Thermal and Structural Behavior of Milk Fat: 1. Unstable Species of Cream

• Published in: Journal of colloid and interface science 2000-09, Vol.229 (1), p.62-71
• Main Authors: Lopez, Christelle, Lesieur, Pierre, Keller, Gérard, Ollivon, Michel
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; cream; DSC; Fat industries; Food industries; Fundamental and applied biological sciences. Psychology; ice cream; milk fat globules; phase transitions; polymorphism; triacylglycerols; X-ray diffraction
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1006/jcis.2000.6988

The thermal and structural properties of unstable varieties of triacylglycerols (TGs) crystallizing in milk fat globules of cream are examined in the range −8– +50°C using a new instrument allowing simultaneously time-resolved synchrotron X-ray diffraction at both wide and small angles as a function of temperature (XRDT) and high sensitivity differential scanning calorimetry (DSC). Small angle X-ray diffraction shows that the unstable α form first formed by cream quenching to −8°C corresponds in fact to two different lamellar phases corresponding to 2L (47 Å) and 3L (70.4 Å) arrangements of TGs. The bilayered structure is very unstable since it disappears during the course of a 20-min isothermal conditioning at −8°C. On fast heating, the crystalline evolution of cream TGs demonstrates the monotropic character of their polymorphism. The structural and thermal behaviors of cream which are compared to that of its anhydrous milk fat isolated from the cream (C. Lopez et al., J. Dairy Sci., submitted) show that the crystallization occurring in emulsion droplets is similar to bulk. However, the comparison of XRD peak widths indicates that the TG crystallization is more disordered in emulsion. This disorder is attributed to the constraints due to the interface curvature in emulsion droplets.