Solid-liquid equilibria of triacylglycerols and vitamin E mixtures

Abstract

Oils and fats are important ingredients for food and pharmaceutical industries. Their main compounds, such as triacylglycerols (TAG), are responsible for determining their physical properties during food storage and consumption. Lipid-rich foods are also sources of minority compounds, which is the case of vitamin E, mainly represented by (±)-α-tocopherol. These compounds can interact with the main lipid molecules in food formulation leading to modification on lipids' physicochemical properties during processes, storage, as well as during digestion, possibly altering their nutritional functionalities, which is the case of vitamin E antioxidant abilities, but also their solubility in the systems. In this case, the study of the phase-behavior between (±)-α-tocopherol and lipid compounds can elucidate these physicochemical changings. Therefore, this work was aimed at determining the solid-liquid equilibrium (SLE) of binary mixtures of TAG (tripalmitin, triolein and tristearin) and (±)-α-tocopherol including the complete description of their phase diagrams. Melting data were evaluated by Differential Scanning Calorimetry, Microscopy, X-Ray Diffraction, and thermodynamic modeling by using Margules, UNIFAC, and COSMO-SAC models. Experimental results showed that systems presented a monotectic-like behavior, with a significant decreasing in TAG melting temperature by the addition of (±)-α-tocopherol. This high affinity and attractive strengths between these molecules were also observed by thermodynamic modeling, whose absolute deviations were below 2 %. Micrographs and X-ray diffraction evidenced the possible formation of solid solutions. Both behaviors are interesting by avoiding phase separation on food in solid and liquid phases, possibly improving the antioxidant role the (±)-α-tocopherol in lipid-base systems.

Keywords: (±)-α-tocopherol; Activity coefficients; DSC; Fats and oils; Thermodynamic modeling.