Influence of different histories of the inoculum on lag phase and growth of Listeria monocytogenes in meat models

Abstract

The aim of this study was to determine the effect of history of inoculum and preservatives on the lag phase and growth rate of Listeria monocytogenes strains in meat products packaged under modified atmosphere conditions. Inocula with different histories were added to meat models, and growth rate and lag phase of two strains of L. monocytogenes were measured at 5 and 10°C. The meat model stored at 10°C contained sodium lactate, but the model stored at 5°C did not. The five different histories of the inocula included cold propagation, biofilm formation, and starvation. The lag phase ranged from 1 to 10 days and was affected by the history of the inoculum, whereas the growth rate was constant except for one combination of history of inoculum and strain, where growth did not start during the incubation period. In a second series of experiments, the growth rate and lag phase of the two Listeria strains and the effects of two different histories of inoculum were tested in meat models with pH 5.7 or 6.5 and increasing amounts of NaCl. The growth rate depended on salt concentration, bacterial strain, and pH, whereas lag phase duration depended on history of inoculum, salt concentration, and pH. The lag phase duration was highly dependent on the history of the inoculum, and higher amounts of preservative (NaCl) made these effects even more noticeable. The results of this study underline the importance of the effects of the history of the inoculum on lag phase duration and could be used to predict lag phase in industrial meat products. Copyright ©, International Association for Food Protection.