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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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