Medycyna Wet. 66 (2), 109-112, 2010

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Kudełka W.
Impact of pasteurisation and type of packaging on probiotic bacteria in bio-yoghurts of goats’ milk during storage
The objective of the research was to determine the impact of the pasteurization process of raw material and of the type of packaging on the survival rate of probiotic bacteria in bio-yoghurts from goats’ milk during storage. The bio-yoghurts investigated were manufactured from goats’ milk using a container method. The milk under processing was centrifuged and normalized to a fat level of 2%. Next, it was pasteurised at a temperature of 95 °C during 5 min and at 90 °C during 10 min, after which it was cooled to 40 °C. The cooled milk was inoculated with DVS ABT1 inoculants added. The bioyoghurts were thermostated (controlled) in containers at a temperature of 40 °C (+/– 1 °C) until they reached a pH level of 4.7. Then, they were cooled again to a temperature below 20 °C and poured into 4 different packagings made of polypropylene (PP), polystyrene (PS), polyethylene (PEHD), and glass (G), each of a capacity of 200 cm3. The bio-yoghurts were subsequently stored in the dark for 21 days at temperatures ranging from 2 to 5 °C. The presence of probiotic bacteria in bio-yoghurt was determined 12 h after the bio-yoghurts were manufactured, and on the 7th, 14th, and 21st day of storage. In total 240 samples were analysed. The applied packagings did not statistically significantly differentiated the count of bacteria in bio-yoghurts manufactured from goats’ milk, except for the Str. thermophilus bacteria count that changed only on the 14th day after manufacturing. The statistically significant impact of the pasteurisation temperature of raw material was found in the case of the L. acidophilus count immediately upon manufacturing. A lower pasteurisation temperature of goats’ milk had a favourable effect on the growth of bacteria, and in such bio-yoghurts the population of all the bacteria was higher. It was found that irrespective of the applied pasteurization temperature of raw material and of the type of packagings, the count of individual bacterial genera was at a level significantly higher than 106 cfu/ml, which ensures that the milk drinks studied achieve the therapeutic minimum. Thus, expanding the production of goat milk bio-drinks can enhance the assortment of healthful diary products available in the market.
Keywords: goats’ bioyoghurt, pasteurisation, packaging type, probiotic bacteria, viability