Gas and Plasma

A resistive barrier discharge (RBD) prototype able to generate gas plasma at atmospheric conditions was set up. The discharge was electrically characterized and the plasma glow was analysed by optical emission spectroscopy. The decontamination power of the device was assessed on samples of shell eggs experimentally inoculated with Salmonella Enteritidis and Salmonella Typhimurium (5.5–6.5 Log CFU/eggshell) and placed in the treatment chamber. Different decontamination times (10, 20, 30, 45, 60 and 90 min) and relative humidity values (RH) of the gas mixture in the chamber (i.e. 35% and 65%, at 25 °C) were considered. All samples were treated in the plasma after-glow chamber where the measured temperature was not much higher than the room temperature, minimizing the risk of egg quality alterations.

The discharge was characterized by a potential difference of about 15 kV; the emission spectra showed the presence of very reactive species such as the positive ion N2+ and OH and NO radicals. After 90 min of treatment, reductions up to 2.5 Log CFU/eggshell and 4.5 Log CFU/eggshell were observed for S. enteritidis using air with low and high moisture contents, respectively. No significant negative effects of the gas plasma were observed on the egg quality traits.

Keywords

• Gas plasma;
• Non-thermal decontamination;
• Shell eggs;
• Salmonella