Purpose: The objectives of this present study were to evaluate a novel in-package ozone generating system (PlasmaLabel) for its effectiveness in inactivating Listeria innocua, and attenuated E. coli O157:H7 and Salmonella Typhimurium on tomatoes and maintaining fruit quality.
Methods: The three bacteria were inoculated either on the smooth surface of the tomato or the stem scar area before being sealed in plastic film bags and subjected to treatment using the PlasmaLabel system for various times (up to 4 min). Non-inoculated fruit were used to assess quality changes during 21 day post-treatment storage at 10°C.
Results: The PlasmaLabel system was able to produce ozone inside of sealed film bags, reaching a concentration of 1000 ppm within 1 min of activation. When L. innocua was inoculated onto the smooth surface of the fruit, the bacterium was reduced to a non-detectable level within 40 sec of treatment and was reduced by 4 log CFU/fruit on the stem scar area. Increase in treatment time did not result in a proportional increase in bacterial inactivation. For E. coli and Salmonella, there was little difference (<1 log) in the effectiveness of the system regardless of inoculation site. Both bacteria were typically reduced by 2-3 log CFU/fruit after a 2-3 min treatment. Ozonation resulted in no significant negative effects on fruit color or texture observed during the 22-day post-treatment storage at 22°C.
Significance: These results suggest that Salmonella, Listeria, and E. coli respond differently to ozonation. Ozonation may be a good alternative to aqueous sanitizers for enhancing microbial safety of tomatoes.