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Solanine is a glycoalkaloid poison found in species of the nightshade family. It can occur naturally in the 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 poisoning is primarily displayed by gastrointestinal and neurological disorders. Symptoms include nausea, diarrhea, vomiting, stomach cramps, burning of the throat, headaches and dizziness. Hallucinations, loss of sensation, and 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.
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
Potatoes naturally produce solanine and chaconine , a related glycoalkaloid, as a defense mechanism against insects, disease, and predators. Potato leaves and stems 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. 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, and most have a solanine content of less than 0.2mg/g. However potatoes that have been exposed to light and started to green can show concentrations of 1mg/g or more. In these situations a single unpeeled potato can result in a dangerous dose.
Most solanine occurs in the skin or just under the skin of potatoes. Peeled potatoes have been found to contain 30-80% less solanine than unpeeled potatoes, and green potatoes should always be peeled if they are to be used at all. Solanine and chaconine are also present in potato shoots.
Deep-frying potatoes at 170° C (306° F) is effective at lowering glycoalkaloid levels, boiling is ineffective, and microwaving only somewhat effective.
Solanine build-up can occur independently of potato greening, and vice-versa.
Other uses of Solanine
Solanine has fungicidal and pesticidal properties, and solanine hydrochloride (a modified version 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 bronchial asthma, as well as for cough and cold medicines. However, its effectiveness for either use is questionable.
- a-Chaconine and a-Solanine, Review of Toxicological Literature
- Medplus Medical Encyclopedia - Green tubers and sprouts
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