Human Foods and Their Nutritive Value - Harry Snyder (e book reader pc TXT) 📗

has food value. Olive oil is slightly laxative and assists 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.—Analyses of a number of canned fruits, made by various Boards of Health, show the presence of small amounts of arsenic, tin, lead, and other poisonous metals. The quantity 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 arsenic, 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 butter 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 butter, 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 constituents in a chemical laboratory. In the fruit, however, the essential oil is associated with a number of other compounds.

CHAPTER V SUGARS, MOLASSES, SYRUP, HONEY, AND CONFECTIONS

73. Composition of Sugars.—The term "sugar" is applied to a large class 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]