Leafy greens showdown: Understanding E. coli risks and storage tips

In the study, the leaves of each vegetable were infected with the E. coli bacteria. Afterwards, they were stored at 4°C, 20°C, and 37°C. Analysis showed that the susceptibility to contamination depends on a combination of temperature and leaf surface characteristics, such as roughness or a natural waxy layer.

As a rule, leafy cabbage and kale were found to be less susceptible to contamination with E. coli bacteria than lettuce. What's more, even if cabbage and kale get contaminated, the bacteria will be removed during the standard thermal processing of these vegetables.

It’s a different story with lettuce, as it is usually consumed raw. Although washing lettuce can help reduce bacteria, it is not always capable of completely removing them.

At room temperature or higher, E. coli rapidly multiplies on lettuce. Meanwhile, storing lettuce at 4°C significantly limits the growth of bacteria. The situation is different for waxed vegetables, like kale or leafy cabbage, where E. coli develops more slowly at higher temperatures but in the cold, it can survive longer — explains Mengyi Dong, lead author of the study.

The study's authors also infected the chopped leaves of the aforementioned vegetables with E. coli bacteria. “Chopped leaves behave differently than whole ones. They release nutrient-rich juice, which facilitates the multiplication of bacteria,” explains Mengyi Dong.

The scientists proved that the juice extracted from spinach, kale, and leafy cabbage has antibacterial properties that are effective against E. coli. They also showed that the lysate from kale and leafy cabbage applied to lettuce leaves can be a natural antibacterial agent.

This could open up new possibilities in controlling food contaminations with pathogens.