saponin

1. (organic chemistry, biochemistry) Any of various steroid glycosides found in plant tissues that dissolve in water to give a soapy froth.Examples: "“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."