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Spectroscopic characterization of various low temperature plasma sources used in food processing

Non-thermal plasma processing in food industry and agriculture is emerging innovative technology showing high potential in solving various problems connected to inactivation of microorganisms, the acceleration of seed germination and crop growth, but recently also used for extraction of bioactive compounds. Various plasma sources are developed for direct or indirect treatment of solid or liquid food samples. We have applied single-electrode atmospheric pressure plasma jets above the sample surfaces, immersed into the liquid or contained in a limited space. For characterisation of plasma during treatment of various samples we use the time resolved Optical Emission Spectroscopy (OES), absorption Cavity Ring-Down Spectroscopy (CRDS), Laser Induced Breakdown Spectroscopy (LIBS). OES and LIBS are based on use of a small fibre optical spectrometers which allows acquisition of tens of spectra within a second covering a full optical range. The proper software allows monitoring composition of many excited atoms and molecules within the plasma and close to interaction region. More advanced absorption techniques based on use of lasers are needed in order to detect non-excited species eventually desorbed from the target samples under cold plasma interaction. Results for several examples will be shown and discussed in terms of applicability to various food treatments. The treatment of liquid food was performed with plasma source orifice placed 1.5 cm above the liquid surface. For the extraction treatments plasma capillary is immersed 1 cm into solvent, while for the treatment of solid food surfaces array of plasma sources enters through the tight holes at PVC box container. Each case ask for different arrangements in order to collect emission from plasma. As plasma treated objects (natural products) are of highly variable parameters such as size, shape, surface characteristics or water content, the real-time in situ monitoring is challenging but it might be necessary to achieve the active control in future plasma reactors at industrial scale.

atmospheric plasma; food technology; agriculture; spectroscopic characterization

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