Milk fat:

• If milk is left to stand, a layer of cream forms on the surface.
• The cream differs considerably in appearance from the lower layer of skim milk.
• Under the microscope cream can be seen to consist of a large number of spheres of varying sizes floating in the milk.
• Each sphere is surrounded by a thin skin—the fat globule membrane, which acts as the emulsifying agent for the fat suspended in milk (Figure 3).
• The membrane protects the fat from enzymes and prevents the globules coalescing into butter grains.
• The fat is present as an oil-in-water emulsion: this emulsion can be broken by mechanical action such as shaking.

There are altogether 11 fatty acids found in the milk. Among them some are volatile and some are non volatile in nature.

Volatile fatty acids: butyric, capronic, caprylic, capric, and lauric acids.

Non volatile fatty acids: Myristic, palimitic, stearic, oleic, linolenic, linoleic.

Volatile fatty acids influence the flavour of milk and milk products like fish flavour. Milk from a cow has higher fat percent with larger size. The large sized fat globules contribute to the easier formation of cream layer.

Large fat globules are important because of

1) easier separation of cream

2) separation of milk

3) shiping of milk or cream

4) cheese making.

Butyric acid, caproic acid, caprylic acid is responsible for typical flavour of milk. Oleic acid influences the hardness or softness of milk fat. Milk fat acts as a solvent for the fat-soluble vitamins A, D, E and K and also supplies essential fatty acids (linoleic, linolenic and arachidonic).

Table:. Principal fatty acids found in milk triglycerides.

The melting point and hardness of the fatty acid is affected by:

• the length of the carbon chain, and
• the degree of unsaturation.

As chain length increases, melting point increases. As the degree of unsaturation increases, the melting point decreases. Fats composed of short-chain, unsaturated fatty acids have low melting points and are liquid at room temperature, i.e. oils. Fats high in long-chain saturated fatty acids have high melting points and are solid at room temperature.

Fats readily absorb flavors. For example, butter made in a smoked gourd has a smokey flavor.

Fats in foods are subject to two types of deterioration that affect the flavor of food products.

1. Hydrolytic rancidity: In hydrolytic rancidity, fatty acids are broken off from the glycerol molecule by lipase enzymes produced by milk bacteria. The resulting free fatty acids are volatile and contribute significantly to the flavor of the product.

2. Oxidative rancidity: Oxidative rancidity occurs when fatty acids are oxidized. In milk products it causes tallowy flavors. Oxidative rancidity of dry butterfat causes off- flavors in recombined milk.

Uses of fats

• It is a good source of energy for human being.
• Butter fat is the one of the principal constituent of almost all the dairy products such as butter, ice cream, etc
• Butter fat contains vitamin A, D, E and K, so it promotes growth in children and meets the requirement of vitamins in old age as well as other age groups
• Used as a cooking medium like preparation of sweets and other fooding materials.