A study of the phase transition behaviours of cholesterol and saturated egg lecithin, and their interaction by differential scanning calorimetry.

The thermal behaviours of hydrogenated egg lecithin (PC) and cholesterol (C) in anhydrous form and in aqueous dispersions were studied by differential scanning calorimetry. The role of C in phase transitions of C-PC mixtures prepared by physical mixing or coprecipitating from chloroform has been examined. C underwent a phase transition at 34 degrees C and a second one at 76-78 degrees C which depended on the thermal history of the samples. C lowered the gel to liquid crystalline phase transition temperature (Tt) of the aqueous dispersions prepared from C-PC coprecipitates, broadened the endothermic peak at the Tt, and at 1:1 molar ratio the C-PC system did not undergo the phase transition. The C-PC interaction was observed below the Tt. In aqueous dispersions prepared from C-PC physical mixtures, C did not influence the phase transition and acted like an inert diluent. Pellets prepared from C-PC mixtures formed myelin bodies as a result of their erosion in 0.185 M borate buffer (pH 7.4) at below Tt, but the thermal behaviours of these myelin bodies were different for pellets prepared differently. Addition of bovine serum albumin (BSA) (10%, w/w) to the physical mixtures or coprecipitates of C-PC, or to PC alone did not show any effect on the thermal behaviours of their aqueous dispersions at the Tt.