Effects of heating on the antibacterial efficacy and physicochemical properties of plasma-activated water

Abstract

Plasma-activated water (PAW), which is the water treated by cold plasma, represents a promising strategy for food decontamination. However, studies of the influences of heating on the antibacterial efficacy and physicochemical characteristics of PAW are limited. Therefore, the present work is aimed at determining the effect of heating on the bactericidal effects and physicochemical properties of PAW. PAW (1.0 mL) was heated in a water bath at 30–80°C for 10 min. After being cooled to room temperature, the antibacterial efficacy and physicochemical properties of PAW were measured. Heating at 40–80°C for 10 min caused a significant decrease in the antibacterial activity of PAW against Listeria monocytogenes and Salmonella typhimurium. After heating at 40–80°C for 10 min, the pH value and oxidation reduction potential (ORP) of PAW remained stable, and the level of nitrate and electrical conductivity of PAW remarkably increased, while hydrogen peroxide and nitrite contents significantly decreased. The combination treatment of PAW and mild heating (40–60°C for 4 min) showed greater antibacterial effect on L. monocytogenes and S. typhimurium. After the combined treatment of PAW with mild heating at 60°C for 4 min, the populations of L. monocytogenes and S. typhimurium decreased by 7.83 log10 CFU/mL and 9.35 log10 CFU/mL, respectively, which were significantly higher than that caused by PAW at 25°C or mild heating at 60°C alone. In summary, the antibacterial activity of PAW is significantly affected by the treatment temperature. This work provides a basis for the practical application of PAW in the food industry.