Solanine is an alkaloid toxin found in members of the nightshade family, such as eggplants, potatoes, tomatoes, and the infamous deadly nightshade or belladonna. This toxin is part of the plant's defense mechanism, and it is designed to make nightshades unappealing and deadly to animals which might attempt to eat them. Most animals, including humans, have learned the lesson and learned to leave nightshades alone. Leaves, roots, flowers, stems, and fruits can all contain solanine in varying levels.
This toxin has neurological and gastrointestinal effects. When it is ingested in large enough quantities, it can cause nausea, cramps, vomiting, and diarrhea, in addition to symptoms like confusion, dizziness, difficulty walking, and slurred speech. Eventually, the body will become overloaded with the toxin, causing organs to fail and eventually leading to death or severe injury. Solanine appears to affect the mitochondria of the cells as it spreads through the body.
Humans eat many members of the nightshade family, although some societies were initially suspicious of foods like potatoes and tomatoes when they were imported from the New World because of concerns about known toxins. Usually, the solanine levels in things like eggplant, potatoes, and tomatoes are too low to cause health problems. However, there are circumstances in which solanine can be elevated. Unripe tomatoes tend to have higher levels of the toxin, as do potatoes which have been damaged or exposed to the sun, because the plants form more solanine in response to perceived threats. Sprouts of potatoes and tomatoes also have high levels of the toxin.
The toxin is heat-stable, but it will eventually break down at high temperatures. Deep frying temperatures of over 170°F (about 76°C), for example, can reduce the risk of solanine toxicity, but baking or microwaving is not as effective, and boiling won't work because the toxin will leach into the water. People who are concerned about the toxin can avoid unripe tomatoes and potatoes which have started to turn green, as the green color indicates that the potato has been exposed to the sun. While the green color itself is harmless, it shows that the potato has been able to photosynthesize, which requires sun exposure.
Historically, solanine was used in the treatment of epilepsy and asthma, in controlled doses. This practice is no longer common, as there are safer and more effective ways to treat these conditions. Solanine also has fungicidal and pesticidal qualities, but extraction and processing of this toxin is so time consuming that the substance is rarely used for these purposes. Another compound found in nightshades is atropine, another alkaloid toxin which is widely used in controlled amounts for various medical applications.
