2.2.1. Milk Fat

Milk fat is the most variable in composition and concentration component of milk [18], its content in cow's milk ranges from 2.8 to 6.3%. Milk sold to the consumer is standardized with a range of different fat content choices. It is a source of energy and essential fatty acids (linoleic, arachidonic), fat-soluble vitamins (A, D, E, K). Until recently, the economic value of milk was based precisely on the fat content of milk.

Milk fat is an ester of a trihydric alcohol of glycerol and fatty acids. Triacylglycerols (triglycerides) represent 97–98% of the total lipids in the milks. It also contains accompanying fat-like substances, or natural impurities [19]. These include phospholipids (the presence of hydrophilic and hydrophobic parts in their molecules contributes to the formation of emulsions that are stable in water), glycolipids (are biologically active components, preventing the production of enterotoxins in the body by certain types of bacteria), sterols (part of the membranes of fat globules), fat-soluble pigments (karotin, etc., determine the color of milk), fat-soluble vitamins. Despite the insignificant amount of impurities, some of them significantly affect the nutritional value of milk fat [20].

Fat in milk is a dispersed system of fat globules and is an oil-in-water emulsion, the properties of which have a marked effect on many properties of milk, such as color, taste and viscosity. The globules in bovine milk range in diameter a mean of ~3.5 μm (from ~0.1 to ~20 μm). The size distribution of fat globules in milk may be determined by light microscopy, light scattering (Malvern Mastersizer), or electronic counting devices (the Coulter counter) [21,22].
