Use of a Moist-heat Bread Proofer for Thermal Inactivation of Listeria on Deli Slicers

Risk assessments have identified ready-to-eat deli meats sliced at the retail level as one of the categories at highest risk of being contaminated with the foodborne pathogen Listeria monocytogenes. The deli slicer can harbor L. monocytogenes on food contact surfaces of the slicer blade, food chute or base and potentially in the motor compartment. Objectives of this study were to determine (1) whether a moist heat treatment can cause a significant reduction of L. monocytogenes inoculated onto aluminum and stainless deli slicer components and (2) whether the deli slicer would remain fully operable after repeated moist thermal treatments. A bread proofer with controlled relative humidity (RH), operated at 65 degree C for 7 hours, achieved a 5-log reduction of a cocktail of L monocytogenes inoculated onto the deli slicer metal surfaces. The RH in the interior of the proofer was maintained at 95% for 45 min, and subsequently at below 10% RH within 2 h, to dry out the electrical components and minimize any potential damage to the slicer. The motor and motor components were not damaged when subjected to repeated moist and dry heat cycles. It should be noted that these cultures were suspended in a laboratory medium. Such media are not representative of the high-fat and high-protein material normally found as contamination on a deli slicer, which would experience considerably less inactivation of L. monocytogenes than we report in this study. Future studies will utilize a slurry of turkey-based luncheon meat that will more accurately represent contamination occurring in commercial settings.