Phase behaviour of beta-sitosterol-cholesterol and beta-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 h ave an effect on cholesterol absorption in the intestinal lumen as well as on the formation of atherosclerotic plaques or gallstones. The purpose of t he present study was to examine the phase behaviour of binary systems of ch olesterol with the most common plant sterol, beta -sitosterol, and its satu rated form, beta -sitostanol. The co-precipitates were prepared by precipit ating the sterol mixtures from ethanol and analysed using X-ray diffraction and differential scanning calorimetry. The co-precipitates of beta -sitost erol and cholesterol were composed of the crystalline cholesterol and beta -sitosterol and a solid solution of beta -sitosterol and cholesterol. The s olid solution dominated, when the beta -sitosterol weight fraction was less than 0.8. The crystal structure of beta -sitosterol dominated in high beta -sitosterol proportions. The binary system of beta -sitostanol and cholest erol displayed features of phase separation, as the co-precipitates were ma inly composed of crystallites of pure beta -sitostanol and cholesterol. In conclusion, because of small differences in the molecular structures betwee n beta -sitosterol and beta -sitostanol, the phase behaviours of their co-p recipitates with cholesterol differed considerably.