May 28, 2023
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Danger of salmonella from packaged salads

The packaged salads we buy in supermarkets should be eaten as soon as possible, according to British microbiologists from the University of Leicester who write in the journal Applied and Environmental Microbiology that they pose a risk of bacterial spread, even if left in the refrigerator.

The researchers’ analysis showed that the liquid environment of the refrigerator in combination with the components of the vegetables that leak from the cut leaves cause the growth of bacteria, including salmonella, which is dangerous to health.

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The scientists said they were surprised by the way the bacteria reproduced even in the refrigerator.

Vegetables are a healthy food but they are often involved in food poisoning epidemics because they can contain a variety of bacteria. That is why experts say that they should be washed well before consumption. The study suggests that placing vegetables in bags aggravates the problem when they are cut into smaller pieces due to the moisture that the bag collects. The cut pieces allow their juices to escape from the vegetables and this causes moisture and the growth of bacteria in the environment of the bag.

“It creates a nutritious cocktail in which bacteria can reproduce,” said study leader Dr. Primrose Freestone.


The study showed that an initial infection of vegetables with 100 salmonella bacteria could turn into a colony of 100,000 bacteria within five days in the refrigerator.

This amount “is enough for more than one person to suffer from food poisoning, while the initial amount is harmless,” Freestone stressed. She added that she was pleasantly surprised by how well the bacteria survive in the cold environment of the refrigerator and especially at 4 degrees Celsius.

Research has shown that the salmonella bacterium grows particularly well in packaged and chopped spinach, while coliform (e.coli) prefers rocket leaves. The juices that escape from the chopped vegetables help the salmonella to spread to the leaves of the vegetables so much that even persistent washing with soap can not remove the bacteria that also stick to the bag.

All this shows that we should eat packaged salads as soon as possible and not store them in the refrigerator for a long time. According to experts, we should buy ready-made salads with as long an expiration date as possible and with coarser leaves. Also do not eat salads when the bag is inflated with air.

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