Inactivation of Salmonella Typhimurium by Non-Thermal Plasma Bubbles: Exploring the Key Reactive Species and the Influence of Organic Matter

Abstract

The key reactive species generated by non-thermal plasma bubbles for the inactivation of Salmonella Typhimurium and the effects of organic matter on the inactivation efficacy were investigated. Plasma, which is primarily composed of ozone (O3), was generated by dielectric barrier discharge and injected into a solution (400 mL) as a bubble. The surviving population of S. Typhimurium decreased in proportion to the treatment time, resulting in a 5.29 log reduction after 5 min of treatment. Verification tests to specify key reactive species were conducted using an O3 destruction unit and reactive oxygen species scavengers. The results indicated that singlet oxygen (1O2) contributes substantially to the inactivation of S. Typhimurium, and that the presence of superoxide anion radicals (O2·−) from O3 is essential for the production of 1O2. When a S. Typhimurium suspension containing organic matter (final concentration: 0, 0.005, 0.05, 0.1, and 0.5 g/L), consisting of beef extract and peptone, was treated with plasma bubbles for 5, 10, 15, 20, 25, and 30 min, respectively, the potential of the plasma bubbles for inactivating S. Typhimurium successfully was verified with longer contact time, despite organic matter attenuating the inactivation efficiency in a dose-dependent manner.