Hydrogen cyanide (HCN), sometimes called prussic acid, is a highly toxic chemical compound that appears in certain foodstuffs as a byproduct of the natural metabolism of cyanogenic glycosides (especially amygdalin), compounds found in various plants.
Notably, hydrogen cyanide can be released from the seeds and pits of some fruits, such as bitter almonds, apricots, peaches, cherries, and apples, as well as in certain roots and tubers like cassava. When these foods are crushed, chewed, or otherwise processed, enzymes break down the cyanogenic glycosides into hydrogen cyanide, which can be harmful or even lethal in sufficient quantities.
The presence of cyanogenic glycosides may necessitate additional processing to reduce cyanide levels to safe amounts. For example, cassava is typically soaked, fermented, or cooked thoroughly to lower its cyanide content. Cooking, roasting, and pasteurization all raise foods to levels that cause HCN to vaporize, reducing it to negligible levels.
Levels of cyanide-bearing foods to reach dangerous levels
The human body routinely processes small doses of hydrogen cyanide. Reaching a dangerous dose would require ingestion of a large quantity of naturally occurring sources.
Specifically, the lethal dose of cyanide for humans is estimated to be 0.5 to 3.5 mg per kilogram of body weight. Complete degradation of 1 g of amygdalin releases 59 mg HCN. Assuming a 70kg adult human, that works out to 30 mg of cyanide, which would be carried by 0.5g of amygdalin.
| Source | Amygdalin density | Dangerous amount | Reference |
|---|---|---|---|
| Apple (seed) | 3.91 ± 0.49 mg/g | 130 grams | Nut. Rev. 20182 |