Saponins are soap-like compounds which are formed only in plants. The individual molecules consist of a hydrophilic and a lipophilic portion. Their structures, properties and modes of action are very diverse.
What are saponins?
Saponins are biological compounds formed exclusively in plant tissues. They represent secondary plant compounds. Furthermore, they are subject to a great structural diversity. In their basic structure, they consist of a sugar moiety and a non-sugar component (aglycone) in the molecule. The sugar component is glycosidically bound to the aglycone. The sugar or carbohydrate components are usually composed of chains of D-glucose, D-fructose, D-galactose, D-glucuronic acid or other sugar building blocks. Three different structural components can serve as aglycones. These are the steroids, steroid alkaloids or terpenes. The aglycones form the lipophilic part and the sugar components the hydrophilic part of the molecule. Since the molecule has both lipophilic and hydrophilic properties, it can reduce the surface tension of water. It therefore foams in water and brings various compounds into solution. Thus, with the help of saponins, fat-soluble substances are also brought into aqueous solution. Saponins are therefore surfactants and appear soap-like. The term saponin comes from Latin and means soap. In plants, saponins usually have fungicidal or antibacterial effects. Due to the similar structure of the sterols found in fungal membranes, larger molecular complexes can form, causing pores to form within the fungal membranes. This results in the destruction of the fungal cells. Antibacterial saponins have a similar effect.
Function, effect, and tasks
For humans, only the saponins occurring in plant foods play a major role. Due to their great structural diversity, the mode of action of the individual saponins is different and often also still unexplored. In most cases, they have positive properties or are neutral. In rarer cases, poisonous effects have also become known. For plants, they are defensive agents that act against fungi, bacteria and insects. The lack of an active immune system in plants makes it necessary for them to develop chemical defense mechanisms. However, some saponins also exert clear positive health effects in humans and animals, so they play an important role in herbal medicine. Depending on the structural composition of individual saponins, anti-inflammatory, tonic, expectorant, diuretic or hormone-stimulating properties of this group of substances have been discovered. Due to their special structure, saponins can also bind cholesterol and thus contribute to lowering cholesterol levels. At the same time, there are studies indicating a preventive effect of saponins against colon cancer by exerting an inhibitory influence on cell division. However, many medicinal influences are not yet fully understood and require further investigation. In addition to cholesterol-lowering effects, saponins also exert blood pressure-increasing effects and can thus be used to treat low blood pressure. Immune modulating influences are also observed.
Formation, occurrence, properties, and optimal values
As mentioned above, saponins are found only in plant tissues. There they are mainly found in particularly nutrient-rich plant parts. These include roots, flowers, leaves, tubers or seeds. Tomatoes, potatoes, peas, soybeans and spinach are particularly rich in saponins. Certain herbs have a positive health effect precisely because of the saponins they contain, such as ginseng or certain types of tea. Chestnuts also contain high concentrations of saponins. In the past, the sap of the roots of the true soapwort was used as a detergent because of the saponins they contain. The saponins are formed by a glycosidic association of aglycones, mainly consisting of a steroid or terpene base structure, with a carbohydrate component. The aglycones have no polar functional groups, so this molecular component dissolves in lipid-like substances. The carbohydrate component contains many hydroxyl groups, which induce intense water solubility of this part of the molecule. Due to this fact, saponins are good solubilizers.They enable many substances to overcome the phase boundary between two components that cannot be mixed with each other. This also explains the interaction of saponins with membrane components of various microorganisms such as bacteria or fungi. Legumes, asparagus, sugar beets, beet, horse chestnut or daisies serve as the most important suppliers of saponins for medicinal purposes.
Diseases and disorders
However, in addition to positive effects, taking saponins can also cause health problems. This usually requires very high concentrations, however, which cannot be achieved even when eating foods that are high in saponins. However, if saponins come into contact with the bloodstream, even lower concentrations are sufficient to trigger hemolysis. As a rule, this is only a hemolytic effect in which blood cells are dissolved due to their interaction with saponins. This fact is used in blood tests, among others, as a standard quantitative method. When the intestinal wall is inflamed, the permeability of the intestinal wall can be increased by the influence of saponins. Overall, however, the amounts supplied by food are rarely sufficient for such an effect. However, certain side effects may occur when eating licorice. Licorice contains large amounts of glycyrrhizic acid. This is a saponin found in the root of the licorice plant. Licorice is made from the licorice plant. Glycyrrhizic acid inhibits the formation of cortisone from cortisol. Cortisone is the inactive form of the hormone. The active cortisol non-specifically occupies the receptors of mineral corticoids, producing effects similar to those of the mineral corticoid hormone aldosterone. In the process, mineral metabolism becomes unbalanced in the form of fluid retention, hypokalemia, and hypertension, a phenomenon that can occur with increased licorice consumption.