Simulated gastric juice was prepared fresh daily containing 3 mg of pepsin (Sigma), 1 ml of NaCl solution (0.5%) and acidified with HCl to pH 2.0 or 3.0. Simulated intestinal juice was consisted of 1 mg of pancreatin (Merck), 1 ml of NaCl solution (0.5%) and adjusted to pH 8.0, with or without 1.5% of bile salts (1:1 mixture of sodium cholate and sodium deoxycholate). Both solutions were sterilized by filtration through 0.22 mm membranes (Millipore, Bedford, USA).