Scitech Daily
Leafy greens are valuable for their dietary fibre and nutrients, yet they may also carry dangerous pathogens. Lettuce, in particular, has frequently been linked to foodborne illness outbreaks in the U.S. A recent study from the University of Illinois Urbana-Champaign investigates the factors influencing E. coli contamination in five different types of leafy greens: romaine lettuce, green-leaf lettuce, spinach, kale, and collard greens.
“We are seeing a lot of outbreaks on lettuce, but not so much on kale and other brassica vegetables. We wanted to learn more about the susceptibility of different leafy greens,” said lead author Mengyi Dong, now a postdoctoral research associate at Duke University. Dong conducted the research as a doctoral student in the Department of Food Science and Human Nutrition (FSHN), part of the College of Agricultural, Consumer, and Environmental Sciences (ACES) at the U. of I.
Findings on Temperature and Leaf Surface Impact
The researchers infected whole leaves from each of the five vegetables with E. coli O157:H7 and observed what happened after storage at 4° C (39° F), 20° C (68° F), and 37° C (98.6° F). Overall, they found that susceptibility was determined by a combination of temperature and leaf surface properties such as roughness and the natural wax coating.
“At room temperature or higher, E. coli grows very fast on lettuce, but if lettuce is refrigerated at 4° C (39° F), we see a sharp decline in the E. coli population. However, for waxy greens like kale and collard, we get the opposite results. On these vegetables, E. coli grows slower under warmer temperatures, but if it is already present, it can survive longer under refrigeration.”
FoodWorld 