Polymorphism of Triacylglycerols and Natural Fats

Abstract

This article reviews the polymorphism of the principal triacylglycerols (TAGs) in single and binary mixture states. In the first section, the basic concepts of fat polymorphism, namely, thermal stability, subcell structure, and chain‐length structure are explained together with the phase equilibria of binary mixture systems. Then, the polymorphic behavior of the principal TAGs is described. The phase behavior of the mixture systems of the principal TAGs and natural fats is discussed with an emphasis on the influence of the polymorphism.

The Influence of Sub-Zero Conditions on the Mechanical Properties of Polylactide-Based Composites

“…They indicate solidification (crystallization) of the vegetable oil [ 49 ]. The presence of the multiple crystallization peaks is typical for vegetable oil, which usually shows polymorphism and can create a hexagonal α form, an orthorhombic perpendicular β’ structure and a triclinic parallel β polymorph, each of them characterized with a different level of stability [ 50 , 53 ]. The crystalline form of the oil depends on solidification conditions as well as the amount of saturated and unsaturated fatty acids of different length [ 50 ].…”

An Insight into the Solid-State Miscibility of Triacylglycerol Crystals

“…Although in a lesser degree, some mobility is expected to remain in the orthorhombic perpendicular subcell that would also clarify the occurrence of miscible β’ phases. However, larger methyl-end stacking gaps at increasing ∆Cn result in an increase of entropy that may lead to phase demixing in LLL/PPP and LLL/SSS systems for any of the polymorphs involved [ 70 , 84 ]. A different case is the triclinic parallel subcell (β), in which the dense molecular packing prevents from the crystallization of non-isomorphic TAGs in the same crystal lattice.…”

“…Thus, β’ most stable forms in TAGs with a C n C n + 2 C n structure (n = even C number), such as CLC (with C being capric acid), LML, MPM, and PSP have been related to their “chair” type configuration, which may not undergo a further solid-state transformation into “tuning fork” type β forms [ 86 , 101 , 102 , 103 ]. The importance of the polymorphic occurrence briefly discussed above (for a more detailed description the readers should refer to recent book chapters [ 28 , 70 , 104 ]) is ultimately revealed on the phase behavior of mixed-acid TAGs and ensuing thermophysical properties shown by complex fats, like the β’ stable coconut oil [ 15 , 105 , 106 ].…”

“…( a ) Synchrotron source light X-ray diffraction (SR-XRD) patterns of a 70LLL/30MMM mixture during a thermal process of cooling and subsequent heating at 100 °C·min −1 and 5 °C·min −1 , respectively; and, ( b ) kinetic phase diagram of LLL/PPP mixtures. Adapted with permission from [ 70 , 82 ], © 2020 John Wiley & Sons, © 2003 American Chemical Society.…”

“…The very first phase diagrams are reviewed in the work of Rossell [ 67 ], and even though their accuracy has been later discussed [ 63 , 68 ], they still deliver valuable empirical information regarding function-molecular interactions in binary mixtures of TAGs with diverse degree of unsaturation and molecular symmetry. Many systems have been re-examined and new ones reported over time using more refined sample materials and experimental techniques, together with theoretical models for describing the phase equilibrium in TAG systems [ 9 , 61 , 68 , 69 , 70 , 71 , 72 ]. In this regard, it is worth mentioning the crucial role of synchrotron source light X-ray diffraction (SR-XRD) and Fourier transform infrared (FTIR) spectroscopy in our current understanding on the role of structural features on mixing states and the complex polymorphic behavior of TAG systems under kinetic conditions.…”