Albumin

COOKING OF NITROGENOUS FOOD-STUFFS.

Cooking should render nitrogenous food more soluble because here, as in every case, digestibility means solubility. Egg albumin is soluble in cold water, bu coagulates at about 160° F. At this point it is tender, jelly-like, and easily digested, while at a higher temperature it becomes tough, hard and dissolves with difficulty. Therefore, when the white of egg (albumin), the curd of milk (casein), or the gluten of wheat are hardened by heat, a much longer time is required to effect solution.

As previously stated, egg albumin is tender and jelly-like when heated from 160° F to 180° F. This fact should never be forgotten in the cooking of eggs. Raw eggs are easily digested and are rich in nutriment; when heated just enough to coagulate the albumin or "the white," their digestibility is not materially lessened; but when boiled, the albumin is rendered much less soluble.

In frying eggs, the fat often reaches a temperature of 300° or over-far above that at which the albumin becomes tough, hard, and well-nigh insoluble.

There is much albumin in the blood, therefore the juices of meat extracted in cold water form a weak albuminous solution. If this be heated to the right temperature the albumin is coagulated and forms the "scum" which many a cook skims off and throws away. In doing this she wastes a portion of the nutriment.

Experiments on the digestibility of gluten have proved that a high temperature largely decreases its solubility. Subjected to artificial digestion for the same length of time, nearly two and one-half times" as much nitrogen was dissolved from the raw gluten as from that which had been baked.

When gluten is combined with starch, as in the cereals, the difficulties of correct cooking are many, for the heat which increases the digestibility of the starch decreases that of the gluten.

Experiment. The gluten in wheat flour may be obtained as follows: Place half a cupful of flour in a muslin bag and knead under water. The starch will work out through the bag. After a time all the starch may be so separated. A brown, elastic, stringy mass remains in the muslin. This is gluten, the nitrogenous part of the flour.

The same principle of cooking applies to casein of milk, although to a less extent. There seems to be no doubt that boiling decreases its solubility, and consequently, its digestibility for persons of delicate digestive power.

The nitrogenous substances of meat consist of soluble albumin, chiefly in the blood and juices, the albuminoids of the fibres, the gelatinoids of the connecting tissues, and the extractives. The cooking should soften and loosen the connective tissue, so that the little bundle of fibre which contains the nutriment may fall apart easily when brought in contact with the

Gluten

Casein

Meat

Broth
and

Soup

Effect of Temperature on Meat

teeth. Any process which toughens and hardens the meat should be avoided.

When it is desired to retain the juices within the meat or fish, it should be placed in boiling water so that the albumin of the surface may be hardened and prevent the escape of the albumin of the interior. The temperature should then be lowered and kept between 160 and 180 degrees during the time needed for the complete breaking down of the connective tissues.

When the nutriment is to be used in broths, stews, or soups, the meat should be placed in cold water, heating very slowly and the temperature not allowed to rise above 180° F until the extraction is complete. The extracted meat still retains the greater part of its original proteid substances. It is tasteless and uninviting, but when combined with vegetables and flavoring materials may be made into a palatable and nutritious food.

Experiment. To show the effect of water at different temperatures upon raw meat, place a bit of lean meat about as large as the finger in a glass of cold. water and let it stand an hour. The water becomes Pour off this water

red, and the meat grows white.
and boil it. A scum rises to the surface. The albu-
min dissolved has been rendered insoluble by heat.

Put a bit of raw meat into boiling water, and boil it hard several minutes. The meat is toughened by the process. The outside of the meat is hardened first, and very little of the nutriment dissolves in the water.

Put the meat into cold water and bring the temperature slowly to the boiling point; then allow it to simmer gently for some time. The meat is tender, and some of the nutriment is in the water. This is the method employed in making a stew. A little fat which is always present even between the fibre of the lean meat will be melted out and rise to the top of the water.

We have seen that the ferment in the saliva changed the starch into a sugar. The ferment in the gastric juice, pepsin, with the help of an acid (principally hydrochloric acid) changes the albuminoids into peptones in the stomach. This change is completed in the intestines. The peptones are soluble in water and are absorbed into the blood.

SUMMARY OF THE EFFECTS OF COOKING

The object of all cooking is to make the food-stuffs more palatable or more digestible, or both combined. In general, the starchy foods are rendered more digestible by cooking; the albuminous and fatty foods. less digestible. The appetite of civilized man craves and custom encourages the putting together of raw materials of such diverse chemical composition that the processes of cooking are also made complex.

Bread-the staff of life-requires a high degree of heat to kill the plant-life, and long baking to prepare the starch for solution; while, by the same process, the gluten is made less soluble. Fats, alone, are easily digested, but in the ordinary method of frying, they

Digestion

of Proteids

Effect on Solubility

Common

Salt

not only may become decomposed themselves, and therefore injurious; but they also prevent the necessary action of heat, or of the digestive ferments upon the starchy materials with which the fats are mixed.

The effects of cooking upon the solubility of the three important food-principles may be broadly stated thus:

Starchy foods are made more soluble by long cooking at moderate temperatures or by heat high enough to change a portion of the starch to dextrine, as in the brown crust of bread.

Nitrogenous foods. The animal and vegetable albumins are made less soluble by heat; the gelatinoids more soluble.

Fats are readily absorbed in their natural condition, but are decomposed at very high temperatures and their products become irritants.

MINERAL MATTER

The remaining ingredient of the food of our breakfast to be considered is the mineral matter which constitutes the ash when food-products are burned. There is only 5 or 6 per cent of mineral elements in our bodies, but these materials are necessary to life and health. They are found chiefly in the bones and teeth, but are present also in the flesh, blood, and other fluids. Phosphate of calcium forms the principal mineral part of the bones.

The food we eat contains a small amount of mineral matter which forms the ashes when food is burned.