Inactivation of Salmonella enterica serovar Typhimurium on egg surface, by direct and indirect treatments with cold atmospheric plasma

- The article addresses both direct and indirect cold atmospheric plasma treatment.
- New high thermal conductivity materials were used for the dielectric barriers.
- To avoid temperature rise, the sinusoidal high voltage was modulated.
- Gas compositions to maximize the Salmonella inactivation effect were established.
- Very good Salmonella inactivation results, egg qualities not affected.

Inactivation of Salmonella enterica on egg surface was investigated using cold atmospheric plasma, either with the eggs immersed in plasma (direct treatment) or with the eggs outside the plasma zone (indirect treatment). The plasma was generated in dielectric-barrier-discharges (DBD) structures, operated with sinusoidal voltage of 25-30 kV peak-peak, and 10-12 kHz frequency. To avoid temperature rise, the voltage was modulated in packages of 2 ms and 20% duty cycle. Each egg was initially contaminated with a population of 108Salmonella cells. Direct treatment was performed in He/O2 mixtures and the optimum volume ratio was established to 1/100. For indirect treatment the working gas was air. Circulating the gas through the plasma reactor was found to be beneficial for decontamination. The experiments confirmed the important contribution of humidity on the inactivation effect, as a consequence of hydroxyl radicals formation. The best results were obtained for a relative humidity of 80%, where Salmonella population on egg surface was reduced below the detection limit (102 cells per egg) after 10 min of direct treatment and 25 min indirect treatment.