Non-edible, toxic mushrooms found in food products

A study has found that dried, canned, frozen and freeze-dried mixed mushroom products sold for cooking purposes often contain species that are not on the label, sometimes including non-edible and toxic types.

Researchers from various groups used a genetic technique known as metabarcoding – which combines next-generating sequencing and DNA barcoding – to look at the species of macrofungi, microfungi and bacteria present in dozens of mushroom products bought in Italian supermarkets.

While the toxic and non-edible species DNA was found in low quantities – likely too low to pose a risk to human health, according to the scientists – the results also showed that around 40 per cent of the samples did not match what was on the label.

That could suggest “voluntary substitution” and, potentially at least, the deliberate adulteration of pricey wild mushrooms with cheaper edible cultivated species to inflate profits in a form of food fraud.

 DNA barcoding tools are available to test mushroom products but according to the team are not widely used, perhaps because mushrooms have always represented a relatively small part of the commercial food supply.

Meanwhile, an earlier study by the same group, published last year, estimated that the mislabelling rate using DNA barcoding alone was less than 3% out of a sample of 71 supermarket-bought products. That study also found signs of potentially deliberate mislabeling as well as the presence of inedible pathogens that could suggest poor attention to good hygiene and manufacturing practices.

“More targeted molecular tools should facilitate the authentication of mushroom-based products not only to protect consumers from possible fraudulent practices, but also from potential health risk,” they write in a paper published in the journal Food Control.

Their method – based on a protocol developed by Illumina but adapted to take into account the varying properties of the mushroom products sampled – could also be used to partially trace the origin of mushroom products by looking at contaminant DNA as well as investigating and authenticating what is on the label, they suggest.

The research was supported by the Italian Ministry of Health and the University of Pisa.

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