P1-158 Effects of Physical Variables on Salmonella Transfer from Produce to Stainless Steel

Monday, August 4, 2014
Exhibit Hall D (Indiana Convention Center)
Beatriz Mazón, Michigan State University, East Lansing, MI
Bradley Marks, Michigan State University, East Lansing, MI
Lin Ren, Michigan State University, East Lansing, MI
Elliot Ryser, Michigan State University, East Lansing, MI
Introduction: Prior work has suggested that bacterial transfer from produce to contact surfaces during slicing is affected by surface roughness, relative contact speed, distance, and normal force. However, mathematical models of these relationships have not been well developed, as prior studies typically tested overall transfer results, but did not elucidate single-variable effects.

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.