Human Foods and Their Nutritive Value

88. String Beans.—String beans—green beans with pod—contain a large amount of water, 85 to 88 per cent. The dry matter is rich in protein, nearly 20 per cent, although in the green beans as eaten, containing 85 per cent water, there is less than 2½ per cent. Lima beans are richer in protein than string beans, as the green pod is not included. String beans are valuable both for the nutrients they contain and for the favorable influence they exert upon the digestibility of other foods.

89. Peas.—In general composition and digestibility, peas are quite similar to beans. They belong to the same family, Leguminosæ, and the protein of each is similar in quantity and general properties. The statements made in regard to the composition, digestibility, and use of beans in the dietary apply with minor modifications to peas. When used in the preparation of soups, they add appreciable amounts of nutrients.

90. Canned Peas.—In order to impart a rich green color, copper sulphate has been used in the canning of peas. Physiologists differ as to its effect upon health. While a little may not be particularly injurious, much interferes with normal digestion of the food and forms insoluble copper proteids. In some countries a small amount of copper sulphate is tolerated, while in others it is prohibited.

91. Peanuts.—Peanuts differ from peas and beans in containing more fat. They should be considered a food, for at ordinary prices they furnish a large amount of protein and fat. Like the other members of the legume family, the peanut is rather slow of digestion and requires considerable intestinal work for completion of the process.

NUTS

92. General Composition.—Nuts should be regarded as food, for they contribute to a ration appreciable amounts of nutrients. The edible portion of nearly all is rich in fat; pecans, for example, contain as high as 70 per cent. In protein content nuts range from 3 per cent in cocoanuts to 30 per cent in peanuts. The carbohydrate content is usually comparatively low, less than 5 per cent in hickory nuts, although there is nearly 40 per cent in chestnuts. On account of high fat content, nuts supply a large amount of heat and energy.^[33]

93. Chestnuts are characterized by containing less fat and protein and much more carbohydrate material, especially starch, than is found in other nuts. In southern Europe chestnuts are widely used as food; the skins are removed, and the nuts are steamed, boiled, or roasted, and sometimes they are dried and ground into flour. Chestnuts are less concentrated in protein and fat, and form a better balanced food used alone than do other nuts.

94. The Hickory Nut, which is a characteristically American nut, contains in the edible portion about 15 per cent protein, 65 per cent fat, and 12 per cent carbohydrates.

95. The Almonds used in the United States come chiefly from southern Europe, although they are successfully raised in California. They contain about 55 per cent fat and 22 per cent protein. The flavor of almonds is due to a small amount of hydrocyanic acid.

96. Pistachio.—Some nuts are used for imparting color and flavor to food products, as the pistachio nut, the kernel of which is greenish in color and imparts a flavor suggestive of almonds. The pistachio has high food value, as it is rich in both fat and protein. It is employed in the manufacture of confectionery and in ice cream for imparting flavor and color.

97. Cocoanuts grow luxuriantly in many tropical countries, and have a high food value. They are characteristically rich in fat, one half of the edible portion being composed of this nutrient. For tropical countries they supply the fat of a ration at less expense than any other food. When used in large amounts they should be supplemented with foods rich in carbohydrates, as rice, and in proteids, as beans. Cocoanut milk is proportionally richer in carbohydrates and poorer in fat and protein than the meat of the cocoanut. In discussing the cocoanut, Woods states:^[34]

98. Use of Nuts in the Dietary.—When nuts can be secured at a low price per pound, ten cents or less, they compare favorably in nutritive value with other staple foods. Digestion experiments with rations composed largely of nuts show that they are quite thoroughly digested. Professor Jaffa of the California Experiment Station, in discussing the nutritive value of nuts and fruits, says:^[35]

Average Composition of Nuts

(From Fifteenth Annual Report, Maine Agricultural Experiment Station.)

CHAPTER VII

99. Importance in the Dietary.—There is no article of food which enters so extensively into the dietary as milk, and it is one of the few foods which supply all the nutrients,—fats, carbohydrates, and proteids.^[36] Milk alone is capable of sustaining life for comparatively long periods, and it is the chief article of food during many diseases. An exclusive milk diet for a healthy adult, however, would be unsatisfactory; in the case of young children, milk is essential, because the digestive tract has not become functionally developed for the digestion of other foods.

It is necessary to consider not only the composition and nutritive value of milk, but also its purity or sanitary condition.

100. General Composition.—Average milk contains about 87 per cent water and 13 per cent dry matter. The dry matter is composed approximately of:

Fat is the most variable constituent of milk. Occasionally it is found as low as 2 per cent and as high as 6 per cent or more. The poorest and richest milks differ mainly in fat content, as the sugar, ash, casein, and albumin, or "solids of the milk serum," are fairly constant in amount and composition. Variations in the content of fat are due to differences in feed and in the breed and individuality of the animal.

101. Digestibility.—Milk is one of the most completely digested of foods, about 95 per cent of the protein and fat and 97 per cent of the carbohydrates being absorbed and utilized by the body.

In a mixed ration, the nutrients of milk are practically all absorbed. Milk also exerts a favorable influence upon the digestibility of other foods with which it is combined. This is doubtless due to the digestive action of the special ferments or enzymes which milk contains. In milk there is a soluble ferment material or enzyme which has the power of peptonizing proteids. It is this ferment which carries on the ripening process when cheese is cured in cold storage, and it is believed to be this body which promotes digestion of other foods with which milk is combined.^[27]

Milk is not easily digested by some persons. The tendency to costiveness caused by a milk diet can be largely overcome by the use of salt with the milk, or of some solid food, as toast or crackers, to prevent coagulation and the formation of masses resistant to the digestive fluids. Barley water and lime water in small amounts are also useful for assisting mechanically in the digestion of milk. Milk at ordinary prices is one of the cheapest foods that can be used.

102. Sanitary Condition of Milk.—Equally as important as composition is the sanitary condition or wholesomeness of milk. Milk is a food material which readily undergoes fermentation and is a medium for the distribution of germ diseases. The conditions under which it is produced and the way in which it is handled determine largely its sanitary value, and are of so much importance in relation to public health that during recent years city and state boards of health have introduced sanitary inspection and examination of milk along with the chemical tests for detecting its adulteration. Some of the more frequent causes of contaminated and unsound milk are: unhealthy animals, poor food and water, unsanitary surroundings of the animals, and lack of cleanliness and care in the handling and transporting of the milk. Outbreaks of typhoid and scarlet fevers and other germ diseases have frequently been traced to a contaminated milk supply.^[37]

103. Certified Milk.—When milk is produced under the most sanitary conditions, the number of bacterial bodies per cubic centimeter is materially reduced. In order to supply high grade milk containing but few bacteria, special precautions are taken in the care of the animals, and in the feeding and milking, and all sources of contamination of the milk are eliminated as far as possible. Such milk, when sold in sterilized bottles, is commonly called "certified milk," indicating that its purity is guaranteed by the producer and that the number of bacteria per unit does not exceed a certain standard, as 8000 per cubic centimeter. Ordinary market milk contains upwards of 50,000.

104. Pasteurized Milk.—In order to destroy the activity of the bacterial organisms, milk is subjected to a temperature of 157° F. for ten minutes or longer, which process is known as pasteurization. When milk is heated to a temperature above 180°, it is sterilized. Below 157°, the albumin is not coagulated. By pasteurizing, milk is much improved from a sanitary point of view, and whenever the milk supply is of unknown purity, it should be pasteurized.^[38] After the milk has been thus treated, the same care should be exercised in keeping it protected to prevent fresh inoculation or contamination, as though it were unpasteurized milk. For family use milk can be pasteurized in small amounts in the following way: Before receiving the milk, the receptacle should be thoroughly cleaned and sterilized with boiling water or dry heat, as in an oven. The milk is loosely covered and placed in a pan of water, a false bottom being in the pan so as to prevent unequal heating. The water surrounding the milk is gradually heated until a temperature of 159° F. is registered, and the milk is kept at this temperature for about ten minutes. It is then cooled and placed in the refrigerator.

105. Tyrotoxicon.—Tyrotoxicon is a chemical compound produced by a ferment body which finds its way into milk when kept in unsanitary surroundings. It induces digestion disorders similar to cholera, and when present in large amounts, may prove fatal. It sometimes develops in cream, ice cream, or cheese, but only when they have been kept in unclean places or produced from infected milk.

601. Color of Milk is often taken as a guide to its purity and richness in fat. While a yellow tinge is usually characteristic of milks rich in fat, it is not a hard and fast rule, for frequently light-colored milks are richer in fat than yellow-tinged ones. The coloring material is independent of the percentage of fat, and it is not always safe to judge the richness of milk on the basis of color.

107. Souring of Milk.—Souring of milk is due to the action of the lactic acid organism, which finds its way into the milk through particles of dust carried in the air or from unclean receptacles which contain the spores of the organism.^[39] When milk sours, a small amount of sugar is changed to lactic acid which reacts upon the casein, converting it from a soluble to an insoluble condition. When milk is exposed to the air at a temperature of from 70° to 90° F., lactic acid fermentation readily takes place. At a low temperature the process is checked, and at a high temperature the organisms and spores are destroyed. In addition to lactic acid ferments, there are large numbers of others which develop in milk, changing the different compounds of which milk is composed. In the processes of butter and cheese making, these fermentation changes are controlled so as to develop the flavor and secure the best grades of butter and cheese.

108. Use of Preservatives in Milk.—In order to check fermentation, boric acid, formalin, and other preservatives have been proposed. Physiologists object to their use because the quantity required to prevent fermentation is often sufficient to have a medicinal effect. The tendency is to use excessive amounts, which may interfere with normal digestion of the food. Milk that is cared for under the most sanitary conditions has a higher dietetic value and is much to be preferred to that which has been kept sweet by the use of preservatives.

109. Condensed Milk is prepared by evaporating milk in vacuum pans until it is reduced about one fourth in bulk, when it is sealed in cans, and it will then keep sweet for a long time. Occasionally some cane sugar is added to the evaporated product. When diluted, evaporated milk has much the same composition as whole milk. When a can of condensed milk has been opened, the same care should be exercised to prevent fermentation as if it were fresh milk.

110. Skim Milk differs in composition from whole milk in fat content. When the fat is removed by the separator, there is often left less than one tenth of a per cent. Skim milk has a much higher nutritive value than is generally conceded, and wherever it can be procured at a reasonable price it should be used in the dietary as a source of protein.

111. Cream ranges in fat content from 15 to 35 per cent. It is generally preferred to whole milk, although it is not as well balanced a food, because it is deficient in protein. Cream should contain at least 25 per cent of fat.

112. Buttermilk is the product left after removal of the fat from cream by churning. It has about the same amount of nutrients as skim milk. The casein is in a slightly modified form due to the development of lactic acid during the ripening of the cream, and on this account buttermilk is more easily digested and assimilated by many individuals than milk in other forms. The development of the acid generally reduces the number of species of other than the lactic organisms, and these are increased.

113. Goat's Milk is somewhat richer in solids than cow's milk, containing about one per cent more proteids, a little more fat, and less sugar. When used as a substitute for human or cow's milk, it generally needs to be slightly diluted, depending, however, upon the composition of the individual sample.

114. Koumiss is a fermented beverage made from milk by the use of yeast to secure alcoholic fermentation. Koumiss contains about one per cent each of lactic acid and alcohol, and the casein and other nutrients are somewhat modified by the fermentation changes. Koumiss is generally considered a non-alcoholic beverage possessing both food and dietetic value.

115. Prepared Milks.—Various preparations are made to resemble milk in general composition. These are mechanical mixtures of sugar, fats, and proteids. Milk sugar, casein, or malted proteids are generally the materials employed in their preparation. Often the dried and pulverized solids of skim milk are used. Many of the prepared milks are deficient in fat. While they are not equal to cow's milk, their use is often made necessary from force of circumstances.

116. Human Milk is not as rich in solid matter as cow's milk. It contains about the same amount of fat, one per cent more sugar, and one per cent less proteids. In human milk nearly one half of the protein is in the form of albumins, while in cow's milk there is about one fifth in this form. The fat globules are much smaller than those of cow's milk. In infant feeding it is often necessary to modify cow's milk by the addition of water, cream, and milk sugar, so as to make it more nearly resemble in composition human milk.

Fig. 25.—Apparatus Used in Testing Milk.

1, pipette; 2, lactometer; 3, acid measure; 4, centrifuge; 5, test bottle.

117. Adulteration of Milk.—Milk is not as extensively adulterated as it was before the passage and enforcement of the numerous state and municipal laws regulating its inspection and sale. The most frequent forms of adulteration are addition of water and removal of cream. These are readily detected from the specific gravity and fat content of the milk. The specific gravity of milk is determined by means of the lactometer, an instrument which sinks to a definite point in pure milk. In watered milk it sinks to greater depth, depending upon the amount of water added. The fat content of milk is readily and accurately determined by the Babcock test, in which the fat is separated by centrifugal action. For the detection of adulterated milk the student is referred to Chapter VI, "Chemistry of Dairying," by Snyder.

BUTTER

118. Composition.—Butter is made by the churning or agitation of cream and is composed mainly of milk fats and water, together with smaller amounts of ash, salt, casein, milk sugar, and lactic acid. Average butter has the following composition:

When butter contains an abnormal amount of water, it is considered adulterated. According to act of Congress standard butter should not contain over 16 per cent of water nor less than 82.5 per cent of fat.

119. Digestibility of Butter.—Digestion experiments show that practically all of the fat, 98 per cent, is digestible and available for use by the body. Butter is valuable only for the production of heat and energy. Alone, it is incapable of sustaining life, because it contains no proteid material. It is usually one of the more expensive items of food, but it is generally considered quite necessary in a ration.^[5] It has been suggested that it takes an important part mechanically in the digestion of food.

120. Adulteration of Butter.—In addition to containing an excess of water, butter is adulterated in other ways. Old, stale butter is occasionally melted, washed, salted, and reworked. This product is known as renovated butter, and has poor keeping qualities. Frequently preservatives are added to such butter to delay fermentation changes. Oleomargarine and butterine are made by mixing vegetable and animal fats.^[40] Highly colored stearin, cotton-seed oil, and lard are the usual materials from which oleomargarine is made. It has practically the same composition, digestibility, and food value as butter. When sold under its true name and not as butter, there is no objection, as it is a valuable food and supplies heat and energy at less cost than butter. The main objection to oleomargarine and butterine is that they are sold as butter.^[41]

The coloring of butter is not generally looked upon as adulteration, for butter naturally has a more or less yellow tinge. According to an act of Congress, butter colors of a non-injurious character are allowed to be used.

CHEESE

121. General Composition.—Cheese, is made by the addition of rennet to ripened milk, resulting in coagulation of the casein, which mechanically combines with the fat. It differs from butter in composition by containing, in addition to fat, casein and appreciable amounts of mineral matter. The composition varies with the character of the milk from which the cheese was made. Average milk produces cheese containing a larger amount of fat than proteids, while cheese from skimmed or partially skimmed milk is proportionally poorer in fat. Ordinarily there is about 35 per cent of water, 33 per cent of fat, and 27 per cent of casein, and albumin or milk proteids, the remainder being ash, salt, milk sugar, and lactic acid. Cheese is characterized by its large percentage of both fat and protein, and has high food value. It contains more fat and protein than any of the meats; in fact, there are but few foods which have such liberal amounts of these nutrients as cheese.

The odor and flavor of cheese are due to workings of bacteria which result in the production of aromatic compounds. The purity and condition of the milk, as well as the method of manufacture and the kind of ferment material used, determine largely the flavor and odor. Cheese is generally allowed to undergo a ripening or curing process before it is used as food. The changes resulting consist mainly in increased solubility of the proteids, with the formation of a small amount of amid and aromatic compounds.^[42]

122. Digestibility.—Cheese is popularly considered an indigestible food, but extended experiments show that it is quite completely digested, although in the case of some individuals not easily digested. In general, about 95 per cent of the fat and 92 per cent and more of the protein is digested, depending upon the general composition of the cheese and the digestive capacity of the individual. As far as total digestibility is concerned, there appears to be but little difference between green and well-cured cheese. So far as ease of digestion is concerned, it is probable that some difference exists. There is also but little difference in digestibility resulting from the way in which milk is made into cheese, the nutrients of Roquefort, Swiss, Camembert, and Cheddar being about equally digestible.^[13] The differences in odor and taste are due to variations in kind and amount of bacterial action. When combined with other foods, cheese may exercise a beneficial influence upon digestion in the same way as noted from the use of several foods in a ration. No material differences were observed in digestibility when cheese was used in small amounts, as for condimental purposes, or when used in large amounts to furnish nutrients. Artificial digestion experiments show that cheese is more readily acted upon by the pancreatic than by the gastric fluids, suggesting that cheese undergoes intestinal rather than gastric digestion. It is possible this is the reason that cheese is slow of digestion in the case of some individuals.

123. Use in the Dietary.—Cheese should be used in the dietary regularly and in reasonable amounts, rather than irregularly and then in large amounts. Cheese is not a luxury, but ordinarily it is one of the cheapest and most nutritious of human foods. A pound of cheese costing 15 cents contains about a quarter of a pound of protein and a third of a pound of fat; at the same price, beef yields only about half as much fat and less protein. Cheese at 18 cents per pound furnishes more available nutrients and energy than beef at 12 cents per pound. In the dietary of European armies, cheese to a great extent takes the place of beef. See Chapter XVI.

124. Cottage Cheese is made by coagulating milk and preparing the curd by mixing with it cream or melted butter and salt or sugar as desired. When milk can be procured at little cost, cottage cheese is one of the cheapest and most valuable foods.^[43]

125. Different Kinds of Cheese.—By the use of different kinds of ferments and variations in the process of manufacture different types or kinds of cheese are made, as Roquefort, Swiss, Edam, Stilton, Camembert, etc. In the manufacture of Roquefort cheese, which is made from goats' and ewes' milk, bread is added and the cheese is cured in caves, resulting in the formation of a green mold which penetrates the cheese mass, and produces characteristic odor and flavor. Stilton is an English soft, rich cheese of mild flavor, made from milk to which cream is usually added. It is allowed to undergo an extended process of ripening, often resulting in the formation of bluish green threads of fungus. Limburger owes its characteristic odor and flavor to the action of special ferment bodies which carry on the ripening process. Neufchatel is a soft cheese made from sweet milk to which the rennet is added at a high temperature. After pressing, it is kneaded and worked, and then put into packages and covered with tin foil.

126. Adulteration of Cheese.—The most common forms of adulteration are the manufacture of skim-milk cheese by the removal of the fat from the milk, and substitution of cheaper and foreign fats, making a product known as filled cheese. When not labeled whole milk cheese, or sold as such, there is no objection to skim-milk cheese. It has a high food value and is often a cheap source of protein. The manufacture of filled cheese is now regulated by the national government, and all such cheese must pay a special tax and be properly labeled. As a result, the amount of filled cheese upon the market has very greatly decreased, and cheese is now less adulterated than in former years. The national dairy law allows the use of coloring matter of a harmless nature in the manufacture of cheese.

127. Dairy Products in the Dietary.—The nutrients in milk are produced at less expense for grain and forage than the nutrients in beef, hence from a pecuniary point of view, dairy products, as milk and cheese, have the advantage. In the case of butter, however, the cost usually exceeds that of meat. In older agricultural regions, where the cost of beef production reaches the maximum, dairying is generally resorted to, as it yields larger financial returns, and as a result more cheese and less beef are used in the dietary. As the cost of meats is enhanced, dairy products, as cheese, naturally take their place.

CHAPTER VIII

128. General Composition.—Animal tissue is composed of the same classes of compounds as plant tissue. In each, water makes up a large portion of the weight, and the dry matter is composed of nitrogenous and non-nitrogenous compounds, and ash or mineral matter. Plants and animals differ in composition not so much as to the kinds of compounds, although there are differences, but more in the percentage amounts of these compounds. In plants, with the exception of the legumes, the protein rarely exceeds 14 per cent, and in many vegetable foods, when prepared for the table, there is less than 2 per cent. In meats the protein ranges from 15 to 20 per cent. The non-nitrogenous compounds of plants are present mainly in the form of starch, sugar, and cellulose, while in animal bodies there are only traces of carbohydrates, but large amounts of fat. Fat is the chief non-nitrogenous compound of meats; it ranges between quite wide limits, depending upon kind, age, and general condition of the animal. Meats contain the same general classes of proteins as the vegetable foods; in each the proteins are made up of albumins, glubulins, albuminates, peptone-like bodies, and insoluble proteids. The larger portion of the protein of meats and cereals is in insoluble forms. The meat juices, which contain the soluble portion of the proteins, constitute less than 5 percent of the nitrogenous compounds. Meats contain less amid substances than plants, in which the amids are produced from ammonium compounds and are supposed to be intermediate products in the formation of proteids, while in the animal body they are derived from the proteids supplied in the food and, it is generally believed, cannot form proteids. Albuminoids make up the connective tissue, hair, and skin, and are more abundant in animal than in plant tissue. One of the chief albuminoids is gelatine. Both plant and animal foods undergo bacterial changes resulting in the production of alkaloidal bodies known as ptomaines, of which there are a large number. These are poisonous and are what cause putrid and stale meat to be unwholesome. The protein in meat differs little in general composition from that of vegetable origin; differences in structure and cleavage products between the two are, however, noticeable.

Fig. 26.—Meat and Extractive Substances.

While meats from different kinds of animals have somewhat the same general composition, they differ in physical properties, and also in the nature of the various nutrients. For example, pork contains less protein than beef, but the protein of pork is materially different from that of beef, as a larger portion is in the form of soluble proteids, while in beef more is present in an insoluble form. Not only are differences in the percentage of individual proteins noticeable, but there are equally as great differences in the fats. As for example: some of the meats have a larger proportion of the fat as stearin than do others. Hence meats differ in texture and taste more than in nutritive value, due to the variations in the percentage of the different proteins, fats, and extractive material, rather than to differences in the total amounts of these compounds. The taste and flavor of meat is to a large extent influenced by the amount of extractive material.

While the nutrients of meats are divided into classes, as proteins and fats, there are a large number of separate compounds which make up each of the individual classes, and there are also small amounts of compounds which are not included in these groups.

Fig. 27.—Standard Cuts of Beef.

(From Office of Experiment Station Bulletin.)

129. Beef.—About one half of the weight of beef is water; the lean meat contains a much larger amount than the fat. As a rule, the parts of the animal that contain the most fat contain the least water. In some meats there is considerable refuse, 25 to 30 per cent. In average meat about 12 per cent of the butcher's weight is refuse and non-edible parts.^[44] A pound of average butcher's meat is about one half water, and over 10 per cent waste and refuse, which leaves less than 40 per cent fat and protein. Meat is generally considered to have a high nutritive value, due to the comparatively large amounts of fat and protein. Beef contains more protein than any vegetable food, except the legumes, and from 1 to 1.5 per cent mineral matter, exclusive of bone. Some of the mineral matter is chemically united with the protein and other compounds. While figures are given for average composition of beef, it is to be noted that wide variations are frequently to be met with, some samples containing a much larger amount of waste and trimmings than others, and this influences the percent of the nutritive substances. In making calculations of nutrients consumed, as in dietary studies, the figures for average composition of meat should be used only in cases where the samples do not contain an excess either of fat or trimmings.^[45] When very lean, there is often a large amount of refuse, and the meat contains less dry matter and is of poorer flavor than from animals in prime condition. In the case of very fat animals, a large amount of waste results, and the flavor is sometimes impaired.

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.