Purpose: The objective was to quantify the effect of four physical variables on Salmonella transfer to stainless steel during sliding contact with potatoes used as the model product.
Methods: Peeled potatoes were cut into 3-cm cubes, spot-inoculated with Salmonella Typhimurium LT2 (~6 log CFU/cm2), and then pulled (using a controlled speed-force machine) across a 304 stainless steel plate with variations in surface roughness (brushed vs. mirror finish), sliding speed (2, 5, 8 mm/s), total contact distance (20, 30, 180 cm), and additional mass placed on the product (30, 60, 90 g) to obtain different normal forces. After contact, Kimwipe® samples collected from the potato/stainless steel contact path were appropriately diluted and plated on modified trypticase soy agar to quantify Salmonella. Bacterial populations along the contact path were analyzed via a repeated measures statistical analysis.
Results: Greater transfer (P < 0.05) was seen to mirror-finished stainless steel. Overall, normal force did not significantly affect transfer, except at long contact distances; however, contact speed and distance impacted cumulative transfer (P < 0.05) for certain cases. For example, greater cumulative transfer (P < 0.05) occurred over 30 cm of contact at 5 mm/s than at 2 mm/s (420,000 vs. 190,000 CFU total).
Significance: Quantifying the effects of individual physical variables is critical to the future development of bacterial transfer models and the refabricating/redesigning of fresh-cut processing equipment and related produce-handling operations to minimize cross-contamination.