Modelling the fate of Listeria Monocytogenes in Beef Meat Stored at Refrigeration Temperatures under Different Packaging Conditions

The objective of this study was to model the fate of L. monocytogenes inoculated in beef at two concentrations (2.5 and 4.0 log CFU/g), packaged under aerobic, vacuum and three modified atmosphere combinations – 70%O₂/20%CO₂/10%N₂, 50%O₂/40%C O₂/10%N₂ and 30%O₂/60%CO₂/10%N₂, and refrigerated at a normal temperature (4°C) and at a mild abuse temperature (9°C). An omnibus model based on the three-parameter Weibull equation proved statistically that L. monocytogenes survives better in vacuum (VP) than in aerobic conditions, although without significant difference in its ability to survive in the temperature range between 4°C and 9°C. Furthermore, regardless of the refrigeration temperature, the presence of CO₂ in package atmosphere exerted a bactericidal effect on L. monocytogenes cells, being approximately 1.5 log of reduction when storage time reached 10 days. Since the pathogen can survive in VP/MAP beef at refrigerated storage, there is a need of maintaining its numbers below 100 CFU/g before packaging by placing efforts on the implementation of control measures during processing.