Abstract
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.