Protective role of indigenous Leuconostoc carnosum against Listeria monocytogenes on vacuum packed Frankfurter sausages at suboptimal temperatures

•A Frankfurter isolate of L. carnosum shows antilisterial activity.•Low T (°C) and high load of L. carnosum act additively against Listeria.•Low T brings into question the validity of the Jameson effect between species.•Dens model describes species interactions and Listeria decrease phase.

Listeria monocytogenes is one of the main target pathogens in the food industry. Novel strategies are continuously being investigated to ensure its absence from food products, such as the use of Lactic Acid Bacteria (LAB). They are known for their inhibitory action against pathogenic species due to the production of antimicrobial compounds and the competition for nutrients. In this work, the combined effect of storage temperature and LAB inoculum level on L. monocytogenes growth and the interaction between both microorganisms is examined on heat-treated Frankfurters. The indigenous LAB isolate from Frankfurter sausages was further identified as Leuconostoc carnosum and characterised as neither a bacteriocinogenic nor H2O2-producing species. However, it produces weak organic acids that acidify the food product and, overall, competes with L. monocytogenes for nutrients. Experiments were performed with vacuum packed, surface inoculated sausages, at different static temperatures (4, 8, 12 and 25 °C) and inoculum levels of L. carnosum (102, 103 and 104 CFU/g) and 102 CFU/g L. monocytogenes. Results showed that at low temperature and high L. carnosum inoculum level, L. monocytogenes stops growing earlier than L. carnosum and the lowest maximum population is reached. The Dens et al. model described species interactions in a mechanistic way, revealing a predominant effect of L. carnosum on L. monocytogenes, and describing the decrease phase of Listeria population. The Baranyi and Roberts model, a special case of the Dens et al. model for monoculture, estimated apparent maximum population levels and brought into question the validity of the Jameson effect at low temperature. Results illustrated that indigenous species of meat products can be protective against foodborne pathogens.