ARS | Publication request: Mathematical modeling the cross-contamination of food pathogens on the surface of ready-to-eat meats while slicing

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: April 1, 2009
Publication Date: September 8, 2009
Citation: Sheen, S., Hwang, C. 2009. Mathematical modeling the cross-contamination of food pathogens on the surface of ready-to-eat meats while slicing. 6th International Conference on Predictive Modeling in Foods, September 8-12, 2009, Washington, DC. p. 101.

Technical Abstract: The knowledge regarding food pathogens (Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella spp.) surface transfer on ready-to-eat (RTE) deli meat and the slicer used for slicing different RTE products are needed to ensure RTE food safety. The objectives of this study were to investigate and to model the surface cross-contamination of the commonly found food pathogens during slicing operation. A three to five-strain cocktail of each pathogen was inoculated directly onto a slicer’s round blade rim area at an initial level of ca. 4, 5, 6, 7, 8 or 9 log CFU/blade (ca. 3, 4, 5, 6, 7 or 8 log CFU/cm-squared of the blade edge area), and then the RTE deli meat (salami or ham) was sliced to a thickness of 1-2 mm. For another cross-contamination scenario, a clean blade was initially used to slice ham (or salami) which was pre-surface-inoculated with food pathogen (ca. 4, 5, 6, 7, 8 or 9 log CFU/100 cm-squared area), then, followed by slicing un-inoculated ham (or salami). Results showed that the developed empirical models were reasonably accurate in describing the transfer trend/pattern of each food pathogen between the blade and meat slices when the total inoculum level was large than or equal to 5 log CFU on the ham (or salami) or blade. With an initial inoculum level at equal to or less than 4 log CFU, the experimental data showed a rather random microbial surface transfer pattern. It was observed that there is a 2-log microbial count reduction between the inoculation and first several meat slices. The confocal microscopy study showed that a significant percentage of microbes died (killed) during slicing which may be due to the surface shear or friction. The models, i.e. a power equation or an exponential equation for direct-blade-surface or meat-surface-inoculation, are microbial load (the initial microbial inoculation/contamination level) and sequential slice index (the slice number in a continuous operation) dependent. When slicing rate is specified, the model can be further converted to a time-dependent function. The surface cross-contamination prediction of the three food pathogens for sliced deli meat (ham/salami) using the developed models were demonstrated. The empirical models may provide a useful tool in developing the RTE meat microbial risk assessment.