Evaluation of plasma-activated water (PAW) as a novel disinfectant: Effectiveness on Escherichia coli and Listeria innocua, physicochemical properties, and storage stability

Plasma-activated water (PAW) is an emerging disinfectant with high antimicrobial activity due to a variety of reactive oxygen and nitrogen species. This study evaluated the inactivation efficacy of PAW against planktonic Escherichia coli and Listeria innocua as representatives of gram-negative and gram-positive bacteria, characterized the physicochemical properties of PAW, and investigated the storage stability of PAW. The effectiveness of PAW increased by extending the plasma activation time over water during PAW preparation or the incubation time of bacteria in PAW. PAW also showed higher effectiveness against E. coli than L. innocua: PAW5 (PAW prepared by plasma activation of water for 5 min) reduced E. coli by > 5 log CFU/mL and L. innocua by 1.8 ± 0.5 log CFU/mL within 5 min of bacterial incubation time, while PAW15 (PAW prepared by plasma activation of water for 15 min) reduced E. coli by > 5 log CFU/mL and L. innocua by 3.5 ± 0.6 log CFU/mL within 5 min of bacterial incubation time. Acidic pH and nitrogen species such as NO2− synergistically contributed to the inactivation efficacy of PAW. Fresh PAW showed the highest inactivation efficacy while refrigerated PAW maintained the inactivation efficacy compared to PAW stored at room temperature due to delayed dissipation of reactive species.