Amygdalin – sweet sugar and lethal cyanide in one molecule

Fruits and berries provide us with necessary vitamins and antioxidants and are especially valuable for balanced nutrition. It is common among dietitians to recommend eating 8 pieces of fruit every day. But what about the fruit seeds? The seed of every plant contains concentrated amount of minerals and nutrients in order to facilitate the growth of a new plant in its primary stage. Grains, nuts, sunflower seeds and alike are ideal resources of energetic value, minerals, rare vitamins, fatty acids and other desired compounds.

Fruit plants concentrate nutrients in the seeds as well. However, the fruit plants have also developed chemical seed defense mechanisms. For instance, apple seeds are commonly known to contain hydrogen cyanide. Even though you are not likely to manage to eat enough of them in order to poison yourself, you should better throw the gnawed apple away.

In fact, apple seeds contain 3.0 mg/g of amygdalin. The lethal dose of amygdalin (LD₅₀) for an average human in the absence of any physical or medical conditions is 675-3,750 mg. The seeds of nectarine, pear, plum, black cherry, red cherry, peach, apricot and greengage also contain amygdalin in concentrations of 0.1, 1.3, 2.2, 2.7, 3.9, 6.8, 14.4 and 17.5 mg/g, respectively. Hydrogen cyanide is a poisonous gas that does not exist in the seeds but is released in the body by metabolism of amygdalin. Amygdalin is not toxic until human or animal enzymes remove the sugar part of the molecule. Undamaged seed would therefore pass through unaffected.

Since humans do not eat large quantities of fruit seeds, no lethal poisonings are reported. However, instances of severe acute poisoning and hospitalization due to ingestion of apricot kernels and lethal cyanide poisonings by cassava root are known. Hydrogen cyanide was used as a chemical weapon by Nazis in the World War II in a form of Zyklon B.

SMILES: C1=CC=C(C=C1)C(C#N)OC2C(C(C(C(O2)COC3C(C(C(C(O3)CO)O)O)O)O)O)O
Molecular formula: C20H27NO11

References

• The written refers to the book Why Does Asparagus Make Your Wee Smell?: And 57 other curious food and drink questions. © Andy Brunning, 2016.

Photos

• Figure 1, left: https://commons.wikimedia.org/wiki/File:Pink_lady_and_cross_section.jpg. Attribution: fir0002  flagstaffotos [at] gmail.com  Canon 20D + Sigma 150mm f/2.8 [GFDL 1.2 (https://www.gnu.org/licenses/old-licenses/fdl-1.2.html)]
• Figure 1, right: https://commons.wikimedia.org/wiki/File:Apricot_and_cross_section.jpg Attribution: Fir0002 [GFDL 1.2 (https://www.gnu.org/licenses/old-licenses/fdl-1.2.html)]
• Figure 2. Structure of amygdalin. By Yikrazuul (talk) - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=28958308 https://commons.wikimedia.org/wiki/File:Amygdalin_structure.svg#/media/File:Amygdalin_structure.svg