Saponins (Latin "sapon", soap + "-in", one of), also selectively referred to as triterpene glycosides, are bitter-tasting usually toxic plant-derived organic chemicals that have a foamy quality when agitated in water. They are widely distributed but found particularly in soapwort (genus Saponaria), a flowering plant, the soapbark tree (Quillaja saponaria) and soybeans (Glycine max L.). They are used in soaps, medicines, fire extinguishers, speciously as dietary supplements, for synthesis of steroids, and in carbonated beverages (for example, being responsible for maintaining the head on root beer). Saponins are both water and fat soluble, which gives them their useful soap properties. Some examples of these chemicals are glycyrrhizin (licorice flavoring) and quillaia (alt. quillaja), a bark extract used in beverages.
Structurally, they are glycosides, which are sugars bonded to one or more organic molecules. In a glycoside molecule, the sugar is the glycone part, while one or more non-sugar organic molecules form the aglycone part.
Glycoside#Steroidal_glycosides_or_cardiac_glycosides
Their aglycone is a steroid.
Their aglycone is a triterpene.
The saponins are a subclass of terpenoids, the largest class of plant extracts. The amphipathic nature of saponins gives them activity as surfactants with potential ability to interact with cell membrane components, such as cholesterol and phospholipids, possibly making saponins useful for development of cosmetics and drugs. Saponins have also been used as adjuvants in development of vaccines, such as Quil A, an extract from the bark of Quillaja saponaria. This makes them of interest for possible use in subunit vaccines and vaccines directed against intracellular pathogens. In their use as adjuvants for manufacturing vaccines, toxicity associated with sterol complexation remains a concern.
Quillaja is toxic when consumed in large amounts, involving possible liver damage, gastric pain, diarrhea, or other adverse effects.
Saponins are used for their effects on ammonia emissions in animal feeding.