Impact of decontamination by plasma-activated fog (PAF) on Listeria monocytogenes mono- and mixed cultures on agar medium and foods.

Abstract

In this study, plasma-activated fog (PAF) technology was exploited as a nonthermal decontamination treatment against five L. monocytogenes strains isolated from human, animal, and food sources and tested both in vitro (on nonselective agar medium) and fresh-cut lettuce. Between the 30 s and 20 min treatments, PAF showed a time-dependent accumulation of long-lived reactive oxygen and nitrogen species (RONS) accompanied by concurrent acidification, with NO3- becoming the dominant species (increasing from approximately 40 to 700 mg L-1) and the pH decreasing from approximately 4.5 to 2.5. In vitro, a marked statistically significant (p < 0.05) reduction of L. monocytogenes was observed after 30 s of treatment (ranging from complete inhibition to ca. 2.69 log CFU/plate) for all the strains at all the tested concentrations (ca. 5 × 104 to ca. 5 × 101 CFU/plate), both as single and five-strain mixtures. Smaller but statistically significant reductions were also observed when PAF was applied to artificially contaminated fresh-cut iceberg and romaine lettuce, with 10 min of treatment reducing L. monocytogenes by ca. 1.29 and 0.87 log CFU/g, respectively. Mathematical modelling revealed that the biphasic model best depicts the inactivation kinetics of L. monocytogenes on agar medium, whereas the log-linear model fits the inactivation kinetics on lettuce. This study paves the way for understanding the applicability of PAF in the food industry and opens the door for future studies to reveal its decontamination properties on different foodborne pathogens and diverse food surfaces.