Do you have bagged salad in your fridge? Make sure you eat it up quickly – new research suggests the precut greens help salmonella grow and fester even when they’re refrigerated.
Just a small amount of damage to salad leaves, such as getting cut, is enough to stimulate bacteria to grow and multiply, especially when they’re stored in bags, according to new research out of the University of Leicester.
The British microbiologists behind the research suggest that juices released from the salad leaves help salmonella, making it even more virulent and likely to cause infection.
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“Salad leaves are cut during harvesting and we found that even microlitres of the juices – less than 1/200th of a teaspoon – which leech from the cut ends of the leaves enabled salmonella to grow in water, even when it was refrigerated. These juices also helped the salmonella to attach itself to the salad leaves so strongly that vigorous washing could not remove the bacteria, and even enabled the pathogen to attach to the salad bag container,” Dr. Primrose Freestone, the study’s lead author, said.
“Even a few salmonella cells in a salad bag at the time of purchase could become many thousands by the time a bag of salad leaves reaches its use by date, even if kept refrigerated,” Freestone warned.
Freestone said over the past few years, there’s been an increase in outbreaks tied to fresh salad produce contaminated with salmonella or E. coli in the United States and Europe.
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But they’re an issue in Canada, too: bagged salads, greens and other pre-cut produce are often subject to recalls.
Sprouts, such as alfalfa, radish and bean, are of utmost concern to Dr. Rick Holley, a University of Manitoba professor emeritus. He’s been working in the food sector since 1979 and still runs an active food safety program out of the Winnipeg-based school.
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When produce is chopped up for convenience, the juices in the fruits and vegetables aren’t compartmentalized anymore because their cell walls are broken. Now, bacteria can grow at room temperature as they mix and mingle.
“Vegetables and fruits are now given a shelf life in a processed state when they shouldn’t have any shelf life at all,” Holley said.
With sprouts, seeds can be contaminated with salmonella, E.coli, or listeria. They’re stored for days at a time, allowing the seeds to grow, but also giving room for bacteria to fester in the seeds’ moisture. It’s the “perfect broth” for foodborne illnesses.
“I do not eat sprouts, unless they’re cooked.”
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He eats the chopped salads from the grocery store, though.
“I’m confessing now that I accept the risk because I value the convenience,” he said.
If you’re chopping up vegetables and fruit, they’re safe to eat for about four hours if kept at room temperature. In the fridge, they can last for up to three days, he said.
Freestone’s full findings were published in the journal Applied and Environmental Microbiology.
carmen.chai@globalnews.ca
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