Physicochemical properties of plasma-activated water and associated antimicrobial activity against fungi and bacteria

Plasma-activated water (PAW), generated through Surface Dielectric Barrier Discharge, was tested against microbial contaminants. We assessed how the time of exposure to plasma treatment and the gas flow rate impact the chemical composition of PAW, and, in turn, how it influences these factors influence its efficacy against microorganisms. The effectiveness of PAW treatments was evaluated against the fungal phytopathogen Botrytis cinerea and both pathogenic (Xanthomonas campestris pv. vesicatoria) and beneficial (Bacillus amyloliquefaciens) bacteria. The physicochemical properties of PAW were assessed as the concentration of reactive species, namely, NO3− and NO2− and H2O2, pH, and oxidation-reduction potential. Higher levels of reactive species and lower pH during longer treatments were associated with greater antimicrobial efficacy. A correlation study and Principal Component Analysis demonstrated that the RONS content in PAW affected antimicrobial activity, with stronger correlations between NO2−, H2O2, and fungal inhibition, as well as between NO2− and bacterial inhibition. Almost complete inhibition was reached after 1 min of treatment for bacteria (log reduction of 4.5 for B. amyloliquefaciens and 5.1 for X. campestris) and after 3 min of treatment for B. cinerea (approximately 90% inhibition of conidial germination). The obtained results contribute to defining optimized treatment conditions using PAW for antimicrobial decontamination of plant products.