In Summary
- Slicing seems to have a negative influence on the shelf-life of cold smoked salmon. The hypothesis being that slicing increases the surface area, meaning more of the finished product is exposed. In addition, more slicing damages more cells of the fish, releasing nutrients for bacteria to use for growth.
- Slicing equipment has a high risk of spreading L. monocytogenes contamination from one fish fillet to another. In addition, slicing blades are at risk from developing L. monocytogenes biofilms, which can then contaminate the fillets they slice.
- Slicing equipment should be cleaned and sanitised regularly to prevent this.
The cutting and slicing of fish fillets have been shown to have a negative influence on the shelf-life of cold smoked salmon. Whole cold-smoked fillets had a significantly longer shelf-life compared with sliced cold smoked salmon (Hansen et al. 1998). This observation may be explained as whole fillets had less processing and there was less opportunity for contamination compared with sliced salmon. In addition, there was a lower surface area to volume ratio for the whole fillets with less damaged fish cells providing potential nutrients for microbial growth on the flesh surfaces (Hansen et al. 1998).
Aarnisalo et al. (2007) undertook work to estimate the numbers of L. monocytogenes transmitted from a slicer blade to fish and from contaminated fish to another slicing machine. A slicing blade that was contaminated with 6-9 log cfu/g of L. monocytogenes initially transferred high numbers of cells up to 5.3 log cfu/g to the first few fish slices. However, after these four slices, the numbers of cells transferred dropped rapidly. A predictive mathematical model extrapolating from the numbers of cells transferred initially, determined that after 39 slices had been cut; the number of L. monocytogenes cell transferred would typically be around 1.6 log cfu/g of slice. When fillets were contaminated with 7.6 log cfu/fillet were cut using an uncontaminated slicer and uncontaminated fillets were subsequently cut, 1.5 log cfu/g slice was predicted to be present on the un-inoculated fillets after 39 slices. Aarnisalo et al. (2007) advised that to minimise contamination from unsanitary slicer blades, processors could discard the first few slices of fish from each new fillet. From a food safety viewpoint, a much better approach is to aim to process using only sanitary equipment. Consequently, Aarnisalo et al. (2007) advised that slicing equipment and blades should be hyperlink to cleaned and sanitised page regularly (i. e. every few hours) to prevent the attachment and establishment of L. monocytogenes biofilms on the slicer surfaces (Aarnisalo et al. 2007). Strategies for the effective decontamination of equipment harbouring L. monocytogenes biofilms are available – decontamination using heat and decontamination using chemicals.
