Cold Atmospheric Plasma Inactivation of Microbial Spores Compared on Reference Surfaces and Powder Particles

Abstract

Heat-resistant spores on a dry, heat-and water-sensitive food matrix are difficult to inactivate. Radioactive or X-ray exposure is allowed and accepted only for some selected commodities. Non-thermal atmospheric pressure plasma treatments could offer an efficient, fast, and chemical-free solution. The effectiveness of direct contact cold atmospheric plasma (CAP) generated by a dielectric barrier discharge (DBD) device and air as process gas was evaluated against spores of Bacillus spp., Geobacillus spp., and Penicillium spp. A maximum of 3 log 10 cycles of inactivation was achieved for B. coagulans spores exposed for only 10 s at low surface energy of 0.18 W/cm 2 determined directly at the electrodes. This corresponds to an initial decimal reduction time of D 1 = 0.1 min. Spores of B. subtilis are the most resistant amongst the studied strains (D 1 = 1.4 min). The determining parameter in the modeling of the inactivation curve is surface energy. Non-porous, native starch granules or shells from diatoms, a highly porous material, were also contaminated with spores and treated by DBD CAP. The inactivation level was significantly reduced by the presence of powders. Considering plasma diagnostics, it can be concluded that the spore shell is the primary and main target for a plasma-induced inactivation. The inactivation affect scales with surface energy and can be controlled directly via process time and/or discharge power.

A Cold Plasma Technology for Ensuring the Microbiological Safety and Quality of Foods

“…Several researchers have demonstrated the efficacy of the technology with arrays of food spoilage and foodborne pathogenic microorganisms including bacteria, and fungi. The effect of cold plasma on resistant spores of Bacillus spp., Geobacillus spp., and Penicillium spp., investigated on food matrix, demonstrated a 3-log 10 inactivation of B. coagulans spores after 10 s [94]. Sporicidal efficacy of cold plasma on C. difficile displayed similar results with ∼3 log reduction in viable spore counts after 5 min of treatment [92].…”

“…To date, the mechanisms of cold plasma-mediated spore inactivation remains unclear. However, spore shell have been suggested as the primary and main target for a plasma-induced inactivation [94]; neutral reactive oxygen species and UV radiation were also reported to play dominant role in the inactivation of spores [98]. Furthermore, an increases in hydrogen peroxide (H 2 O 2 ) concentrations in plasma-treated cells and the increased nitrate (NO 3 − ) concentrations indicated the role of plasma generated radical ions [61].…”

Development of Antimicrobial Phototreatment Tolerance: Why the Methodology Matters

“…The principal mecha-nisms of CAP involve cell membrane permeabilization, activity of reactive oxygen and ni-trogen species as well as the chemical reactions leading to DNA damage [ 54 ]. CAP was demonstrated to be an efficient bactericidal treatment leading to Bacillus subtilis and Clos-tridium difficile spores inactivation [ 55 ], eradication of MRSA and E. coli in in vitro porcine skin model [ 56 ], as well as inactivation of other Gram-positive and Gram-negative species [ 51 , 53 , 57 ]. A study aimed at investigating the development of CAP tolerance was described by Matthes et al, employing S. aureus biofilm culture in medium to mimic an artificial wound environment.…”

Microbial Decontamination of Rice Germ Using a Large-Scale Plasma Jet-Pulsed Light-Ultraviolet-C Integrated Treatment System

“…Plasmas are ionized gases containing reactive oxygen species, reactive nitrogen species, ultraviolet (UV) photons, radicals, electrons, and charged particles (Beyrer et al 2020;Liao et al 2017;Scholtz et al 2015). Plasma treatment has been reported to effectively inactivate vegetative bacteria and endospores (Butscher et al 2016;Patil et al 2014) and fungi (Dasan et al 2016;Selcuk et al 2008).…”