Inactivation mechanisms and parameter optimization of argon-oxygen low-pressure cold plasma against foodborne...

This study quantified the bactericidal efficacy of Ar/O₂ low-pressure cold plasma (LPCP) against Escherichia coli, Staphylococcus aureus and Listeria monocytogenes in suspension and on cheese surfaces. A 1-min treatment (250 W) produced reductions of 2.64 ± 0.19, 2.45 ± 0.06 and 2.68 ± 0.16 log CFU/ml, respectively, without significant inter-species differences. Growth curves showed delayed mid-log times and lower maximal densities (p < 0.01). Membrane disruption was confirmed by increased malondialdehyde and protein leakage (p < 0.01), while scanning electron microscopy revealed extensive cell disruption. Fourier-transform infrared spectroscopy indicated loss of lipid and protein signals, and flow cytometry showed up to 50% membrane-compromised cells for L. monocytogenes. Response-surface optimization (power 110 W, 1.7 min, 8% O₂) predicted 2.47 log CFU/ml reduction for S. aureus; validation on cheese yielded 1.64 ± 0.10, 1.17 ± 0.58 and 1.33 ± 0.25 log reduction for E. coli, S. aureus and L. monocytogenes, respectively. Confocal laser scanning microscopy indicated preserved cheese microstructure after <1 min, whereas longer exposures generated dehydration cracks. Thiobarbituric acid-reactive substances remained unchanged at 0.83 min but rose significantly after 1.67 min (p < 0.05); sensory scores for odour and texture declined at 2.5 min, with slight oxidized flavor yet unchanged overall acceptability. Ar/O₂ LPCP affords a rapid, non-thermal route for food-surface decontamination that enhances safety by disrupting bacterial membrane integrity.