Danger! Frozen berries can contain hepatitis A viruses or noroviruses

Norovirus and hepatitis A infections are possible!

Every summer we receive inquiries as to whether this is really true! Yes, because berries are in peak season in summer and yet many people want to enjoy berries all year round in the form of frozen berries. Last year, the Federal Office of Consumer Protection and Food Safety (BVL) warned that frozen berries could be contaminated with pathogens such as noroviruses or hepatitis A viruses.

Strawberries in particular can be contaminated with microorganisms to varying degrees due to their contact with the soil. In addition to germs that are harmless to humans, zoonotic pathogens can also get onto strawberries. Zoonotic pathogens are pathogens that are transmitted from animals to humans and can cause illness in them. The animals excrete some of these pathogens in their feces, which leads to their spread in the environment and, under certain circumstances, to contamination of plant foods.

Microbiological contamination of frozen berries

In order to estimate the contamination of fresh strawberries with zoonotic pathogens, a total of 825 samples of strawberries from agricultural producers and retailers were tested for the presence of Salmonella spp. , Campylobacter spp. , Listeria monocytogenes and shigatoxin/verotoxin-producing Escherichia coli (STEC/VTEC). The results indicate that fresh strawberries pose only a low risk of human infection with zoonotic pathogens, as neither Salmonella nor STEC/VTEC were detected and only individual samples were found to contain Campylobacter (0.3% positive samples from retail outlets) and Listeria monocytogenes (around 1% positive samples from producers and retailers) were contaminated.

Viruses in frozen food

Frozen soft fruit is imported in large quantities and is used particularly for the production of products such as fruit yoghurt, jam, ice cream or baked goods. Frozen berries contaminated with hepatitis A viruses or noroviruses have been the cause of foodborne illness outbreaks on several occasions. This was the case in Germany in 2012, when thousands of children and young people fell ill after eating frozen strawberries from China that were contaminated with norovirus in their school meals. The incident led to increased controls on frozen strawberries from China imported EU

checked for noroviruses EU since October 2015 Serbia currently supplies more than 60% of the frozen raspberries imported into the EU (around 40,000 tonnes per year). The results of these increased controls show that frozen raspberries that contain noroviruses are repeatedly being imported. Causes of contamination with noroviruses can be, for example, contaminated irrigation water, improper fertilization and poor personal hygiene when harvesting and processing the berries.

However, as part of the 2017 zoonoses monitoring, in which retail goods were examined, noroviruses were only detected in one of 432 samples of frozen raspberries and hepatitis A viruses were not detected in any samples. Similar results were also achieved as part of the risk-oriented investigation program Federal Monitoring Plan ( BÜp ) in 2015. There, noroviruses were detected in a sample of frozen strawberries out of more than 150 frozen berry samples examined. Hepatitis A viruses were not found in any samples. However, testing food for the presence of noroviruses and hepatitis A viruses is a complicated and error-prone laboratory analysis in which molecular biological detection is not always possible. False negative results cannot therefore be ruled out.

Residues of pesticides

Due to their popularity with consumers, strawberries are often tested for pesticide residues by the official food control authorities of the federal states. In recent years there have been around 750 samples per year. Excessive residues, i.e. residues above the applicable maximum residue levels, were only found in exceptional cases. In 2017, excessive residues of pesticides were detected in 0.4% and in 2016 in 0.8% of the samples examined. However, almost 90% of the samples contained quantifiable pesticide residues. A good three quarters of the samples contained multiple residues with up to 17 different active ingredients. Significantly fewer residues are detected in organic strawberries: not even in every fourth sample. In no case was a maximum residue level exceeded.

The situation is similar with raspberries and blueberries. In recent years, between 120 and 260 samples have been examined for pesticide residues. For blueberries and raspberries, excessive residues were found in 0.8% of the samples examined in 2017 (2016: blueberries 1.9%, raspberries 1.5%). Around two thirds of the raspberry and blueberry samples examined showed quantifiable residues. In the case of blueberries, multiple residues with up to 12 active ingredients were found in almost every second sample. In the case of raspberries, 65% and 83% of the samples examined showed multiple residues.

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The residue situation for currants and blackberries is somewhat worse. A good 200 samples were examined, of which 5% to almost 10% exceeded the maximum residue levels. Residues of pesticides were found in around 90% of the samples. In most cases there were multiple residues.

In addition, a monitoring project in 2016 investigated whether the residue situation of frozen goods differs from fresh fruit and vegetables due to processing steps, post-harvest treatments and global distribution channels. Four products of plant origin were examined as examples. These include frozen currants, for which almost 100 samples were examined for pesticide residues. In contrast to the fresh produce, 16.3% of the samples examined, i.e. almost twice as many samples, had excessive residues of pesticides. The origin of the berries could not be determined for the majority of the samples examined, as there is no legal obligation to provide this information.

Exceeding the maximum level does not equate to a health risk for consumers. The maximum residue level refers only to the amount of plant protection product residues that should not be exceeded if the product is used correctly. As a rule, health-based guidelines are only achieved at much higher concentrations.

Tips for consumers

Due to the residues mentioned and possible microbiological contamination, it is recommended that fresh berries and other fruit be washed thoroughly before consumption in order to reduce the contamination accordingly. Since it has been proven that human infections, for example with viruses, have occurred through the consumption of frozen berries, it is recommended to heat them before using them in desserts, cakes or drinks in order to remove any pathogens that may be present. The Federal Institute for Risk Assessment ( BfR ) advises particularly sensitive consumer groups such as small children, older people, people with weakened immune systems and pregnant women to only consume frozen berries when they are sufficiently heated.

Source: BVL
Article image: Shutterstock / By Ankomun711