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

Composition of Milk

Composition of Milk
The average gross composition of cow’s milk is as follows:

• Water – 87%
  
• Fat – 3.7%
  
• Lactose – 4.9%
  
• Proteins – 3.5%
• Ash – 0.7%

However, the composition of milk from individual cows may vary considerably from these average values. Breed differences, the time of year, the time of day, individual differences, the age of the cow, the period of lactation, the portion of any one milking, feeding, etc., are some factors that may contribute to variation in the composition of milk.

Variation in milk composition due to breed are of the greatest magnitude. Jersey, Guernsey and Ayrshire cows gives milk richer in fat than Holstein cows. Usually milk obtained in the fall and early winter is richer than obtained in the spring and the summer. The morning milk usually is richer in fat than evening milk, at times by almost 2%.

The first portion (or fore milk) of milk drawn in the milking process are lower in fat than the last portions (or strippings). Milk obtained the first few days after calving is known as colostrum and differs materially from normal milk. During the final stages of lactation, when the daily production of milk is decreasing, there is some increase in percentages of fat and casein. The differences in milk composition occur mainly in the relative amounts of fat, protein, and water. The percentages of ash and lactose remain fairly constant in normal milk regardless of the amount of other components.
Composition of Milk