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VITOVA, E., BABAK, L., MOKAŇOVA, R., HÝSKOVA, E., ZEMANOVA, J.: The content of sensory active compounds and fl avour of several types of yogurts. Acta univ. agric. et silvic. Mendel. Brun., 2010, LVIII, No. 5, pp. 407–412 The aim of this work was to identify and quantify several sensory active compounds in various types of yogurts using gas chromatography and simultaneously to judge their infl uence on fl avour of yogurts using sensory analysis. In total 4 types of white and 10 types of fl avoured yogurts (creamy and low-fat) with various fl avourings, produced in Dairy Valasske Meziřici, Ltd., were analysed. The highest content of sensory active compounds (P < 0.05) was found in strawberry yogurts, with high amount of ethyl butyrate. Excepting ethanol no signifi cant diff erences (P < 0.05) were found between low-fat and creamy varieties. The total content of sensory active compounds in white yogurts was signifi cantly (P < 0.05) lower than in fl avoured fruit types. The highest content was in low-fat and lowest in white bio yoghurts. Flavour of yogurts was evaluated sensorially using scale and ranking test. All creamy yogurt varieties were evaluated as signifi cantly (P < 0.05) more tasty than low-fat ones. Similarly in case of white yogurts creamy yogurts were evaluated as the most tasty and low-fat ones as the worst. Bio yogurts were evaluated equally tasty as classic yogurts with the same fat content. yogurt, fl avour, sensory active compounds, GC, SPME, sensory analysis Yogurts are the most widespread fermented dairy products worldwide. They are appreciated for nutritive and dietetic properties, however, the or ga nolep tic properties, i.e. appearance, colour, texture, taste and aroma, formed by so called sensory active compounds (SAC), are the most important for con su mers. SAC are all the odorous and taste compounds that form fl avour of foods. Fermentation process and thermal treatment of foods are the main processes where these compounds are created from their precursors (Kailasapathy, 2006; Nongonierma et al., 2006). Several hydrocarbons, oxygen derivatives (aldehydes, alcohols, ketones, ethers, fatty acids and their esters), nitrogen (amines) or sulphur (thiols) compounds are included in SAC (Gardini et al., 1999). The understanding of conditions and re gu lari ties of SAC creation and their infl uence on sensory perception of fl avour is necessary for production of high-quality and tasty products. The Czech legislation, Directive 77/2003 Coll. (2003), amended by 124/2004 Coll. (2004), defi nes yogurt as a fermented dairy product acquired by fermentation of milk, cream, buttermilk or their mixture, using microorganisms Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus. Technological process of yogurt production consists of several steps. The fermentation phase, where not only characteristic taste and aroma, but also structure and consistence of yogurts are developed, is the most important. Taste and aroma active compounds are products of metabolism of used cultures. They arise by enzymatic decomposition of lactose, proteins and fat in milk (Beshkova et al., 1998). Several SAC come directly from milk used for production (aldehydes, ketones, alcohols). The anaerobic transformation of saccharides to lactic acid is the basic biochemical pathway during yogurt production. The produced lactic acid 408 E. Vitova, L. Babak, R. Mokaňova, E. Hýskova, J. Zemanova imparts fi ne refreshing acid taste to these pro ducts and extends their durability. It also precipitates milk proteins, which are then easier to digest and improves utilization of calcium, phosphorus and iron. The part of lactic acid comes to colon, where acidifi es environment and prevents de ve lop ment of putrefactive microfl ora (Roginski et al., 2003). The proteolytic activity of lactic acid bacteria changes physico-chemical properties of casein, which infl uences rigidity, texture and viscosity of yogurt coagu late. Arisen peptides and free amino acids are precursors for enzymic reactions producing taste compounds. However, too intensive pro teo ly sis can cause taste defects and creation of so yogurt coagu late. Similarly SAC can arise by lipolytic activity. Released fatty acids (FA) are precursors for methyl ketones, alcohols, lactones and esters, which impart characteristic fl avour to yogurts (Roginski et al., 2003). Many authors were interested in fl avour and SAC content of various types of yogurts. Although many SAC were identifi ed in yogurts until now, only a small part of them probably infl uences the fi nal aroma of yogurt, primarily these which are present in high concentrations (Beshkova et al., 1998). Most of authors agree, that acetaldehyde (10–20 mg . kg−1), acetic acid (20–30 mg . kg−1), suffi cient acidity caused by lactic acid and free volatile saturated FA are neces sa ry for typical fl avour of yogurt (Georgala et al., 1995; Ott et al., 2000b; Mei et al., 2004). The aim of this work was to identify and quantify SAC in various types of white and fl avoured yogurts using gas chromatography-mass spectrometry (GCMS) with SPME (solid-phase microextraction) extraction and to judge their infl uence on fl avour of yogurts using sensory analysis. MATERIALS AND METHODS

The content of sensory active compounds and flavour of several types of yogurts