Chemistry of Mushrooms

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Today’s post is an excerpt from the Compound Interest book, “Why Does Asparagus Make Your Wee Smell? & 57 Other Curious Food & Drink Questions”. The book is now available to purchase, both from online retailers such as Amazon and in UK bookstores. If you’re not in the UK, it’s worth noting that the Book Depository offers free shipping to a large number of countries!

There’s a reason that it’s strongly recommended not to pick wild mushrooms unless you’ve had training in recognising the different types; some mushrooms containing deadly toxins can look almost identical to those that are perfectly safe to eat. Of the various types of mushroom toxins, those which cause the greatest number of deaths are the amatoxins and orellanine.

The sinisterly named ‘Death Cap’ and ‘Destroying Angel’ mushrooms both contain amatoxins. The amatoxins are a family of structurally similar compounds, with minor changes in parts of the structure determining the different types, of which ten are currently known. The main amatoxins commonly found in significant quantities are α-amanitin, β-amanitin and γ-amanitin, all three of which have a median lethal dose of around 0.5-0.75 milligrams per kilogram of body weight.

It can take between six and twenty-four hours for the symptoms of amatoxin poisoning to being to manifest. The initial symptoms are stomach cramps, vomiting, and diarrhoea; these can actually improve after a few days, but ultimately the toxin can cause liver and kidney failure, leading to death within five to eight days of consumption of the mushrooms. It’s estimated that between 10-20% of diagnosed cases of amatoxin poisoning result in death, with many of those that survive requiring liver transplants to do so.

The ‘Deadly Webcap’ and ‘Fool’s Webcap’ mushrooms both contain orellanine; this particular toxin initially causes thirst, stomach cramps and nausea, and can go on to cause a low output (or even no output) of urine. The initial symptoms can take up to three weeks to appear, though usually they are notable two to three days after ingestion. The later symptoms are due to kidney damage, which can, in severe cases, culminate in kidney failure. Again, in these cases, transplant is often the only option to treat the poisoning, with no known antidote for orellanine. The median lethal dose is around 12-20 milligrams per kilogram of body weight in mice, though it is thought to be lower than this figure in humans.

The most recognisable poisonous mushroom is probably Fly Agaric. This red, white-spotted specimen contains the compound muscarine, although in lower concentrations than some other mushroom species – it’s estimated that it only constitutes around 0.0003% of the mushroom’s weight. Muscarine was originally thought to be the source of the toxicity of Fly Agaric, but it has since been discovered that another compound, muscimol, is largely responsible. It’s also found in another common poisonous mushroom, the Panther Cap. No deaths have been officially attributed to either Fly Agaric or Panther Caps, but their ingestion can cause dizziness, stomach irritation, and hallucinogenic effects.

Unfortunately, there’s no tell-tale clue when it comes to spotting which mushrooms are poisonous, and which are not. Some of the deadliest can taste delicious, and look benign. It’s also not always enough to just cook these mushrooms thoroughly; this won’t necessarily make them safe to eat, as the poisonous compounds are often not broken down by heat.

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