A Simulation Study to Evaluate the Microbiological Safety of School Lunches Stored in Insulated Coolers during Field Trips

Introduction: Field trips, often during warm weather seasons, present a food safety challenge for school nutrition programs, as providing a nutritious meal that has been stored and handled properly until serving may be difficult. Sack lunch meals are often stored in insulated coolers that accompany students on the field trip. The coolers are commonly stored on school buses, which are not temperature regulated, and may pose a risk to food safety.

Purpose:  Understanding foodborne pathogen growth in school lunch meals that have been packaged in insulated coolers, transported on field trips, and exposed to elevated environmental temperatures prior to serving was the purpose of this research.

Methods:  Turkey sandwiches, baby carrots, and sliced apples were inoculated with Listeria monocytogenes or Salmonella spp., packaged into sack lunches, and arranged in a cooler with no ice packs, or a cooler with one layer of ice packs on the bottom. Packed coolers were placed in a commercial smokehouse and subjected to a five-hour program that simulated temperature increases within a school bus on a hot day. Product samples were analyzed by direct selective plating to quantify changes in initial pathogen levels after the applied storage treatment.

Results:  Thermocouple data from both coolers indicate that food products were subjected to temperatures conducive for foodborne pathogen growth (top layers reaching up to 32°C after 5 h). However, no pathogen growth was observed during the five-hour storage simulation in any food product in either cooler packing scenario (P>0.05).

Significance:  Although sandwiches, carrots, and apple slices were subjected to temperature abuse in both cooler packing scenarios, pathogen populations did not increase during the five-hour simulation. Therefore, storage time as a public health control is effective for preventing foodborne pathogen growth on these products.