Human Foods and Their Nutritive Value Part 3

62. Grape Fruit.--The rind and seed of this fruit make up about 25 per cent, leaving 75 per cent as edible portion. The juice contains 14 per cent solids, of which nearly 10 per cent is sugar and 2.5 per cent is citric acid. There is more acid in grape fruit than in oranges and appreciably less than in lemons. The characteristic flavor is due to a glucoside-like material. Otherwise the composition and food value are about the same as of oranges.

[Ill.u.s.tration: FIG. 14.--GRAPHIC COMPOSITION OF STRAWBERRY.]

63. Strawberries contain from 8 to 12 per cent of dry matter, mainly sugar and malic acid. The protein, fat, and ash usually make up less than 2 per cent. Essential oils and coloring substances are present in small amounts. It has been estimated that it would require 75 pounds of strawberries to supply the protein for a daily ration. Nevertheless they are valuable in the dietary. It has been suggested that the malic and other acids have antiseptic properties which, added to the appearance and palatability, make them a desirable food adjunct. Strawberries have high dietetic rather than high food value.

64. Grapes contain more dry matter than apples or oranges. There is no appreciable amount of protein or fat, and while they add some nutrients, as sugar, to the ration, they do not contribute any quant.i.ty. Their value, as in the case of other fruits, is due to palatability and indirect effect upon the digestibility of other foods. In the juice of grapes there is from 10 to 15 per cent or more of sugar, as sucrose, levulose, and dextrose. Grapes contain also from 1 to 1.5 per cent of tartaric acid, which, during the process of manufacture into wine, is rendered insoluble by the alcohol formed, and the product, known as argole, is used in the preparation of cream of tartar. Differences in flavor and taste of grapes are due to variations in the sugar, acid, and essential oil content.

65. Peaches contain about 12 per cent of dry matter, of which over 10 per cent is sugar and other carbohydrates. There is less than 1.5 per cent of protein, fat, and mineral matter and about 0.5 per cent of acid.

The peach contains also a very small amount of hydrocyanic acid, which is more liberally present in the kernel than in the fruit. Flavor is imparted mainly by the sugar and essential oils. Peaches vary in composition with variety and environment.[23]

66. Plums contain the most dry matter of any of the fruits, about 22 per cent, mainly sugar. About one per cent is acid and about 0.5 per cent are protein and ash. There are a great many varieties of plums, varying in composition. Dried plums (prunes) have mildly laxative properties.

67. Olives.--The ripe olive contains about 15 per cent of oil, exclusive of the pit, which makes up 20 per cent of the weight. In green, preserved olives there is considerably less oil. Because of the oil the olive has food value. Olive oil is slightly laxative and a.s.sists mechanically in the digestion of foods.

68. Figs.--Dried figs contain about 50 per cent of sugar and 3.5 per cent of protein. The fig has a mildly laxative action.

69. Dried Fruits.--Many fruits are prepared for market by drying. The dried fruit has a slightly different composition from the fresh fruit because of loss of the volatile and essential oils, and minor chemical changes which take place during the drying process. When free from preservatives, dried fruits are valuable adjuncts to the dietary and can be advantageously used when fresh fruits are not obtainable.

70. Canning and Preservation of Fruits.--To obtain the best results in canning, the fruit should not be overripe. After the ripened state has been reached fermentation and bacterial changes occur, and it is more difficult to preserve the fruit than when not so fully matured.[24] When a fruit has begun to ferment, it is hard to destroy the ferment bodies and their spores so as to prevent further ferment action. The chemical changes that occur in the last stages of ripening are similar to those which take place during the cooking process whereby the pectin or jelly-like substances are rendered more soluble and digestible.

71. Adulterated Canned Fruits.--a.n.a.lyses of a number of canned fruits, made by various Boards of Health, show the presence of small amounts of a.r.s.enic, tin, lead, and other poisonous metals. The quant.i.ty dissolved depends upon the kind, age, and condition of the canned goods and the state of the fruit when canned. The longer a can of fruit or vegetable has been kept in stock, the larger is the amount of tin or metal that has been dissolved. When fresh canned, there is usually very little dissolved tin, but in old goods the amount may be comparatively large.

The tin used for the can is occasionally of poor quality and may contain some a.r.s.enic, which also is dissolved. The occasional use of canned goods preserved in tin is not objectionable, but they should not be used continually if it can be avoided. Preservatives, as borax, salicylic acid, benzoic acid, and sodium sulphate, are sometimes added to prevent fermentation and to preserve the natural appearance of the fruit or vegetable.[18]

72. Fruit Flavors and Extracts.--Formerly all fruit extracts and flavors were obtained from vegetable sources; at present many are made in the chemical laboratory by synthetic methods; that is, by combining simpler organic compounds and radicals to produce the material having the desired flavor and odor. The various fruit flavors are definite chemical compounds, and can be produced in the laboratory as well as in the cells of plants. When properly made, there is no difference in chemical composition between the two. As prepared in the laboratory, however, traces of acids, alkalies, and other compounds, used in bringing about the necessary chemical combination, are often present, not having been perfectly removed. Hence it is that natural and artificial flavors differ mainly in the impurities which the artificial flavors may contain.

Some of the flavoring materials have characteristic medicinal properties, as the flavor of bitter almond, which contains hydrocyanic acid, a poisonous substance. Flavors and extracts should not be indiscriminately used. In small amounts they often exert a favorable influence upon the digestion of foods, and the value of some fruits is in a large measure due to the special flavors they contain. A study of the separate compounds which impart flavor to fruits, as the various aldehydes, ethers, and organic salts, belongs to organic chemistry rather than to foods. Some of the simpler compounds of which flavors are composed may exist in entirely different form or combination in food products; as for example, pineapple flavoring is ethyl butrate. This can be prepared by combination of butyric acid from stale b.u.t.ter with alcohol which supplies the ethyl radical. The chemical union of the two produces the new compound, ethyl butrate, the distinctive flavoring substance of the pineapple. Banana flavor can be made from stale b.u.t.ter, caustic soda, and chloroform. None of these materials, as such, go into the flavor, but an essential radical is taken from each. These manufactured products, when properly made, are in every essential similar to the flavor made by the plant and stored up in the fruit. The plant combines the material in the laboratory of the plant cell, and the manufacturer of essences puts together these same const.i.tuents in a chemical laboratory. In the fruit, however, the essential oil is a.s.sociated with a number of other compounds.

CHAPTER V

SUGARS, MOLa.s.sES, SYRUP, HONEY, AND CONFECTIONS

73. Composition of Sugars.--The term "sugar" is applied to a large cla.s.s of compounds composed of the elements carbon, hydrogen, and oxygen. Sugars used for household purposes are derived mainly from the sugar cane and the sugar beet.[25] At the present time about two fifths are obtained from the cane and about three fifths from the beet. When subjected to the same degree of refining, there is no difference in the chemical composition of the sugars from the two sources; they are alike in every respect and the chemist is unable to determine their origin.

The production of sugar is an agricultural industry; the methods of manufacture pertain more to industrial chemistry than to the chemistry of foods, and therefore a discussion of them is omitted in this work.[26]

[Ill.u.s.tration: FIG. 15.--SUGAR CRYSTALS.]

74. Commercial Grades of Sugar.--Sugars are graded according to the size of the granule, the color and general appearance of the crystals, and the per cent of sucrose or pure sugar. Common granulated sugar is from 98.5 to 99.7 per cent pure sucrose. The impurities consist mainly of moisture and mineral matter. In the process of refining, sulphur fumes are frequently used for bleaching and clarifying the solution.[26]

The sulphurous acid formed is neutralized with lime, which is rendered insoluble and practically all removed in subsequent filtrations. There are, however, traces of sulphates and sulphites in ordinary sugar, but these are in such small amounts as not to be injurious to health. When sugar is burned, as in the bomb calorimeter, so as to permit collection of all of the products of combustion, granulated sugar yields about 0.01 of a per cent of sulphur dioxid.[13] Occasionally coloring substances, as a small amount of indigo, are added to yellow tinged sugars to impart a white color, much on the same principle as the bluing of clothes. The amount used is usually extremely small, and the effect on health has never been determined. Occasionally, however, bluing is used to such an extent that a blue sc.u.m appears when the sugar is boiled with water.

Sugar has high value for the production of heat and energy. Digestion experiments show that when it is used in the dietary in not excessive amounts, it is directly absorbed by the body and practically all available. It can advantageously be combined with other foods to form a part of the ration.[27] When a ration contains the requisite amount of protein, sugar is used to the best advantage. Alone it is incapable of sustaining life, because it does not contain any nitrogen. When sugar was subst.i.tuted for an excess of protein in a ration, it was found to produce heat and energy at much less expense. Many foods, as apples, grapes, and small fruits, contain appreciable amounts of sugar and owe their food value almost entirely to their sugar content. In the dietary, sugar is too frequently regarded as a condiment instead of a nutrient, to be used for imparting palatability rather than for purposes of nutrition. While valuable for improving the taste of foods, the main worth of sugar is as a nutritive substance; used in the preparation of foods it adds to the total heat and energy of the ration. Sugar is sometimes used in excessive amounts and, as is the case with any food or nutrient, when that occurs, nutrition disturbances result, due to misuse of the food. Statistics show that the average consumption of sugar in the United States is nearly 70 pounds a year per capita. In the dietary of the adult, sugar to the extent of four ounces per day can be consumed advantageously. The exclusion of sugar from the diet of children is a great mistake, as they need it for heat and energy and to conserve the protein for growth.

"Sugar is one of the most important forms in which carbohydrates can be added to the diet of children. The great reduction in the price of sugar which has taken place in recent years is probably one of the causes of the improved physique of the rising generation. The fear that sugar may injure children's teeth is, largely illusory. The negroes who live largely on sugar cane have the finest teeth the world can show. If injudiciously taken, sugar may, however, injure the child's appet.i.te and digestion. The craving for sweets which children show is no doubt the natural expression of a physiological need, but they should be taken with, and not between, meals."[28]

[Ill.u.s.tration: FIG. 16.--NUTRIENTS OF A RATION WITH SUGAR.

The hacket parts represent the proportion of nutrients not digested.]

75. Sugar in the Dietary.--Sugar has an important place in the dietary. It not only serves for the production of heat and energy in the body, but is also valuable in enabling the proteids to be used more economically. In reasonable amounts, it is particularly valuable in the dietary of growing children, as the proteids of the food are then utilized to better advantage for growth. The unique value of sugar depends upon its intelligent use and its proper combination with other foods, particularly with those rich in the nitrogenous compounds or proteids. Sugar alone is incapable of sustaining life, but combined with other foods is a valuable nutrient. The amount which can be advantageously used depends largely upon the individual. Ordinarily three to five ounces per day is sufficient, although some persons cannot safely consume as much as this. In the case of diabetes mellitus, the amount of sugar in the ration must be materially reduced. Persons in normal health and engaged in outdoor work can use sugar to advantage.[29] Many of the "harvest drinks," made largely from mola.s.ses with a little ginger, and used extensively in some localities, are not without merit, as they contain an appreciable amount of nutrients. Milk contains more sugar as lactose or milk sugar than any other nutrient.

[Ill.u.s.tration: FIG. 17.--NUTRIENTS OF A RATION WITHOUT SUGAR.

The hacket parts represent the proportion of nutrients not digested.]

The craving for sugar by growing children and athletes is natural.

Sugar, however, is often injudiciously used, and a perverted taste may be established which can be satisfied only by excessive amounts. This results in impaired digestion and malnutrition.

76. Maple Sugar.--Sugar obtained by evaporation from the sap of the maple tree (_Acer saccharinum_) is identical, except for the foreign substances which it contains, with that from the beet and sugar cane.

The mottled appearance and characteristic color and taste of maple sugar are due to the various organic acids and other compounds present in the maple sap and recovered in the sugar. Maple sugar, as ordinarily prepared, has 0.4 of a per cent or more of ash or mineral matter, while refined cane sugar contains less than one tenth as much.[30] Hence, when maple sugar is adulterated with cane and beet sugars, the ash content is noticeably lowered, as is also the content of organic acids. It is difficult, however, to determine with absolute certainty pure high grade maple sugar from the impure low grade to which a small amount of granulated sugar has been added.

77. Adulteration of Sugar.--Sugar at the present time is not materially adulterated. Other than the substances mentioned which are used for clarification and color, none are added during refining which remain in the sugar in appreciable amounts. Sugar does not readily lend itself to adulteration, as it has a definite crystalline structure, and materials that would be suitable for its adulteration are of entirely different physical character.[31] Cane sugar is not easily blended with glucose, or starch sugar, because of the physical differences between the two. The question of the kind of sugar to use in the household, as granulated, loaf, or pulverized, is largely one of personal choice, as there is no appreciable difference in the nutritive value or purity of the different kinds.

78. Dextrose Sugars.--Products known as glucose and dextrose sugars are made from corn and other starches; they can also be prepared from cane sugar by the use of heat, chemicals, or ferments for carrying on the process known as inversion. The dextrose sugars differ from cane sugar in containing a dissimilar number of carbon, hydrogen, and oxygen atoms in the molecule. The formula of the dextrose sugars is C_{6}H_{12}_O{6}, while that of cane sugar is C_{12}H_{22}O_{11}. By the addition of one molecule of water, H_{2}O, to a molecule of sucrose, two molecules of invert sugar (dextrose and glucose) are produced:[1]

C_{12}H_{22}O_{11} + H_{2} = C_{6}H_{12}O_{6} + C_{6}H_{12}O_{6}. In bringing about this change, acids are employed, but the acid in no way enters into the chemical composition of the final product; it is removed as described during the process of sugar manufacture. The action of the acid brings about a catalytic change, the acid being necessary only as a presence reagent to start the chemical reaction. When properly prepared and the acid product thoroughly removed, dextrose and glucose have practically the same food value as sugar. When they are digested, heat and energy are produced, and a given weight has about the same fuel value as an equal weight of sugar. Some of the glucose-yielding products can be made at less expense than sugar, and when they are sold under their right names there is no reason why they should not be used in the dietary, as they serve the same nutritive purpose.

79. Mola.s.ses is a by-product obtained in the refining of sugar. It is a mixture of cane sugar and invert sugars, as levulose and dextrose.

When in sugar making the sucrose is removed by crystallization, a point is finally reached where the solution, or mother liquid, as it is called, refuses to give up any further crystals;[31] then this product, consisting of various sugars and small amounts of organic acids and ash, is partially refined and clarified to form mola.s.ses. The term "New Orleans" mola.s.ses was formerly applied to the product obtained by the use of open kettles for the manufacture of sugar, but during recent years the vacuum pan process has been introduced, and "New Orleans"

mola.s.ses is now an entirely different article. The terms first, second, and third mola.s.ses are applied to the liquids obtained after the removal of the first, second, and third crops of sugar crystals; first mola.s.ses being richer in sucrose, while third mola.s.ses is richer in dextrose and invert sugars. The ash in mola.s.ses ranges from 4 to 6.5 per cent. Some of the low grades of mola.s.ses are used in the preparation of animal foods.

The taste and physical characteristics of mola.s.ses are due largely to the organic acids and impurities that are present, as well as to the proportion in which the various sugars occur. When used with soda in cooking and baking operations, the organic acid of the mola.s.ses liberates carbon dioxide gas, which acts as a leavening agent. Because of the organic acids, mola.s.ses should not be stored in tin or metalware dishes, as the solvent action results in producing poisonous tin and other metallic salts.

The food value of mola.s.ses is dependent entirely upon the amount of dry matter and the per cent of sugar. A large amount of water is considered an adulterant; ordinarily mola.s.ses contains from 20 to 33 per cent. If a sample of mola.s.ses contains 75 per cent of dry matter, it has slightly less than three fourths of the nutritive value of the same weight of sugar.

80. Syrups.--The term "syrup" is applied to natural products obtained by evaporation and purification of the saccharine juices of plants.

Sorghum syrup is from the sorghum plant, which is pressed by machinery and the juice clarified and evaporated so as to contain about 25 per cent of water. In sorghum syrups there are from 30 to 45 per cent of cane sugar, and from 12 to 20 per cent of glucose and invert sugars.

Cane syrup is made from the clarified juice of the sugar cane, and has about the same general composition as sorghum syrup. Maple syrup, prepared from the juice of the sugar maple, is characteristically rich in sucrose and contains but little glucose or reducing sugars. The flavor of all the syrups is due mainly to organic acids, ethereal products, and impurities. In some instances the essential flavor can be produced synthetically, or derived from other and cheaper materials; and by the use of these flavors, mixed syrups can be prepared closely resembling many of the natural products. When properly made, they are equal in nutritive value to natural syrups. When sold under a.s.sumed names, they are to be considered and cla.s.sified as adulterated, and not as syrups from definite and specific products. Low-grade syrups and mola.s.ses are often used for making fuel alcohol. They readily undergo alcoholic fermentation and are valuable for this purpose, rendering it possible for a good grade of fuel alcohol to be produced at low cost.

The manufacture of sugar, syrups, and mola.s.ses has been brought to a high degree of perfection through the a.s.sistance rendered by industrial chemistry. Losses in the process are reduced to a minimum, and the various steps are all controlled by chemical a.n.a.lysis. Sugar has the physical property of deflecting a ray of polarized light, the amount of deflection depending upon the quant.i.ty of sugar in solution. This is measured by the polariscope, an instrument by means of which the sugar content of sugar plants is rapidly determined.

[Ill.u.s.tration: FIG. 18.--GRAPHIC COMPOSITION OF SYRUP.]

81. Honey is composed largely of invert sugars gathered by the honeybee from the nectar of flowers. It varies in composition and flavor according to its source. The color depends upon the flower from which it came, white clover giving a light-colored, pleasant-flavored honey, while that from buckwheat and goldenrod is dark and has a slightly rank taste. The comb is composed largely of wax, which has somewhat the same general composition as fat, but contains ethereal instead of glycerol bodies. On account of the predominance of invert sugars, pure honey has a levulo or left-handed rotation when examined by the polariscope. Honey contains from 60 to 75 per cent of invert sugars, and from 12 to 20 per cent of water, while the ash content is small, less than one tenth of one per cent. Strained honey is easily adulterated with glucose products. Adulteration with cane sugar is readily detected, as pure honey contains only a very small amount of sucrose. Honey can be made by feeding bees on sugar; the sugar undergoes inversion, with the production of dextrose. Such honey, although not adulterated, is inferior in quality and lacking in natural flavor.[18]

82. Confections.--By blending various saccharine products, confections are made. Usually sucrose (cane and beet sugar) is used as the basis for their preparation. Sucrose has definite physical properties, as crystalline structure, and forms chemical and mechanical combinations with acid, alkaline, and other substances; it also unites with water, and when heated undergoes changes in structural composition. The presence of small amounts of acid substances, or variations in the concentration of the sugar solution, materially affect the mechanical relation of the sugar particles to each other, and their crystallization. Usually crystallization takes place when there is less than 25 per cent of water present. The form, size, and arrangement of the crystals are influenced by agitation during cooling. To secure desired results, often small quant.i.ties of various other substances are employed for their mechanical action. Glucose is frequently used, and is said to be necessary for the production of some kinds of candy.

Candies are colored with various dyes and pigments, many of which are harmless, although some are injurious. Coal tar dyes are frequently employed for this purpose. Objection has generally been urged against their use, as it is believed many of them are injurious to health. It cannot be said, however, that all are poisonous, as some are known to be harmless. The use of a few coal tar dyes is allowed by the United States government. Mineral colors are now rarely, if ever, used.

Impure candies result from objectionable ingredients, as starch, paraffin, and large amounts of injurious coloring substances. Coal tar coloring materials are identified in the way described in Experiment No.

13. Confectionery, when properly prepared and unadulterated, has the same nutritive value as sugar and the other ingredients, and is ent.i.tled to a place in the dietary for the production of heat and energy. Much larger amounts of candies are sold and consumed during the winter than the summer months, suggesting that in cold weather candy is most needed in the dietary.

83. Saccharine is an artificial sweetening, five hundred times sweeter than cane sugar. It contains in its molecule, chemically united, benzine, sulphuric acid, and ammonia radicals. It is employed for sweetening purposes in cases of diabetes mellitus, where physicians advise against the use of sugar. It has no food value. A small amount is sometimes added to canned corn and tomatoes to impart a sweet taste. The physiological properties of saccharine have not been extensively investigated.

CHAPTER VI

LEGUMES AND NUTS