Quantitative microbial assessment for Escherichia coli after treatment by high voltage gas phase plasma

Abstract

High voltage electrical discharge (gas and liquid) plasmas are new developing techniques used for food and water decontamination. This study investigates the influence of high voltage gas phase plasma treatment on several parameters: inactivation of Escherichia coli K12, recovery, proteomic analyses, cellular leakage and influence of pH and generated H2O2 species on inactivation of the E. coli cells. Samples were treated in a glass reactor with a point-to-plate electrode configuration. Electrical conductivity (100 and 800 μS/cm), polarity (+/−), time (5 and 10 min) and frequency (60, 90 and 120 Hz) were chosen in order to determine their influence on listed parameters. Statistical analyses were obtained to optimize conducted treatments. Treatment regime of 90 Hz, positive polarity, 100 μS/cm and 10 min resulted in the highest reduction (7.8 log10 CFU/mL) of E. coli. Recovery of cells after the treatment suggested oxidative stress overcome. Plasma processing is an energy effective process, comparing to traditional thermal processes like pasteurization and sterilization. Plasma treated liquid remains at low temperature, which lowers electrical energy consumption during industrial processes. The proposed study investigates the possible application of high voltage gas phase electrical discharge plasmas for inactivation of Escherichia coli K12 MG1655 in water. The main aim was to confirm effectiveness of plasma treatment conducted in argon (which is uninfected by plasma and can be recycled) on inactivation and cell recovery of E. coli K12. This research is a first step towards the development of the gas phase plasma technology for disinfection of liquids. However, future development, optimization and application of this technology for food sterilization will lead to acceptable ecological regulations like lowering greenhouse gas emissions.