Sterilization of Food Contacting Surfaces via Non-Thermal Plasma Treatment: A Model Study with Escherichia coli-Contaminated Stainless Steel and Polyethylene Surfaces
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This study focuses on the utilization of glow discharge technique for the reduction of microorganisms on food contacting surfaces to determine whether non-thermal, low-pressure plasma could provide an effective alternative to current sterilization methods. Radio frequency (13.6 MHz) plasma environment was developed and tested for the inactivation of E. coli K12. Different plasma parameters (discharge power 0-100 W, exposure time 0-30 min) and selected gases (nitrogen, oxygen, air, water vapor) were tested. Following plasma treatment, survival curves and D values were determined. Contact angle measurements were performed to state the change of surface hydrophilicity. Determinations of structural changes on microorganisms were accomplished by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Improved bacterial inactivation efficiency was achieved when air was used instead of pure oxygen or nitrogen gases. Water vapor was found to be the most effective (approximately 7 log(10) reduction) agent in destruction of the microorganisms. The results showed that surface topography and hydrophilicity also have an effect on the efficiency of plasma treatment. In this study, the E. coli inoculated on polyethylene surfaces showed more resistance to plasma treatment. Fragmentation of bacterial cell wall and leakage of cytoplasmic matter were observed following plasma experiments. This study demonstrates that plasma is a promising technology for sterilization of food contacting surfaces, because of its safety, easy handling, capability of processing at low-temperature ( < 44 A degrees C), relatively rapid sterilization.