Microorganism Microbiological results (cfu/g) Mesophilic Aerobes 1.0 x 108 Spores of Mesophilic Aerobes 5.6 x 107 Enterobacteriaceae 1.5 x 102 Sulf-red anaerobes 4.7 x 107 Escherichia coli 1.0 x 103 Coag-posit Staphylococcus 4.95 x 104 Presumptive Bacillus cereus 5.6 x 107 Clostridium perfringens 2.7 x 103 Moulds and yeasts 6.0 x 103 Salmonella (in 25 g) DETECTED 3/14 eFOOD-Lab international 21 complex food raw materials have been performed and showed in some cases promising results. These studies primarily focus on the inactivation of unwanted microorganisms on heat-sensitive foods such as fresh fruit and vegetables, meat, and eggs where conventional thermal decontamination methods are often not applicable (Schlüter et al., 2013). Hence, after identifying a promising process, a large scale technical application should be feasible, due to the experiences with other large scale plasma systems. Existing equipment for environmental applications, like flue gas cleaning, which are used to substitute wet-chemical processes (Weltmann et al., 2008), might be adapted. At the moment the only application of plasma technology in the food industry is the sterilization and surface modification of packaging material. Consequently a plasma treatment is also regarded as a potential alternative to other chemical (e.g. chlorine treatment) or physical preservation methods (e.g. high-pressure, pulsed electric fields, ionizing irradiation). Further advantages of plasma processes in comparison to other food preservation technologies are: high efficiency at low temperatures (generally < 70 °C); precise generation of plasmas suitable for the intended use; just in time production of the acting agent; low impact on the internal product matrix; application free of water or solvents; no residues on the treated surface and resource-efficiency (Schlüter et al., 2013). What is low temperature atmospheric plasma? Plasma is an ionized gas and also called the 4th state of matter. For the formation of plasma, a gas can be heated or an excess of free electrons is needed to displace electrons in the atoms and molecules of the bulk gas. A plasma can be described as a quasineutral particle system in the form of gaseous or fluidlike mixture of free electrons and ions, frequently containing neutral particles (atoms and molecules), activated and metastable species (NOx*) as well as free radicals like Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS) (Knorr et al., 2011; Rutscher, 2008) (Figure 1). In the field of plasma research we can find a complex nomenclature considering the temperature of the electrons and the bulk gas and/or the surrounding pressure (Roth, 1995). In nonthermal plasmas, the electron temperature is much higher than the bulk gas temperature. Whereas the electron can reach several ten thousands K, the gas temperature remains at temperature levels below 40 °C (Knorr et al., 2011; Mastwijk and Nierop Groot, 2010). Most plasma source are operated in a vacuum, however the most suitable system for food processing is an atmospheric-pressure plasma device where no extreme conditions are required, low process temperatures are possible and no evaporation of water from high-moisture food products occurs. The plasma application on food can be subdivided into two different approaches. During a direct plasma application the treated food is in direct contact with the ignited plasma or plasma afterglow. For an indirect plasma application, the plasma source and the food to be treated are separated. This classification can also be used for the plasma systems used within this study. All tested plasma sources, can ignite a stable plasma at ambient pressure and temperature. The PLEXc Thermal radiation Visible light Electromagnetic Plasma fields Charged particles UV radiation Radicals and stable chemical species Figure 1. Reactive and irradiating species in plasma (source Leibniz Institute for Plasma Science and Technology (INP). Table 1. Natural occurring microflora in the black pepper tested in accordance to ISO-standards. Figure 2. UVC emission spectra of the used plasma jet for pure Argon (dotted black line), Argon + 0.135 % vol. oxygen, (dashed red line) and Argon + 0.135 % vol. oxygen + 0.2 % vol. nitrogen (solid blue line).
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