Lipids in Milk
Triglycerides make up 98.3% of cow milk fat; these molecules are made up of three joined fatty acid tails (University of Guelph). Triglycerides (aka triacylglycerols), comprising both saturated and unsaturated fats, are the main kind of fat in our diets. The triglyceride molecule looks a bit like a fork. At the base is the glycerine (aka glycerol). This substance on its own tastes sweet, and it forms the backbone of all triglycerides.
The diagram below shows one specific triglyceride with a saturated fat tail (top) an unsaturated fat tail (middle) and a polyunsaturated fat tail (bottom). In general, any batch of triglycerides will contain many statistical variants (e.g., two unsaturated tails or one unsaturated tail). We will return to this idea shortly.
A triglyceride molecule with a saturated fat tail (top), an unsaturated fat tail (middle) and a polyunsaturated fat tail (bottom).
In this video, Matt shows you the molecular structure of triglyceride.
The Milk Fat Globule
In fresh milk, the fat molecules assemble in globules, and each globule is protected by a membrane. You can see the remnants of these membranes when you fry butter in a pan. The white part that separates from the yellow part is in part the protein unwrapping from the triglyceride in the centre of the milk fat globule. See a complete analysis of what the membrane is made from here. When fully intact in fresh milk, the fat globules are quite large (up to 15 um in diameter) and prone to what is called ‘creaming’, which is the rising of the globules to the surface of the milk (University of Guelph). It is this rising process that homogenisation seeks to prevent.
The reason the globule forms in the first place is similar to the reason casein micelles form.