Removing mechanism of ultrasound and slightly acidic electrolyzed water against Listeria monocytogenes biofilms

Biofilms formed by Listeria monocytogenes on food-contact surfaces exhibit strong resistance to cleaning and disinfection, posing persistent challenges to food safety. This study investigated the antimicrobial efficacy and removal mechanisms of ultrasound, slightly acidic electrolyzed water (SAEW), and their combined treatment against L. monocytogenes biofilms. Results demonstrated that ultrasound–SAEW treatment (ultrasound pretreatment followed by SAEW immersion) achieved optimal performance, reducing viable cell counts by 2.86 log CFU/mL within 30 s and resulting in no detectable culturable cells by plate counting at 60 s. Crystal violet staining confirmed excellent biofilm removal efficiency, reaching 63.40% at 60 s. Ultrasound–SAEW treatment significantly enhanced membrane permeability, with PI fluorescence intensity reaching 236.99%, while simultaneously reducing the absolute zeta potential to 1.25 mV, consequently decreasing cellular metabolic activity, hydrophobicity, and auto-aggregation capacity to 6.04%, 5.67%, and 44.60%, respectively. Confocal laser scanning microscopy further validated the remarkable biofilm removal effects of ultrasound–SAEW treatment from a microstructural perspective. The ultrasound–SAEW approach facilitates biofilm removal by altering L. monocytogenes biofilm characteristics, including reduced biomass, metabolic activity, hydrophobicity, and auto-aggregation capacity. This study provides scientific evidence for the potential application of ultrasonic vapor cleaning in the disinfection and sterilization of food materials and processing equipment. • Ultrasound–SAEW treatment can effectively cleaned up L. monocytogenes biofilms. • Ultrasound–SAEW treatment had higher biofilm clearance efficacy. • Ultrasound–SAEW intensified the disruption of L. monocytogenes cell membranes. • Ultrasound-SAEW reduced the hydrophobicity and auto-aggregation of L. monocytogenes.