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What is solanine and is it toxic ?

A bitter poisonous glyco-alkaloid, C45H73NO15, derived from potato sprouts, tomatoes, and nightshade and having narcotic properties formerly used to treat epilepsy. It is made of the alkaloid solanidine and carbohydrate (glyco-) side-chains, see structure below.

Structure of solanine : blue : solanidine backbone (alkaloid structure), red : carbohydrate residues

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. 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.

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 (see greening) can show concentrations of 1 mg/g or more. In these situations a single unpeeled potato can result in a dangerous dose.

Solanine Poisoning

Solanine poisoning is primarily displayed by gastrointestinal and neurological disorders. Symptoms include nausea, diarrhoea, 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.

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 is effective at lowering glycoalkaloid levels, boiling is ineffective, and microwaving only somewhat effective.

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