Solanum alkaloids

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The Solanum alkaloids are a chemical group and form a subgroup of the alkaloids . Structurally, they can be assigned to the steroid alkaloids . They bear the name because they can be found in representatives of the plant genus of the nightshade ( Solanum ).

Occurrence

Solanum alkaloids are found in Solanum tuberosum ( potato ), S. lycopersicum ( tomato ), S. dulcamara ( bittersweet nightshade ) and S. nigrum ( black nightshade ).

Partially green potato tubers contain solanine.

The importance of the Solanum alkaloids to the plants from which they are produced has now been explored. The poisonous alkaloids serve to ward off pests and pathogens, but also to ward off predators . Solanum alkaloids have a bitter taste that is noticeable from around 11 mg per 100 g of food. The content of Solanum alkaloids in food is usually harmless. In damaged or improperly stored potatoes, harmful concentrations can be reached.

Chemical structure

Structure of solanidine, the aglycon of solanine.

Solanum alkaloids consist of an aglycon (non-sugar component) with a steroid structure and a carbohydrate component made up of one or more sugars . This makes them one of the saponins . Due to the hydrophobic steroid part of the molecule and the ( hydrophilic ) carbohydrate side chain, the substances have a membrane-damaging effect.

The alkaloids α- solanine and α- chaconine contained in potatoes consist of the same aglycon and different trisaccharide side chains. In contrast, the two most important alkaloids of tomato differ in the aglycon, while the carbohydrate residue is identical.

Solanum alkaloids are made from cholesterol in the plant . Nitrogen sources are amino acids such. B. arginine .

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Solanine is often used in the advisory literature and in the daily press as a collective name for nightshade alkaloids or as a synonym for individual substances such as α-tomatin in tomatoes. However, it is just one of many glycoalkaloids found in food. Potatoes, for example, contain over 20 different substances. Differentiating the alkaloids is important because they differ in terms of their toxicological properties.

The following are of greatest importance in the food sector:

  • in the potato: α-solanine and α-chaconine
  • in the tomato: α-tomatin and dehydrotomatin

Absorption and metabolism

Solanum alkaloids are only absorbed to a small extent. The maximum concentration in the blood is reached four to eight hours after consumption. The half-life was determined to be 19 hours for α-chaconin and 11 hours for α-solanine. Excretion takes place mainly unchanged via the intestines and the kidneys. The main metabolite of the potato alkaloids is the aglycon solanidine. Its plasma concentrations are lower compared to the glycoalkaloids. However, solanidine is stored in the liver and excreted much more slowly. In the event of metabolic stresses such as hunger, pregnancy or illness, stored solanidine can probably be released again.

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