Cold atmospheric plasma disinfection of cut fruit surfaces contaminated with migrating microorganisms

The efficacy of cold atmospheric gas plasmas in decontaminating freshly cut fruit of Escherichia coli type 1, Saccharomyces cerevisiae, Gluconobacter liquefaciens and Listeria monocytogenes ScottA deposited onto either membrane filters or the cut surfaces of mango and melon was examined. These were all exposed to a cold atmospheric plasma plume generated by an ac voltage of 8 kV at 30 kHz. The cold atmospheric plasma used in this study was very efficient in reducing the microbial load on the surfaces of filter membranes. However, its efficacy was markedly reduced for microorganisms on the cut surface of fruit. This was shown not to be the result of ‘quenching’ of reactive plasma species responsible for microbial inactivation but principally the result of the migration of microorganisms from the exterior of the fruit tissue to its interior. The velocity of migration through melon tissues was estimated at around 300 μm min-1 for E. coli and S. cerevisiae, whereas that through mango tissues was between 75 – 150 μm min-1. The data presented here serves in effect to set operational targets for optimizing the performance of gas plasma inactivation processes. Finally, the current capability of cold atmospheric plasmas is reviewed and ways to improve their bactericidal efficacy are identified and discussed. It is concluded that considerable scope exists to enhance significantly the efficacy of cold atmospheric plasmas in decontaminating fresh cut fruits.