Updated Models for the Effects of Temperature, Initial pH, NaCl, and NaNO2 on the Aerobic and Anaerobic Growth of Listeria monocytogenes

Abstract

Data from several studies were appended to aerobic and anaerobic data sets that had been previously used to develop response surface models describing the growth kinetics of Listeria monocytogenes (Buchanan and Phillips, 1990). The expanded data sets included 709 aerobic and 358 anaerobic growth curves fitted with the Gompertz equation, and representing 189 and 150 unique combinations of four variables (temperature, pH, NaCl, NaNO2), respectively. Response surface models were developed for (1) the Gompertz B and M terms and (2) lag phase durations (LPD) and generation times (GT). In addition to modeling NaCl as a variable, a second set of response surface models was developed by substituting calculated water activity as a variable. A number of data transformations were evaluated in an attempt to better utilize no-growth data. Full quadratic models of the natural logarithm transformation of the data (no-growth data excluded) predicted values that fit the observed data well. The assignment of GT=50[emsp4 ]h and LPD=600[emsp4 ]h (the approximate maximum duration of experiments) for the variable combinations that did not support growth proved to be the most effective means of making use of the no-growth data. However, this approach did not offer any clear advantage over quadratic models where the no-growth data were excluded. Error matrices were developed for the LPD and GT models to provide 95 % confidence intervals. The agreement between observed and predicted growth kinetics was excellent considering the number and ranges of the variables encompassed in the models. The models provide reasonable predictions of the growth of L. monocytogenes in foods. The full quadratic models of LPD and GT without inclusion of the no-growth data were selected for inclusion in the USDA Pathogen Modeling Program, release 5.1.