Purpose: In this study, the inactivation of the 2001 outbreak strain Salmonella Enteritidis PT 30 (ATCC BAA-1045) on the surface of unpeeled almonds by cold plasma was investigated.
Methods: Inoculum preparation and inoculation of almonds was done according to the guidelines recommended by the Almond Board of California. For plasma treatment, a diffuse coplanar surface barrier discharge (DCSBD) plasma system was used. Almond samples (15g) were inoculated in a treatment chamber with a static gas atmosphere between two DSCBD plates. The chamber was flushed with the process gas (air, N2, O2) and the almonds were treated up to 15 min. Generated plasma was characterized using optical emission spectroscopy, by the quantification of ozone, and by temperature measurement in the plasma. After treatment, the almond color was measured.
Results: Plasma treatment successfully inactivated S. Enteritidis. The inactivation and, also, the color of the almonds were affected by the process gas. Air-plasma emitted different reactive oxygen and nitrogen species and showed the highest inactivation, with up to 6 log10 after 15 min treatment with a peak treatment temperature of 69°C. The O2-plasma had a peak temperature of 71°C and generated the highest ozone concentration of about 20,000 ppm in the treatment chamber, which might be responsible for the achieved 5 log10 inactivation. The lowest inactivation of 2 log10 was obtained using N2, whereby N2-plasma emitted the amount of UV-C photons with a peak temperature of 72°C. Plasma treatment with air and N2 resulted in a browning of the almonds.
Significance: The results showed that plasma treatment can effectively inactivate S. Enteritidis PT 30 on the surface of almonds, while maintaining the color.