Phase Equilibria and Phase Properties in Systems Containing Lecithins, Triglycerides, and Water.

Abstract

The phase behavior and molecular interaction in systems of lecithins (egg lecithin, dipalmitoyl lecithin) and triglycerides (triolein, tristearin) with and without water were studied with differential thermal analysis, X-ray diffraction, IR spectrometry and polarizing microscopy. A maximum of 15% (wt/wt) triolein can be incorporated into the lamellar liquid crystalline phase of hydrated lecithin. Low-angle X-ray diffraction measurements of this phase indicate that the triolein is mostly located at the lipid water interface; a minor part is dissolved in the apolar region. Triolein induced a broadening of the gel-liquid crystalline transition of dipalmitoyl lecithin, but no change in the transition temperature. The solubilities of the lecithins in triolein were found to be less than 1%. No pronounced molecular interaction between tristearin and the lecithins was recorded, neither with differential thermal analysis nor X-ray diffraction. On heating, pure tristearin shows a complex phase behavior which is preserved also in mixtures with lecithins, but the .alpha.L form is less stable. IR spectrometry appears to be a convenient method to recognize different polymorphic forms of triglycerides also in mixtures with other lipids.