Solid–Liquid Equilibrium of Binary Mixtures Containing Fatty Acids and Triacylglycerols

Abstract

SolidÀliquid phase diagrams of the following systems were measured using differential scanning calorimetry (DSC): tristearin (2,3-di(octadecanoyloxy)propyl octadecanoate) + tripalmitin (2,3-di(hexadecanoyloxy)propyl hexadecanoate), tristearin (2,3-di(octadecanoyloxy)propyl octadecanoate) + palmitic acid (n-hexadecanoic acid), tristearin (2,3-di(octadecanoyloxy)propyl octadecanoate) + linoleic acid (cis-9,cis-12-octadecadienoic acid), tripalmitin (2,3-di(hexadecanoyloxy)propyl hexadecanoate) + triolein (2,3-bis[[(Z)-octadec-9-enoyl]oxy]propyl (Z)-octadec-9-enoate), and tripalmitin (2,3-di(hexadecanoyloxy)propyl hexadecanoate) + commercial oleic acid (commercial (Z)-octadec-9-enoic acid). The eutectic point was observed for two systems, tristearin with tripalmitin or with palmitic acid. Polarized optical microscopy was employed to investigate the solid phase of the systems and confirmed the occurrence of a solid solution at the extreme of the phase diagram rich in the component with a higher melting temperature. Margules-2-suffix, Margules-3-suffix, nonrandom two-liquid (NRTL), and universal quasichemical functional group activity coefficient (UNIFAC) models were employed to describe the liquidus line of the studied systems, except for the system formed by tripalmitin (2,3-di(hexadecanoyloxy)propyl hexadecanoate) + commercial oleic acid (commercial (Z)-octadec-9enoic acid) which is a pseudobinary system that was well-described by the UNIFAC model. The best results for the other systems were obtained when employing the Margules-3-suffix and NRTL models.

Trends and demands in the solid–liquid equilibrium of lipidic mixtures

“…Some examples can be easily mentioned. a) Optimization of fractionation processes in which the material are separated into fractions depending on the melting point by a set of crystallization procedures 89 ; b) Optimization of interesterification processes in 50 which fatty acids moieties are added or removed from the triacylglycerols in order to obtain lower or higher melting points materials. This process is a classical alternative for the replacement of the hydrogenation procedure which promotes the formation of saturated or trans-unsaturated fatty compounds 55 related as precursors of cardiovascular diseases 10 ; c) Development of structured lipids for the improvement of the nutritional or physicochemical characteristics of the product.…”

“…Consequently, apart from the fact that such phenomena 45 largely affect microstructural changes and, therefore, the set of industrial quality requirements of products, numerous operational and economical reasons emphasize the importance of a critical thermodynamic evaluation of the fatty systems for process design and optimization. 50 This review is aimed at providing an overview on the current understanding of the solid-liquid equilibrium behavior of fatty systems and on the approaches used in the literature for their modeling, taking into account that a deeper knowledge on solidliquid equilibrium of fatty compounds is still required. The 55 complex nature of fats and oils suggests that the discussion on their phase equilibrium is best tackled starting with the simplest systems.…”

“…In case of lipidic systems, solid solutions are particularly interesting because they can be intentionally developed such that physicochemical 95 properties could be adjusted to specific requirements [46][47][48] . Several fatty binary mixtures present solid solution formation at some concentrations, especially those composed of triacylglycerols or fatty alcohols 4,8,49,50 . The phase diagrams of such mixtures comprise 6 domains as shown in Figure 2 B.…”

“…The eutectic point in this case establishes a triphasic equilibrium in which the liquid phase is in equilibrium with two solid solutions with 105 distinct compositions. The evaluation of the eutectic point and the solubility region of the solid phase is usually carried out using the Tammann plot ( Figure 3) [50][51][52][53] . This diagram relates the enthalpy of the eutectic reaction as a function of the mixture concentration in which the enthalpy rises up to the eutectic point when it begins 110 to decrease.…”

“…Brief overview on the techniques for measuring SLE data 50 The temperatures and enthalpies of the transitions of both solidliquid and solid-solid phenomena, including those due to the polymorphic transitions, can be obtained by differential scanning calorimetry (DSC). Such a technique is classically used for the description of solid-liquid phase diagrams of fatty systems.…”