A calorimetric, NMR and X-ray diffraction study of the melting behavior of tripalmitin and tristearin and their mixing behavior with triolein

Abstract

X-ray diffraction, differential scanning calorimetry and NMR have been used to give information on the molecular order and melting of tripalmitin and tristearin crystals. They also have been used to study the melting and solubility of these pure triglycerides when mixed with triolein. From these studies we propose demixing in the liquid state and observe modification of the crystallization kinetics of these saturated triglycerides such that the highest melting (β-polymorphic) form is observed within a minute at 298K for cooling rates up to 120K/min. In the mixtures the long d-spacing, corresponding to the distance between layers in the crystals, was observed to be approximately 0.5 nm greater after cooling in excess of 60K per min than for close packed layers in the β form crystals. A study carried out after rapid cooling showed that two processes occurred. Initially, the α polymorphic form is produced; this transformed to the β-like crystals in a matter of a few minutes. There is then a much more gradual decrease in the long d-spacing as a slow annealing into the tightly packed β polymorphic form occurs.