Drying is a popular way of preserving mushrooms, but what about the safety

Although Czechs are a nation of mushroom pickers, dried mushrooms, chanterelles, Judas ear or shiitake are a regular item in the shops. In the latest test, dTest examined the quality of these goods and the presence of undesirable substances. Together with products from the shops, the consumer organisation also tested three samples of home-grown dried mushrooms. Expectations that the mushrooms were a cocktail of pesticides and heavy metals were not entirely confirmed.

The popularity of mushrooms is high in the Czech Republic. It is not surprising that shops and e-shops offer them in dried form on a regular basis. The dTest tested a total of ten types of dried mushrooms, five of which were forest mushrooms typical of the Czech Republic and the other five were mushrooms used in Asian cuisine. For interest, three samples of home-dried mushrooms from the Lusatian Mountains, Pošumava and Liberec were added to the test. “We were checking whether the mushrooms are sufficiently dried and whether they harbour moulds or their poisonous products – mycotoxins. We were also interested in the extent to which health-damaging heavy metals are present in the mushrooms. For commercially available mushrooms, we looked for pesticides or sulphur dioxide, which is sometimes used to treat mushrooms to prevent darkening,” says Hana Hoffmannová, editor-in-chief of dTest magazine.

Drying is a popular way to preserve mushrooms. During the drying process, 80 to 90% of the water evaporates from the mushrooms, and the weight of the mushrooms is reduced by the same proportion. For packaged dried mushrooms that can be bought in shops, the Decree prescribes a maximum moisture content of 12 %. In terms of moisture, the mushrooms tested had no problem, although two Judas ears (Golden Turtle Brand Black Fungus and Holoubek & Great Grandchildren Black Fungus) only just fit the limit.

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The presence of fungi was assessed by the number of colony-forming units found. The more there were, the lower the products received a grade. “The best performing mushrooms were the Holoubek & great-grandchildren Spruce mushroom, where we found only in the order of tens of these colonies per gram. Satisfactory marks went to the mushrooms Metro Chef Forest Mix from Makro and Holoubek & great-grandchildren Black Mushroom,” says Hana Hoffmannová and adds: “This part of the test generally went well, we found no toxigenic moulds that have the ability to produce poisonous substances, nor mycotoxins that persist in food even after the mould itself is destroyed.”

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The more interesting findings came from the heavy metal portion of the test. It examined the presence of arsenic, cadmium, lead, mercury, copper and chromium. The measured values were then assessed according to the now-expired Decree No 298/1997 Coll., which set limits for individual heavy metals in mushrooms. Today, the limits apply only to selected species of freshly grown mushrooms and concern only lead and cadmium. Only two products scored well in the test. More than half of the products tested failed mainly because at least one of the elements tested was close to the permissible limit under the Decree. Home-dried mushrooms were also subjected to this part of the test. The result? The cadmium content was particularly problematic. The sample from the Lusatian Mountains exceeded the former decree limit by almost 100% and the samples from the Pošumava and Liberec regions were at ¾ of the limit.

When it came to the presence of pesticides, the situation was more complicated. There are legal limits for individual pesticide substances, but these apply to fruit and vegetables. “In the case of mushrooms, the maximum level of pesticides is set only for fresh mushrooms. We therefore recalculated the values found and took into account whether the mushrooms were forest or cultivated,” explains Hana Hoffmannová. Almost all samples contained residual amounts of pesticides. The exception was the Holoubek & great-grandchildren shiitake, which did not contain any of the substances examined. On the other hand, the product Makro/Metro Chef Forest Blend was measured to have levels above the maximum limit even after taking into account the uncertainty of the measurement.

The focus of the laboratory test was to verify the presence of sulfur dioxide, an allergen that must be prominently displayed on food packaging. It is also an antioxidant that is used to treat food to prevent it from darkening and the spread of microorganisms. Among the mushrooms tested, there were two (Czech Asian Blend and Diamond Shiitake) that mentioned sulphur dioxide in their ingredients. However, analyses did not show its presence in the dried mushrooms.