Air Discharges and Plasma Activated Water for Applications in Bio-decontamination, Agriculture and Food Processing
Machala Z.
Material Research Society Fall Meeting and Exhibit, Symposium BM06, Boston, USA, Nov 25-30, p. BM06.08.01 (2018)
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Abstract: Non-thermal plasmas generated by electrical discharges in atmospheric pressure air are rich sources of various reactive species. Plasmas enable the transfer of reactive oxygen and nitrogen species (RONS) into the water or aqueous solutions when generated in contact with water and so generate the plasma activated water (PAW). PAW is typically a strong antibacterial agent and besides multiple uses in medicine for disinfection it has the potential for food processing or agriculture applications.
We prepare PAW by a self-pulsing streamer corona (SC) and transient spark (TS) discharges operated in air with water electrospray or water electrode. The production of active species (e.g. O3, NO, NO2 and OH) in the gas and consequently the PAW properties can be controlled by the discharge regime and gas-flow and liquid-flow parameters. Low power air corona discharge are dominated by O3 production, which enhanced the biocidal effects. In the higher power TS, dominant gaseous products are NOx that lead to significant NO2- and NO3- in the PAW and practically no O3. Both discharges produce H2O2. The antibacterial action is then mainly due to the synergy of H2O2, NO2- and acidic milieu (via ONOOH formation) and typically decays in time within several hours post plasma activation, depending on temperature and pH. We use UV-VIS colorimetric and fluorescence methods for the analysis of RONS in the PAW.
PAW produced by TS air discharge has been tested for agriculture applications, such as enhanced plant growth (lettuce, radish, tomato, wheat) or seed germination rate. Testing various medical applications of PAW or plasma activated media in dentistry (periodontal biofilms, endodontics), wound disinfection, urinary tract infections, or cancer cells are under way.
In a similar concept, TS air discharge was successfully demonstrated to induce antimicrobial effects in fresh fruit juices to extend their shelf lifetime without thermal pasteurization and without reducing their composition and nutrition/vitamin qualities. Potential effects of cold plasma on chemical (changes of pH, degradation of organic acids, polyphenols, sugars) and sensory juice properties (color, taste) were carefully tested and it was shown that the juice quality was not significantly affected.
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