28 August 2017

Solanine – The reason your mother told you not to eat green potatoes

Natural toxin

Solanine is a general name for a family of alkaloidal glycosides that are produced by plants in the nightshade family.

The name is derived from the Latin for European black nightshade (Solanum nigrum), from which solanine was first isolated in 1820 (1).

Structure of α-solanine. Solanine is a glycoalkaloid, which means it consists of a sugar (the solatriose moiety) that is chemically bound to an alkaloid (the solanidine moiety). (Figure credit: Wikipedia user Leyo, https://commons.wikimedia.org/wiki/User:Leyo). Click image for 3D structure

The familiar potato found in your grocery store is also produced by a member of the nightshade family (Solanum tuberosum).  Normal potato tubers contain a very small amount of solanine in the skin, and none in the potato itself (2). However, potatoes that have been exposed to sunlight or stored improperly can begin to produce solanine, which is usually accompanied by the development of a green color or sprouting of shoots.  Cooking green potatoes is not effective at lowering concentrations of glycoalkoloids such as solanine (3).

Potatoes with a green color that indicates they have produced solanine and related glycoalkaloids. (Photo reproduced under the GNU Free Documentation License. Original by Wikipedia user Rasbak https://commons.wikimedia.org/wiki

Cases of acute solanine poisoning are rare, since green potatoes are not usually sold and prepared for food (4).  A 1979 report describing accidental solanine poisoning of 78 schoolboys in London lists abdominal pain, vomiting and diarrhea as the predominant symptoms (2).  A few of the boys became comatose and had convulsions, and some were confused and experienced hallucinations for several days (2). 

An investigation by the myth-busting website Snopes (snopes.com) concludes that there is some truth to your mother’s advice not to eat green potatoes (5).  However, Snopes reports that healthy adults would need to consume approximately 2 kg of green potatoes in a single meal to incur significant risk of symptoms.  Thus one should not worry about the occasional greenish potato! But avoid the leaves, shoots and stems of potato plants, which have naturally high concentrations of solanine and a related glycoalkaloid called chaconine (3).

SMILES: C[C@H]1CC[C@@H]2[C@H]([C@H]3[C@@H](N2C1)C[C@@H]4[C@@]3(CC[C@H]5[C@H]4CC=C6[C@@]5(CC[C@@H](C6)O[C@H]7[C@@H]([C@H]([C@H]([C@H](O7)CO)O)O[C@H]8[C@@H]([C@H]([C@@H]([C@H](O8)CO)O)O)O)O[C@@H]9[C@@H]([C@@H]([C@H]([C@@H](O9)C)O)O)O)C)C)C

(1) https://en.wikipedia.org/wiki/Solanum_nigrum
(2) "Solanine poisoning". BMJ. 2 (6203): 1458–9. 1979. PMC 1597169. doi:10.1136/bmj.2.6203.1458-a.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1597169/pdf/brmedj00103-0006b.pdf
(3) Bushway, R.J. and Ponnampalam, R. (1981). alpha-chaconine and alpha-solanine content of potato products and their stability during several modes of cooking.  J. Agric. Food Chem., 29: 814-817. https://pubs.acs.org/doi/abs/10.1021/jf00106a033?journalCode=jafcau
(4) http://www.nytimes.com/2007/07/03/health/nutrition/03real.html
(5) http://www.snopes.com/food/ingredient/greenpotatoes.asp