Composition of milk fatWhat is milk fat?

From a chemical point of view fats are essentially triacylglycerides, i.e. substances made up of three fatty acids and glycerol.

Milk fat is characterised by very wide fatty acid distribution, ranging from butyric acid to arachidonic acid. In addition to saturated (medium and long-chain) fatty acids it also contains physiologically important unsaturated and short-chain fatty acids in amounts of up to 40 %. Milk fat also contains mono- and diglycerides, phospholipids, free fatty acids, cholesterol, fat soluble vitamins A, D, E and K, enzymes, as well as aromatic and decomposition substances.The composition of milk is affected by various factors, the most important of which are: Fodder: influences the content of saturated and unsaturated fatty acids as well as vitamin E and A Lactation stage: influences the content of short- and long-chain fatty acids Heredity, state of health, animal age: influences the predisposition of unsaturated fatty acids to lipolysis and oxidation.How is milk fat present in milk?Milk fat is present in milk in the form of globules approx. 1-10 m in diameter. These globules are enclosed and protected by a membrane called the primary fat globule membrane. This membrane is composed predominantly of substances with an emulsifying character, particularly phospholipids, lipoproteins and cholesterol, which contribute to the uniform distribution of fat globules in the aqueous phase. Obviously the membrane is not formed until the final stage of milk creation, but despite this the milk fat is fully protected when it leaves the teat. The fat globule membrane can be damaged even during milking, resulting in free fat.

The fat globules are reduced in size by mechanical or thermal action, leading to a shortage of primary membrane material since the surface of the fat globules increases when viewed as a whole. In this case milk proteins are called upon to form the so-called secondary fat globule membrane, causing casein and serum proteins and, increasingly, enzymes such as lipase to bind with the fat globule membrane.How does the composition of milk fat depend on fodder?

Green fodder and dried fodderAs a rule green fodder produces milk with a high fraction of unsaturated fatty acids. Dried fodder causes a reduction in unsaturated fatty acids. This increases the melting point and hardness of the milk fat, as the long-chain fatty acids of the milk fat are absorbed from the feed.When this happens the polyunsaturated fatty acids (linoleic and linolenic acids) are generally hydrogenated in the digestive tract. Normally a double bond is maintained, so oleic acid represents the most important fatty acid in milk fat. Cows also have what is known as a desaturase enzyme, which can reconstitute oleic acid from stearic acid. This mechanism allows the "melting point" of the milk fat always to be kept below body temperature.Unsaturated fatty acids are plentiful in young, high quality green fodder, but scarce in dried fodder, beet and maize silage.

Extremely high fractions of oleic acid are found during alpine summering (up to 30 %).

The data in the table below are based on a wide-ranging study carried out by FAM in 1997. Extreme values such as those occurring during alpine summering have not been taken into account, as the proportion of production is low when measured against overall Swiss milk production.Table 1: Average fatty acid composition of milk fat in summer and winter, given in relative percentages of fatty acid methyl esters.Fatty acid methyl esterWinter butterSummer butter

Butyric acid methyl ester4.354.35

Caproic acid methyl ester2.632.63

Caprylic acid methyl ester1.41.4

Capric acid methyl ester3.02.83

Caproleic acid methyl ester0.30.3

Lauric acid methyl ester3.783.5

Myristic acid methyl ester11.5310.65

Myristoleic acid methyl ester1.281.25

Pentadecanoic acid methyl ester1.181.1

Pentadecylic acid methyl ester0.30.3

Palmitic acid methyl ester32.0327.0

Palmitoleic acid methyl ester1.751.63

Heptadecanoic acid methyl ester0.650.6

Heptadecenoic acid methyl ester0.380.38

Stearic acid methyl ester8.89.68

Oleic acid methyl ester21.125.8

Linoleic acid methyl ester1.952.3

Linolenic acid methyl ester1.081.28

Arachidic acid methyl ester0.651.25

EPA-methyl ester0.150.2

DHA-methyl ester