Non-Thermal Microbial Inactivation Using Underwater Plasma: Synergistic Effects of Capillary Discharge on E. coli and M. testaceum

This study investigated the synergistic effects of microorganism inactivation using underwater plasma, focusing on applications relevant to food safety. The underwater plasma was generated by capillary electrodes in 10% saltwater circulated at 5 t/h. Two representative bacteria, Escherichia coli (Gram-negative) and Microbacterium testaceum (Gram-positive), were selected due to their relevance to food and water contamination. Inactivation kinetics were assessed through first-order rate constants (k) under direct, indirect, and total (combined) treatments. The rate constant (k-value) difference between total and indirect treatment for E. coli reached 0.1015 at 5 min of discharge, while M. testaceum showed a smaller difference of 0.0083 at 20 min. These results suggest that microorganisms pre-damaged by direct plasma exposure become more susceptible to long-lived reactive species like hydrogen peroxide. The findings indicate that underwater plasma holds significant potential as an effective non-thermal disinfection method for brine solutions, fresh produce, and food-contact surfaces.