ternary mixtures, fairly simple equations are available, but the relations are
intricate for more components.
Natural Fats. Figure 15.18 gives some examples of melting curves.
The natural fats are cacao bean fat, generally called cocoa butter, and milk
fat. Although they have about the same clear point, they vary greatly in
melting curve. Cocoa butter consists for a very large part of high-melting
triglycerides (fatty acid pattern:> 60 %PþS,> 30 %O), leading to a narrow
melting range for most of the fat: about 70%over 10 K. This gives cocoa
butter a special property: it behaves like a solid at room temperature (e.g.,
258 C) and it is fully liquid at body temperature. This is very desirable when
handling and eating chocolate (consisting of cocoa particles and sugar
crystals embedded in cocoa butter); it also makes the fat quite suitable as a
base for lipstick. Milk fat has a far wider compositional range (fatty acid
pattern from C4:0 to C18:0þabout one third unsaturated). Consequently,
its melting range spans about 80 K, and its properties vary gradually with
temperature.
These fats represent two extremes. Many animal body fats have a
melting pattern more or less comparable to milk fat. Some vegetable fats,
like palm oil and coconut oil, behave like cocoa butter (here the word oil is a
misnomer since the clear points are about 40 and 30 8 C, respectively). A third
type includes most vegetable oils, like sunflower, soybean, and peanut oil,
that contain a high proportion of polyunsaturated fatty acid residues;
marine oils also are in this category. They generally have clear points in the
range5to5 8 C.
Melting curves can vary greatly for one and the same type of fat; shifts
in the curve over 10 K are often observed. Following are the main causes.
Natural variation in triglyceride composition, due to variation in
cultivar and in growth conditions. Also the type and concentration
of impurities can vary.
Thetemperature historyof the fat, including the rate of heating during
the experiment.
Inaccuracyof the analytical results, which varies with the method
applied.The latter two points will be discussed later on.
Modification. Natural fats can be modified to give them desirable
crystallization properties. The most applied methods are as follows.
Hydrogenation(or hardening), i.e., saturation of (part of) the double
bonds. This is frequently applied to vegetable and marine oils. An example
is the vegetable shortening in Figure 15.18. It is seen thatcSchanges weakly