Human Foods and Their Nutritive Value Part 6

130. Veal differs from beef in containing a smaller amount of dry matter, richer in protein, but poorer in fat. Animals differ in composition at different stages of growth in much the same way as plants. In the earlier stages protein predominates in the plant tissue, while later the carbohydrates are added in larger amounts, reducing the percentage content of protein. In animals the same is noticeable. Young animals are, pound for pound, richer in protein than old animals. While in the case of vegetables the increase in size, or rotundity, is due to starch and carbohydrates, in animals it is due to the addition of fat.

But plants, like animals, observe the same general laws as to changes in composition at different stages of growth.

[Ill.u.s.tration: FIG. 28.--STANDARD CUTS OF MUTTON.

(From Office of Experiment Station Bulletin.)]

131. Mutton.--There is about the same amount of refuse matter in mutton as in beef. In a side of mutton about 19 percent: are tr.i.m.m.i.n.gs and waste, and in a side of beef 18.5 per cent. Mutton, as a rule, contains a little more fat and dry matter than beef, and somewhat less protein. A side of beef, as purchased, contains about 50 per cent of water, 14.5 per cent protein, and 16.8 per cent of fat, while a side of mutton, as purchased, contains 42.9 per cent water, 12.5 per cent protein, and 24.7 per cent fat. A pound of beef yields a smaller number of calories by 25 per cent than a pound of mutton. At the same price per pound more nutrients can be purchased as mutton than as beef. The differences in composition between lamb and mutton are similar to those between veal and beef; viz. a larger amount of water and protein and a smaller amount of fat in the same weight of the young animals. Differences in composition between the various cuts of lamb are noticeable. The leg contains the least fat and the most protein, while the chuck is richest in fat and poorest in protein. As in the case of beef, many of the cheaper cuts contain as much or more nutrients than the more expensive cuts. They are not, however, as palatable and differ as to toughness and other physical characteristics.

[Ill.u.s.tration: FIG. 29.--STANDARD CUTS OF PORK.

(From Office of Experiment Station Bulletin.)]

132. Pork is characterized by a high per cent of fat and a comparatively low per cent of protein. It is generally richest in fat of any of the meats. The per cent of water varies with the fatness of the animal; in very fat animals there is a smaller amount, while lean animals contain more. In lean salt pork there is about 20 per cent water, and in fat salt pork about 7 per cent. There is less refuse and waste in pork than in either beef or mutton. Ham contains from 14 to 15 per cent of refuse, and bacon about 7 per cent. Bacon has nearly twice as much fat and a smaller amount of protein than ham. A pound of bacon, as purchased, will yield nearly twice as much energy or fuel value as a pound of ham. Digestion experiments show that bacon is quite readily and completely digested and is often a cheaper source of fat and protein than other meats. There is about three times as much fat in bacon as in beef. When prepared for the table bacon contains, from 40 to 50 per cent of fat. A pound of high grade, lean bacon furnishes from 0.1 to 0.3 of a pound of digestible protein and from 0.4 to 0.6 of a pound of digestible fat, which is about two thirds as much fat as is found in b.u.t.ter. Bacon contains nearly as much digestible protein as other meats and from two to three times as much fat, making it, at the same price per pound, a cheaper food than other meats. In salt pork there is from 60 to 85 per cent of fat, and less protein than in bacon. The protein and fat of pork differ from those in beef not only in percentage amounts, but also in the nature of the individual proteins and fats. The composition of pork varies with the nature of the food that is consumed by the animal.

Experiments show that it is possible by judicious feeding in the early stages of growth to produce pork with the maximum of lean meat and the minimum of fat. After the animal has pa.s.sed a certain period, it is not possible by feeding to materially influence the percentage of nutrients in the meat. The flavor, too, of pork, as of other meats, is dependent largely upon the nature of the food the animal consumes. When there is a scant amount of available protein in the ration, the meat is dry, nearly tasteless, and contains less of the soluble nitrogenous compounds which impart flavor and individuality.

133. Lard is prepared from the fat of swine, and is separated from a.s.sociated tissue by the action of heat. A large amount of fat is found lining the back of the abdominal cavity, and this is known as leaf lard.

Slight differences are noticeable in the composition and quality of lard made from different parts of the hog. Leaf lard is usually considered the best. Lard is composed of the three fats, olein, stearin, and palmatin, and has a number of characteristic physical properties, as specific gravity, melting point, iodine absorption number, as well as behavior with various reagents, and these enable the mixing of other fats with lard to be readily detected. Lard is used in the preparation of oleomargarine, and it is also combined with various vegetable oils, as cotton-seed oil, in the making of imitation or compound lards.[46]

Lard subst.i.tutes differ little in general composition from pure lard, except in the structure of the crystals and the percentage of the various individual fats.

134. Texture and Toughness of Meats.--In discussing the texture of meats, Professor Woods states:[45]

"Whether meats are tough or tender depends upon two things: the character of the walls of the muscle tubes and the character of the connective tissues which bind the tubes and muscles together. In young and well-nourished animals the tube walls are thin and delicate, and the connective tissue is small in amount. As the animals grow older or are made to work (and this is particularly true in the case of poorly nourished animals), the walls of the muscle tubes and the connective tissues become thick and hard. This is the reason why the flesh of young, well-fed animals is tender and easily masticated, while the flesh of old, hard-worked, or poorly fed animals is often so tough that prolonged boiling or roasting seems to have but little effect on it.

"After slaughtering, meats undergo marked changes in texture. These changes can be grouped under three cla.s.ses or stages. In the first stage, when the meat is just slaughtered, the flesh is soft, juicy, and quite tender. In the next stage the flesh stiffens and the meat becomes hard and tough. This condition is known as _rigor mortis,_ and continues until the third stage, when the first changes of decomposition set in. In hot climates the meat is commonly eaten in either the first or second stage. In cold climates it is seldom eaten before the second stage, and generally, in order to lessen the toughness, it is allowed to enter the third stage, when it becomes soft and tender, and acquires added flavor. The softening is due in part to the formation of lactic acid, which acts upon the connective tissue. The same effect may be produced, though more rapidly, by macerating the meat with weak vinegar. Meat is sometimes made tender by cutting the flesh into thin slices and pounding it across the cut ends until the fibers are broken."

135. Influence of Cooking upon the Composition of Meats.[47]--It is believed by many that losses are prevented and the nutritive value conserved when, in the cooking of meat, it is placed directly into boiling water rather than into cold water and then brought to the boiling point and cooked. Extensive experiments have been made by Dr.

Grindley in regard to this and other points connected with the cooking of meats, and in general it was found that the temperature of the water in which the meat was placed made little difference in its nutritive value or the amount of material extracted. It was found that by both methods there was dissolved 2.3 percent of the protein matter, 1 percent of the nitrogenous extractives, 1.6 per cent of non-nitrogenous material, and 0.8 per cent of ash, of the raw meat, which was equivalent to about 13 per cent of the total proteid material and 81 percent of the ash. The cold water extract contained bodies coagulated by heat. Cold water did not extract any of the fat, but during the process of cooking, appreciable amounts were lost mechanically. Cooked meats were found to be less soluble in cold water than raw meats. During the process of boiling, meat shrinks in weight about 40 or 45 per cent, depending mainly upon the size of the pieces and the content of fat. The loss in weight is practically a loss of water, and the loss of nutrients, all told, amounts to about 4 per cent, or more, depending upon the mechanical loss.[48] But slight differences were found in the composition of the meats cooked three and five hour periods.

"Careful study in this laboratory has shown that when meat is cooked in water at 80 to 85 C., placing meat in hot or cold water at the start has little effect on the amount of nutrients in the meat which pa.s.ses into the broth. The meat was in the form of cubes, one to two inches, and in pieces weighing from one to two pounds.

"It is commonly supposed that when meat is plunged into boiling water, the alb.u.min coagulates and forms a crust, which prevents the escape of nutritive materials into the broth. It is also believed that if a rich broth is desired, to be used either as a soup or with the meat as a stew, it is more desirable to place the meat in cold water at the start. From the results of these experiments, however, it is evident that, under these conditions, there can be little advantage in using hot or cold water at the beginning. When meats were cooked by dry heat, as in roasting, a larger amount of nutrients was rendered soluble in water than during boiling. The losses of nutrients were much smaller when meats were cooked by dry heat than when cooked in water, being on the average, water 35 per cent, nitrogenous extractives 9 per cent, non-nitrogenous extractives 17 per cent, fat 7 per cent, ash 12 per cent, and a small loss of protein."

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 princ.i.p.ally 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 (pota.s.sium 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. a.n.a.lyses, 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 a.s.sociated with putrefaction. Cases of poisoning from eating unsound fish are not infrequent.[55]

Sh.e.l.lfish 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, At.w.a.ter states:[7]

"They come nearer to milk than almost any other food material as regards both the amounts and relative proportions of nutrients."

139. Eggs, General Composition.--Eggs are a type of concentrated nitrogenous food. About 75 per cent (sh.e.l.l removed) is water, about one third is yolk, and a little over 50 per cent is alb.u.min or white. The sh.e.l.l 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 alb.u.min. 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 a.s.sociated with the alb.u.min. There is no material difference in chemical composition between white and dark sh.e.l.led 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 alb.u.min, 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.

[Ill.u.s.tration: FIG. 30.--GRAPHIC COMPOSITION OF AN EGG.]

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 alb.u.min and proteids are dissolved in a pepsin solution. In general, it was found that, when the alb.u.min 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 is a matter of importance. Provided mastication is thorough, marked differences in the completeness of digestion of the three sorts of eggs, in the opinion of the writer cited, will not be found."

141. Use of Eggs in the Dietary.--When eggs are at the same price per dozen as meat is per pound, they furnish a larger amount of nutrients.

In general, a dozen eggs have a little higher food value than a pound of meat. Eggs are usually a cheaper source of food because a smaller amount is served than of meat. When eggs are 25 cents per dozen, the cost of ten eggs for a family of five is less than that of a pound or a pound and a quarter of beef at 22 cents per pound. The meat, however, would furnish the larger amount of nutrients. Eggs are valuable, too, in the dietary because they are frequently combined with flour, cereal products, and vegetables, which contain a large amount of starch, and some of which contain small amounts of protein. This combination furnishes a balanced ration, as well as secures palatability and good mechanical combination of the foods. Eggs in combination with flour, sugar, b.u.t.ter, and other materials have equally as great a value as when used alone and as a subst.i.tute for meat.

Eggs vary in weight from 17.5 to 28 ounces, and more per dozen. They should be purchased and sold by weight. When stored, eggs lose weight.

The egg cannot be considered as entirely germ proof, and care is necessary in its handling and use, the same as with other food articles.

The cause of the spoiling of eggs is due largely to exterior bacterial infection.

CANNED MEATS

142. General Composition.--Canned meats differ but little in composition from fresh meats. Usually during the process of cooking and canning there is a slight increase in the amount of dry matter, but the relative proportion of protein and fat is about the same as in fresh meat. It is frequently stated that the less salable parts are used in the preparation of canned meats, as it is possible by cooking and the addition of condiments to conceal the inferior physical properties. As to the accuracy of these statements, the author is unable to say. The shrinkage or loss in weight during canning amounts to from 30 to 40 per cent. The liquids in which the cooking and parboiling are done are sometimes used in the preparation of beef extracts. Salt, saltpeter, and condiments are generally added during the canning process. Saltpeter is used, as it a.s.sists in retaining the natural color and prevents some objectionable fermentation changes. In moderate amounts it is not generally considered an adulterant. An extensive examination by Wiley and Bigelow of packing-house products and preserved meats showed that of the latter only a small amount contained objectionable preservatives.

The authors, after an extended investigation, reported favorably upon their composition and sanitary value, saying they found "so little to criticise and so much to commend in these necessary products." In this bulletin they do not cla.s.sify saltpeter as an adulterant.[51]

Where fresh meats cannot be secured, canned meats are often indispensable. Usually the nutrients of canned meats cost more than those of fresh meats, and in their use as food much care should be exercised to prevent contamination after opening the cans. Occasionally the meat contains ferment materials that have not been entirely destroyed during cooking, and these, when the cans are stored in warm places, develop and cause deleterious changes to occur. Consequently canned meats should be stored at a low temperature. By recent congressional act, these preparations are now made under the supervision of government inspectors. All diseased animals are rejected, and the sanitary conditions under which the meat is prepared have been greatly improved. Formerly, the most frequent forms of adulteration were subst.i.tution of one meat for another, as the mixing of veal with chicken, and the use of preservatives, as borax and sulphites.

While the cost of the nutrients in canned meats is generally much higher than in fresh meats, the latter are not always easily obtained, or capable of being kept for any length of time, and hence canned meats are often indispensable.

CHAPTER IX

CEREALS

143. Preparation and Cost of Cereals.--The grains used in the preparation of cereal foods are wheat, oats, corn, rice, and, to a less extent, barley and rye. For some of these the entire cleaned grain is ground or pulverized, while for others the bran and germ are first removed. In order to improve their keeping qualities, they are often sterilized before being put up in sealed packages. Special treatment, as steaming or malting, is sometimes given to impart palatability and to lessen the time required for cooking. As a cla.s.s, the cereal foods are clean, nutritious, and free from adulteration. Extravagant claims are sometimes made as to their food value, and frequently excessive prices are charged, out of proportion to the cost of the nutrients in the raw material. Within recent years the number of cereal preparations has greatly increased, due to improvements and variations in the methods of manufacture.[56]

Cereal foods are less expensive than meats and the various animal food products. They contain no refuse, are easily prepared for the table, and may be kept without appreciable deterioration. Some of the ready--to-eat brands are cooked, dried, and crushed, and sugar, glucose, salt, and various condimental materials added to impart taste.

Others contain malt, or are subjected to a malting or germinating process to develop the soluble carbohydrates, and such foods are sometimes called predigested. It is believed that the cereals are being more extensively used in the dietary, which is desirable both from an economic and a nutritive point of view. Special care is necessary in the cooking and preparation of cereals for the table, in order to develop flavor and bring about hydration and rupturing of the tissues, as explained in Chapter II.

144. Corn Preparations.--Corn or maize is characterized by a high percent of fat and starch, and, compared with wheat and oats, a low content of protein.[57] Removal of the bran and germ lessens the per cent of fat. The germ is removed princ.i.p.ally because it imparts poor keeping qualities. Many of the corn breakfast foods contain 1 per cent or less of fat and from 8 to 9 per cent of protein. Coa.r.s.ely ground corn foods are not as completely digested and a.s.similated as those more finely ground. As in the case of wheat products, the presence of the bran and germ appears to prevent the more complete absorption of the nutrients. Finely ground corn meal compares favorably in digestibility with wheat flour. Corn flour is prepared by removal of the bran and germ and granulation of the more starchy portions of the kernel, and has better keeping qualities than corn meal from which the bran and germ have not been so completely removed. At times corn flour has been sufficiently low in price to permit its use for the adulteration of wheat flour. The mixing of corn and wheat flours, however, is prohibited by law unless the product is so labeled. When combined with wheat flour, corn bread and various other articles of food are prepared, but used alone corn flour is not suitable for bread making, because its gluten lacks the binding properties imparted to wheat flour by the gliadin. It is essential that corn be used with foods of high protein content so as to make a balanced ration; for when it forms a large part of the dietary, the ration is apt to be deficient in protein. In a mixed dietary, corn is one of the cheapest and best cereals that can be used.

Too frequently, however, excessive prices are charged for corn preparations that contain no more nutrients than ordinary corn meal.