Purpose: The objective was to assess the impact of multiple processing variables on Salmonella transfer during commercial slicing of tomatoes.
Methods: Red round tomatoes were dip-inoculated to contain avirulent Salmonella Typhimurium LT2 at ~ 5 log CFU/g and air-dried for 2 h. After slicing one inoculated tomato with a manual (Prince Castle Model 943) or electric slicer (Edlund Model 350), the blade, back/bottom or back/side-plate was sanitized before slicing 20 uninoculated tomatoes to quantify Salmonella transfer. Thereafter, the impact of processing temperature (4, 10 or 23°C), slicer post-contamination hold time (0 or 30 min), tomato surface (wet or dry), slice thickness (3/16, 1/4 or 3/8 inch), and tomato variety (Torero, Rebelski or Bigdena) on Salmonella transfer was assessed using the manual slicer. The top, middle, and bottom slice from each tomato and the blade, back-plate, and bottom/side-plate surface samples collected using Kimwipes® were homogenized by stomaching in lactose broth for 1 min and then surface-plated on trypticase soy agar containing 0.6% yeast extract, 0.05% ferric ammonium citrate and 0.03% sodium thiosulfate w/o 0.45 μm membrane filtration to quantify Salmonella.
Results: Significantly greater Salmonella transfer (P < 0.05) was seen using the manual as compared to electric slicer with populations linearly and logarithmically decreasing 2.73 and 4.36 log CFU/tomato, respectively, after slicing 20 tomatoes. The bottom/back-plate of the manual slicer and the blade of the electric slicer were the primary contributors to Salmonella transfer. Statistically similar Salmonella transfer rates were observed at 4 (0.6%), 10°C (0.1%) and 23°C (1.1%). Increasing the slicer post-contamination hold time from 0 to 30 min prolonged Salmonella transfer during slicing. A significantly higher (P < 0.05) Salmonella transfer rate (12.2%) was observed when tomatoes were wet. Thinner tomato slices resulted in relatively higher Salmonella populations on uninoculated tomatoes. Concerning tomato variety, Salmonella transfer was significantly greater (P < 0.05) for Torero (1.11%) as compared to Rebelski (0.08%) and Bigdena (0.07%) tomatoes.
Significance: Commercial slicing of tomatoes is best conducted using an electric slicer at 4°C to minimize potential transfer of Salmonella. These findings will also be useful in the development of science-based transfer models for risk assessments.