Purpose: To investigate the transfer of Listeria monocytogenes (cross-contamination) during slicing of Ready-to-Eat roast beef.
Methods: Experiments were carried out with Ready-to-Eat roast beef pieces purchased in local supermarkets and checked for the absence of Listeria monocytogenes using the ISO 11290-2:1998 method. To start, a meat matrix was created in a manual meat slicer by slicing a L. monocytogenes-negative piece of roast beef. Another piece of roast beef was experimentally contaminated with L. monocytogenes by immersion in a suspension containing 8 log CFU/ml of the pathogen and sliced, causing the experimental contamination of the slicer. Subsequently, new pieces of non-contaminated roast-beef were sliced, until 200 slices were obtained. To assess the extent of the pathogen transfer (cross-contamination), counts of L. monocytogenes were carried out in the first slice, in every 5th slice up to the 50th slice and in every 10th slice up to the 200th slice. The experiment was repeated three times.
Results: Average counts of L. monocytogenes in first cross-contaminated slice were 4 log CFU/g and remained the same up to the 25th slice. After the 30th slice, a long tailing effect was observed until the 105th slice, with counts around 2 log CFU/g. From the 110th slice, counts of L. monocytogenes were below the detection limit (< 10 CFU/g)
Significance: The study demonstrated that careless handling of slicing machines can result in cross-contamination of Ready-to-Eat products, to an extent that can hazardous for the consumer.