Specifically, the study began with an analysis of randomly selected transportation data from industry partners to determine crucial variables that would affect raw leafy greens during forward processing. The researchers also collected new temperature, humidity, and barometric pressure data from romaine lettuce source- and forward-processing facilities. Samples were also collected from freshly harvested lots of romaine that were source- and forward-processed at different facilities, both before the goods’ shipments to the processing facilities and after their arrivals.

The romaine samples were examined for product quality, and were assayed to determine overall microbial load present on the lettuce. Significantly, a larger overall microbial load was measured on the forward-processed romaine; however, after a laboratory experiment in which romaine was inoculated with E. coli O157:H7 and stored under conditions simulating source and forward processing, the researchers found that slightly less pathogens survived under forward-processing conditions than source-processing conditions.

The fact that the microbial growth observed on forward-processed leafy greens was not reflected in the behavior of E. coli under corresponding laboratory conditions suggests to Dr. Nou that lettuce microbiome plays a role in foodborne pathogen growth (or lack thereof). Future analysis is required to better understand the microbial dynamics on leafy greens.

Dr. Nou was joined on the project by co-investigators Yaguang Luo, Ph.D. and Patricia Millner, Ph. D. from USDA-ARS, as well as Shirley Micallef, Ph.D. from the University of Maryland. The project was funded by CPS, and its findings will be presented at the 2024 CPS Research Symposium, taking place June 18–19 in Denver, Colorado.