High-pressure destruction kinetics of Listeria monocytogenes on pork

Packaged fresh pork chops (30-g samples) containing an indigenous bacterial population of similar to 10(7) CFU/g were inoculated with 10(7) CFU of Listeria monocytogenes Scott A per g, heat sealed, and subjected to high-pressure processing at 200 to 400 MPa for up to 90 min. Total counts and the number of surviving L. monocytogenes cells were determined by a spread plate technique on tryptic soy agar and modified Oxford medium, respectively. The pressure destruction was characterized by a dual-behavior, consisting of a step change in the number of survivors (P(ko)) with the application of a pressure purse and a first-order rate drop in the number of survivors during the pressure hold period. Higher pressures resulted in higher rates of microbial inactivation, as indicated by their associated lower D values (and higher k values). The pressure sensitivities of the kinetic parameters were evaluated on the basis of Arrhenius and pressure death time (PDT)-type models. The results suggested that L. monocytogenes was more resistant to pressure inactivation than the indigenous microflora (the volume change of activation, Delta V(not equal) [Arrhenius model]), and z(p) values (PDT model) were -4.17 x 10(-5) m(3) mole(-1) and 134 MPa for indigenous microflora and -3.43 x 10(-5) m(3) mole(-1) and 163 MPa for L. monocytogenes respectively.