University of California

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Fresh-cut quantitative microbial risk assessment: transfer during slicing and growth during transport

Ann Charles (Rutgers University), Elliot Ryser (Michigan State University) and Donald Schaffner (Rutgers University)

Salmonella, Escherichia coli O157:H7 and Listeria monocytogenes have been implicated in a number of outbreaks linked to fresh-cut produce. This presentation presents models for bacterial transfer during slicing and bacterial growth during transport for inclusion in a fresh-cut quantitative microbial risk assessment. Three separate scenarios are considered: (1) Transfer of Salmonella during tomato slicing considering four variables: slicing method, slicing temperature, blade thickness and moisture on the tomato before slicing. (2) Transfer of L. monocytogenes during onion slicing considering three different inoculation concentrations between 8.5 and 5.5 log CFU/onion. (3) Temperature data collected from sixteen tractor-trailer leafy green shipments over a 1-year period to model E. coli O157:H7 and Listeria monocytogenes growth. Temperature loggers were located in pallets at the front, middle and rear and along the sidewalls of each trailer. About 17% of the sensors used in the study recorded temperatures greater than 5 degrees C. Our results showed that the concentration of Salmonella and Listeria generally decreased logarithmically slicing. Because such a model would be difficult to incorporate into a QMRA, an alternative modeling approach considering transfer as a function the number of microorganisms remaining on the slicer was also investigated, and found suitable. Growth modeling results showed that L. monocytogenes growth was more likely than E. coli O157:H7 growth, but that no significant growth was the most likely occurrence. Prediction of Salmonella and Listeria transfer during onions and tomato slicing and E. coli O157:H7 and Listeria monocytogenes growth during transport of leafy greens appears complex but feasible.

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