Solid triacylglycerols within human fat globules: β crystals with a melting point above in-body temperature of infants, formed upon storage of breast milk at low temperature

- Breast milk is essential to infant nutrition.
- Storing breast milk at 4 °C induces TAG crystallization in fat globules.
- TAG crystals were described by X-ray diffraction and DSC.
- Melting temperature of TAG crystals is above in-body temperature.
- Implication in the mechanisms of lipid digestion in infants

Breast milk fat globules are the natural colloidal assemblies secreted by lactating mothers to provide dietary energy and bioactive molecules to infants. Although they are important in newborn infant nutrition, growth and health, their physical properties remain poorly known. In this study, the crystallization and melting properties of breast milk triacylglycerols (TAG; 98% of milk lipids) were investigated in fat globules and in anhydrous state. The thermal and structural properties of breast milk TAG were characterized by differential scanning calorimetry and synchrotron radiation X-ray diffraction, respectively. Breast milk fat globules have a mean diameter of 4 to 5 μm. They contain 48-57% saturated fatty acids with 27-29% of C16:0. Storage of breast milk at 4 °C in the refrigerator leads to the crystallization of high-melting point TAG within fat globules in β 2L (41.7 Å) lamellar structures. The final melting point of these TAG crystals, Toffset = 41.1 ± 1.6 °C, is above in-body temperature of infants. Hence, the solid TAG phase could affect the mechanisms of breast milk fat globules digestion and absorption for T < Toffset of β TAG crystals, by decreasing the rate of TAG hydrolysis and solubilization.