The effect of minor components on milk fat crystallization

Milk fat is composed of 97-98% triacylglycerols and 2-3% minor polar lipids . In this study triacylglycerols were chromatographically separated from mi nor components. Isolated diacylglycerols from the polar fraction were also added back to the milk fat triacylglycerols. The crystallization behaviors of native anhydrous milk fat (AMF), milk fat triacylglycerols (MF-TAG), and milk fat triacylglycerols with diacylglycerols added back (MF-DAG) were st udied. Removal of minor components and addition of diacylglycerols had no e ffect on dropping points or equilibrium solid fat contents. Presence of the minor components, however, did delay the onset of crystallization at low d egrees of supercooling. Crystallization kinetics were quantified using the Avrami model. Sharp changes in the values of the Avrami constant k and expo nent n were observed for all three fats around 20.0 degrees C. Increases in n around 20.0 degrees C indicated a change from one-dimensional to multidi mensional growth. Differences in k and n of MF-DAG from AMF and MF-TAG sugg ested that the presence of milk fat diacylglycerols changes the crystal gro wth mechanism. Apparent free energies of nucleation (Delta G(c,apparent)) w ere determined using the Fisher-Turnbull model. Delta G(c,apparent) for AMF was significantly greater than Delta G(c,apparent) for MF-TAG, and Delta G (c,apparent) for MF-DAC was significantly less than those for both AMF and MF-TAG, The microstructural networks of AMF, MF-TAG, and MF-DAG, however, w ere similar at both 5.0 and 25.0 degrees C, and all three fats crystallized into the typical beta'-2 polymorph. Differential scanning calorimetry in b oth the crystallization and melting modes revealed no differences between t he heat flow properties of AMF, MF-TAG, and MF-DAG.