MICROBIAL QUALITY AND SOME PHYSICO-CHEMICAL PROPERTIES OF HIGH PRESSURE PROCESSED COW MILK
 
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Pol. J. Food Nutr. Sci. 2000;50(4):19–26
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ABSTRACT
The effect of high pressure treatment (200 to 1000 MPa for 15 min) on microflora, enzymes (alkaline phosphatase, peroxidase, proteases, lipases), and coagulation properties of cow’s milk was studied. The microbiological quality of raw milk pressurized at 800 MPa was comparable to the quality of milk pasteurized at 72°C/15 s. The number of yeasts and moulds, psychrotrophs and coliforms decreased more rapidly with an increase in pressure than that of acidic and proteolytic bacteria. Yeasts and moulds were inactivated at 400 MPa and psychrotrophs and coliforms at 600 MPa. Within the applied range of pressure, the 100% reduction of acidic and proteolytic bacteria was not obtained. The high pressure treatment (200-1000 MPa) of the pasteurized milk (63°C, 30 min) or the pasteurization (63°C, 30 min) of pressurized milk (200-1000 MPa) caused further reduction in the content of microorganisms as compared to the action of the single factor. The milk enzymes were much less sensitive to pressure than the majority groups of microorganisms. A little effect of pressure (200-1000 MPa) on peroxidase and lipases activity of milk was observed. Among analysed enzymes, only alkaline phosphatase and proteases completely lost their activity at 1000 MPa. The shortest time of rennet coagulation was obtained for milk subjected to pressure treatment at 200 MPa and it was decreased by 22 - 26% as compared to raw milk. Protein retention into curd after acid or rennet coagulation of pressurized milk increased along the pressure rise. In the milk, subjected to pressure 200 MPa or 1000 MPa and then rennet coagulation, the nitrogen content in whey decreased by 3 - 7% or 20-30%, respectively.
ISSN:1230-0322