87-2 |
Kinetics of high pressure destruction of E. coli and indigenous microorganisms in milk at two temperatures |
P. K. PANDEY1, H. S. Ramaswamy1, and E. S. Idziak2. (1) Dept. of Food Science, McGill Univ., Macdonald Campus, 21111 Lakeshore Rd., Sainte Anne de Bellevue, QC H9X 3V9, Canada, (2) Dept. of Natural Resource Sciences, McGill Univ., Macdonald Campus, 21111 Lakeshore Rd., Sainte Anne de Bellevue, QC H9X 3V9, Canada High pressure (HP) processing is a physical process which may allow selective destruction of microorganism (including pathogens) in milk while protecting several key enzymes that are important in cheese ripening. A considerable amount of cheese is produced from non-pasteurized milk in many countries. The production of safe raw milk cheese depends on the successful inactivation of pathogens in milk without affecting other quality parameters, which are responsible for developing the strong characteristic flavor in raw milk cheeses. The main objective of this study was to study the effect of different high pressure treatment conditions (pressure level, time and temperature) on the destruction of E. coli and indigenous micro-flora in milk in order to develop an HP process for milk processing to deliver safer cheese. Raw milk with a high count of indigenous micro-flora was subjected to high pressure treatment (250-400 MPa) for various holding times (0-80 min) at two temperatures (3 and 21°C). Raw milk inoculated with a high concentration of E. coli K-12 (ATCC-29055) was also subjected to pressure treatment simultaneously under the same conditions. From the microbial survivor data, the instantaneous pressure kill value (IPK) which represented the effect of a pressure pulse with no holding time, and kinetic parameters (rate constant, D-value, z- value and change in activation volume) were evaluated based on hold-time first order kinetics. Results confirmed the dual effect pressure destruction of microorganisms (IPK plus kinetics). Both IPK values and kinetic parameter, D, were dependent on pressure level and temperature. The kinetics parameters indicated a greater pressure resistance for indigenous micro-flora than for E. coli. Higher pressures, longer holding times and lower temperatures resulted in higher destruction of microorganisms, and E. coli was more pressure sensitive than indigenous micro-flora. Successful application of HP processing of milk for cheese making relies on the selective destruction of naturally occurring pathogens and contaminant microorganism.
Session 87, Food Microbiology: General
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