Salmonella outbreaks have been historically linked to tomatoes, with cross-contamination during post-harvest processing having become a major public health concern. In response, a series of studies were developed to assess the extent to which dump tanks, conveyors, slicers, and dicers can spread Salmonella and other microorganisms. An evaluation of the microbiological quality of tomatoes and dump tank water was conducted during three visits to a local tomato packinghouse. At the beginning of whole-day processing and after 3 h of operation, bacteria and yeast/mold populations decreased < 2 logs on tomatoes, with these microbial counts greatly impacted by changes in organic load and sanitizer concentration during washing. When the spread of Salmonella was assessed during washing of tomatoes with various sanitizers and subsequent conveying in a pilot-scale packing line, ~ 90% of the original Salmonella inoculum transferred to sanitizer-free water. Acidified chlorine yielded the greatest Salmonella reduction on tomatoes (3.1 log CFU/g). After processing with sanitizers, Salmonella populations decreased to non-detectable levels (< 0.2 log CFU/100 cm2) on the equipment surfaces. Thereafter, Salmonella transfer was assessed during conveying of tomatoes with plastic, foam, or brush rollers. Overall, cross-contamination was greatest using foam, followed by plastic and brush rollers (P < 0.05). After 5 inoculated tomatoes were roller conveyed, 24 and 76% of all uninoculated subsequently conveyed tomatoes were cross-contaminated with Salmonella of 10 - 100 and 1 - 10 CFU/tomato, respectively, compared to 8% of 25 tomatoes using brush rollers.The next two studies focused on Salmonella transfer during slicing and dicing of tomatoes. For tomato slicing, one red round tomato was inoculated with Salmonella Typhimurium LT2 (~ 5 log CFU/g) and sliced using a manual or electric slicer, followed by 20 uninoculated tomatoes, all of which yielded quantifiable numbers of Salmonella after slicing. The quantitative data was fitted to a two-parameter exponential model (Y = A e(B X)). While significantly higher (P ≤ 0.05) percentages of Salmonella were transferred to wet (12.2%) as opposed to dry tomatoes (1.1%), with the variety of tomato also impacting transfer, post-contamination hold time, processing temperature and tomato slice thickness did not significantly impact the overall percentage of cells transferred. When one 0.9 kg batch of inoculated Roma tomatoes (~5 log CFU/g) was mechanically diced, followed by ten batches of uninoculated tomatoes, all uninoculated tomatoes yielded Salmonella, with populations exponentially decreasing from 3.3 to 1.1 log CFU/g. Flume tank washing in sanitizer-free water or water containing 80 ppm peroxyacetic acid, 80 ppm mixed peracid, or 80 ppm total chlorine decreased the Salmonella populations on diced tomatoes 1.3 ± 0.2, 2.3 ± 0.3, 2.4 ± 0.4, and 2.4 ± 0.1 log CFU/g, respectively. Spray sanitation on conveyor belts proved to be an effective way to enhance safety of diced tomatoes, with electrolyzed water being especially attractive due to its relatively low cost and ease of preparation.Finally, the impact of temperature, pH, and wash water organic load on Salmonella morphology and early-biofilm formation was assessed on different surfaces encountered in tomato packing houses. Both pH and temperature significantly affected the surface hydrophobicity of Salmonella. Early-biofilm formation on tomatoes was significantly affected by both time (P = 0.0004) and temperature (P < 0.0001). After 6 d, early-biofilms consistently developed on stainless steel and HDPE surface, with the former being more evenly distributed.
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