Berries as carriers of pathogens?
Frozen berries more heavily polluted
Whether fresh strawberries, frozen raspberries in summer drinks or blends of different berries on cakes and desserts - especially in summer berry fruit is eaten very often. Berries not only taste delicious, they also contain many vitamins, minerals and fibre. However, soft fruits can also be carriers of pathogens and contain residues of plant protection products, as shown by the results of various food monitoring investigation programmes. The Federal Office of consumer protection and food safety (BVL) recommends that fresh fruit should always be thoroughly washed and frozen foods heated before consumption.
Strawberries in particular can be contaminated to varying degrees with microorganisms due to their contact with the ground. In addition to germs that are harmless to humans, zoonotic agents can also reach the strawberries. Zoonotic agents are pathogens that are transmitted from animals to humans and can cause diseases in humans. The animals excrete some of these pathogens via the faeces, which leads to their spread in the environment and possibly to contamination of plant foods.
Microbiological load
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In order to estimate the contamination of fresh strawberries with zoonotic agents, a total of 825 samples of strawberries from agricultural holdings and retail outlets were tested for the presence of Salmonella spp., Campylobacter spp., Listeria monocytogenes and shigatoxin/verotoxin-forming Escherichia coli (STEC/VTEC) in 2013 as part of the zoonosis monitoring coordinated by the Federal Office of Consumer Protection and Food Safety (BVL). The results indicate that fresh strawberries pose only a low risk of human infection with zoonotic agents, as neither Salmonella nor STEC/VTEC were detected and only individual samples were contaminated with Campylobacter (0,3 % positive samples from retail) and Listeria monocytogenes (about 1 % positive samples from production and retail).
Viruses in frozen food
Frozen soft fruits are imported in large quantities and are used in particular for the production of products such as fruit yoghurt, jam, ice cream or bakery products. Frozen berries contaminated with hepatitis A viruses or noroviruses have repeatedly been the cause of food-borne outbreaks. In Germany, for example, in 2012, thousands of children and young people fell ill after eating frozen strawberries from China contaminated with noroviruses in their school meals. The incident subsequently led to increased controls on frozen strawberries imported into the EU from China.
Due to corresponding notifications in the Rapid Alert System for Food and Feed, frozen raspberries from Serbia have been increasingly checked for noroviruses when imported into the EU since October 2015. Serbia currently supplies more than 60% of the frozen raspberries imported into the EU (approx. 40,000 tonnes per year). The results of these increased controls show that frozen raspberries containing noroviruses should be imported again and again. Contamination with noroviruses can be caused, for example, by contaminated irrigation water, improper fertilisation and inadequate personal hygiene during harvesting and processing of the berries.
However, only one out of 432 samples of frozen raspberries of noroviruses and none of hepatitis A viruses were detected in the course of the zoonoses monitoring in 2017, which examined goods from the retail trade. Similar results were also achieved within the framework of the risk-oriented investigation programme Bundesweiter Überwachungsplan (BÜp) in 2015. Noroviruses had been detected in a sample of frozen strawberries from more than 150 examined samples of frozen strawberries. Hepatitis A viruses were not found in any sample. However, food tests for the presence of noroviruses and hepatitis A viruses are complicated and susceptible laboratory analyses, in which molecular biological detection is not always successful. False negative results are therefore not excluded.
Residues of plant protection products
Due to their popularity among consumers, strawberries are frequently tested for residues of pesticides by the official food monitoring authorities of the federal states. Over the past few years, there have been around 750 samples per year. Only in exceptional cases were excessive residues found, i.e. residues in excess of the current MRLs. In 2017, too high residues of plant protection products were found in 0.4 % of the samples examined, and in 2016 in 0.8 %. However, almost 90 % of the samples showed quantifiable residues of plant protection products. A good three quarters of the samples contained multiple residues with up to 17 different active substances. With organic strawberries, significantly fewer residues are detected: not even in every fourth sample. In no case has an MRL been exceeded.
The situation is similar for raspberries and blueberries. In recent years, between 120 and 260 samples have been tested for pesticide residues. In 2017, too high residues were found in blueberries and raspberries in 0.8 % of the samples examined (2016: blueberries 1.9 %, raspberries 1.5 %). Approximately two thirds of the raspberry and blueberry samples analysed showed quantifiable residues. In blueberries, multiple residues with up to 12 active substances were found in almost every second sample. In raspberries, even 65 % and 83 % of the samples examined showed multiple residues.
The residue situation is somewhat worse for currants and blackberries. A good 200 samples were examined in each case, 5 % to just under 10 % of which exceeded the MRLs. Residues of plant protection products were found in about 90 % of the samples. In most cases, these were multiple residues.
In addition, in 2016 a monitoring project was carried out to investigate whether the residue situation of frozen goods differs from that of fresh fruit and vegetables due to processing steps, post-harvest treatments and worldwide distribution channels. Four products of plant origin were examined as examples. These included frozen currants for which almost 100 samples were tested for pesticide residues. In contrast to the fresh product, 16.3 % of the samples examined, i.e. almost twice as many samples, showed 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 constitute a health risk for consumers. The maximum residue level refers only to the amount of pesticide residues that should not be exceeded if the product is used correctly. As a rule, health-based guideline values are only reached at much higher concentrations.
Tips for consumers
Due to the above-mentioned residues and possible microbiological contamination, it is recommended that fresh berries and other fruit be thoroughly washed before consumption in order to reduce the load accordingly. Since it has been proven that humans have already been infected, for example with viruses, by consuming frozen berries, it is recommended to heat them before using them in sweets, cakes or drinks in order to remove any pathogens that may be present. The Federal Institute for Risk Assessment (BfR) advises in particular sensitive consumer groups such as small children, elderly and immunocompromised people as well as pregnant women to consume frozen berries only sufficiently heated in any case.
Note: This article has been translated using a computer system without human intervention. LUMITOS offers these automatic translations to present a wider range of current news. Since this article has been translated with automatic translation, it is possible that it contains errors in vocabulary, syntax or grammar. The original article in German can be found here.
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Topic world Food safety
Food safety is at the heart of the food and beverage industry. It ensures that the food we eat every day is not only nutritious, but also free of harmful contaminants. From field to plate, the industry monitors and regulates every step of the process with strict quality controls, advanced testing methods and continuous research.
Topic world Food safety
Food safety is at the heart of the food and beverage industry. It ensures that the food we eat every day is not only nutritious, but also free of harmful contaminants. From field to plate, the industry monitors and regulates every step of the process with strict quality controls, advanced testing methods and continuous research.
