Phase behaviour of some palmito-oleo triglyceride systems

Systematic Investigation of Co-Crystallization Properties in Binary and Ternary Mixtures of Triacylglycerols Containing Palmitic and Oleic Acids in Relation with Palm Oil Dry Fractionation

This work investigates the molecular interactions within the main triacylglycerols constitutive of palm oil, all having a key role in the multi-step dry fractionation process. Identification of these interactions is possible thanks to the establishment of binary and ternary phase diagrams, using differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) at variable temperature. The following systems were selected: PPP-POP, PPP-OPP, PPP-POO, POP-OPP, POP-POO, OPP-POO, PPP-POP-POO and PPP-OPP-POO (P: palmitic acid and O: oleic acid), and analyzed in direct mode (heating at 5 °C/min., after melting and quenching at -60 °C), and after tempering for three months at 20 °C (tempered mode). DSC makes it possible to bring out crystallization and melting phenomena associated to polymorphic transitions, which are further characterized (crystalline forms) by XRD. The results show that unsaturated are poorly soluble in fully saturated triacylglycerols, that the intersolubility decreases in proportion to the number of unsaturated fatty acids, that positional isomerism (POP/OPP) has a major impact, that OPP may induce formation of molecular compounds and that co-crystallization properties are highly modified by tempering depending on the polymorphic properties of the systems. This provides a better understanding and allows for effective control of the palm oil dry fractionation process.

An Insight into the Solid-State Miscibility of Triacylglycerol Crystals

The crystallization properties of triacylglycerols (TAGs) strongly determine the functional properties of natural lipids. The polymorphic and mixing phase behavior of TAG molecules have long been, and still are, a hot topic of research with special relevance for the cosmetic, pharmaceutical, and food industry. To avoid the difficulties arising from the study of whole real fats, studies at the molecular level on mixtures of a limited number of TAGs has become an indispensable tool to identify the underlying causes of the physical properties in lipid systems. In particular, phase diagrams of binary mixtures of TAGs exhibiting a different degree of heterogeneity (monoacid or mixed fatty acids; molecular symmetry; the presence of cis or trans double bonds) have resulted in a significant breakthrough in our knowledge about structure-interaction-function relationships. The present work aims to provide an overview of the main reports regarding binary and ternary TAG systems, from the early studies to the most recent developments.

Phase behavior of a binary mixture of 1,3-dipalmitoyl-2-oleoyl-sn-glycerol and 1,3-dioleoyl-2-palmitoyl-sn-glycerol in n-dodecane solution

The phase behavior of a binary mixture of triacylglycerol (TAG), POP (1,3-dipalmitoyl-2-oleoyl-sn-glycerol), and OPO (1,3-dioleoyl-2-palmitoyl-sn-glycerol) in an organic solvent, n-dodecane, was examined by DSC and synchrotron radiation X-ray diffraction (SR-XRD). In our previous study on POP-OPO mixtures in neat liquid, the formation of molecular compound (MC) crystals of POP/OPO = 50/50 was observed (Minato et al. J. Am. Oil Chem. Soc. 1997, 74, 1213-1220). The purpose of the present study was to determine whether MC is formed in the POP-OPO mixture system in diluted solution when n-dodecane (C(12)) is added to the mixture as a solvent. Two solution systems having weight concentration ratios of POP and OPO to n-dodecane ((POP+OPO):C(12)) of 50:50 (50% solution) and 20:80 (20% solution) were prepared. We found that MC formed at a ratio of POP/OPO = 50/50 in both 50% solution and 20% solution in the stable and metastable states. Differences between the neat liquid and solution systems appeared in two results. In the first, the melting temperatures of MC crystals were lowered from 32.0 degrees C (neat liquid) to 20.4 degrees C (50% solution) and 18.0 degrees C (20% solution). In the second, the beta polymorph of the MC was always observed in the two solutions under the conditions examined in the present study, whereas alpha and beta polymorphs were observed in the neat liquid. These differences were caused by thermodynamic solvent effects. However, we conclude that aliphatic chain-chain interactions through palmitic and oleic acid moieties forming the MC of POP-OPO having a double chain length structure are not disturbed by solute-solvent interactions.

Molecular interactions and kinetic properties of fats

This article has reviewed the recent work on the molecular interactions and kinetic properties of the polymorphic transformations of the TAGs in the single and mixed states. Progress has recently been made in the molecular-level understanding of the polymorphic transformations of the TAGs. Particularly, the use of the time-resolved X-ray diffraction with Synchrotron radiation (SR-XRD) has provided precise information of the structural changes of the fat crystals at a time scale of 10 sec. Therefore, fruitful information was obtained on the kinetic and molecular aspects of crystallization and mixing processes of the various types of mixed-acid TAGs, which were not obtained with the traditional thermal and structural techniques because of their complicated structural properties. One may anticipate that, although the experimental sites and machine times are limited, the SR-XRD techniques will be more applied to the fat systems involving the following materials and systems; (a) multicomponent natural fats with and without additives of emulsifiers, proteins and carbohydrates, (b) fats in dispersed phases such as oil-in-water (O/W) and water-in-oil (W/O) emulsions, (c) crystallization and transformation processes under external influences of hydrostatic pressure and shear stress [68].