The milk processing by «Bilotserkivskiy Dairy Plant», JSC «Galakton» and JSC «ZHLK-Ukraine» for the production of yoghurt using Reservoir method, is based on normalized fermentation mixture in tanks. For the yoghurt produced reservoir means inherent liquid consistency. This is due to the fact that in this mode of production and increase the acidity of clot formation occurs periodically stirring, and only after reaching the required level of acidity of the products dispensed in consumer packaging and sent to cold storage for maturation. The quality of dairy products depends on the quality of raw materials, organoleptic properties, their structure and texture.

During the investigation of organoleptic characteristics of yogurt depending on the shelf life of change observed on the 14th day of storage. In the product, produced at LLC «Bilotserkivskiy Dairy Plant», one has revealed small-gassing, but the consistency was smooth, jelly-like. Taste and flavor were somewhat sour, but without the tastes and smells, taste as sweet. Yogurt of PJSC «Galakton» had too liquid consistency with severe flatulence. Taste, aroma and color of the product remained one-term throughout the period of storage (2-, 7-, 10-, 14- and days).

In products of PJSC «ZHLK-Ukraine» for consistency there was observed structure nonuniformity with little granularity, observed slight gas formation. Taste and flavor are of milk, but taste was sweet at the end of shelf life.

The taste and flavor of dairy products caused by acids and carbonyl compounds – acetaldehyde, diacetyl, acetone and others. Their content and proportion depends on the specific taste and smell of sour milk products. Some strains of Streptococcus thermophilus produce small amounts of acetaldehyde and diacetyl. However, the main role in the formation of taste and flavor of yogurt fulfills Lactobacillus bulgaricus. Therefore, the decrease in the number of Bulgarian bacillus ferment in stock will facilitate the deterioration of taste and flavor of yogurt.

Important processes that occur during manufacturing sour milk products are casein coagulation and gelation. Coagulation of casein makes lactic acid, which is formed by the lactic fermentation of lactose, thereby increasing the acidity of the product.

In the test yoghurt from three manufacturers titrated acidity increase was observed after 14 days shelf life of the product, but these values were within the normal range (80–140 here).

Active acidity during the study period was within 4,0–4,58 (normal 4,8–4,0). Yogurt Ltd. «Bilotserkivskiy Dairy Plant» volumetric ratio of the active acidity in 14- and 18-day of storage was 130 From: 4,0, yogurt PJSC «ZHLK-Ukraine» – 100 From: 4.82. This acidity may provide a sweet taste at the end of the product.

The most sensitive and promising for evaluating the quality sour milk products are rheological properties and synerezysni bunch, including viscosity and degree of syneresis. They depend on the composition of milk and bacterial starter cultures are, modes of thermal and mechanical treatment, method and duration of coagulation of milk proteins.

After 2 days storage of yoghurt syneresis highest rate of 45 % was observed in the product PJSC «ZHLK-Ukraine» Viscosity was 92 s. Throughout the period of storage structure-rheological performance of the product is gradually changing. So, on day 14, the degree of syneresis zbi lshyvsya to 69 %, and Viscosity decreased to 35 s.

During the study, yogurt LLC «Bilotserkivskiy Milk combine» throughout the shelf-life observed a similar trend to decrease the viscosity and increase the number of separated whey – 80 % and 28 s, respectively.

The highest values of the degree of syneresis (45 %) and the lowest viscosity (40 s) of yogurt PJSC «Galakton» observed at the beginning (2- day) and the end (14- day) of the product. These results confirm the rheological parameters acetate organoleptic evaluation - a liquid consistency of yogurt.

The analysis of rheological parameters yogurt showed that after 14 days of storage rheological parameters of product change: Viscosity decreases the degree of syneresis increases. Structural and mechanical properties of dairy products depend on the method and production process parameters and species composition of bacterial cultures.

For fermenting milk using bacterial ferments, produced in pure cultures of the respective types of microorganisms. From the selection of crops depend on flavor, texture and other qualities of the product. Ferment quality depends on the purity of culture, the ability to form acid flavor, accumulation of antibiotics.

Producer of «Bilotserkivskiy Dairy Plant» uses thermophilic yogurt company Chr. Hansen frozen (Yo-Flex DVS). DVS-culture – a highly concentrated and standardized bacterial preparations are to receive products with extended shelf life and very high strength structure, delicate flavor and low acidity increase during storage.

Manufacturers of PJSC «Galakton» and PJSC «ZHLK – Ukraine» use the term «pure culture of lactic acid microorganisms», «yogurt Ferment-on» without deciphering exactly which bacteria have been used to make yogurt. Therefore, the deterioration of rheological properties of yogurt PJSC «Galakton» and PJSC «ZHLK-Ukraine» can be explained as the species composition of bacterial cultures used for fermentation of milk at these companies. The use of starter cultures that are actively fermenting milk and form viscous clots, make positive effect on the improvement of the rheological indices of dairy products.

Key words: yogurt, texture, chemical composition, titrated acidity, active acidity, viscosity, degree of syneresis.