Saponins - amphipathic glycosides
Saponins are distinguished by their bitter taste, and ability to haemolyse red blood cells.
Saponins are a class of chemical compounds found in particular abundance in various plant species. More specifically, they are amphipathic glycosides grouped phenomenologically by the soap-like foaming they produce when shaken in aqueous solutions, and structurally by having one or more hydrophilic glycoside moieties combined with a lipophilic triterpene derivative. They are glycosides with a non-sugar aglycone portion which is termed a sapogenin.
Figure 1 presents the structure of the alkaloid phytotoxin solanine, a monodesmosidic, branched-saccharide steroidal saponin (the lipophilic steroidal structure is the series of connected six- and five-membered rings at the right of the structure, while the three oxygen-rich sugar rings are at left and below).
Saponins are distinguished by their bitter taste, and ability to haemolyse red blood cells. They are classified according to the chemical nature of the sapogenin into two major groups: steroidal and triterpenoid saponins.
Saponins are widely distributed in the plant kingdom and can occur in all parts of plants, although the concentration is affected by variety and stage of growth. They are found in soybeans, sugar beets, peanuts, spinach, asparagus, broccoli, potatoes, apples, eggplants, alfalfa and ginseng root.
Regarding toxicity, they are considered natural plant toxins because they are capable of disrupting red blood cells and producing diarrhea and vomiting. Their toxic effects are related to the reduction of surface tension. Saponins are generally harmless to mammals and other warm-blooded animals except at large doses. The body is able to detoxify when saponin is taken in a small amount since intestinal microflora can destroy them and blood plasma can inhibit their action. However, in large quantities they can be irritating to the gastrointestinal tract causing vomiting and diarrhea.
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References for photos:
- Nigella_sativa. By k yamada from Yokohama, Japan - Nigella sativa, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4418771
- Bacopa monniera. By Forest & Kim Starr, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=6109556
- Bryonia alba. By Aung - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4459404
Prof. Óscar Núñez Burcio