Phase behaviour of β-sitosterol-cholesterol and β-sitostanol-cholesterol co-precipitates

Plant sterols reduce the absorption of cholesterol in the intestinal lumen. Although the absorption of plant sterols is limited, several plant sterols have been found in small quantities in plasma lipoproteins, in human bile and gallstones. The phase behaviour of plant sterols with cholesterol can have an effect on cholesterol absorption in the intestinal lumen as well as on the formation of atherosclerotic plaques or gallstones, The purpose of the present study was to examine the phase behaviour of binary systems of cholesterol with the most common plant sterol, β-sitosterol, and its saturated form, β-sitostanol. The co-precipitates were prepared by precipitating the sterol mixtures from ethanol and analysed using X-ray diffraction and differential scanning calorimetry. The co-precipitates of β-sitosterol and cholesterol were composed of the crystailine cholesterol and β-sitosterol and a solid solution of β-sitosterol and cholesterol. The solid solution dominated, when the β-sitosterol weight fraction was less than 0.8. The crystal structure of β-sitosterol dominated in high β-sitosterol proportions. The binary system of β-sitostanol and cholesterol displayed features of phase separation, as the co-precipitates were mainly composed of crystallites of pure β-sitostanol and cholesterol. In conclusion, because of small differences in the molecular structures between β-sitosterol and β-sitostanol, the phase behaviours of their co-precipitates with cholesterol differed considerably.