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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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