Abstract
Previous (biofilm) inactivation studies using Cold Atmospheric Plasma (CAP) focused on helium (with or without the addition of oxygen) as feeding gas since this proved to result in a stable and uniform plasma. In industry, the use of helium gas is expensive and unsafe for employees. Ambient air is a possible substitute, provided that similar inactivation efficacies can be obtained. In this research, 1 and 7 day-old (single/dual-species) model biofilms containing L. monocytogenes and/or S. typhimurium cells were treated with an air-based Surface Barrier Discharge (SBD) plasma set-up for treatment times between 0 and 30 min. Afterwards, cell densities were quantified via viable plate counts, and predictive models were applied to determine the inactivation kinetics and the efficacy. Finally, the results were compared to previously obtained results using a helium-based SBD and DBD (Dielectric Barrier Discharge) system. This study has demonstrated that the efficacy of the air-based CAP treatment depended on the biofilm and population type, with log-reductions ranging between 1.5 and 2.5 log10(CFU/cm2). The inactivation efficacy was not significantly influenced by the working gas, although the values were generally higher for the air-based system. Finally, this study has demonstrated that the electrode configuration was more important than the working gas composition, with the DBD electrode being the most efficient.
Highlights
Biofilms are highly resistant consortia of cells which are embedded in a matrix of self-produced extracellular polymeric substances (EPS) and attached to a biotic or an abiotic surface [1,2,3,4]
Ambient air was used as operating gas, the input voltage was set at 24.88 V, and the applied frequency was set at 12 kHz
Comparing the efficacy of the air-based Surface Barrier Discharge (SBD) set-up with those obtained using the helium-based SBD and DBD set-ups proved that the efficacy of the Cold Atmospheric Plasma (CAP) treatment was more influenced by the electrode configuration than by the operating gas
Summary
Biofilms are highly resistant consortia of cells which are embedded in a matrix of self-produced extracellular polymeric substances (EPS) and attached to a biotic or an abiotic surface [1,2,3,4]. They are omnipresent in nature and in industrial environments such as the food industry, causing economic and health-related problems such as contamination/spoilage of food products, an impeded heat transfer in heat exchangers, and corrosion of surfaces [3,5,6,7]. Cold Atmospheric Plasma (CAP) is one of these promising novel methods for biofilm inactivation as log-reductions up to 4 log (CFU/cm2 ) have been obtained for inactivation of L. monocytogenes and
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