The effect of minor components on milk fat crystallization |
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Authors: | Amanda J Wright Richard W Hartel Suresh S Narine Alejandro G Marangoni |
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Affiliation: | (1) Department of Food Science, University of Guelph, N1G 2W1 Ontario, Canada;(2) Department of Food Science, University of Wisconsin-Madison, 53706 Madison, Wisconsin |
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Abstract: | Milk fat is composed of 97–98% triacylglycerols and 2–3% minor polar lipids. In this study triacylglycerols were chromatographically
separated from minor 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 studied. Removal of minor components and addition of diacylglycerols had no
effect on dropping points or equilibrium solid fat contents. Presence of the minor components, however, did delay the onset
of crystallization at low degrees of supercooling. Crystallization kinetics were quantified using the Avrami model. Sharp
changes in the values of the Avrami constant k and exponent n were observed for all three fats around 20.0°C. Increases in n around 20.0°C indicated a change from one-dimensional to multidimensional growth. Differences in k and n of MF-DAG from AMF and MF-TAG suggested that the presence of milk fat diacylglycerols changes the crystal growth mechanism.
Apparent free energies of nucleation (ΔGc,apparent) were determined using the Fisher-Turnbull model. (ΔGc,apparent) for AMF was significantly greater than ΔGc,apparent for MF-TAG, and ΔGc,apparent for MF-DAG was significantly less than those for both AMF and MF-TAG. The microstructural networks of AMF, MF-TAG, and MF-DAG,
however, were similar at both 5.0 and 25.0°C, and all three fats crystallized into the typical β′-2 polymorph. Differential
scanning calorimetry in both the crystallization and melting modes revealed no differences between the heat flow properties
of AMF, MF-TAG, and MF-DAG. |
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Keywords: | Avrami equation crystallization minor components milk fat |
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