Plasma technology for sterilization of food packaging material

An efficient inactivation of surface contaminants like micro organisms or toxins is a requirement for the manufacturing of safe and high-quality products in food industry. In a research project funded by the BMBF (FKZ 13N7609) the so called cascaded dielectric barrier discharge was developed (CDBD). This patented system is a further development of a dielectric barrier discharge which combines generation of UV light with a chemically reactive plasma. For this a gas-filled gap (mm up to cm), between a flat excimer lamp and a ground electrode, is excited by high voltage and this leads to micro-discharges (plasma filaments) directly above the sample with a lifetime in the range of nanoseconds, which enable a treatment at low-temperature. Due to the plasma filaments the sample is exposed to various plasma effects that can be controlled by the applied power or the used process gas. Simultaneously, the gas in the excimer lamp is excited and monochromatic UV radiation with high conversion efficiency is released. In this way the cascaded dielectric barrier discharge combines various inactivation pathways, which effects synergistically and inactivates micro organisms efficiently. Microbiological tests with the CDBD, equipped with a XeBr*-Excimer and laboratory air as process gas, has shown a high microbicidal effect against a wide range of different test strains. In case of B. atrophaeus endospores for example, a count reduction of nearly 6 log10 within one second was achieved. The cascaded dielectric barrier discharge was developed for the sterilization of polymer films. A treatment with the CDBD does not affect negatively the properties of the packaging material. Studies with food related polymers like PET, PE or PS did not show significant modifications of characteristic parameters like sealing strength, gas permeability or friction coefficient. Generally, the plasma technology has the potential to establish as a new sterilization method in various industrial applications.