Influence of argon modified atmosphere packaging on the growth potential of strains of Listeria monocytogenes and Escherichia coli

Modified atmosphere packaging (MAP) based on carbon dioxide (CO₂) – nitrogen (N₂) gas mixtures has been applied to maintain the safety and quality of ready-to-eat (RTE) meat products. The use of argon (Ar) gas as a supplement to CO₂–N₂ mixtures or as substitute for N₂ is a current approach to enhance the effectiveness of MAP. As there is limited information on the effect of Ar MAP on the growth behaviour or the survival of pathogenic bacteria in RTE foods, the aim of the present study was to assess the influence of Ar in MAP on the growth of Listeria monocytogenes and Escherichia coli strains under different conditions. For this purpose, a CO₂–N₂ (20:80) atmosphere was compared with a CO₂–N₂–Ar (30:30:40) and CO₂–Ar (30:70) atmosphere based on the assessment of bacterial growth (δ) on a gelatin-agar medium and ham. Additionally, a shelf life monitoring study was performed to evaluate the effect of these treatments on the background microflora of ham. The findings suggest that under the CO₂–N₂ MAP the product matrices supported the growth (δ > 0.5 log CFU g⁻¹) of L. monocytogenes throughout an observation period of 21 days at 4 ± 2 °C. On the contrary, both MAP containing Ar were equally able to reduce the δ below 0.5 log CFU g⁻¹. In this regard it was irrelevant whether L. monocytogenes was inoculated in depth (per slice) or at the surface (top slice) of the ham. Regarding the influence of the different gas atmospheres on E. coli all gas mixtures applied had the capacity to reduce the δ of E. coli below −0.5 log CFU g⁻¹. Further, shelf-life extension could not be managed with the gas atmospheres considered.