What acid is there in a tomato?

Hydrocyanic acid in tomatoes: how harmful can tomatoes be?


Tomatoes are known to be extremely healthy fruits because they contain numerous vitamins and minerals. It is also known that green, unripe fruits contain the poisonous substance solanine and that only ripe specimens should therefore be consumed. But what about the thesis that tomatoes also contain hydrocyanic acid? We get to the bottom of the question and also explain what hydrogen cyanide actually is and how it works!

What is hydrogen cyanide?

Hydrocyanic acid is understood to mean the aqueous solution of the highly volatile substance hydrogen cyanide (HCN). The term “prussic acid” is derived from the extraction of iron hexacyanidoferrate, a deep blue color pigment, which is also known as “Berlin blue”. The substance occurs both in the wild, but can also be obtained in the laboratory. Hydrocyanic acid is highly toxic and even in small amounts it is life-threatening.

  • is a secondary plant substance
  • colorless to yellowish
  • water soluble
  • Boiling point: approx. 26 degrees Celsius
  • The smell is reminiscent of bitter almonds

Note: Hydrocyanic acid has its own odor, but not everyone can perceive it. It is believed that only around 60 to 70 percent of all people are genetically able to actually smell hydrogen cyanide.

Hydrocyanic acid in history

While the toxic effect of this substance is used today, among other things, to control pests, it was previously used against people on a number of occasions. For example, at the time of National Socialism, people in the Auschwitz concentration camp were poisoned with hydrogen cyanide. Hydrogen cyanide was also used in the USA to carry out the death penalty until 1999 by putting the convicts in a gas chamber and then suffocating them with hydrogen cyanide.

How does hydrogen cyanide work?

Hydrocyanic acid can enter the human organism through direct ingestion as well as through breathing and through the skin. There the substance inhibits an important enzyme that is responsible for cell respiration. The consequences are drastic: the cells can no longer use the oxygen, so that within a very short time there can be a lack of oxygen and subsequent death from suffocation.

  • Burning plastic can release hydrogen cyanide
  • Sweat-inducing activities favor absorption through the skin

How much is hydrocyanic acid poisonous?

Just one to two milligrams of hydrogen cyanide per kilogram of body weight can be fatal. But absorption through the air can also lead to symptoms of poisoning and ultimately death. The following guideline values ​​are used as a basis, with ppm standing for “parts per million” in German “parts per million”:

  • 2 - 4 ppm: Limit of perception through smell
  • 10 ppm: PEL exposure limit
  • 20 - 40 ppm: appearance of slight symptoms after several hours
  • 45 - 54 ppm: tolerable for about 30 to 60 minutes
  • 100 - 200 ppm: fatal after 30 to 60 minutes
  • 300 ppm: immediately fatal

Note: It is essential to consult a doctor even if small amounts are consumed!

Symptoms of hydrocyanic acid poisoning

Contact and / or ingestion of hydrocyanic acid does not always end immediately fatally. Because both the concentration in the air and the amount of hydrocyanic acid absorbed play an essential role here. Accordingly, the symptoms also vary depending on the severity of the poisoning. It is typical of hydrocyanic acid intoxication that the exhaled air of the affected person smells of bitter almonds. In addition, the following symptoms of poisoning can occur, which vary depending on the severity of the poisoning:

Slight hydrocyanic acid poisoning

  • Shortness of breath
  • a headache
  • Dizziness
  • nausea
  • Vomit

Acute hydrocyanic acid poisoning

  • from about 70 mg or 1-2 mg / kg body weight
  • lack of oxygen supply
  • Cell death
  • epileptic convulsions
  • Fainting
  • rosy skin color
  • Organ failure
  • Suffocation

Hydrocyanic acid poisoning in animals

Animals can also suffer from hydrocyanic acid poisoning, which can also lead to death within a very short time! Typical symptoms in animals include excessive salivation, breathing difficulties with increased breathing rate and dilated pupils. In the event of severe poisoning, the animals also suffer from cramps, tremors and are highly excitable. A rigid head posture, bright red mucous membranes and the typical smell of bitter almonds in the exhaled air are typical symptoms. If severe hydrocyanic acid poisoning is not treated immediately, the animals fall into a coma and die.

Which plants and foods contain hydrocyanic acid?

Over 1000 different plants that produce hydrogen cyanide are known worldwide. However, the toxic substance is usually only released when the plants are injured by insects. Accordingly, this is probably a natural protective mechanism, although the ecological function has not yet been fully clarified at this point in time. Hydrocyanic acid is found in the following plant-based foods, among others:

  • Bitter almonds
  • bitter apricot kernels
  • Stone fruit pips
  • raw legumes
  • linseed
  • Millet

Do tomatoes contain hydrocyanic acid?

In addition to solanine, tomatoes also contain hydrocyanic acid, but only in an extremely small amount. Because one kilogram of tomatoes only contains around 16 µg hydrogen cyanide. To illustrate this in numbers: There are around 0.0000016 grams of hydrocyanic acid in 1000 grams. According to this, a person would have to consume an extraordinarily large amount of tomatoes in order to cause poisoning with hydrogen cyanide. Because the tolerance range of the human body is between 1 and 60 milligrams of hydrogen cyanide per kilogram of body weight.

Eating tomatoes: this is how they are safe

While the hydrocyanic acid content of tomatoes does not pose a risk in principle, the solanine it contains could cause unpleasant side effects. Because this is also a toxin, but it occurs almost exclusively in the green parts of the plant. Life-threatening poisoning from eating green, unripe tomatoes is extremely unlikely, but side effects such as stomach upset, diarrhea or drowsiness can occur. If you want to be on the safe side when consuming tomatoes, you should therefore pay attention to the following:

  • eat only ripe fruit
  • Remove green parts of the plant
  • Allow unripe fruits to ripen
  • or further processing (e.g. boiling down to make sauces)