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Solanine
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Solanine is a glycoalkaloid poison found in species of the nightshade family, such as potatoes. It can occur naturally in any part of the plant, including the leaves, fruit, and tubers. It is very toxic even in small quantities. Solanine has both fungicidal and pesticidal properties, and it is one of the plant's natural defenses. Solanine was first isolated in 1820 by Desfosses from the berries of the European Black Nightshade (Solanum nigrum), after which it was named.
Solanine poisoning
Symptoms
Solanine poisoning is primarily displayed by gastrointestinal and neurological disorders.
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Encyclopedia
Solanine is a glycoalkaloid poison found in species of the nightshade family, such as potatoes. It can occur naturally in any part of the plant, including the leaves, fruit, and tubers. It is very toxic even in small quantities. Solanine has both fungicidal and pesticidal properties, and it is one of the plant's natural defenses. Solanine was first isolated in 1820 by Desfosses from the berries of the European Black Nightshade (Solanum nigrum), after which it was named.
Solanine poisoning
Symptoms
Solanine poisoning is primarily displayed by gastrointestinal and neurological disorders. Symptoms include nausea, diarrhea, vomiting, stomach cramps, burning of the throat, heart arrhythmia, headache and dizziness. Hallucinations, loss of sensation, paralysis, fever, jaundice, dilated pupils and hypothermia have been reported in more severe cases.
In large quantities, solanine poisoning can cause death. One study suggests that doses of 2 to 5 mg per kilogram of body weight can cause toxic symptoms, and doses of 3 to 6 mg per kilogram of body weight can be fatal.
Symptoms usually occur 8 to 12 hours after ingestion, but may occur as rapidly as 30 minutes after eating high-solanine foods.
The lowest dose to cause symptoms of nausea is about 25 mg solanine for adults, a life-threatening dose for a regular-weight adult ranges about 400 mg solanine.
Mechanism of Action
One study suggests that the toxic mechanism of solanine is caused by the chemical's interaction with mitochondrial membranes. Experiments show that solanine exposure opens the potassium channels of mitochondria, increasing their membrane potential. This in turn leads to Ca2+ being transported down its concentration gradient into the mitochondria, and it is this increased concentration of Ca2+ in the cell that triggers cell damage and apoptosis.
Correlation with birth defects
Some studies show a correlation between the consumption of potatoes suffering from late-blight (which increases solanine and other glycoalkaloid levels) and the incidence of congenital spina bifida in humans. However, other studies have shown no correlation between potato consumption and the incidence of birth defects.
Solanine in potatoes
Solanine occurs naturally in many species of the genus Solanum, including potatoes (Solanum tuberosum), tomatoes (Solanum lycopersicum), eggplant (Solanum melongena), and bittersweet nightshade (Solanum dulcamara).
Potatoes naturally produce solanine and chaconine, a related glycoalkaloid, as a defense mechanism against insects, disease, and predators. Potato leaves, stems and shoots are naturally high in glycoalkaloids.
When potato tubers are exposed to light, they turn green and increase glycoalkaloid production. This is a natural defense to help prevent the uncovered tuber from being eaten. The green colour is from chlorophyll, and is itself harmless. However, it is an indication that increased level of solanine and chaconine may be present.
Some diseases, such as potato blight, can dramatically increase the levels of glycoalkaloids present in potatoes. Mechanically damaged potatoes also produce increased levels of glycoalkaloids. This is believed to be a natural reaction of the plant in response to disease and damage.
Commercial varieties of potatoes are screened for solanine levels[in which countries?], and most have a solanine content of less than 0.2 mg/g. However, potatoes that have been exposed to light and started to green can show concentrations of 1 mg/g or more. In these situations a single unpeeled potato can result in a dangerous dose.
In potato tubers 30–80% of the solanine develops in and close to the skin.
Showing green under the skin strongly suggests solanine build-up in potatoes although each process can occur without the other. A bitter taste in a potato is another, potentially more reliable indicator of toxicity. Because of the bitter taste and appearance of such potatoes, solanine poisoning is rare outside conditions of food shortage. The symptoms are mainly vomiting and diarrhea, and the condition may be misdiagnosed as gastroenteritis. Most potato poisoning victims recover fully, although fatalities are known especially when victims are undernourished or do not receive suitable treatment. Fatalities are also known from solanine poisoning from other plants in the nightshade family, such as the berries of Solanum dulcamara (woody nightshade).
The National Institute of Health's information on solanine says to never eat potatoes that are green below the skin.
Deep-frying potatoes at 170°C (306°F) is known to effectively lower glycoalkaloid levels (because they move into the frying fat), whereas microwaving is only somewhat effective, freeze drying or dehydration has little effect and boiling has no effect.
Solanine in green tomatoes
While ripe (red or yellow) tomatoes do not contain significant amounts of solanine, the amount of solanine in unripe (green) tomatoes is quite high. A dose of 25 mg is about the dose where symptoms of nausea start to show. Depending on the variety of tomatoes the amount of 25 mg solanine may be reached with as less than 80 g of raw green tomatoes, and the potentially life-threating dose for adults of 400 mg may be reached between 1.25 kg to 4.5 kg of raw green tomatoes. As with potatoes, deep-frying them does reduce the solanine level significantly (up to 50%) while solanine dissolves into the frying fat. Therefore only small portions of no more than 80 g of raw green tomatoes or 150 g of deep-fried green tomatoes should be consumed per day by adults.
Other uses of solanine
Solanine has fungicidal and pesticidal properties, and solanine hydrochloride (a salt of solanine) has been used as a commercial pesticide, but never on a large scale.
Solanine has sedative and anticonvulsant properties, and has been used as a treatment for asthma, as well as for cough and cold medicines. However, its effectiveness for either use is questionable.
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