A new study shows that fluctuating temperatures during transportation, in the back room at the store and on the shelves leads to pathogen growth and diminishes the quality of salads.

The study, published in the February Journal of Food Protection, looked at the growth of E. coli O157:H7 and Listeria monocytogenes in packaged fresh-cut romaine mix at fluctuating temperatures during commercial transport, retail storage and display.

Over a 16-month period, a series of time-temperature profiles for bagged salads were obtained from five transportation routes covering four geographic regions, as well as during retail storage and display, according to the study.

Five time-temperature profiles were collected during two to three days of transport, one and three days of retail storage, and three days of retail display. Pathogens in the samples were then duplicated in a programmable incubator to assess E. coli O157:H7 and L. monocytogenes growth in commercial bags of romaine lettuce mix, according to the abstract.

“Based on the simulation, both pathogens generally increased during transport, storage and display,” the authors said. “However, retail storage duration can significantly impact pathogen growth.”

Researchers said they believe the data gathered will be useful in measuring food safety risk.

“This large-scale U.S. study — the first using commercial time-temperature profiles to assess the microbial risk of leafy greens — should be useful in filling some of the data gaps in current risk assessments for leafy greens,” the authors said in the abstract.

Study results can be found online