Source and Preparation
All kinds of cholic acids can be combined with glycine or taurine with peptide bonds to form various bile acids. The bile of pig, cow and sheep was hydrolyzed with cholecylanin and alkali, and the pH was adjusted to 3.0 with hydrochloric acid. The precipitates were extracted and washed to neutral, refined with ethanol and activated carbon, washed with glacial acetic acid, and recrystallized. There are several kinds of cholic acids due to the different number and location of hydroxyl groups. The main ones are 3, 7, 12-trihydroxycholic acid and deoxycholic acid (i.e. 3, 12-dihydroxycholic acid).