Effects of Crystal Growth and Polymorphism of Triacylglycerols on NMR Relaxation Parameters. 2. Study of a Tricaprin−Tristearin Mixture

Abstract

Being able to determine the physical properties of fats such as polymorphism and crystal size is very important for the food industry. After a relationship was observed between spin−lattice relaxation time and crystal size in a solid−liquid mixture of triacylglycerols, the effects of polymorphism and crystal size were investigated by low-field NMR relaxation and powder X-ray diffraction on three binary mixtures of tricaprin and tristearin in the solid state. Second moment (M2) was proven to be only sensitive to polymorphism. Its measurements permitted the quantification of polymorphic forms in a binary mixture, with a model based on M2 of the pure components. As for the spin−lattice relaxation time (T1), it was proven to be only sensitive to crystal size and not to polymorphism. Quantification was not possible with T1 measurements, but information on the pattern of the crystal thickness distribution was obtained using the maximization entropy method algorithm. The determination of polymorphism was thus possible because of the difference in size between the α and β triacylglycerol crystals. Finally, a phase diagram mainly based on NMR data was constructed for the tricaprin/tristearin system.