Investigation of the chemical composition of plasma-treated water by MidiPLexc and its antimicrobial effect on L. monocytogenes and Pseudomonas fluorescens monospecies suspension cultures

Plasma-generated compounds conceived by microwave-induced plasma (MidiPLexc) were physicochemically investigated in their molecular compositions. Therefore, plasma-treated water (PTW) was generated by treatment with the MidiPLexc within a 1 l glass bottle for a pre-treatment time of 100 s, 300 s and 900 s. The PTW was further investigated in its composition of reactive oxygen/nitrogen species. For this purpose, the hydrogen peroxide (H₂O₂) concentration of the PTW was determined electrochemically using chronoamperometry, and the anionic components were determined using ion chromatography. As a result, H₂O₂ concentrations of up to 720 mg l^-1, nitrite concentrations of 1600 mg l^-1 and nitrate concentrations of 72.3 mg l^-1 could be detected after 900 s pre-treatment time of the water. The compounds obtained by ion chromatography were fractionated and subsequently confirmed by mass spectrometry. Once an overview of the chemical composition of PTW had been obtained, its effects on pathogens like Pseudomonas fluorescens and L. monocytogenes, which are both of particular importance as pathogenic contaminants during food production, were tested. In that process, a maximum reduction in the colony forming units of 4 log₁₀ steps for P. fluorescens and 3 log₁₀ steps for L. monocytogenes could be observed. The LIVE/DEAD assay showed a maximum reduction in the ratio G/R of 67% for P. fluorescens and 38% for L. monocytogenes. In addition, the XTT assay results showed a maximum cell metabolism reduction of 96% for P. fluorescens and 91% for L. monocytogenes.