Impact of preheating on the behavior of Listeria monocytogenes in a broth that mimics Camembert cheese composition

Abstract

The effect of preheating on the survival of L. monocytogenes in Richard's broth, which mimics the composition of Camembert cheese composition, was examined. Experiments were carried out to reproduce contamination of cheese with environmental heat-stressed cells of L. monocytogenes surviving hot-cleaning procedures. Cells in mid-log phase were heated for 30 min at 56°C before being inoculated into Richard's broth. The pHs and temperatures of Richard's broth were chosen to recreate the conditions of curd dripping (pH 5, 25°C), of the beginning of cheese ripening (pH 5, 12°C), and of the beginning (pH 5, 4°C) and the end (pH 7, 4°C) of cheese storage. Immediately after heat treatment, the viability loss was especially high for strain 306715, which exhibited only 0.6% ± 0.2% survival, compared with 22% ± 8.7% for strain EGD. The percentages of the surviving heated cells that were injured were 93% ± 8% for strain 306715 and 98% ± 3% for strain EGD. The destruction of the surviving L. monocytogenes cells was accelerated when they encountered the pH and temperature conditions of Camembert cheese during manufacturing, ripening, and cold storage (pH 5 at 25, 12, and 4°C, respectively). The multiplication of the surviving heated cells was retarded under favorable growth conditions similar to those of storage by the distributor and the consumer (pH 7 at 4 and 12°C, respectively).