transitions, since these invariably cause the melting temperature to increase.
In the figure we see that the new peak is at a lower temperature than the
original second peak. It is also seen that the area under the curve, i.e., the
amount of fat melting, increased during storage.
The following phenomena can be seen as consequences of the
occurrence of solid solutions in the fat.
- The melting range is narrowed. If two multicomponent fats of
different melting range are mixed in the liquid state and then cooled, the
differential melting curve of the mixture is observed to be narrower than the
average of the melting curves of the original fats. The initial melting point is
higher and the clear point is lower, and the shape of the curve tends to be
significantly altered. - The temperature at which most of the fat melts depends on the
temperature at which crystallization took place, as discussed. - Crystallization in steps of decreasing temperature gives less solid
fat than direct crystallization at the lowest temperature. Taking the example
of Figure 15.24, crystallization atT 3 gives a fraction solid of
ða 3 a 1 Þ
ða 4 a 1 Þ¼ 0 : 72
FIGURE15.25 Differential melting curve (expressed as%of the fat melting per K
temperature increase) for a milk fat sample. The fat was held for 1 day at 19 8 C and
then at 10 8 C for 2 h or 8 days. (From data in H. Mulder, P. Walstra. The Milk Fat
Globule. Pudoc, Wageningen, 1974.)