saponin

noun

1. Any of various steroid glycosides found in plant tissues that dissolve in water to give a soapy froth.

   ““Saponins aren't absorbed by the intestines. You've got to get the stuff into the blood.””

   “Soapnuts are the dried fruit of a tree called Sapindus mukorossi (Chinese Soapberry) and contain saponin, a natural surfactant that foams just like soap.”