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21.06.2019

Ready-made salad: a hotbed for germs

Pre-packaged salads and sprouts are often microbially contaminated. This is the result of a recent study by the Max Rubner Institute. Unprocessed products, however, came off well.

Gurken und Karotten sind mikrobiologisch unbedenklich.
Cucumbers and carrots pose no microbiological risk.
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stevepb/Pixabay; CC0

In 2011, a scandal shook the food industry: In Germany, around 4,000 cases of infection with EHEC, the enterohaemorrhagic bacterium Escherichia coli, occurred, and a quarter of these cases were particularly severe. 53 people died. Contaminated sprouts were identified as the cause of the EHEC outbreak. Scientists at the Max Rubner Institute (MRI), the Federal Research Institute for Nutrition and Food, have now investigated the extent to which vegetables and salads are currently microbially contaminated. The results vary greatly, but reveal a major problem.

Problems with ready-made salads and sprouts

The MRI researchers have investigated around 600 fresh herbal products from supermarkets in northern and southern Germany over a period of three years. The results for ready-to-eat mixed salads were alarming: 42% of the samples were above the level recommended by the German Society for Hygiene and Microbiology for microbial contamination. 9% of the samples even exceeded the higher safety levels for Bacillus cereus and 22% of the samples those for to moulds. B. cereus produces food poisoning by toxic substances, and a subgroup of the bacterium can cause a anthrax-like disease.

These results are particularly worrying as ready-to-eat products are not re-washed and thus freed from some of the germs, the scientists warn. In the case of sprouts, they also found that every ninth sample exceeded the safety level for B. cereus. In a communication on their final report, the researchers summed up: "Since the safety level for presumtive Bacillus cereus was exceeded in some ready-to-eat mixed salads and sprouts, a health hazard for consumers cannot be ruled out".

Cucumbers, carrots and mushrooms are safe

Herbs were also found to be highly contaminated with microorganisms in the study, but no pathogenic germs were found. The picture is similar for lettuce: Although there is a certain bacterial load, only a few germs are problematic for humans. Additionally, the number of germs is likely to decrease significantly before consumption as a result of washing. Carrots and edible mushrooms showed very good test results. With cucumbers, there were no objections at all.

The MRI researchers suspect that the reason for the high germ contamination may have been overly long and warm storage conditions. They recommend never eating sprouts raw, but rather blanching them, and storing ready-to-eat mixed salads only briefly and at less than four degrees Celsius and consuming them directly after opening the packaging.

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