Foods : nutritive value and cost / by W.O Atwater.

  • Atwater, W. O. (Wilbur Olin), 1844-1907.
Date:
1894
Catalogue details

Licence: Public Domain Mark

Credit: Foods : nutritive value and cost / by W.O Atwater. Source: Wellcome Collection.

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    18 per cent in a leg of mutton, 40 per cent in chicken, and 50 per cent or more in some kinds of fish. In such food materials as milk, flour, and bread there is of course no refuse. Water and nutrients.—Meat freed from bone, milk, and flour all con¬ tain more or less water. This can be dried out by heating, as is done in the chemical analysis of food materials. The proportions of water in different food materials vary greatly. Ordinary flour contains about 12J per cent, or one-eighth. The fatter kinds of meat have from 15 to 50 per cent and the leaner meats from 50 to 75 per cent of water. One- third of the weight of bread and three-fourths of the weight of potatoes consist of water. The water in all these substances is precisely the same as any other water and has no more value for nutriment. The material Avhich remains in the edible portion of the food after removal of the water is called by chemists u water-free substance.’’ It includes all of the actually nutritive ingredients or nutrients of the food. The nutrients are of several kinds. They are commonly divided into four classes called protein, fats, carbohydrates, and mineral matters. Water permeates all parts of the body and is indispensable for nourish¬ ment, but the water of the food is not transformed in the body as are the protein, fats, and carbohydrates, and it is not usually taken into account in estimates of nutritive value. Protein.—Meat consists of lean and fat. Part of the fat is in large lumps, which can be easily separated from the lean. Indeed, we often cut out the fat of the meat which is served on our plates at the table and reject it. But a portion of the fat is in very fine particles diffused throughout the lean. Much of this finely divided fat is in particles so small as to be invisible to the naked eye, but it is possible to separate them very completely from the lean by processes of analy¬ sis common in the laboratory. After the water and the fat have been removed from the lean meat, the material which remains will contain a little mineral matter, which would be left as ash if it were burned $ the rest consists chiefly of so called protein compounds. The protein is the chief nutritive constituent of fish and eggs as well as of lean meat. The albumen and casein of milk are also protein compounds. The gluten of wheat consists of protein compounds. These compounds occur in corn, beans, potatoes, and indeed all kinds of vegetable foods. One trouble in speaking of these substances is that they are known by so many different names. The terms u nitrogenous compounds,” u albuminoids,” and “ proteids ” are often applied to them. The first term is very proper, because the protein compounds contain the element nitrogen, which is not found in the other classes of nutrients. The term u albuminoids” comes from albumen, a substance familiar to us in the white of egg, and is applied to the compounds which are similar to albumen. Some writers prefer the word “proteids” for substances of this class.