The impact of different process gas compositions on the inactivation effect of an atmospheric pressure plasma jet on Bacillus spores

• A systematically testing of argon plasma with admixtures of oxygen and nitrogen was done.
• Highest UV-emission for a mixture of argon with 0.135 vol.% O2 and 0.2 vol.% N2.
• Similar sporicidal effects were found for a pure argon plasma compared to the one with highest UV-emission.
• UV-sensitive spore strains confirmed the sporicidal effect of emitted UV-photons.
• Biphasic spore inactivation was found, with a dominant effect of UV-photons on the first inactivation phase.

Atmospheric plasma provides the advantages of high microbial inactivation that can be performed under ambient conditions. It is consequently regarded as potential alternative to traditional food preservation methods.In this study we systematically tested the influence of argon as plasma carrier gas with admixtures of oxygen (0–0.34 vol.%) and nitrogen (0–0.3 vol.%) towards its emission intensity of UV-C light, excited OH and N2-species and atomic oxygen. A mixture of argon, 0.135 vol.% oxygen and 0.2 vol.% nitrogen emitted four fold more UV photons than pure argon. However, sporicidal effects on Bacillus atrophaeus (3.1 log10) and Bacillus subtilis spores (2.4 log10) were found for pure argon plasma, which were similar as compared to the sporicidal effect of the plasma with highest UV-emission. To distinguish lethal effects caused by emitted UV-light and reactive species, UV-sensitive mutant spore strains (PS578 and FB122) were exposed to plasmas with different UV-emission intensities and a significant impact of UV-light on the first phase of spore inactivation was confirmed.Industrial relevanceAs an efficient method for the inactivation of microorganisms at low temperatures and atmospheric pressure, plasma is already commercially used for the sterilization of medical devices. The results presented in this study could be useful for a process optimization regardless if the plasma is applied for food preservation or surface decontamination. Especially the impact of emitted UV photons from the plasma on the first inactivation phase of endospores attached to surfaces, depicts a high potential of such plasmas for a rapid spore inactivation.