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The solubility of milk fat, fully hardened milk fat and milk fat hard fraction in liquid oils

Authors: R.E. Timms


Solubilities were studied by determining softening points of appropriate mixtures. The systems studied were: (i) milk fat with soyabean, sunflower or cottonseed oils, (ii) fully hardened milk fat with sunflower oil, (iii) milk fat or a hard fraction of milk fat with a soft fraction of milk fat. In the range 0-60% liquid oil or soft fraction, the results fitted the ideal solubility equation, except for system (ii). However, heats of fusion determined using the equation were always higher than corresponding heats of fusion determined by differential scanning calorimetry. It is suggested that the higher heats of fusion are attributable to the more saturated, higher melting triglycerides which are not completely dissolved at the softening point. Deviations from ideal solubility are discussed in terms of molecular weight differences between milk fat and vegetable oil triglycerides, solid solutions and imperfect crystals.

For mixtures of butter oil with liquid vegetable oils, an approximate version of the ideal solubility equation is proposed:

log10 (% weight / 100) = C.?T

where % weight is the percentage of milk fat in the mixture. C is a constant and equals 0.0589 and ?T is the difference in the softening points of the milk fat and the mixture. This equation is independent of either the milk fat or the liquid oil. It may be used (i) to deduce the composition of a mixture from a knowledge only of its softening point and the softening point of the original milk fat, or (ii) to deduce the oil addition required to yield a mixture with a given softening point.

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