Impact of the contamination level and the background flora on the growth of Listeria monocytogenes in ready-to-eat diced poultry.

UNLABELLED: The food safety criteria that have been incorporated in European regulation (EC) No2073/2005 (Official Journal of the European Union L, 338, 2005, 1), for Listeria monocytogenes in ready-to eat (RTE) foods, specify a maximum allowable concentration of 100 CFU g(-1) or ml(-1) . Some factors such as pH, salt and modified atmosphere packaging (MAP) are used to prevent the growth of L. monocytogenes in order to comply with the limit. Interactions between background microflora (BM) and L. monocytogenes may limit the growth of L. monocytogenes. The aim of this study was to investigate the mechanisms behind the observed inhibition by natural BM of the growth of L. monocytogenes in ready-to-eat diced poultry meat whose pH and water activity were favourable to its growth. The dynamics of L. monocytogenes and natural BM were therefore monitored in mono-culture and co-culture experiments with various combinations of contamination levels. In the absence of BM, the growth potential of L. monocytogenes depended only on the initial inoculum. With both BM and L. monocytogenes, whatever the combination of concentrations studied, the growth potentials of L. monocytogenes were lower than in a mono-culture through a partial Jameson effect. Thus, the use-by date of this product can be optimized by using models that take into account interactions with BM. SIGNIFICANCE AND IMPACT OF THE STUDY: The study of the growth of Listeria monocytogenes in a diced poultry meat, a matrix whose pH and water activity characteristics are favourable to L. monocytogenes growth, showed that it was inhibited by natural background microflora. This highlights the importance of knowing the product's composition, and in particular the natural background microflora, which can impact the use-by date.