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Aims: This study aimed to compare the efficacy of plasma‐activated water (PAW) generated by two novel plasma reactors against pathogenic foodborne illness organisms. Methods and results: The antimicrobial efficacy of PAW produced by a bubble spark discharge (BSD) reactor and a dielectric barrier discharge‐diffuser (DBDD) reactor operating at atmospheric conditions with air, multiple discharge frequencies and Milli‐Q and tap water, was investigated with model organisms Listeria innocua and Escherichia coli in situ. Optimal conditions were subsequently employed for pathogenic bacteria Listeria monocytogenes, E. coli and Salmonella enterica. DBDD‐PAW reduced more than 6‐log of bacteria within 1 min. The BSD‐PAW, while attaining high log reduction, was less effective. Analysis of physicochemical properties revealed that BSD‐PAW had a greater variety of reactive species than DBDD‐PAW. Scavenger assays designed to specifically sequester reactive species demonstrated a critical role of superoxide, particularly in DBDD‐PAW. Conclusions: DBDD‐PAW demonstrated rapid antimicrobial activity against pathogenic bacteria, with superoxide the critical reactive species. Significance and impact of study: This study demonstrates the potential of DBDD‐PAW produced using tap water and air as a feasible and cost‐effective option for antimicrobial applications, including food safety. [ABSTRACT FROM AUTHOR]

The chemistry, antimicrobial efficacy and energy consumption of plasma-activated water (PAW) was optimized by altering the discharge frequency, ground-electrode configuration, gas flow rate and initial water conductivity for two reactor configurations, i.e., air pin-to-liquid discharge and air plasma-bubble discharge in water. The ratio of NO 2 − and NO 3 − formation was altered to optimise the antimicrobial effects of PAW, tested against two Gram-negative bacteria. An initial solution conductivity of 0.2 S·m−1 and 2000-Hz discharge frequency with the ground electrode positioned inside the pin reactor showed the highest antimicrobial effect resulting in a 3.99 ± 0.13-log 10 reduction within 300 s against Escherichia coli and 5.90 ± 0.24-log 10 reduction within 240 s for Salmonella Typhimurium. An excellent energy efficiency of reactive oxygen and nitrogen species (RONS) generation of 10.1 ± 0.1 g·kW−1·h−1 was achieved. Plasma-activated water (PAW) is deemed as an eco-friendly alternative to chemical disinfection because its bactericidal activity is temporary. Optimizing the design and operation of PAW reactors to achieve high inactivation rates of more than 5-log 10 reductions, as demonstrated in this work, will support the industrial application of this technology and the scaleup at industrial level. • Increasing discharge frequency from 1000 to 2000 Hz improved the antimicrobial characteristics of PAW by the pinreactor • Increasing initial liquid conductivity in the pin reactor increased the bacterial inactivation to 1.74–4.4-log 10 reduction • Ground electrode inside the pin reactor caused higher E. coli (3.99-) and S. Typhimurium (5.90-log 10 reduction) inactivations • Altering ground-electrode position from inside to outside the bubble reactor changed the NO 2 −/ NO 3 − ratio from 0.92 to 2.69 • The optimal PAW configuration, achieving more than 5-log reduction of S. Typhimurium , was the pin-to-liquid discharge [ABSTRACT FROM AUTHOR]