Abstract
This study investigated the inactivation efficiency of cold atmospheric pressure plasma treatment on Bacillus subtilis endospores dependent on the used feed gas composition and on the surface, the endospores were attached on. Glass petri-dishes, glass beads, and peppercorns were inoculated with the same endospore density and treated with a radio frequency plasma jet. Generated reactive species were detected using optical emission spectroscopy. A quantitative polymerase chain reaction (qPCR) based ratio detection system was established to monitor the DNA damage during the plasma treatment. Argon + 0.135% vol. oxygen + 0.2% vol. nitrogen as feed gas emitted the highest amounts of UV-C photons and considerable amount of reactive oxygen and nitrogen species. Plasma generated with argon + 0.135% vol. oxygen was characterized by the highest emission of reactive oxygen species (ROS), whereas the UV-C emission was negligible. The use of pure argon showed a negligible emission of UV photons and atomic oxygen, however, the emission of vacuum (V)UV photons was assumed. Similar maximum inactivation results were achieved for the three feed gas compositions. The surface structure had a significant impact on the inactivation efficiency of the plasma treatment. The maximum inactivation achieved was between 2.4 and 2.8 log10 on glass petri-dishes and 3.9 to 4.6 log10 on glass beads. The treatment of peppercorns resulted in an inactivation lower than 1.0 log10. qPCR results showed a significant DNA damage for all gas compositions. Pure argon showed the highest results for the DNA damage ratio values, followed by argon + 0.135% vol. oxygen + 0.2% vol. nitrogen. In case of argon + 0.135% vol. oxygen the inactivation seems to be dominated by the action of ROS. These findings indicate the significant role of VUV and UV photons in the inactivation process of B. subtilis endospores.
Highlights
In recent years, the application of cold atmospheric pressure plasma (CAPP) for the decontamination of food products, food packing material and/or food contact surfaces raised in attention (Pankaj et al, 2014; Schlüter and Fröhling, 2014)
To study the inactivation mechanisms of CAPP on endospores, B. subtilis endospores inoculated on different surfaces were plasma treated using three different feed gas compositions
A strong thermal inactivation effect on the B. subtilis endospores during the CAPP treatment could not be detected in this study
Summary
The application of cold atmospheric pressure plasma (CAPP) for the decontamination of food products, food packing material and/or food contact surfaces raised in attention (Pankaj et al, 2014; Schlüter and Fröhling, 2014). Plasma-induced inactivation of B. subtilis spores species such as atoms, molecules, and radicals, UV photons. Depending on their thermodynamic properties plasmas can be classified as thermal and non-thermal plasmas (Schlüter et al, 2013). Thermal plasmas are characterized by a local thermodynamic equilibrium between the electrons, ions and neutral species, whereby the temperature of the plasma can reach several 1000 kelvins under atmospheric pressure (Moreau et al, 2008). The electron temperature can reach several 1000 kelvins, whereas the bulk gas temperature can be closed to ambient These so called “cold” plasmas can be directly applied to thermal sensitive surfaces (Ehlbeck et al, 2011)
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