Tuesday, June 15, 2010

Physical and Chemical Properties of Milk

Physical and Chemical Properties of Milk
Milk is a white or yellow-white, opaque liquid. The color is influenced by scattering and absorption of light by milk globules and protein micelles.

Therefore, skim milk also retains its white color. A yellowish, i.e. yellow –green, color is derived from carotene (ingested primarily during pasture grazing) present in that fat phase and from riboflavin present in the aqueous phase.

Milk tastes mildly sweet, while its odor and flavor are normally quite faint.

Milk occurs in the form of droplets or globules, surrounded by a membrane and emulsified in milk serum (also called whey).

The fat globules (called cream) separate after prolonged storage or after centrifugation.

The fat globules float on the skim milk. Homogenization of milk so finely divides and emulsifies the fat globules that cream separation does not not occur even after prolonged standing.

Proteins of various sizes are dispersed in milk serum. They are called micelles and consists mostly of calcium salts of casein molecules.

Furthermore, milk contains lipoprotein particles, also called milk microsomes, which consists of the residue of cell membranes, microvilli, etc, as well as somatic cells which are mainly leucocytes.

Various proteins, carbohydrates, minerals and other ingredients are solubilized in milk serum. The specific density of milk decreases with the increasing fat content, and increases with increasing amounts of protein, milk sugar and salts.

The specific density of cow’s milk ranges from 1.029 to 1.039 (15 degree C). Defatted (skim) milk has a higher specific density than whole milk.
Physical and Chemical Properties of Milk
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