45. The Albumins

There are several albumins. They are found in the juice of plants, in certain liquids of the animal body such as the serous fluids, in muscle, blood, and milk, and abundantly in eggs. Unlike other proteins, these compounds are soluble in pure cold water, and when such a solution is heated to the boiling point, they separate from the liquid by coagulation and become insoluble unless acted upon by some strong chemical.

When macerated beef is treated with cold water the albumin in it goes into solution, and if this extract is boiled to make beef tea, it is a matter of common observation that the albumin separates in clotted masses. None remains in the tea. It is well for the housewife to know that all lean meat contains this substance, which by prolonged treatment with cold water may be removed to the detriment of the residue.

The clear serous fluid which is left after removing the clot from blood contains albumin, which may also be coagulated by heat. After the casein is removed from milk by acid or rennet, the albumin of the milk remains in the whey. It is this which in part causes milk to clot if brought to the boiling point. One of the most familiar examples of this class of proteins is the white of an egg, which, when cooking in boiling water, becomes a hard, white, coagulated mass. Albumin in the serous fluids and in blood is called serum-albumin; in milk, lact-albu-min; and in eggs, ova-albumin.

A small proportion of the proteins of plants is found to be albumin; for instance, Osborne found .3 to .4 per cent in wheat, 43 per cent in rye,. 3 per cent in barley,. 5 per cent in soja beans, and some in most seeds. This possesses essentially the same characters as the animal albumin described previously. Whenever a vegetable substance is leached with water, it is probably this protein which would be the first to suffer removal or destructive fermentation.