Sterilization of Escherichia coli by a coaxial microwave plasma flow

An atmospheric low temperature plasma flow generated by microwave discharge utilizing a coaxial cable for microwave transmission has some advantages such as portability, simple configuration, and low power operation. It mainly consists of a cavity, a quartz discharge tube, a coaxial cable, a microwave power source and a gas supply system. Using this argon plasma source, we investigated to clarify effects of exposure temperature, exposure time, exposure distance, input power and gas flow rate on the number of surviving cells of Escherichia coli. A log reduction number of E. coli of at least 3 (10^-3) was obtained at exposure temperatures of 353 K when the exposure time was 600 seconds with a gas flow rate of 5 Sl/min and an input power of 400 W. Number of surviving cells decreases with increase of exposure time in any sterilization conditions.