Steroid alkaloids have a fairly complex nitrogen containing nucleus. Two important classes of steroid alkaloids are
- the Solanum type - one example is solanidine. This steroid alkaloid is the nucleus (i.e. aglycone) for two important glycoalkaloids, solanine and chaconine, found in potatoes. Other plants in the Solanum family including various nightshades, Jerusalem cherries, and tomatoes also contain solanum-type glycoalkaloids. Glycoalkaloids are glycosides of alkaloids.
- the Veratrum type. There are more than 50 Veratrum alkaloids including veratramine, cyclopamine, cycloposine, jervine, and muldamine occurring in plants of the Veratrum spp. The Zigadenus spp., death camas, also produces several veratrum-type of steroid alkaloids including zygacine.
Solanum-type alkaloids are found in plants in the form of glycosides of alkaloids. Glycosides are ethers that join a noncarbohydrate moiety , the aglycone, by a ester bond to a carbohydrate moiety. In solanum-type glycoalkaloids, the aglycone is a steroid alkaloid. Solanine and chaconine cause poisoning in potatoes. They have the same aglycone, solanidine, but the structure of their carbohydrate sidechains is different. Tomatine is a glycoalkaloid found in tomatoes. Its aglycone is tomatidine.
Production of solanum-type glycoalkaloids is favored by the same conditions that promote the development of chlorphyll. Therefore, the concentration of these glycoalkaloids is highest in potato sprouts and green potato skins, and tomato vines and green tomatoes. Care should be taken to prevent the exposure of potatoes to sunlight. These alkaloids are not destroyed by cooking or drying at high temperatures. New potato varieties can not be introduced unless they contain less than 20 mg glycoalkaloids/100 g.
*The glycoalkaloids are more poisonous than the steroid alkaloid aglycones. Humans and all classes of livestock are susceptible to poisoning by solunum- type glycoalkaloids. Luckily,
- glycoalkaloids are poorly absorbed by the gastrointestinal tract of mammals,
- an appreciable amount of solanum-type glycoalkaloids is hydrolized in the gut of mammals to the less toxic aglycones,
- these metabolites are rapidly excreted in the urine and feces of mammals. Because exposure to these poisons is generally by ingestion, it takes a relatively large amount of them to cause death.
In potatoes, solanum-type glycoalkaloids cause:
- a bitter taste above 14mg/100g, and
- a burning sensation to mouth and throat above 20mg/100g.
Solanum-type glycoalkaloids are:
- gastrointestinal tract irritants -->
- inflamed intestinal mucosa, ulceration, hemorrhage, stomach pains, constipation or diarrhea
- apathy, drowsiness,salivation, labored breathing, trembling -->
- ataxia, muscle weakness, convulsions, involuntary urination -->
- paralysis, loss of consciousness, coma, death due to respiratory paralysis