High pressure (HP) destruction kinetics of Listeria monocytogenes Scott A in raw milk

Raw milk containing the natural microflora (NM) and an inoculated 24 h culture of Listeria monocytogenes Scott A (10(6) cfuml(-1) each) were heat sealed in dual peel sterilization pouches and subjected to high pressure (HP) treatment at 150 to 400 MPa for selected holding times of up to 120 min. HP destruction of NM and L. monocytogenes were evaluated based on first order kinetics, pressure destruction time (PDT) and Arrhenius type models. Results showed a dual effect pressure destruction of microorganisms consisting of (i) an instantaneous pressure kill effect (IPK) with the application of a pressure pulse (no holding time) and (ii) a subsequent first order rate of destruction during the pressure holding time. In general, both IPK and rate constants (k-values) increased with an increase in pressure while the corresponding decimal reduction times (D-values) decreased. The IPK was more pronounced with L. monocytogenes than NM. However, the kinetic parameters indicated a larger pressure resistance for L. monocytogenes. Pressure dependency of kinetic parameters was well described by both pressure destruction time (PDT) and Arrhenius models (R-2 > 0.95). The z(p) values (PDT) were 266 and 244 MPa and Delta V-not equal (Arrhenius) values were -2.11 and -2.30 x 10(-5) m(3)mol(-1) for L. monocytogenes Scott A and NM, respectively. (C) 1999 Published by Elsevier Science Ltd on behalf of the Canadian Institute of Food Science and Technology.