Saponins molecular properties

Considerable use of a number of its chemical and physical properties has been made in the isolation and quantitative determination of cholesterol. Cholesterol forms a very stable and quite insoluble molecular compound with the saponin, digitonin. The majority of sterols with hydroxyl groups at Cs in the 3 orientation likewise form more or less sparingly soluble digitonides. When treated with strong mineral acid, cholesterol forms a variety of colored complexes useful for the qualitative and quantitative determination of the compound. The most widely recognized of these is the Liebermann-Burchard reaction, in which the sterol Windaus, A., Ber. deut. diem. Oee. 42, 238 (1909). 

---