Purpose: Although current industry practice is to remove the slicer head for submersion in hot water, this practice must be validated for elimination of Listeria. In this study, effective thermal sanitization treatment parameters for mushroom disk slicers were determined.
Methods: A L. monocytogenes cocktail, which included strains isolated from mushrooms and environmental samples, was inoculated into trypticase soy broth with yeast extract (TSBYE) or attached onto stainless steel coupons for up to 7 days. Thermal death time curves were generated by immersing samples in a circulating water bath at 50, 60, and 70°C and surviving cells were enumerated by plating onto trypticase soy agar with yeast extract (TSAYE).
Results: Planktonic cells treated immediately after inoculation were the most heat tolerant (P ≤ 0.05) and were used to calculate D-values of 11.53 ± 0.36, 1.90 ± 0.04, and 0.99 ± 0.02 minutes, respectively. Complete inactivation times, evidenced by absence after enrichment, were 120, 20, 10 minutes, respectively. The theoretical cold spot within the slicer assembly, determined using numerical software (Comsol), was the inside surface of the spacers. This was confirmed by attaching thermocouples at locations within the slicer head, immersing it in a clean-out of-place (COP) tank filled with water at temperatures between 55 and 75°C, and monitoring temperatures using a data logger.
Significance: These results were used to validate thermal sanitization treatments for eliminating Listeria monocytogenes from mushroom disk slicers.