Purpose: The purpose of this study was to determine the effects of cold plasma corona discharge on the inactivation of Salmonella on prepackaged, tomato and lettuce mixed salads. Two different inoculation methods were evaluated, as well as the cross-contamination of Salmonella from cherry tomatoes to lettuce and vice versa following cold plasma treatment.
Methods: In separate studies, either cherry tomatoes (10 g) or romaine lettuce (10 g) were inoculated with a Salmonella cocktail (Salmonella Anatum, Salmonella Enteriditis PT30, and Salmonella Stanley) and placed into a commercial PET plastic container and thoroughly mixed together with its uninoculated counterpart. Mixed salads were allowed to dry in a biosafety cabinet for one hour. Samples were treated with 35 kV cold plasma corona discharge inside plastic containers for three minutes. Samples were stomached and serially diluted in BPW. Dilutions were plated onto APC Petrifilm and incubated for 18 h at 37°C.
Results: After three minutes of cold plasma treatment, Salmonella was significantly reduced (P=0.002;α=0.05) in the mixed salad (0.53±0.31 log CFU/g) when cherry tomatoes were the inoculated material, but not when lettuce was the inoculated material. In both scenarios, recoverable Salmonella populations increased on lettuce and decreased on tomatoes following cold plasma treatment.
Significance: Cold plasma can kill Salmonella in a in a prepackaged, mixed salad, with efficacy dependent on the nature of contamination and on the surface topography of the contaminated commodity.