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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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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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Study of yogurt composition in process of its preparation
Fajtl, Zbyněk ; Vítová, Eva (referee) ; Veselá, Mária (advisor)
This thesis deals with the study of yogurt preparation and changes during its storage. The theoretical part contains information about parameters affecting both the preparation and properties of the final product. The experimental part describes methods and procedures used for determination of critical parameters such as lactic acid, lactose, glucose and galactose concentrations (HPLC-RI), amounts of streptococci and lactobacilli. The data was graphically evaluated and commented on. The work also included sensory analysis in which the prepared yogurt was compared with commercially available products. The results of this work can serve both consumers and smaller yogurt producers.
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Effect of dry matter content on the profile of volatile substances of selected fermented milk products
Kirchdorfer, Jakub ; Gross, Michal (referee) ; Vítová, Eva (advisor)
This bachelor thesis deals with the production of yogurt and its characterization in terms of sensory quality and volatile (flavour) profile. The theoretical part deals with the characterization of yogurt, production technology, sensory quality, and possibilities of determination of volatile compounds in yogurt samples. In the experimental part, the production process of the samples was first optimized to achieve the best possible sensory quality. To achieve the desired thick consistency of the yogurt, the dry matter content was increased by the addition of non-fat milk powder and whey powder. For the sensory evaluation, graphical scales were used to assess appearance, colour, consistency, aroma, and taste, as well as a ranking test and a paired comparison test. The results showed that in the case of milk powder, as expected, the higher addition resulted in the desired thicker consistency, while the higher addition also softened the flavour and aroma of the yogurt. In the case of whey powder, on the other hand, the density of the yogurt decreased with higher additions and the taste and flavour were not significantly affected. Yogurts with 6 % w/w milk powder and 2 % w/w whey powder were selected as “optimal”. Both had an optimum consistency, a pleasant colour and aroma and a slightly sour taste. The volatile matter profile was determined by HS-SPME-GC-MS; a total of 16 compounds were identified in the samples, with ketones and acids predominating. The most abundant compounds were diacetyl, acetoin, acetic acid and caproic acid. The results show that the addition of dry matter did not significantly influence the overall profile of volatiles in the samples, no clear trend can be identified. The effect on the sensory quality of the samples was more evident, but even here the results are not conclusive. While some evaluators preferred the thick consistency of yogurt with the addition of milk powder, some preferred the better taste of yogurt with the addition of whey powder.
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Optimization of the production of yogurt with increased protein content from wheat bran
Adamczyková, Michaela ; Vítová, Eva (referee) ; Pořízka, Jaromír (advisor)
This thesis deals with the use of wheat bran in the form of protein isolate as an additive in the food industry, optimalization of the formula of fortified yoghurts and the encapsulation of plant proteins, used as a method to mask the negative sensory properties of products with the addition of these proteins. The theoretical part deals with the characterization of fermented milk products, wheat bran as a source of protein and the possibilities of masking the negative sensory properties of protein isolates. The produced yoghurts were sensory evaluated and their nutritional and technological properties were analyzed in the experimental part. By sensory analysis of yoghurts made from different types of milk, full-fat UHT milk was determined to be the best for the production of fortified yoghurts. Yoghurts prepared from this milk were fortified with wheat bran protein isolate. The products thus had an increased nutritional value, but their sensory values deteriorated. The yoghurts had a gritty feel, which was subsequently mitigated by grinding the protein isolate to finer parts. The formula for the production of fortified yoghurts was optimized by the addition of alternative protein, which had a positive effect especially for yoghurts with a 10% protein content. Yoghurts with protein isolate were evaluated with a negative score for the bitter taste parameter. Encapsulation of proteins significantly reduced the intensity of the bitter taste. Synergy of all prepared samples was determined by filtration. Yoghurt from full-fat UHT milk showed a syneresis of 31.76 ml per 100 g of yoghurt. The addition of protein led to a change in the synergy of this yoghurt. From the rheological analysis, it was determined that 10% yoghurt with encapsulated particles had a higher value of dynamic viscosity and yield stress. Sensory analysis data were evaluated using principal component analysis.
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Classic vs. traditional bulgarian yogurt - chemical, microbiological and sensory characterization
Jasimová, Zahraa ; Zemanová, Jana (referee) ; Vítová, Eva (advisor)
This diploma thesis deals with the production and characterization of yogurt. In total, three types of yogurt were produced: "classic" white yogurt, Bulgarian yogurt made from commercial culture, and traditional Bulgarian yogurt obtained by inoculation of yogurt brought from Bulgaria. The products were characterized in terms of sensory quality, volatile profile (HS-SPME-GC-MS), and microbial profile (qPCR). The aim was to find out whether and how the mentioned samples differ in terms of the mentioned parameters. In the theoretical part, Bulgarian yogurt and its method of production technology are characterized. Sensory quality, the possibilities of sensory evaluation of yogurts, the determination of the presence of volatile substances, and the method of their determination are also mentioned. In the last chapter of the theoretical part, the microbial profile is characterized, the possibilities of identifying microbial cultures, and finally the nutritional value of yogurts is described. In the experimental part, the production process of Bulgarian yogurt samples was first optimized, and these were subsequently compared with "classic" white yogurt. For sensory evaluation, graphic scales were used to evaluate appearance, color, consistency, aroma, and taste, as well as a profile test (sweet, sour, bitter, yeasty, and possibly other tastes) and an ordinal test. The results show that the Bulgarian yogurts were assessed sensorially worse than the classic yogurt, mainly because of the sour taste. Samples of Bulgarian yogurts also showed a yeasty taste, the presence of yeast was confirmed using the qPCR method. The profile of volatile (aromatic) substances in the samples was determined using the HS-SPME-GC-MS method. A total of 24 volatile substances were identified in all yogurt samples, of which 6 alcohols, 2 esters, 6 acids, 7 carbonyl compounds, 3 and sulfur compounds.
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Iodine content in milk and milk produkts
DAVIDOVÁ, Lucie
The subject of the dissertation was to find out and evaluate the iodine content in milk products in a distribution network in the Czech Republic. The dissertation brings update information about the iodine content in consumer milk and white yogurt which are a common part of alimentation for the majority of human population. Sampling was carried out in a sale network during 2007 and 2008. Altogether, 43 samplers of consumer milk and 59 samplers of white yogurt were taken. The iodine content in products was determined with colometric method by Sandell-Kolthoff. The average iodine content in consumer milk in 2007 was 300,5 {$\mu$}g {$\bullet$} l-1 and 310,2 {$\mu$}g {$\bullet$} l-1 in 2008. The maximal iodine content in milk reached the level of 404,8 {$\mu$}g {$\bullet$} l-1 (2007) and 732,0 {$\mu$}g {$\bullet$} l-1 (2008). The lowest level of iodine content in white yogurt in 2007 was at the level of 406,0 {$\mu$}g {$\bullet$} kg-1 and 422,7 {$\mu$}g {$\bullet$} kg-1 in 2008. Comparing years 2005 and 2006 there was recorded a slight decrease at these products. Some differences were recorded at different milk product producers and as well as the season has got a considerable influence. If the overall average milk and milk products consumption makes 0,64 litre per person then the daily recomended portion is covered by 130 per cent.
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Dairy products in human nutrition, labelling according to czech legislation; consumer information and preferences
Dovolová, Barbora ; Kudlová, Eva (advisor) ; Dostálová, Jana (referee)
This bachelor thesis evaluates the dairy products labelling in the Czech Republic based on the requirements of the Czech legislation. It also pursues consumer's taste preferences, their interest and awareness of the dairy products labelling. The theoretical section mentions the history of dairying and the importance of milk products in human nutrition. The following chapters present individual dairy products and it described their production, labeling and division into kinds. The practical section reveals that the dairy products are labeled in accordance with the Czech legislation. The results are presented in the form of photos and tables (mini photobook). This part also examines whether the adult people interest in the dairy product labeling, how to orient in a range of dairy products and which products they prefer. The product evaluation was carried out in two big stores in Jablonec nad Nisou by using photographs. It was found that majority of companies indicates their milk products correctly. Identified deviations were discovered in the labelling of nutrition declaration or allergens. This is a relatively new requirements but very important. The questionnaire was found that 68 percent of people read informations on dairy products voluntarily. Most of the respondents consume especially milk, yoghurts and...
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