Principles of cooking

. Heat hardens or coagulates any form of protein and makes it harder to digest. When protein hardens, it forms a crust which aids in retaining juices and flavor. Mineral matter, extractives, and volatile oils are soluble in water. Acids soften cellulose. Acids invert sugar. Heat kills bacteria and other parasites found in foods. Heat makes foods more attractive and palatable, and while it may lessen their ease of digestion, it may by improving their flavor cause an increased flow of digestive fluids and in that way balance the difficulty. SALMON FOR CANNING, (From Carpenter’s How the World is Fed.) / ( CHAPTER SEVEN Uses of Foods. — Proteins build tissue and yield heat and energy. Starch and sugar when oxidized yield heat and energy. Cellulose furnishes bulk, which, by stimulating the walls of the stomach and intestines, promotes the flow of the digestive juices and aids peristalsis. Fats when oxidized yield heat and energy. Mineral salts and acids aid in tissue building, promote osmotic pressure, regulate the acidity or alkalinity of the digestive juices, and because they are decomposed in the body and form alkaline carbonates they help to keep the blood alkaline and control the acidity of the excretions. Water aids in tissue building, forms the great part of the blood, digestive fluids, and excretions. It regulates the temperature of the body and aids in the elimination of waste. Extractives stimulate the appetite and aid in digestion. Classification of Foods. — Foods are classified for the purpose of study into animal and vegetable foods. In general it may be said that vegetable foods are mainly _ carbohydrate and animal foods mainly protein. Vegetable foods are classed as : — 1. Fruits 4. Cereals 2. Green Vegetables® 5. Legumes 3. Roots and Tubers 6. Nuts All vegetables have two things in common. They all contain valuable mineral salts which help to keep the blood alkaline; they contain carbohydrate in the form of starch, sugar, and cellulose, and thus furnish bulk to food. Roots and tubers are pure, starchy foods containing little or no available protein. Cereals contain starch and protein in proportion of about FP Legumes contain starch and protein in proportion of about 23 : 1. | Green vegetables are valuable mostly for their mineral salts and cellulose; fruits, for their acids and sugar. Nuts are similar to the legumes in composition. They are not consumed to any great extent as a food, but are merely used as a relish or confection. FRUITS Typical Food: Apple. — All fresh fruits are similar in composition and structure and have practically the same food value. They contain 75-80 per cent water, .5 per cent protein, 8-20 per cent» carbohydrate, 1-3 per cent cellulose, .5 per cent mineral matter, and practically no fat. They are eaten for their mineral salts, which help to preserve the alkalinity of the blood, for their refreshing juices and flavor, and because the cellulose furnishes bulk for the intestines and thus stimulates peristalsis. Some fruits contain enough sugar so that they may be considered valuable carbohydrate foods. In structure fruits consist of walls of cellulose inclosing water, sugar, mineral salts, and acids, with very little protein and fat. Cooking of Fruits. — Most fruits are eaten raw when they can be procured fresh. Fruits are also dried, canned, preserved, and cooked in various ways. Cooking softens the cellulose, and during the process the action of the acid —— . in the fruit on the cellulose hastens the softening. If fruits are cooked in water, some mineral salts, acids, and sugar are dissolved in the water. If the water is served with the fruit, there is no loss of nutrients.