Simulation of Time and Temperature as a Public Health Control for Food Served during Field Trips

Field trips present a challenge to school nutrition programs to provide a nutritious meal that is stored and handled properly to ensure food safety. During a field trip, coolers containing sack lunches might remain on school buses for extended periods of time, without temperature regulation, resulting in a potential food safety hazard. This study was designed to investigate this concern by monitoring changes in Salmonella and Listeria monocytogenes populations on turkey sandwiches, sliced apples, and baby carrots subjected to simulated field trip conditions. Inoculated products were packaged into individual sack lunches and packed into two coolers: a cooler with no ice and a cooler with one layer of ice on the bottom. These coolers were subjected to conditions simulating those in a school bus on a day with elevated temperatures. Thermocouple data collected from both coolers indicate that temperatures were conducive to foodborne pathogen growth. However, L. monocytogenes and Salmonella populations did not significantly (P > 0.05) increase during the 5-hour simulation. These data suggest that establishing time (< 5 hours) as a public health control may reduce risk of Salmonella and Listeria monocytogenes growth in deli sandwiches, apple slices, and baby carrots stored in coolers during field trips.