Enrichment in unsaturated fatty acids and emulsion droplet size affect the crystallization behaviour of milk triacylglycerols upon storage at 4 °C

Increasing the unsaturated fatty acid (UFA) content in milk fat is of primary importance to improve the long-term health of consumers. However, such changes can affect the crystallization properties of milk triacylglycerols (TAG) and their functional properties. The objectives of this study were to investigate the crystallization properties of milk fat as a function of its FA composition and emulsion droplet size upon storage at refrigerated temperature. UFA-enriched TAG were obtained using cow diet supplemented with linseed oil and compared to control TAG. Homogenization was used to vary the size of emulsion droplets, from 1.7 to 0.2 μm. The crystallization properties of TAG were studied using synchrotron X-ray diffraction coupled to differential scanning calorimetry. We characterized the coexistence of several solid fat phases with a liquid phase, the characteristics of which depended on the temperature, FA composition and droplet size. The enrichment in UFA from 29 to 51 wt.% led to a decrease in the enthalpy ratio (ΔHpartial/ΔHtotal) from 64 ± 4 to 54 ± 4% at 4 °C and to the formation of 2 L (41.8 Å) structure with β1, β′1, and β′2 polymorphic forms while 2 L (39.5 Å) and 3 L (56.6 Å) structures with β1, β2, β′1 and β′2 polymorphic forms were formed with control TAG. The size of the emulsion droplets also affected the structural and thermal properties of milk TAG. Such experiments increased the knowledge about the crystallization properties of TAG dispersed in emulsion and will be useful for industrial applications and the development of UFA-enriched dairy products with improved nutritional properties.