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Are raw mushrooms toxic ?

It is often advised to cook the common white mushroom (Agaricus bisporus) before use, as raw mushrooms are considered toxic.

There are two reasons why it is advisable to cook raw mushrooms.

The common white mushroom contains a number of potential toxic substances, such as agaritine (figure A; (beta-N-(gamma-L-(+)-glutamyl-hydroxymethylphenylhydrazine), a derivative of glutamic acid (one of the common amino acids, the building blocks of proteins). On average, mushrooms contain about 15 mg agaritine per kilogram.

Agartine was found to be carcinogenic in mice, and is thus a suspected carcinogen for humans. More recent research, however, indicates that the risk for humans is very low. A daily intake of 10 grams of mushrooms would not result in a measurable increase in the incidence of cancer among the population.

In the liver agaritine is broken down to glutamic acid and hydrazine (figure B). The hydrazine is responsible for the carcinogenic properties of agaritine. As agaritine is not heat-stable, heating mushrooms (boiling, frying) further reduces the potential risk.

Agaritine (A) and hydrazine (B)

The second reason to heat mushrooms is to kill potential pathogenic bacteria. Mushrooms are commonly cultivated on horse manure. The manure is generally sterilised before use, but it is still a very rich medium for bacterial growth. There is thus a considerable risk for pathogenic bacteria to be present on raw mushrooms. Cooking (or frying) destroys the bacteria (including the potential pathogens) on the surface of the mushrooms.