« 이전계속 »
liquid character which are classed as beverages rather than as foods. All of these bodies have nutritive properties, although their chief value is condimental and social.
CLASSIFICATION OF FOODS.
That large class of food products, also, which is known as condiments is properly termed food, since they not only possess nutritive properties but through their condimental character promote digestion and by making the food more palatable secure to a higher degree the excellence of its social function.
It is now possible to condense into a distinct expression the definition of food in the following language: Food in a general sense embraces those substances taken into the body which build tissues, restore waste, and furnish heat and energy.
CLASSIFICATION OF FOODS.
Foods may be considered under different classifications. First, as to general appearance and use three classes may be made,-foods, beverages and condiments. As types of the first division of these foods may be mentioned cereals and their preparations, meat and its preparations (except meat extracts), fish, fowl, and game. Beverages are those liquid food products which are more valued for their taste and flavor than actual nutritive value. As types of beverages may be mentioned wines, beers, distilled spirits and liquors of all characters, tea, coffee, cocoa, chocolate, etc. Under wines, in this sense, may be included the fermented beverages made of fruit juices, such as cider, perry, etc. Types of condiments are salt, pepper, spices, vinegar, etc. Milk, although a liquid substance, is hardly to be considered a beverage, and on account of its high nutritive properties may be classed, together with its preparations, under the first head.
Foods may also be classified as nitrogenous, starchy, oily, and condimental. Nitrogenous foods are those in which the proportion of their material containing nitrogen is large. Lean meat may be regarded as a type of nitrogenous food, since it consists almost exclusively of tissues known as protein and contains nitrogen and sulfur as essential ingredients. The white of an egg is also a typical nitrogenous food and, to a less extent, the yolk. Among vegetables, peas and beans are typical foods containing large percentages of nitrogenous matter. The gluten of wheat is also a typical nitrogenous food and the zein of Indian corn, corresponding to gluten, is a nitrogenous material. Practically all the vegetables used as foods contain more or less protein. in their constituents. Among the cereals oats has the largest quantity and rice the smallest of this valuable food material. Of oily foods the fat of animals, including butter, is a typical representative. All meats, fish, fowl, and game contain more or less fat. Of vegetables and fruits there are many
which contain large quantities of fat, such as nuts, oily seeds, etc. All vegetables contain more or less fat, although the succulent vegetables usually contain but little thereof. Of starchy foods there are no types in animal food, the quantity of carbohydrate material therein being extremely limited. The lobster and horse-flesh contain perhaps a little more than 1 percent of carbohydrate food, but most meats contain much less than that. Sugar and starch are typical carbohydrate foods.
The cereal grains are composed largely of starchy foods, and so are certain tubers, such as the potato, cassava, etc. Of the common cereals rice contains more starch than any other and oats the least. Sugars are intimately related to starch and are included under the term starchy food or carbohydrate food. The carbohydrate matter in the flesh mentioned above, namely glycogen, is of the nature of a sugar. Among the typical sugar foods are beets, melons, and fruits, some of which contain large percentages of sugar. All fruits contain greater or less quantities of sugar, and that is true, also, of all vegetables.
Of the plants which produce the sugar of commerce there may be mentioned the sugar-cane, the sugar-beet, the maple, and palm trees. The principal sources of the sugar of commerce are the sugar-cane and the sugar-beet.
Of the condimental foods may be mentioned spices, including pepper, mustard, cinnamon, allspice, and other foods of this class. Common salt occupies a unique position in food products. It is the only mineral substance which has any value as a condiment in human food. But it also has a more important function than its condimental character, namely, it furnishes the supply of hydrochloric acid without which digestion in the stomach could not take place. For this reason common salt must be regarded as an essential food product as well as a condiment.
EXPLANATION OF CHEMICAL TERMS.
Inasmuch as this manual is not solely intended for expert chemists and physiologists but also for the general public, a simple explanation of the use of the terms used in analytical data and tables is advisable.
Under the term moisture is included all the water which is present in a free state, that is, not combined in any way with the ingredients of the material, and other substances volatile at the temperature of drying. The water is determined by drying to a constant weight at the temperature of boiling water or slightly above. In bodies which are easily oxidized this drying takes place in a vacuum or in an inert gas like hydrogen or carbon dioxid.
Protein. Under this term is included all the nitrogenous compounds in a food product which contain in their composition sulfur, nitrogen, car
bon, hydrogen, and oxygen, forming that class of tissues represented by the gluten in wheat, the white of an egg, muscular and tendinous fibers, etc.
EXPLANATION OF CHEMICAL TERMS.
Ether Extract. Under this term is included the fats and oils, the term fat being applied to animal fat and the term oil to vegetable products. These bodies are all soluble in ether and therefore are grouped together under the term "ether extract." There are some fats both in animal and vegetable substances insoluble in ether, but they exist in minute quantities and therefore are not separated from the extracts, but the whole matter is given together and represents practically the fats and oils in food.
There are also minute quantities of bodies not fats in foods soluble in ether, and these are included in the ether extract.
Ash. The term ash is applied to the residue left after the burning of food products in the air at a low temperature until the carbon has disappeared. Ash is rather an indefinite term and is applied to that residual material of a mineral nature composed of sand or silica and the carbonates or oxids of alkaline earth or alkalies. The ash also contains the principal part of phosphorus present in food products and usually a small proportion of sulfur. These bodies in the ash exist as phosphoric and sulfuric acids or their salts.
Fiber. The term fiber is applied to those carbohydrate products in food which are insoluble in solutions of dilute acid and dilute alkalies at the boiling temperature. Inasmuch as these separated bodies are not wholly pure cellulose they are often designated as crude fiber.
Starch and Sugar. The terms starch and sugar are applied to the carbohydrates in a food product of a starchy or saccharine nature, together with the other carbohydrates present which are soluble in dilute acids and alkalies.
Calories. The term calorie is used to denote the amount of heat-forming material contained in one unit weight of a food product. The number given represents the number of degrees of temperature produced in a unit mass of water by the heat formed in burning the unit weight of food. The unit weights employed are usually as follows: Of the food product, one gram (15 grains); unit weight of water to be heated, one kilogram (2.2 pounds); unit increment of temperature, 1° C. (1.8° F.). The expression 4000 calories therefore means that if one gram of food substance in a dry state be burned the heat produced will raise one gram of water through a temperature of 4000°C., or the unit of water (one kilogram) through a temperature of 4° C. For convenience the calories are usually expressed as small calories, namely 4000, instead of large calories, namely 4. In this manual the expression in terms of small calories, that is, the temperature increase of one kilogram of water produced by burning one gram of substance, multiplied by 1000, will be uniformly employed.
One great division of human food is meat. Technically, perhaps, the edible flesh of every animal used for human food might be described as meat. In this manual, however, preference is given to the common meaning of the term.
The flesh of animals is by common consent divided into three principal classes, namely, the flesh of terrestrial mammals, or animals not provided with wings; second, aerial animals, or animals provided with wings, and, third, aquatic animals. A very common classification of these three kinds of food is flesh, fowl, and fish. There are animals, the flesh of which is eaten by many, which are not exactly included in this classification; for instance, animals of an amphibious nature, living partly on land and partly on sea. Also many of the animals classed as aerial live chiefly upon the earth; although having wings they do not use them, such as domesticated fowls. This classification, however, is sufficiently exact for the practical purposes of a food manual and, therefore, under the head of meat is included the edible flesh of mammals living on the land.
Animals Whose Flesh is Edible.-Probably the only complete classification of this kind would be to include every animal living on the face of the earth since, perhaps, the flesh of every animal living has been more or less eaten by man. In a civilized community, however, except in times of disaster and dire necessity, certain classes of animals only furnish the principal meat food. Nearly all the meat food consumed in the United States is derived from cattle, sheep, and swine. Goat flesh is eaten only to a limited extent and horse meat scarcely at all, and the only other meats of importance are those of