Study of Cholesterol—Sitosterol Crystallization Mixtures by DTA

Abstract

DTA analysis was used to confirm evidence from X‐ray diffraction studies for the existence of 1:1 mixed sitosterol—cholesterol crystals. The curve of melting point against composition has an inflection point at about 1:1 ratio. The DTA peaks for 1:1 mechanical mixtures and for 1:1 mixed crystals are different with respect to symmetry and width. The curve of the heat of enthalpy against the composition of crystals also changes indicating a change in entropy. This can be attributed to the difference between melting mixed crystals (high order) and solid solution (low order). The solubility curve in the sitosterol—cholesterol—alcohol system has also a region of inflection confirming the previous conclusions.

Thermal analysis

“…Adding small amounts of pig or buffalo body fat to cow or buffalo ghee (butterfat) results in the appearance of an extra peak located at higher temperatures in the melting and crystallization DSC curve (201). DTA was used to confirm X-ray diffraction evidence for the existence of 1:1 mixed sitosterol-cholesterol crystals (176). DSC revealed phase transitions in the surfactant lipids from sheep, rat, and rabbit, with the upper limit of the transition being 30.1 °C in sheep, 36.8 °C in rat, and 36.3 °C in rabbit (220).…”