No class of foods on the market has less need for antiseptics than canned goods, yet their use is rather common. Products thus treated are easier canned and are not so apt to spoil. The chemicals used as preservatives are sulfurous acid, and the sulfites, salicylic acid and saccharin, benzoic acid, and sometimes formaldehyde. Sulfurous acid is used to bleach such foods as canned corn. Saccharin possesses some antiseptic properties, but its main use is as a sweetener. Alum is used to make pickles hard and crisp.
Some canned or bottled goods, as tomato-catsup, is colored with cochineal or coal-tar dyes. Green pickles, beans, peas, and such vegetables are colored by copper salts or are cooked in copper vessels, with the addition of acetic acid, hence the beautiful green color. Turmeric is sometimes used to color mixed pickles.
The heavy metals as lead, zinc, and tin are generally present in canned goods, the amount varying with the corrosive power of the vegetable.
When there is a year of scarcity in corn, peas, beans, and such vegetables, the dried product is often soaked and canned. Some of this goods is sold for the regular green vegetable, while some may be properly marked “Soaked Goods.”
PRESERVATIVES
It is best to make a systematic examination for the different preservatives. The sample may be prepared by mixing 50 grams of the pulped material with sufficient water in a 250 cc. graduated flask. Add phosphoric acid till distinctly acid in reaction. Fill to the mark with water. Place in a distilling flask, and distil in a linseed oil or a paraffin bath till 30 cc. have been collected. Save this distillate for the following tests.
Formaldehyde
To 5 cc. of the above distillate in a test tube, add 2 or 3 drops of a 1 per cent aqueous solution of phenol and mix well. Incline the tube and carefully pour down the side 5 cc. of concentrated commercial sulfuric acid so that the two liquids do not mix. If formaldehyde is present there will be a crimson zone at the plane of union of the solutions. This coloration takes place when the formaldehyde is present in the proportion of 1 part in 100,000 parts. When there is a greater quantity of formaldehyde present a white turbidity or a light-colored precipitate forms above the coloring.
Phenylhydrazine Hydrochloric Test.—Dissolve 2 grams of phenylhydrazine hydrochlorid and 3 grams of sodium acetate in 20 cc. of water. Add 2 to 4 drops of this reagent and the same number of drops of sulfuric acid to 1 or 2 cc. of the above distillate, to be examined in a test tube. A green coloration is produced when formaldehyde is present.