Effect of in‐package atmospheric cold plasma discharge on microbial safety and quality of ready‐to‐eat ham in modified atmospheric packaging during storage

Listeria monocytogenes is often responsible for postprocessing contamination of ready‐to‐eat (RTE) products including cooked ham. As an emerging technology, atmospheric cold plasma (ACP) has the potential to inactivate L. monocytogenes in packaged RTE meats. The objectives of this study were to evaluate the effect of treatment time, modified atmosphere gas compositions (MAP), ham formulation, and post‐treatment storage (1 and 7 days at 4 °C) on the reduction of a five‐strain cocktail of L. monocytogenes and quality changes in ham subjected to in‐package ACP treatment. Initial average cells population on ham surfaces were 8 log CFU/cm². The ACP treatment time and gas composition significantly (P < 0.05) influenced the inactivation of L. monocytogenes, irrespective of ham formulations. When MAP1 (20% O₂ + 40% CO₂ + 40% N₂) was used, there was a significantly higher log reduction (>2 log reduction) in L. monocytogenes on ham in comparison to MAP2 (50% CO₂ + 50% N₂) and MAP3 (100% CO₂), irrespective of ham formulation. Addition of preservatives (that is, 0.1% sodium diacetate and 1.4% sodium lactate) or bacteriocins (that is, 0.05% of a partially purified culture ferment from Carnobacterium maltaromaticum UAL 307) did not significantly reduce cell counts of L. monocytogenes after ACP treatment. Regardless of type of ham, storage of 24 hr after ACP treatment significantly reduced cells counts of L. monocytogenes to approximately 4 log CFU/cm². Following 7 days of storage after ACP treatment, L. monocytogenes counts were below the detection limit (>6 log reduction) when samples were stored in MAP1. However, there were significant changes in lipid oxidation and color after post‐treatment storage. In conclusion, the antimicrobial efficacy of ACP is strongly influenced by gas composition inside the package and post‐treatment storage. PRACTICAL APPLICATION: Surface contamination of RTE ham with L. monocytogenes may occur during processing steps such as slicing and packaging. In‐package ACP is an emerging nonthermal technology, which can be used as a postpackaging decontamination step in industrial settings. This study demonstrated the influence of in‐package gas composition, treatment time, post‐treatment storage, and ham formulation on L. monocytogenes inactivation efficacy of ACP. Results of present study will be helpful to optimize in‐package ACP treatment and storage conditions to reduce L. monocytogenes, while maintaining the quality of ham.