Since childhood, most people have held the belief, often repeated, that leafy greens (aka “salads”) are the healthiest choice in food. And while there is a great deal of truth to this, from a certain point of view, leafy greens are also a common conduit for food borne illness pathogens like Salmonella, E. coli, Campylobacter, Listeria, certain viruses like hepatitis A, and parasites, like Cyclospora. But recent research has also noted that the propensity to contain or carry such pathogens is not equal among the common leafy greens. In fact, one particular leafy green, romaine lettuce, seems to have been at the heart of a number of significant e. coli outbreaks in recent years while a number of its cousins have had a “clean” record during the same time-frame.
Interestingly, this is not mere chance. In fact, in a recent study out of the University of Illinois Urbana-Champaign, researcher Mangyi Dong discussed the roll of leafy greens in the spread of e. coli and noted some significant differences. First off, there is the simple fact that leafy greens like kale (or other brassica vegetables such as cauliflower, broccoli, and cabbage), are much less likely to carry e. coli than romaine lettuce, statistically speak. But in this study the researchers wanted to know why. To answer this question, they conducted an experiment. The elements of the experiment were as follows:
- Study concerned E. coli O157:H7, the most common strain of Shiga-toxin producing E. coli linked to outbreaks in the U.S.
- Five distinct types of whole leaves of five different vegetables were used in the study.
- The leaves were maintained at three different temperatures: Refrigeration, or 4°C (39°F); Room temperature, or 20°C (68°F); and Warm temperatures, or 37°C (98.6°F).
- Significant differences included both the surface of the leaves (roughness) and any natural wax coating.
- Both the roughness and wax coating turned out to be significant factors in E. coli O157:H7 bacterial growth.
When the results came in, the findings pointed to several interesting realities:
- As expected, warmer temperatures were correlated to increased E. coli O157:H7 bacterial growth.
- When the lettuce leaves were maintained in refrigeration, or cold at 4 °C (39°F), there was a significant reduction (slowing) in E. coli O157:H7 bacterial growth.
- The “waxy” greens, like kale and collard, saw significant reductions in E. coli O157:H7 bacterial growth, BUT, E. coli O157:H7 bacteria survived longer when these leaves were refrigerated.
- Cutting leaves releases juices. Spinach, kale and collard juices actually inhibit E. coli O157:H7 bacterial growth.
The study also reaffirmed a few facts that were already well-established:
- Washing lettuce can reduce, but does not eliminate, E. coli O157:H7 bacteria.
- Kale and other “waxy” vegetables re less likely to have E. coli O157:H7 bacteria on them in the first place.
- Kale and collard greens are often cooked, which is a “kill step” rendering them safe to eat even when contaminated with E. coli O157:H7 bacteria.
- Leafy greens like romaine and other “lettuce” are nearly always eaten raw, increasing the likelihood of infection.
According to one national food safety attorney:
“this research both supports ‘old knowledge’ and added new and fascinating findings for food safety experts seeking to make food safe in the U.S. Every day, through research like this, we get closer adn closer t ensuring that our food supply is disease adn pathogen free!”
Food Poisoning Lawyer Ron Simon
The key take-aways in this research, for the average consumer include:
- Wash all leafy greens well; and
- Keep them refrigerated!”
