299. Effect Of Cooking On Tissues

All methods of applying heat, whether dry or wet, modify the mechanical condition of raw foods. Both dry and wet heat harden the tissues of meat, and wet heat, or boiling, disintegrates the fibers, softens the connective tissue, and renders the meat more easily masticated. In the case of cereals, whether with dry or wet heat, the starch grains that are confined in the vegetable cells are expanded, and the cellulose covering of the cells is burst, liberating the cell contents. In the case of boiled vegetables their fiber is disintegrated, the contents of the cells are more or less liberated, and the tissue is rendered much more tender. Cooking foods at boiling, temperature by any process whatever coagulates and hardens certain of the proteins such as the albumin and myosin of meat and the white of egg. Boiling milk causes a coagulum. The same thing occurs to a limited extent in vegetable foods, but the result is not so evident. Dry heat converts starch into dextrin, a soluble carbohydrate, as in the brown crust of corn and wheat breads, the surface of toasted bread and of baked potatoes. When apples or other fruits are baked, their tissue is gelatinized through the conversion by hydrolysis of pectin into pec-tose. In cooking food of whatever class by steaming or boiling, more or less of the soluble matter is extracted.

300. Losses In Cooking Meats

The various meats contain from five to eight per cent of soluble constituents, including ash compounds, albumin, the extractives creatin and creatinin, organic acids, glycogen, inosite, and other organic bodies. When meat is cooked by any method whatever, a portion of these compounds, together with some of the fat, is taken into solution or is found in the drippings. At a boiling temperature, the collagen of the connective tissue is changed to gelatin, which is soluble in hot water, and assumes a semi-solid state when meat broth is cooled.

Extensive experiments by Grindley1 revealed the following losses from the meat by the various methods of cooking: -

Table LX. Losses From Meat By Various Methods Of Cooking

301. Relative Loss From Meats By Different Methods Of Cooking

These data are important because meats are the most costly part of the family diet. The results of Grindley's conclusions are summarized in. the following statements: 1 Bui. 141, O.E.S. 2 Apparent gain.

Table LXI. Losses From Vegetables When Cooked In Various Wats

1. The chief loss in weight with any method of cooking is water, except that in roasting much fat goes into the drippings.

2. The smallest loss was in pan broiling, sauténg causing but little more. Much the largest loss was by roasting and boiling, averaging the most for fat in roasting, and most for proteins (extractives and gelatin largely) and ash in boiling.

3. The temperature of the water into which the meat was introduced, whether boiling heat or 68-77° F., seemed to have little influence upon the contents of the broth.

4. Large pieces of meat lost less relatively than small pieces.

5. The loss increased with the time of cooking.

302. Losses In Cooking Vegetables

In cooking vegetables in water; a much greater loss by solution occurs than is generally realized. The extraction of ash ingredients is especially large, and in throwing away the water in which potatoes and other vegetables are cooked a considerable waste of nutritive material occurs. The method of preparing vegetable food determines the proportion of loss. Peeling potatoes, carrots, beets, and turnips greatly increases the loss as the experimental results given in Table LXI show.1

303. Relative Loss From Vegetables By Different Methods Of Cooking

Several conclusions are clearly warranted by the foregoing figures.

1. When potatoes with their skins removed are boiled, beginning with cold water, after previous soaking, the loss is large. Omitting the soaking greatly diminishes the loss, as also does placing the potatoes immediately in hot water.

2. When potatoes are boiled without removing the skins, the loss is small, almost negligible.

3. The loss in boiling carrots is large, one-quarter or more of the dry matter, but is greatest when they are cut in small pieces.

4. The loss in cooking cabbage is still larger, amounting to more than one-third of the dry matter. The loss is not very much diminished by using hot water at the start. It was found that making the water alkaline increased the loss of protein nitrogen.

1Bul. 43, O.E.S.

304. Influence Of Cooking Upon Nutritive Efficiency

The effect of these complex changes upon the nutritive efficiency of foods it is not easy to measure. There is no reason for supposing that-the various nutrient compounds are, in any case, so modified as to change the office they perform in building and maintaining the human body. The only factor to consider, then, is the influence of cooking upon digestibility. Such observations as have been made with raw and cooked meats indicate that the digestion of the latter may be no less complete, but is slower. Doubtless the same is true of eggs. On the other hand, the cooking of cereals and vegetables can but greatly increase the ease and rapidity of digestion. Unless the cells were previously ruptured, the digestive juices would slowly reach and act upon the starch granules and other bodies inclosed in the cellulose covering. With many foods cooking may be said with truth to be the preliminary step to rapid and the completest possible digestion.