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A Talk on Food: Proteids

Now we wish to look more closely at these proximate principles. Let us begin with the most important and the most expensive, the proteids. PROTEIDS There are five important substances and quite a number of less important ones that we group under the term proteids. These substances are thus grouped, because each and every one of them has a similar chemical composition and thus performs the same function in the body. They contain nitrogen, an element found in no other food principle, carbon, hydrogen, oxygen, sulphur, and are tissue builders. These five proteids have marked physical characteristics which we can note in our kitchens, if we do not have a laboratory in which to study their chemical composition. Carefully try the following experiments and you will, in the future, have a fairly good understanding of what is meant by the term proteid.

PHYSICAL PROPERTIES OF PROTEIDS Gradually stir two tablespoonfuls of water into half a cup of flour, to form a dough; knead the dough until it becomes smooth and elastic, then work it (in the hands or on a sieve) under a faucet of running water until the water, running off from the dough, loses its milky appearance. The gray substance left in your hands you will find tenacious and elastic; you can stretch and fold it as you would molasses candy or rubber bands. This elastic mass is gluten, one of the five representative proteids.

Add one or two tablespoonfuls of vinegar to half a cup of milk and let the whole become slightly warm; drain off the whey and wash the curd remaining; this curd is elastic and tenacious; it is casein, a second representative proteid. The white of an egg, which is largely albumin, another proteid, is also elastic and tenacious. The pulp of lean meat, scraped from the white connective tissues, represents the chief proteid in meat, by name myosin. The fifth of the group is legumin, the proteid found in the pulse family (peas, beans, lentils, etc.) When you come to have experience in cooking these five substances, you will learn that all are toughened by a high degree of heat. All of them when dried may be reduced to a similar, fine, powdery state. GELATINOIDS When we first spoke of proteids, we referred to a number that were of less importance than the five true proteids, which we have now referred to under the names gluten, casein, albumin, myosin and legumin; these others are set in a class by themselves, for, though they contain nitrogen, they can not alone supply the nitrogen needed by the body-they lack something present in the true proteids, though they may replace a part of the proteid in the diet. The best known of these substances is gelatine; others are ossein of which bone is largely composed, heratin, present in the hair and in the horns and hoofs of animals, and collagen, which forms the greater part of the connective tissue of meat. All of these are not toughened by boiling, but are changed into gelatine. These are the gelatinoids.

EXTRACTIVES In meat there are nitrogenous substances that give it flavor; we notice these prominently in beef-tea and clear soup; these are called extractives; they are not true foods, inasmuch as they do not build tissue or supply heat, but they influence digestion.

PROTEIN The proteids, gelatinoids and extractives are classed together under the name protein.

CARBOHYDRATES A carbohydrate is composed of the elements, carbon, hydrogen and oxygen, the last two in the proportion in which they are found in water. The principal carbohydrates may be arranged in three groups as below. The letters C H O stand for the three elements of which this principle is composed; the figures indicate the number of atoms of the different elements that enter in combination, in each group.