Thermal inactivation of Listeria monocytogenes in ground beef under isothermal and dynamic temperature conditions

The objective of this research was to compare the suitability of three kinetic models for describing the survival of a cocktail of Listeria monocytogenes in ground beef under both isothermal and dynamic temperature conditions. Ground beef (93% lean), inoculated with a 4-strain cocktail of L. monocytogenes, was subjected to heating at 57, 60, 63, or 66 °C to develop isothermal kinetic models. Experimental data showed that the isothermal survival curves were not strictly linear and were downwardly concaved. The isothermal inactivation of L. monocytogenes in ground beef was better described by two nonlinear kinetic models, the Weibull-type and the modified Gompertz models. Analytical results showed that root mean square error values (RMSE) of the Weibull-type and the modified Gompertz models were 0.19 and 0.20 log(CFU/g), both significantly smaller than that of the linear model (0.48 log(CFU/g)). Under linear heating dynamic conditions, however, only the modified Gompertz model, with a RMSE of only 0.71 log(CFU/g), was suitable for describing the survival of the pathogen. Both linear and Weibull-type models grossly underestimated the survival of L. monocytogenes in ground beef during dynamic heating.