The major constituent of milk is water, but according to species milk contains varying quantities of lipids, proteins, and carbohydrates which are synthesized within with mammal gland.
Disaccharides lactose in milk imparts sweetness. Human milk has a major concentration of lactose (7.4%) compared to milk of other species. Milk lactose serves to major functions:
*It provides galactose, a structural unit for the growing infant
*In the intestine, it gets metabolized to lactic acid which eliminates harmful bacteria.
The lipid content of mammalian milk varies from 16 g/liter (horse) to 105 g/liter (deer), human milk contains about 38 g of fat per liter.
When milk is dried and the residue is burned, a white powder is obtained which is known as ash or mineral part of the milk. The major portion of ash is composed of the chlorides and oxides of potassium, calcium and phosphorus. It is of interest to note that these three elements are in greater concentration in milk than in blood, thus the mammary gland exerts a selective action to concentrate these elements.
Milk contains more calcium than most foods because of the distribution of calcium in milk. About two thirds of the total calcium in milk is in colloidal form as calcium caseinate, citrate and phosphate; the remaining third is in true solution.
Milk contains lot of vitamins, among them vitamin B complex is dissolved in the water and vitamins A and D in the fat. Only ascorbic (vitamin C) is present in limited amount and it may absent from pasteurized milk.
Major constituent of milk