Temperature-assisted pressure inactivation of Listeria monocytogenes in Turkey breast meat

Ready-to-eat turkey breast meat samples were surface-inoculated with a five-strain cocktail of Listeria monocytogenes cultures to a final concentration of approximately 107 CFU/g. The inoculated meat samples were vacuum-packaged and pressure treated at 300 MPa for 2 min, 400 MPa for 1 min, and 500 MPa for 1 min at initial sample temperatures of 1, 10, 20, 30, 40, 50, and 55 °C. L. monocytogenes was most resistant to pressure at temperatures between 10 and 30 °C. As temperature decreased below 10 °C or increased over 30 °C, its pressure sensitivity increased. This enhanced inactivation effect was more pronounced when meat samples were treated at higher temperature than at lower temperature. For example, a 1-min treatment of 500 MPa at 40 °C reduced the counts by 3.8 log10, while at 1 and 20 °C the same treatment reduced counts by 1.4 and 0.9 log10, respectively (P < 0.05). The survival curves of L. monocytogenes were obtained at 300 MPa and 55 °C, 400 MPa and 50 °C, and 500 MPa and 40 °C. With increasing treatment time, the three survival curves showed a rapid initial drop in bacteria counts with a diminishing inactivation rate or tailing effect. The survival data were fitted with a linear and a nonlinear, Weibull, models. The Weibull model consistently produced better fit to the survival data than the linear model.