Milk fat — Composition, organization and properties

Milk is an emulsion of fat in an aqueous liquid similar to blood plasma.

Among milk's major components, fat is the most variable in terms of both proportion and composition. It is present in globular and dispersed form in the aqueous phase represented by skimmed milk. The oil-in-water type emulsion is relatively unstable due to the large size of the fat globules (0.1 to 20 µm) and their propensity, under certain conditions, to agglomerate. As in any dispersed system, the level of stored energy, in the form of interfacial free energy, is high, making the system thermodynamically unstable. What's more, these globules, mostly made up of triglycerides, are protected by a complex outer membrane with limited resistance capabilities. Based on this observation, the various technologies will seek to :

• or to preserve globular integrity, as far as possible, in order to limit the processes of alteration of intraglobular fat, such as enzymatic hydrolysis or lipolysis and the oxidation of unsaturated fatty acids, which are detrimental to the quality of milk and dairy products;

• or to separate the fat phase from the milk as part of the skimming process;

• or, on the contrary, to partially or totally destructure the globular organization through treatments such as homogenization, expansion, butyrification, concentration and dehydration.