Читать книгу Dietetics for Nurses - Fairfax T. Proudfit - Страница 39

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The adulteration of food, which formerly was practised by unscrupulous dealers to cover up inferior articles, or by manufacturers to prevent or arrest decomposition in canned goods, is regulated by law. The passage of the National Pure Food and Drug Act gave the Government authority to regulate the preservatives and coloring matter used in canned and bottled goods, forcing the manufacturers to state on the label the exact contents of each bottle or can. There are likewise stringent laws governing the adulteration of milk, butter, and other articles of food.

Tests for Adulterants.—Boric acid, borax, and formaldehyde are the preservatives more often found in milk. These chemicals are introduced to arrest the natural souring and decomposition which takes place after milk reaches a certain age. Occasionally salicylic acid and sodium carbonate are used. Formaldehyde may be detected by placing about 20 c.c. of milk in a small glass vessel or tube. Dilute with an equal amount of pure water, add commercial sulphuric acid, allowing it to flow gently down the inside of the tube. A purple ring will appear at the zone of contact if formaldehyde is present. “Boric acid and borax may be detected by adding a drop or two of hydrochloric acid to a few drops of milk in a white dish and then several drops of a saturated alcoholic solution of turmeric. The dish is then heated gently for a few minutes, and, if boric acid or borax is present, a pink or dark red color will appear. A dark blue-green should appear when the dish is cooled and a drop of ammonia added.”[28]

Canned goods must be carefully examined before being used. The domestic canned goods are rarely adulterated, but imperfect sterilization and defective cans may bring about a condition of fermentation and gas formation due to bacterial action. Cans should have a concave appearance on the top. If there is a bulging of the can it may be due to gas formation, and a small hole should be made in the can to note any escape of this gas. Should there be any indication of fermentation, the contents should be discarded. It is advisable to look with suspicion on cans that appear old, rusty, and soiled; they are probably left-over stock and liable to be bad. Peas which have been imperfectly sterilized produce a type of gas which is soluble in the liquid. After decomposition has occurred there will be no apparent evidence by the escape of gas, but the liquid will be found to be excessively acid, and will present a muddy appearance. Certain foreign importations of canned goods are preserved in color by the introduction of certain color preservatives. Peas—petits pois, for example—and the very small string beans which are imported are intensely green from the copper sulphate used. Its presence may be detected by adding a few drops of hydrochloric acid to some of the colored material, then dropping in a bright steel nail, knitting needle, or knife blade. There will be a deposit of copper salts (like copper plating) upon the steel if the preservative is present in the can. Canned corn is often artificially sweetened with saccharine, which may be detected by shaking several tablespoonfuls of the liquid in an equal amount of chloroform. Saccharine is soluble in chloroform, while sugar is not. Allow the mixture to stand a few minutes and remove some of the chloroform which has settled at the bottom. Place in a small dish, evaporate the chloroform by gently heating the dish; taste the residue; if sweet, saccharine is present.

Coffee is adulterated more often when it is put up in ground or powdered form than when sold in the bean. Real coffee contains a small percentage of oil, and will float when thrown into a glass of water. Substitutes generally sink to the bottom. Coffee substitutes are often made up of starch-containing materials, such as cereals, beans and peas. This starch may be detected by mixing one tablespoonful of the suspected coffee in a little cold water, adding one cup of boiling water; allow it to boil two minutes, filter through cotton, and pass the liquid through charcoal to remove the color. When it is cold, add a few drops of dilute iodine solution. If starch is present, a blue color will appear.