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Solanine is a glycoalkaloid poison found in species of the Solanaceae family within the genus Solanum, such as the potato ( Solanum tuberosum). It can occur naturally in any part of the plant, including the Leaf, fruit, and . Solanine has Pesticide properties, and it is one of the plant's natural defenses. Solanine was first isolated in 1820 from the berries of the European black nightshade ( Solanum nigrum), after which it was named. It belongs to the chemical family of .
Ingestion of solanine in moderate amounts can cause death. One study suggests that doses of 2 to 5 mg/kg of body weight can cause toxic symptoms, and doses of 3 to 6 mg/kg of body weight can be fatal. Executive Summary of Chaconine & Solanine
Symptoms usually occur 8 to 12 hours after ingestion, but may occur as rapidly as 10 minutes after eating high-solanine foods.
Though the structures of the intermediates in this biosynthetic pathway are shown, many of the specific involved in these chemical processes are not known. However, it is known that in the biosynthesis of solanine, cholesterol is first converted into the steroidal alkaloid solanidine. This is accomplished through a series of hydroxylation, transamination, oxidation, cyclization, dehydration, and reduction reactions. Specifically, solanidine formation involves sequential hydroxylation, transamination, and cyclization reactions.The solanidine is then converted into solanine through a series of glycosylation reactions catalyzed by specific glycosyltransferases.
Plants like the potato and tomato constantly synthesize low levels of glycoalkaloids like solanine. However, under stress, such as the presence of a pest or herbivore, they increase the synthesis of compounds like solanine as a natural chemical defense. This rapid increase in glycoalkaloid concentration gives the potatoes a bitter taste, and stressful stimuli like light also stimulate photosynthesis and the accumulation of chlorophyll. As a result, the potatoes turn green, and are thus unattractive to pests. Other stressors that can stimulate increased solanine biosynthesis include mechanical damage, improper storage conditions, improper food processing, and sprouting. The largest concentration of solanine in response to stress is on the surface in the peel, making it an even better defense mechanism against pests trying to consume it.
Calculations have shown that 2 to 5 mg/kg of body weight is the likely toxic dose of glycoalkaloids like solanine in humans, with 3 to 6 mg/kg constituting the fatal dose. Other studies have shown that symptoms of toxicity were observed with consumption of even 1 mg/kg.
The majority (30–80%) of the solanine in potatoes is found in the outer layer of the potato. Therefore, peeling potatoes before cooking them reduces the glycoalkaloid intake from potato consumption. Fried potato peels have been shown to have 1.4–1.5 mg solanine/g, which is seven times the recommended upper safety limit of 0.2 mg/g. Chewing a small piece of the raw potato peel before cooking can help determine the level of solanine contained in the potato; bitterness indicates high glycoalkaloid content. If the potato has more than 0.2 mg/g of solanine, an immediate burning sensation will develop in the mouth.
In 1899, 56 German soldiers fell ill due to solanine poisoning after consuming cooked potatoes containing 0.24 mg of solanine per gram of potato. (1993). 9789241660327, World Health Organization. ISBN 9789241660327 There were no fatalities, but a few soldiers were left partially paralyzed and jaundiced. In 1918, there were 41 cases of solanine poisoning in people who had eaten a bad crop of potatoes with 0.43 mg solanine/g potato with no recorded fatalities.
In Scotland in 1918, there were 61 cases of solanine poisoning after consumption of potatoes containing 0.41 mg of solanine per gram of potato, resulting in the death of a five-year old.
A case report from 1925 reported that 7 family members who ate green potatoes fell ill from solanine poisoning two days later, resulting in the deaths of the 45-year-old mother and 16-year-old daughter. The other family members recovered fully. In another case report from 1959, four members of a British family exhibited symptoms of solanine poisoning after eating Baked potato (baked potatoes) containing 0.5 mg of solanine per gram of potato.
There was a mass solanine poisoning incident in 1979 in the U.K., when 78 adolescent boys at a boarding school exhibited symptoms after eating potatoes that had been stored improperly over the summer. Seventeen of them ended up hospitalized, but they all recovered. The potatoes were determined to have between 0.25 and 0.3 mg of solanine per gram of potato.
Another mass poisoning was reported in Canada in 1984, after 61 schoolchildren and teachers showed symptoms of solanine toxicity after consuming baked potatoes with 0.5 mg of solanine per gram of potato.
When potato 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. In potato tubers, 30–80% of the solanine develops in and close to the skin, and some potato varieties have high levels of solanine.
Some potato diseases, such as late blight, can dramatically increase the levels of glycoalkaloids present in potatoes. Tubers damaged in harvesting and/or transport also produce increased levels of glycoalkaloids; this is believed to be a natural reaction of the plant in response to disease and damage.
Also, the tuber glycoalkaloids (such as solanine) can be affected by some chemical fertilization. For example, different studies have reported that glycoalkaloids content increases by increasing the concentration of nitrogen fertilizer.
Green colouring 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.
The United States National Institutes of Health's information on solanine strongly advises against eating potatoes that are green below the skin.
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