Lethality of Moist Heat and Silver Dihydrogen Citrate Sanitizer Combinations on Listeria Strains Adhered to Components of a Deli Meat Slicer

Introduction: Deli meat slicers have been implicated in cross-contamination of ready-to-eat (RTE) foods with Listeria monocytogenes that has resulted in several listeriosis outbreaks. We investigated the lethality of moist heat and silver dihydrogen citrate (SDC) sanitizer on Listeria strains that were inoculated on stainless steel (SS) and cast aluminum (AL) coupons cut from actual components of a deli meat slicer. 

Purpose: Combined effect of sanitizers and thermal treatment could provide better control of Listeria monocytogenes on food contact surfaces.

Methods: The coupons inoculated with Listeria strains were subjected to treatments inside and outside of meat slicer using a commercial bread proofer oven that was operated for 7 h at 66°C. Post treatment recoveries of the inoculated Listeria from the treated coupons were enumerated using MOX growth medium. 

Results: All treatments produced significant (P = 0.05) reductions compared with positive and untreated negative controls. Moist heat reduced the inoculated strains to non-detectable levels when the coupons were placed inside the motor compartment of the slicer and the sanitizer plus moist heat gave same results for the coupons placed inside and outside of the slicer. Chemical sanitizer treatment alone showed average log reductions of around 5 CFU/cm² on AL and SS coupons, respectively, and the moist heat alone treatment on both AL and SS coupons showed a log reduction of 4.49 and 4.87 logs when placed externally and above 6 logs when placed inside the motor compartment. Sanitizer plus moist heat treatments showed highest log reductions of Listeria strains to non-detectable levels on deli meat slicer components when placed inside or outside the motor compartment of the slicer.

Significance: The sanitizer and moist heat combination treatments can effectively reduce the Listeria cells attached to food contact surfaces of a deli meat slicer.