple anonymous questionnaire was created in order to obtain the necessary data about the popularity of each flavour among university students. The questionnarie was presented to a selected group of university students in the age of 20-35 years and it was completed by a total of 400 respondents. The results showed that the most popular yogurt is the one with pieces of fruit, the most popular flavour is strawberry. Banana flavour is the least favorite flavour among the consumers. The survey also showed that the most important criterion when choosing a yogurt is the producer and price.
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Kondenzace vlhkosti u balených potravin v průběhu dopravy a skladování
Herůdková, Tereza
This thesis deals with the condensation of moisture in the packaged food during transport and storage. The thesis describes changes of food and influences on the products during transport and storage. The main part deals with the water activity, dew point, humidity and modified atmosphere. In the practical part was used yogurt as a sample. There were added ingredients (sugar and salt) to the yogurt and yogurt was then packed into three different atmospheres (free atmosphere, MAP with nitrogen and MAP with carbon dioxide) and after that it was stored at temperature 8°C and 20°C. In these samples were measured water activity, pH and moisture. The results were summarized in charts and graphs. The results show that MAP prevents the condensation at packaged food. It was confirmed that 10% NaCl had the best effect on reduction of water activity.
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Determination of probiotic bacteria in selected fermented milk products
KORANDOVÁ, Květa
The aim of the thesis was to monitor presence of probiotic microorganisms in representative fermented dairy products. Three samples of white yoghurt available in the market, in which the manufacturer declared presence of bifidobacteria, were chosen for determination of strains of Lactobacillus delbrueckii ssp. bulgaricus, Streptococcus salivarius ssp. thermophilus and the genus of Bifidobacterium. Bibliographic research deals with explanation of the wider context of probiotic microorganisms and the process of fermentation, fermented dairy products and in particular of yoghurt as one type of fermented dairy products. In the experimental part, the thesis focusses on evaluation of microbiological analyses and pH of selected yoghurts in relation to the samples and storage time. The results show that the number of live bacteria of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus salivarius ssp. thermophilus strains complied with the statutory requirements, while the number of bacteria of Bifidobacterium genus could have been affected by various factors which caused that according to the results of the work, certain samples lacked the sufficient numbers of these bacteria.
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