Med. Weter. 76 (12), 709-713, 2020

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Qualitative changes in selected dairy products during their shelf life
The aim of the study was to assess changes in qualitative characteristics of selected dairy products that occur during their shelf life. The research covered 2% pasteurized drinking milk, 18% cream and semi-fat tvarog produced in 3 regional processing plants (A, B and C) and purchased in the local retail network. A total of 186 samples were taken, including 20 samples of each of the above products from plants A and B, and 22 samples of these products from plant C. The following parameters were determined: chemical composition, density, potential acidity (°SH), freezing point, and the number of Enterobacteriaceae in drinking milk; as well as the content of fat, protein and dry matter, potential acidity (°SH), and the number of β-glucuronidasepositive Escherichia coli in cream and tvarogs. The research showed that the dairy products available in the retail network generally met the requirements of Polish standards. Deviations from the standards were found in the fat content of drinking milk and cream compared to that declared by the manufacturer. On both measurement dates, the acidity of the products did not exceed the prescribed limits, which indicates that the quality of the products was maintained during the storage period. The assessment of microbiological quality showed that on both dates the limit of E. coli contamination was exceeded in tvarog samples from dairy C, which indicates an unsatisfactory microbiological quality of the production process in this plant and the need to take corrective actions in the field of production hygiene. Drinking milk and cream, on the other hand, met the legal requirements in terms of process hygiene.
Keywords: drinking milk, cream, tvarog, quality, storage, shelf life