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20Gas plasmas generated at atmospheric pressure and ambient temperatures offer a possible 21 decontamination method for poultry products. The efficacy of cold atmospheric gas plasmas 22 for decontaminating chicken skin and muscle inoculated with Listeria innocua was examined. 23Optimization of operating conditions for maximal bacterial inactivation was first achieved 24 using membrane filters on which L. innocua had been deposited. Higher values of AC 25 voltage, excitation frequency and the presence of oxygen in the carrier gas resulted in the 26 greatest inactivation efficiency, and this was confirmed with further studies on chicken 27 muscle and skin. Under optimal conditions, a 10 s treatment gave > 3 log reductions of L. 28innocua on membrane filters, an 8 min. treatment gave 1 log reduction on skin, and a 4 min.

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The large potential of cold atmospheric plasma (CAP) for food decontamination has recently been recognized. Room-temperature gas plasmas can decontaminate foods without causing undesired changes. This innovative technology is a promising alternative for treating fresh produce. However, more fundamental studies are needed before its application in the food industry. The impact of the food structure on CAP decontamination efficacy of Salmonella Typhimurium and Listeria monocytogenes was studied. Cells were grown planktonically or as surface colonies in/on model systems. Both microorganisms were grown in lab culture media in petri dishes at 20°C until cells reached the stationary phase. Before CAP treatment, cells were deposited in a liquid carrier, on a solid(like) surface or on a filter. A dielectric barrier discharge reactor generated helium-oxygen plasma, which was used to treat samples up to 10min. Although L. monocytogenes is more resistant to CAP treatment, similar trends in inactivation behavior as for S. Typhimurium are observed, with log reductions in the range [1.0-2.9] for S. Typhimurium and [0.2-2.2] for L. monocytogenes. For both microorganisms, cells grown planktonically are easily inactivated, as compared to surface colonies. More stressing growth conditions, due to cell immobilization, result in more resistant cells during CAP treatment. The main difference between the inactivation support systems is the absence or presence of a shoulder phase. For experiments in the liquid carrier, which exhibit a long shoulder, the plasma components need to diffuse and penetrate through the medium. This explains the higher efficacies of CAP treatment on cells deposited on a solid(like) surface or on a filter. This research demonstrates that the food structure influences the cell inactivation behavior and efficacy of CAP, and indicates that food intrinsic factors need to be accounted when designing plasma treatment.

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