An evaluation of domestic refrigerator temperatures has led to an update of guidance on shelf-life studies.
Work by scientists at the French Agency for Food, Environmental and Occupational Health Safety (ANSES) prompted a revision in the reference temperature for calculating dates for ready-to-eat refrigerated foods. It takes into account temperatures observed in household refrigerators in 16 European countries and was set to help prevent foodborne infections caused by pathogenic bacteria, such as Listeria monocytogenes.
Keeping food at a low temperature slows the growth of microorganisms responsible for foodborne illnesses. It is recommended to set the temperature of the refrigerator to below 4 degrees C (39.2 degrees F).
A Europe-wide study by scientists from the Salmonella and Listeria Unit of the ANSES Food Safety Laboratory found the average temperature of domestic refrigerators in Europe is 6.4 degrees C (43.5 degrees F), and 95 percent of them are below 10 degrees C (50 degrees F).
Reasonable storage expectations
Producers of ready-to-eat foods are required to test the development of bacteria under conditions in which the food will actually be stored. This includes demonstrating that the concentration of Listeria monocytogenes will not exceed 100 colony forming units per gram (CFU/g) at the end of shelf life.
In the absence of data on domestic refrigerator temperatures, the European Union Reference Laboratory (EURL) for Listeria monocytogenes recommended simulating storage at 12 degrees C (53.6 degrees F) in consumers’ homes.
To obtain data to support these recommendations, the Salmonella and Listeria Unit analyzed the scientific literature from 2002 to 2020. Scientists reviewed the results of 17 studies and 10 national surveys conducted in 16 countries — 14 in the European Union, plus the United Kingdom, and Norway. Findings were published in the journal Food Microbiology.
Temperature variability for refrigerators studied primarily depended on age of the appliance, the thermostat setting, the frequency and duration of door opening, and the refrigerator’s occupancy rate.
Based on these results, the EURL recommends that operators use 10 degrees C (50 degrees F), which covers 95 percent of domestic refrigerators, as a benchmark for studying the shelf life of food with regard to the risk of listeriosis and other pathogenic bacteria. This new value has been included in the technical guidance document for shelf life studies for food producers to simulate the reasonably foreseen storage conditions in domestic refrigerators.
ANSES said this reference temperature for manufacturers should not be interpreted by consumers as advice to increase the temperature of their refrigerator. The lower the food storage temperature, the slower the growth of microorganisms and the lower the risk of infection. A temperature below 4 degrees C (39.2 degrees F) stops the growth of the majority of pathogens, particularly Salmonella, which is a major source of foodborne illness in Europe.
Plant picking advice
ANSES has also warned about the risk of confusion between edible and poisonous plants.
ANSES and Poison Control Centres repeated a warning of intoxications linked to the consumption of autumn crocus, which was confused with wild garlic. Between 2020 and 2022, 28 cases and two deaths occurred because of autumn crocus poisoning.
Poisonings occurred between March and May, mainly in the Grand Est and Auvergne-Rhône-Alpes regions. Half of the affected people used the leaves to make a pesto sauce. The other half had eaten them in salads, pan-fried them, or used them in a quiche.
Some people had prolonged symptoms such as persistent diarrhea or vomiting and four people showed severe, life-threatening symptoms including acute digestive, liver and hematological disorders. Severity of poisoning depends on the quantity of leaves ingested, the concentration of colchicine in the plant, and whether it is in combination with certain common drugs.
The flowers of autumn crocus, which are different from those of wild garlic or leek, only appear in autumn, after wild and many-flowered garlic. Autumn crocus leaves are stiffer and stemless, and its bulb is round and dark. Wild garlic is an edible wild plant, 15 to 40 cm high when mature. Its star-shaped flowers and elongated bulb are both white.
Recommendations include checking that each leaf has a garlic odor when rubbed; avoid gathering different types of plants together as toxic species could be mixed with edible ones, and take photographs of picked plants for easier identification in the event of poisoning.
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