Animal milk is first known to have been used as human food at the beginning of animal domestication. Cow milk was first used as human food in the Middle East. Goats and sheep were domesticated in the Middle East between 9000 and 8000 B,C,

Milk is an emulsion (or colloid of butterfat globules within a water-based fluid(. Each fat globule is surrounded by a membrane consisting of phospholipids and proteins; these emulsifiers keep the individual globules from joining together into noticeable grains of butterfat and also protect the globules from the fat-digesting activity of enzymes found in the fluid portion of the milk. In unhomogenized cow milk, the fat globules average about four micrometers across. The fat-soluble vitamins A, D, E, and K are found within the milkfat portion of the milk.

Both the fat globules and the smaller casein micelles, which are just large enough to deflect light, contribute to the opaque white color of milk. Skimmed milk, however, appears slightly blue because casein micelles scatter the shorter wavelengths (blue compared to red).

The fat globules contain some yellow-orange carotene, enough in some breeds

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