Polymorphism and crystallization behaviour of triacylglycerols. From pure components to mixtures rich in oleic acid
[eng] Quality attributes of food products such as visual appearance, melting behavior, or shelf-life are strongly determined by the crystallization behavior of natural fats and oils within. In turn, this behavior depends on the polymorphism and the sort of mixing states (eutectic phase, solid soluti...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2022 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/188067 |
| Acceso en línea: | https://hdl.handle.net/2445/188067 http://hdl.handle.net/10803/675001 |
| Access Level: | acceso abierto |
| Palabra clave: | Cristal·lografia Polimorfisme (Cristal·lografia) Mescles Lípids Triglicèrids Crystallography Polymorphism (Crystallography) Mixtures Lipids Triglycerides |
| Sumario: | [eng] Quality attributes of food products such as visual appearance, melting behavior, or shelf-life are strongly determined by the crystallization behavior of natural fats and oils within. In turn, this behavior depends on the polymorphism and the sort of mixing states (eutectic phase, solid solution phase, molecular compound formation) displayed by their major triacylglycerol components. Therefore, it becomes essential that studies regarding lipid crystallization cover from pure molecular components and their mixtures to real fats and oils. In connection with the above, this thesis focuses on gaining further fundamental knowledge about the polymorphism and crystalline behavior of lipid systems with varying degrees of complexity. Thus, the first stage of the research involved a study of pure triacylglycerols based on palmitic, lauric, and oleic acids (P, L, and O, respectively), which are typical of natural fats and oils such as lard and palm, olive, and coconut oils. During the second stage, binary and ternary mixtures including these triacylglycerols were examined to obtain an insight into their solid-state miscibility properties. Concretely, the mixtures were composed of a fully saturated triacylglycerol and one or two saturated-unsaturated triacylglycerols able to form a molecular compound. Despite the presumable crucial role of interactions including triacylglycerols forming molecular compound in the physical behavior of natural lipids and their blends, the phase behavior of triacylglycerol mixtures with such configuration is barely known. Finally, the third stage consisted of a more applied investigation of the crystalline and thermal properties of blends including natural fats. More specifically, binary blends of cocoa butter and shea butter stearin. Regarding the investigation of pure TAGs, calorimetric and X-ray diffraction techniques were used to examine the polymorphic occurrence and transformation behavior of PPP, LLL, OPO, and PPO during the application of dynamic thermal treatments at varying cooling and heating rates. The results showed that the polymorphic occurrence on cooling, as well as the sequence and type of transformations during heating, were influenced by the rate of the thermal treatments applied. However, it was also found that the extent of the kinetic influence depended on the intrinsic properties of triacylglycerols such as the length of the fatty acid chains or the characteristic polymorphism. The mixtures under examination during the phase behavior studies included the binary systems PPP/POP, PPP/PPO, PPP/OPO, LLL/POP, and LLL/PPO, and the ternary systems PPP/POP/OPO, PPP/POP/PPO, and LLL/POP/PPO (keeping an equimolecular ratio of POP/OPO or POP/PPO to favor molecular compound formation). Eutectic behavior with partial miscibility was observed under metastable and stable conditions. Furthermore, the results obtained for stable binary mixtures showed that the degree of miscibility was primarily influenced by the oleic acid content of the unsaturated component, as well as the differences in the size of the triacylglycerols within the mixture. From the solid-state miscibility observed in ternary systems containing LLL or PPP, it was concluded that third components may affect the mixing interactions associated with molecular compound formation. In addition, the results suggested that the ternary interactions studied may help to explain the crystallization behavior of edible lipids like palm oil and be useful in fat structuring applications. As a case study of real fat blends, combinations of cocoa butter and shea butter stearin at varying proportions were examined through calorimetric, X-ray diffraction, spectroscopic, and microscopic techniques. These made possible to characterize the effect of composition on the polymorphic crystallization and transformation properties, the melting profile, and the microstructural development. The results obtained for some of the parameters under study suggested that specific combinations might be considered for its application in chocolate-type confectionery products. |
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