Unsaturated fatty acid enriched vs. control milk triacylglycerols: Solid and liquid TAG phases examined by synchrotron radiation X-ray diffraction coupled with DSC

Abstract

The fatty acid composition of milk triacylglycerols (TAGs) can be modified to improve their nutritional properties and the long-term health of consumers. However, the consequences of an increase in unsaturated fatty acid (UFA) content on the physical properties of milk TAGs remain to be elucidated. This study aimed at comparing the crystallisation properties and melting behaviour of control vs. UFA-enriched milk TAGs using the coupling of time-resolved synchrotron X-ray diffraction and differential scanning calorimetry on cooling and then heating at 3°C/min. On cooling from the melt, high crystallisation temperature (HCT) TAGs solidify from 15.8°C in α 2L (45–49Å) structures, then low crystallisation temperature (LCT) TAGs form α 3L structures with a higher thickness (75.5Å vs. 71.5Å) and a delay (8.5°C vs. 12.1°C) for UFA-enriched TAG. On heating, melting of TAGs crystals and formation of 3L2 (64.7–80.1Å) and β′ 2Lf (40–44Å) crystals associated with polymorphic reorganisations have been characterised. The organisation of TAG molecules in their liquid state revealed a higher thickness for UFA-enriched TAGs as compared to control TAGs. Such results improve the knowledge about the mechanisms of TAG crystallisation as a function of their FA composition and are important for the technological utilisation of UFA-enriched TAGs in food products.