Saponins

Saponins belongs to a class of chemical compounds, one of the many secondary metabolites found in natural sources, particularly abundant in various plant species. Specifically, they are amphipathic glycosides grouped phenomenologically by the soap-like foaming they produce when shaken in aqueous solutions, and structurally by their composition of one or more hydrophilic glycoside moieties combined with a lipophilic triterpene derivative. A ready and therapeutically relevant example is the cardio-active agent digoxin, from common foxglove.

Saponins are glucosides with foaming characteristics. Saponins consist of a polycyclic aglycones attached to one or more sugar side chains. The aglycone part, which is also called sapogenin, is either steroid (C27) or a triterpene (C30). The foaming ability of saponins is caused by the combination of a hydrophobic (fat-soluble) sapogenin and a hydrophilic (water-soluble) sugar part. Saponins have a bitter taste. Some saponins are toxic and are known as sapotoxin.
Saponins are phytochemicals which can be found in most vegetables, beans and herbs. The best known sources of saponins are peas, soybeans, and some herbs with names indicating foaming properties such as soapwort, saoproot, soapbark and soapberry. Commercial saponins are extracted mainly from Yucca schidigera and Quillaja saponaria.

Saponins have many health benefits. Studies have illustrated the beneficial effects on blood cholesterol levels, cancer, bone health and stimulation of the immune system. Most scientific studies investigate the effect of saponins from specific plant sources and the results cannot be applied to other saponins.

Cholesterol reduction

Saponins bind with bile salt and cholesterol in the intestinal tract. Bile salts form small micelles with cholesterol facilitating its absorption. Saponins cause a reduction of blood cholesterol by preventing its re-absorption.
Reduce cancer risk

Studies have shown that saponins have antitumor and anti-mutagenic activities and can lower the risk of human cancers, by preventing cancer cells from growing. Saponins seem to react with the cholesterol rich membranes of cancer cells, thereby limiting their growth and viability. Roa and colleagues found that saponins may help to prevent colon cancer and as shown in their article "Saponins as anti-carcinogens" published in The Journal of Nutrition (1995, 125, 717s-724S). Some studies have shown that saponins can cause apoptosis of leukemia cells by inducing mitotic arrest.
Immunity booster

Plants produce saponins to fight infections by parasites. When ingested by humans, saponins also seem to help our immune system and to protect against viruses and bacteria.
Reduce bone loss

Studies with ovariectomized induced rats have shown that some saponins, such as the steroidal saponins from Anemarrhena asphodeloides, a Chinese herb, have a protective role on bone loss.
Antioxidant

The non-sugar part of saponins have also a direct antioxidant acitivity, which may results in other benefits such as reduced risk of cancer and heart diseases.

Saponins from Yucca and Quillaja are used in some beverages, such as beer, to produce a stable foam. The detergent properties of saponins have led to their use in shampoos, facial cleansers and cosmetic creams.