Synergistic bactericidal effects of combined sterilization strategies against Listeria monocytogenes: Mechanistic insights and practical validation in prepared salad

Listeria monocytogenes is a common pathogen in contaminated salads. The objective of this study was to investigate the synergistic bactericidal efficacy of ultrasound (US), slightly acidic electrolyzed water (SAEW), and phenyllactic acid (PLA) sterilization methods against L. monocytogenes . The viable cells and viable but non-culturable (VBNC) cells were quantified, and 8-aniline-1-naphthalenesulfonic acid (ANS) fluorescence, zeta potential, ortho-nitrophenyl- d -galactopyranoside (ONPG) permeability, and protein content of L. monocytogenes were assessed after different sterilization treatments. Microscopic techniques and flow cytometry were also employed to confirm the bactericidal effects. Furthermore, the impacts of combined sterilization method on total plate counts, color, and hardness of prepared salad were investigated. The results showed that the combined sterilization method in group UG (US + 1 MIC PLA + 1/2 MIC SAEW), which achieved a total plate count of 0 log CFU/mL, exhibited significantly higher effectiveness compared to the individual method in group B (2 MIC SAEW) with a total plate count of 3.88 log CFU/mL. No VBNC cells were detected after the combined sterilization, while they were observed in samples treated with single sterilization methods. The combined sterilization method effectively eradicated L. monocytogenes and demonstrated potential application in the sterilization of prepared salads.