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This research will investigate the use of a plasma-aided approach (Dense Medium Plasma and Array Electrode Reactor) to open up novel ways for the development of low cost, efficient, and in-line disinfection technologies for surfaces of processing equipment, such as cutting blades, conveyor systems, log feeders, etc., that are in contact with RTE meat and poultry products during processing, and for disinfection and decontamination of water and air. The aim of this project is to provide a means to reduce L. monocytogenes (as well as other pathogens and spoilage organisms) contamination levels and biofilm formation during the RTE meat preparation processes by using these technologies. Efficient sterilization of packaging materials (e.g. plastic films, paper) by AER-plasma approaches, will also reduce post-processing contamination of RTE meat products.<p>
The specific objectives of this research are: <ol>
<li> Develop advanced atmospheric-pressure (AP) Array Electrode Reactor (AER) plasma-aided technologies for an in-line, continuous disinfection of metal and plastic material surfaces, which are in direct contact with RTE meat and poultry products during processing;
<li> Develop Dense Medium Plasma (DMP) and AER continuous-flow-system plasma technologies for an efficient disinfection of water and air:
<li> Design and develop plasma techniques for the disinfection of packaging materials (e.g. plastic films, aluminum foil, paper, etc.) used in the food industry;
<li> Understand the plasma-induced reaction mechanisms responsible for the disinfection reactions, and optimize the plasma parameters for the most efficient bacterial annihilation mechanisms; and
<li> Evaluate the scaling-up possibilities of laboratory plasma technologies to pilot and industrial levels.</ol>
Status: The AER plasma reactor developed recently at Center for Plasma-Aided Manufacturing/ Biological Systems Engineering-University of Wisconsin Madison laboratories is provided with a specially designed multrcylinder/wire electrode array system, which
allows the processing of gases or gas mixtures at atmospheric pressure and under continuous-flovusystem mode operation. The electrode array system is built up of individual electrode pairs (rectangular-shaped, grounded, stainless-steel, solid-block electrode, provided with a multitude of 5 mm ID, 100 mm length cylindrical holes, and 8 cm length, solid-bar, interior tungsten electrodes). The grounded multi-hole electrode is
insulated from the central, stressed- wire electrode by individual 5 mm OD and 4 mm ID high-dielectric-quality ceramic tubes. The ceramic tubes extend above and below the upper and lower surfaces of the stainless steel block-electrode and their superior- and inferior-parts are embedded (by using high quality castable ceramic material) into a rectangular-shaped gas-mixing, ceramic chamber, covered with a ceramic plate. All stressed electrodes are interconnected and their top ends are also embedded into the ceramic top-cover of the gas-mixing chamber.<p> The gas-mixing chamber is provided with a porous ceramic or stainless steel plate for the control and uniform distribution and flow of the plasma gases.
This electrode configuration provides a uniform flow of plasma gases or gas mixtures through the individual cylindrical discharges, which are initiated and sustained between the grounded and stressed electrodes. The array electrode system assures a high stability of the individual plasma zones owing to the wire-cylinder (point/ plane) configuration of and to the small gap existing between the electrodes. This unique design allows plasma-processing of gases or gas mixtures in a wide flow-rate domain.
This reactor configuration avoids the formation of the arclet-induced "particle wind" in the vicinity of the target surface, and assures the directing of plasma toward the surfaces considered for modification (e.g. Functionalization, disinfection, coating, etc.). It is noteworthy, that both metal and dielectric surfaces can be surface-modified in the absence of often-damaging plasma filaments, that usually accompany conventional atmospheric pressure discharges.
Preliminary results from AER plasma-enhanced disinfection of artificially contaminated glass and stainless steel substrates:<p>
The efficacy of the AER to inactivate biofilms of L. monocytogenes was tested. Over 99.76% of the biofilm bacteria (original concentration 5.44 log cfu/chip) was inactivated after 2 minutes of air plasma treatment. No L. monocytogenes was recovered after a 5-minute treatment. Oxygen plasma was more effective and inactivated all the biofilm cells after a 2-minute treatment. Dried biofilm cells were slightly more resistant. After 2 minutes of oxygen plasma, 93% of the cells were inactivated.<p>
These initial results demonstrate that the AER is effective. Optimization of plasma conditions will continue for more efficient disinfection of L. monocytogenes biofilms developed under various simulated RTE meat-processing conditions.