Human Foods and Their Nutritive Value by Harry Snyder (red novels .txt) 📖
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The nutrients in the broth of the meat started in hot water amounted to about 1 per cent of protein, 1 per cent of fat, and O.5 per cent of ash, the amount of nutrients being directly proportional to the length of time and temperature of the cooking. In general, the larger the pieces, the smaller the losses. Beef that has been used in the preparation of beef tea loses its extractive materials, which impart taste and flavor, but there is only a small loss of actual nutritive value. Clear meat broth contains little nutriment—less than unfiltered broth. Most of the nitrogenous material of the broth is in the form of creatin, sarkin, and xanthin, nitrogenous extractives or amid substances having a much lower food value than proteids. Experiments show that some of these extractives have physiological properties slightly stimulating in their action, and it is believed the stimulating effect of a meat diet is in part due to these.[49] They are valuable principally for imparting taste and flavor, and cannot be regarded as nutrients. The variations in taste and flavor of meats from different sources are due largely to differences in extractive material.
"In general, the various methods of cooking materially modify the appearance, texture, and flavor of meat, and hence its palatability, but have little effect on total nutritive value. Whether it be cooked in hot water, as in boiling or stewing, or by dry heat, as in roasting, broiling, or frying, meat of all kinds has a high food value, when judged by the kind and amount of nutrient ingredients which are present." [50]
Beef extracts of commerce contain about 50 per cent of extractive matters, as amids, together with smaller amounts of soluble proteids; ash, mainly added salt, is also present in liberal amounts (20 per cent). Beef extracts have condimental value imparting taste and flavor, which make them useful for soup stocks, but they furnish little in the way of nutritive substance.
136. Miscellaneous Meat Products.—By combining different parts of the same animal, or different meats, a large number of products known as sausage are made. These vary in composition with the ingredients used. In general, they are richer in fat than beef and contain about the same amount of protein. Potato flour and flour from cereals are sometimes used in their preparations, but the presence of any material amount, unless so stated on the package, is considered an adulterant.
Pickled meats are prepared by the use of condiments, as salt, sugar, vinegar, and saltpeter. During the smoking and curing of meats, no appreciable losses of nutrients occur.[51] The smoke acts as a preservative, and imparts condimental properties. Saltpeter (potassium nitrate) has been used from earliest times in the preparation of meats; it preserves color and delays fermentation changes. When used in moderate amounts it cannot be regarded as a preservative or injurious to health. Excessive amounts, however, are objectionable. Smoked meats, prepared with or without saltpeter, give appreciable reactions for nitrites, compounds formed during combustion of the wood by which the meat was smoked. Many vegetables contain naturally much larger amounts of nitrates, taken from the soil as food, than meat that has been preserved with saltpeter.[52]
137. Poultry.—The refuse and waste from chickens, as purchased on the market, ranges from 15 to 30 per cent. The fat content is much lower than in turkeys or ducks, the largest amount being found in geese. The edible portion of all fowls is rich in protein, particularly the dark meat, and the food value is about equal to that of meat in general. When it is desired to secure a large amount of protein with but little fat, chicken supplies this, perhaps, better than any other animal food. A difference is observed in the composition of the meat of young and old fowls similar to that between beef and veal. The physical composition and, to a slight extent, the solubility of the proteids are altered by prolonged cold storage, the difference being noticeable mainly in the appearance of the connective tissue of the muscles. In discussing poultry as food, Langworthy states:[53]
"A good, fresh bird shows a well-rounded form, with neat, compact legs, and no sharp, bony angles on the breast, indicating a lack of tender white meat. The skin should be a clear color (yellow being preferred in the American market) and free from blotches and pin feathers; if it looks tight and drawn, the bird has probably been scalded before being plucked. The flesh should be neither flabby nor stiff, but should give evenly and gently when pressed by the finger."
138. Fish.—From 30 to 60 per cent of the weight of fresh fish is refuse. The edible portion contains from 35 to 50 per cent, and in some cases more, of water. The dry matter is rich in protein; richer than many meats. The nutrients in fish range between comparatively wide limits, the protein in some cases being as low as 6 per cent, in flounder, and in others as high as 30 per cent, in dried codfish. The amount of fat, except in a few cases, as salmon and trout, is small. Salmon is the richest in fat of any of the fishes. When salted and preserved, the proportion of water is lessened and that of the nutrients is increased. Fish can take the place of meat in the dietary, but it is necessary to add a larger amount of fat to the ration because of the deficiency of most fish in this ingredient. Fish has about the same digestibility as meats. It is believed by many to be valuable because it supplies a large amount of available phosphates. Analyses, however, show that the flesh of fish contains no more phosphorus compounds than meats in general, and its food value is due to protein rather than to phosphates.[54]
Fish appears to be as completely and easily digested as meats. Differences in flavor, taste, and palatability are due to small amounts of flavors and extractive materials, varying according to the food consumed by the fish and the conditions under which they lived. The flesh of fish decays more readily than that of other meats and produces ptomaines, or toxic substances, which are the result of fermentation changes usually associated with putrefaction. Cases of poisoning from eating unsound fish are not infrequent.[55]
Shellfish have about the same general composition as fish. In clams there is a larger amount of dry matter than in oysters, which contain about 12 per cent, half of which is protein. When placed in fresh water, the oyster increases in size and undergoes the process known as "fattening." Oftentimes impure water is used for this purpose, which makes the eating of raw oysters a questionable practice from a sanitary point of view, as the water in which they are floated often contains disease-producing germs, as typhoid. During the process of fattening, although the oyster increases in size and weight, it decreases in percentage of nutrients. In discussing the composition of oysters, Atwater states:[7]
"They come nearer to milk than almost any other food material as regards both the amounts and relative proportions of nutrients."
Fig. 30.—Graphic Composition of an Egg.
139. Eggs, General Composition.—Eggs are a type of concentrated nitrogenous food. About 75 per cent (shell removed) is water, about one third is yolk, and a little over 50 per cent is albumin or white. The shell makes up from 10 to 12 per cent of the weight. The yolk and white differ widely in composition. The yolk contains a much larger per cent of solids than the white, and is rich in both fat and protein, from a third to a half of the weight being fat. The white has about the same amount of water, 88 per cent, as average milk, but, unlike milk, the dry matter is mainly albumin. The entire egg (edible portion) contains about equal parts of fat and protein; 12 to 13 per cent of each and an appreciably large amount of ash or mineral matter,—from 0.8 to 1 per cent, consisting mainly of phosphates associated with the albumin. There is no material difference in chemical composition between white and dark shelled eggs, or between eggs with different colored yolks. It is simply a question of coloring matter. The egg is influenced to an appreciable extent by feed and general care of the fowls. The egg and the potato contain about the same amount of water. They are, however, distinct types of food, the potato being largely composed of carbohydrates and the egg of protein and fat. Eggs resemble meat somewhat in general composition, although they contain rather less of protein and fat. When eggs are boiled there is a loss of weight due to elimination of water; otherwise the composition is unaltered, the coagulation of the albumin, as stated in Chapter I, consisting simply in a rearrangement of the atoms of the molecule. The egg is particularly valuable in the dietary of the convalescent, when it is desired to secure the maximum amount of phosphorus in organic combination.
The flavor of eggs is in part due to the food supplied to the fowls, as well as the age of the egg. Experiments show that onions and some other vegetables, when fed to fowls, impart odors and taste to the eggs. The keeping qualities of eggs are also dependent upon the food supplied. In experiments at the Cornell Experiment Station, when hens were fed on a narrow, nitrogenous ration, a large number of eggs were produced containing the minimum amount of solid matter and of poor keeping quality, while a larger sized egg of better keeping quality was obtained when a variety of foods, nitrogenous and non-nitrogenous, was supplied.
140. Digestibility of Eggs.—Digestion experiments show that there is but little difference in the digestibility of eggs cooked in different ways. A noticeable difference, however, is observed in the rapidity with which the albumin and proteids are dissolved in a pepsin solution. In general, it was found that, when the albumin was coagulated at a temperature of 180°, it was more rapidly and completely dissolved in the pepsin than when coagulated at a temperature of 212°. When eggs were cooked at a temperature of 212°, the hard-boiled eggs appeared to be slightly more digestible than the soft-boiled eggs, but the digestion was not as complete as when the cooking was done at a temperature of 180°; then no difference in digestibility was found between eggs cooked for a short or a long time. The egg is one of the most completely digested of all foods, practically all the protein and fat being absorbed and available to the body. Langworthy, in discussing Jorissenne's investigations on the digestibility of eggs, states:[53]
"The yolk of raw, soft-boiled, and hard-boiled eggs is equally digestible. The white of soft-boiled eggs, being semi-liquid, offers little more resistance to the digestive juices than raw white. The white of a hard-boiled egg is not generally very thoroughly masticated. Unless finely divided, it offers more resistance to the digestive juices than the fluid or semi-fluid white, and undigested particles may remain in the digestive tract many days and decompose. From this deduction it is obvious that thorough mastication
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