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 (/~-polymorphic) form is observed within a minute at 298K for cooling rates up to 120K/rain. 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 13 form crystals. A study carried out after rapid cooling showed that two processes occurred. Initial/y, the a polymorphic form is produced; this transformed to the ~-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/~ polymorphic form occurs.

Study of triacylglycerol polymorphs by nuclear magnetic resonance: effects of temperature and chain length on relaxation parameters

“…This was higher than the ratio of 1 : 7 reported by Norton et al [6] at 60 MHz and Azoury et al at 20 MHz. [7] These differences can be easily explained by the different tempering procedures, as well as the different magnetic fields and temperatures studied.…”

“…The current results are in agreement with previous studies performed with one or two TAs at a single temperature. [6,7,13,14] The present study demonstrated that a general dynamic behavior can be observed for TAs at low or high NMR field whatever the chain length and the temperature studied. The results obtained from the proton T 1 measurements displayed a minimum ratio of 1 : 10 between the α and the β forms for the TA family chosen.…”

“…For example, low-field TD-NMR could be used to distinguish an α polymorph from a β polymorph using spin-lattice relaxation times, where a T 1 almost 10 times greater was observed for β polymorphs of tripalmitin and tristearin than for α polymorphs. [6] Others T 1 measurements have suggested that the mobility of the terminal methyl group of tristearin was more constrained in the β polymorph than in the α polymorph. [7] T 1 relaxation time measurements have also made it possible to the study of lipid crystallization in complex food systems.…”

Effect of unsaturated acyl chains on structural transformations in triacylglycerols

“…Thus, the introduction of unsaturated acyl chains in a saturated fat system by the blending of saturated and unsaturated TAG (StStSt and OOO, respectively) does not significantly change the principal sequence of structural transformations, apart from the formation of mixed crystals of the phases already known for the components of the blend. Fast cooling introduces more randomness in the structure detected by DSC [25]. These experiments suggest that the formation of the a 2 -phase in the mixed saturated/unsaturated TAG is solely the result of a molecular composition including both saturated and unsaturated hydrocarbon chains in one molecule and not the result of a mixed composition of saturated and unsaturated hydrocarbon chains.…”

Polymorphism of sugars studied by time domain NMR

“…In contrast, the T 1 of the α form of tristearin (hexagonal form) has been measured at 250 ms, while that of the β form (triclinic form) is 1.7 s [10]. According to Azouri [10], Norton [11] was the fi rst to use the parameter T 1 to diffe re n t i ate poly m o rp h i c forms.…”