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.
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
