Inactivation of Listeria monocytogenes and Salmonella Typhimurium by piezoelectric cold plasma: oxidative, structural and metabolic pathways

Cold atmospheric plasma (CAP) is an innovative, non-thermal decontamination technology with promising applications in food safety. This study investigated the antimicrobial mechanisms of CAP against the foodborne pathogens Salmonella Typhimurium and Listeria monocytogenes. CAP was applied using piezoelectric direct discharge (PDD) technology for 0, 1, 6, 9, and 15 min to simulate nonthermal decontamination conditions relevant to food processing. Antimicrobial effectiveness was evaluated using culture-based enumeration, while CAP-induced cellular damage was assessed using scanning electron microscopy (SEM), and assays measuring lipid peroxidation, reactive oxygen species accumulation, membrane permeability and malate dehydrogenase activity. Bacterial viability significantly decreased by up to 5.7 log CFU/mL after 6 min and ≤ 6.6 log CFU/mL after 9 and 15 min treatments, compared with untreated pathogens. These reductions were accompanied by corresponding increases in membrane permeability of 50%, 65%, and 94%, respectively. Culture-based enumeration confirmed reductions of ~ 4.5 log CFU/mL after 6 min and ≤ 6.5 log CFU/mL following 9 and 15 min treatments. CAP treatment for at least 6 min significantly elevated intracellular reactive oxygen species, which triggered lipid peroxidation as evidenced by elevated malondialdehyde and peroxide values. Furthermore, CAP treatment resulted in a significant reduction in malate dehydrogenase activity, indicating disruption of cellular metabolic function. SEM supported CAP-induced cellular alterations by revealing morphological damage, including porosityshrinkage and cytoplasmic leakage. Overall, PDD-generated CAP induced a multi-targeted antimicrobial effect, supporting its potential as a nonthermal decontamination method in food processing. Further research should focus on its application to a range of food matrices and its impact on quality parameters.