What are the main constituents of cow's milk?

Milk is the normal secretion of the mammary glands of all mammals. Its purpose is to nourish the young of the species. 

The principal constituents of milk –water, fat, protein, milk sugar or lactose and the minerals.

Water 
Water is the medium in which all the other components of milk are dissolved or suspended. Water content varies from 85.4% to 87% in different species of cows.

Protein 
Casein is the major protein, in contrast to lactalbumins in human milk. The major milk proteins are casein, alpha-lactalbumins, beta-lactoglobulin and the relatively smaller amounts are contributed by milk, enzymes. 

Fat
The cream portion of milk is primarily due to the presence of fat. This family occupies about 4% of the total milk space in cow milk. The major lipid content of cow’s milk is triglyceride, which makes up about 98% of milk fat. The other 2% of milk lipids consist of diglycerides, monoglycerides, cholesterol, phospholipids, free fatty acids, cerebrosides and gangliosides.

Carbohydrate 
Milk contains unique sugar lactose. It is responsible for imparting sweetness to milk although it is onw0offth as sweet as sucrose.

Minerals
Average normal is considered to contain 0.70% ash and this amount represents a salt of about 0.90%. Mineral make-up f milk is crucial to the stability of the physicochemical equilibrium in milk.

Vitamin 
Milk is a unique food having at least 10 to 11 vitamins present in different proportion. Milk contains both fat soluble (A, D, E and K) and soluble water soluble vitamins.

Age is not an important factor effecting the composition of milk although there appears to be tendency for the fat content to decrease with increasing age. However, the health of the cow may affect milk composition considerably.

The most important single factor governing the composition of cow’s milk is the breed of the cow.

The principal milk producing breeds are the Ayrshire, Brown Swiss, Guernsey, Holstein and Jersey. Holstein generally produces the most milk, but Guernseys and Jerseys produce milk with the highest fat contents.
What are the main constituents of cow's milk?

Major Constituent of Milk

Major Constituent of 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.

Too, a fact frequently overlooked is the greater weight percentage of the potassium over that of calcium.

This kind of information can be used to detect injured udders because in the injured udder the composition of the milk becomes more like that of the blood.

The changes in chloride content and in acidity are easily measured.

Milk from cows suffering from mastitis contains a higher sodium and chloride content than normal milk.

Chloride content in milk in excess of 0.14% suggests the possibility of mastitis milk.

All cases of toward the end of lactation and colostrums secreted at the beginning of lactation contain more sodium and chloride than normal milk.

Small variations in the concentrations of Ca and Mg relative to the concentrations of citrate and phosphate are known to affect the ability of milk to resist coagulation when heated.

The ration between the different components seems to be more important that the actual amounts present.

The term salt balance is used to refer to the ratio of these components.

In general, the most common manifestation of a disturbed salt balance is a deficiency of citrate and phosphate ions (particularly when cows are off pasture), which would suggest that in such circumstances addition of sodium citrate or phosphate would correct the balance through its sequestering effect on calcium ions and render the milk heat stable.

Milk contains more calcium that 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.

Only because of these phenomena is it possible for milk to have an osmotic pressure equal to that of the blood.

When milk is heated or pasteurized, the equilibrium between the colloidal and soluble phrases is altered in the direction of the colloidal phase.

In cheese making, this change in the ration between of soluble and colloidal calcium is an important factor in the time taken by rennet to coagulate the milk.
Major Constituent of Milk