Saponins are a class of chemical compounds of glycosides found in particular abundance in various plant species. In plants, saponins may serve as anti-feedants, and to protect the plant against microbes and fungi[1].
Saponins are glycosides with a distinctive foaming characteristic. Saponins consist of a polycyclic aglycone that is either a choline steroid or triterpenoid attached via C3 and an ether bond to a sugar side chain. The ability of a saponin to foam is caused by the combination of the nonpolar sapogenin and the water soluble side chain. Saponins are bitter and reduce the palatability of livestock feeds. Some saponins reduce the feed intake and growth rate of nonruminant animals while others are not very harmful. For example, the saponins found in oats and spinach increase and accelerate the body's ability to absorb calcium and silicon, thus assisting in digestion. Certain pasture weeds contain substantial quantities of dangerous saponins and result in life threatening toxicities for certain animal species[1].
References:
[1]. "Saponins". Cornell University. 14 August 2008. Retrieved 23 February 2009.