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.

Hydrochloric Acid Test.—Add 5 cc. of the distillate to be tested to about 5 cc. of milk known to be pure, and about 10 cc. of concentrated hydrochloric acid (sp. gr. 1.2) which contains 1 cc. of a 10 per cent ferric chlorid solution to each 500 cc. of the acid. Heat slowly to 80° or 90° C. over the free flame, agitating it at the same time to break up the curd. A violet coloration indicates formaldehyde.

Sulfurous Acid and the Sulfites

Free sulfurous acid is not largely used as a food preservative, though its salts are quite commonly employed.

Detection.—Mix 150 grams of the finely ground sample with enough water to make a thin paste. Acidify with phosphoric acid and distil till 25 cc. have been collected. (The delivery tube of the condenser should dip below the surface of a little water.) Treat the distillate with a few drops of bromine water and boil for a short time. If a precipitate forms on the addition of barium chlorid the presence of sulfurous acid is indicated.

Salicylic Acid

Acidify 50 cc. of the sample with sulfuric acid, and shake vigorously with 50 cc. of a mixture of equal parts of ether and petroleum spirit. When the liquids have separated, draw off as much as possible of the solvent and filter. If an emulsion forms use a centrifugal machine, and evaporate with a small flame. If needle-shaped crystals form, salicylic acid is present. Add a few drops of water and a drop of very dilute ferric chlorid solution in such a way that the solutions will come together slowly. The presence of salicylic acid gives a purple or violet color.

Saccharin

This is used quite extensively as a sweetening agent in canned sweet corn, and other similar products.

Macerate about 20 grams of the sample after mixing with 30 to 40 cc. of water and strain through muslin. Acidify with 1 or 2 cc. of sulfuric acid (1 to 3) and extract with ether. (If an emulsion forms, use a centrifugal machine.) Separate the ether layer and let the ether evaporate spontaneously and use the residue in the following tests:

Take up a part of the residue with water and taste. If it is very sweet saccharin is present. Confirm by the following:

Schmidt’s Test.—Add about 1 gram of sodium hydroxide to another part of the residue, and heat in an air-oven or oil bath, for half an hour at about 250° C., to convert the saccharin into salicylic acid. After it has cooled, acidify with sulfuric acid, extract and test for salicylic acid with 2 or 3 drops of ferric chlorid solution, letting the solutions come together slowly. A purple or violet coloration proves the presence of salicylic acid, which in turn indicates the presence of saccharin. This test cannot be used if salicylic acid was used as a preservative in the original product. A test for the acid should first be made.

Bornstein’s Test.—Heat the remainder of the above ether residue with resorcin and a very little sulfuric acid till it begins to swell. (It is best to do this heating in a test-tube.) Let cool till the action stops, heat again and repeat the operation several times. After cooling the last time, dilute with water and add sodium hydrate till neutral. If saccharin is present, there will be a red-green fluorescence.

Benzoic Acid

Acidify 50 cc. of the sample with sulfuric acid and shake vigorously with 50 cc. of a mixture of equal parts of ether and petroleum spirit. Let the liquids separate, then draw off as much as possible of the solvent and filter. (Use a centrifugal machine if an emulsion forms.) Separate the extract into 2 parts and evaporate each to dryness over a small flame and make the following tests:

Ferric Chlorid Test.—Dissolve one of these residues in ammonia, and evaporate to dryness on a water-bath. Take up the residue with warm water, filter, and collect the filtrate in a small test tube. Add a drop of ferric chlorid solution, and if benzoic acid is present a characteristic flesh or brownish colored precipitate of ferric benzoate forms. Sometimes in such products as sweet pickles, a basic ferric acetate precipitate comes down and the following test had better be applied.

Peter’s Method.—Take about 0.1 gram of the second part of the above ether residue, place in a large test tube (about 50 cc.) and dissolve in 5 to 8 cc. of concentrated sulfuric acid. Add from 0.5 to 0.8 gram of barium peroxide, a little at a time. Shake each time and cool in water if necessary. This should produce a permanent froth on the sulfuric acid. Let stand 25 or 30 minutes, then fill the tube three fourths full of water, shake and cool rapidly to the temperature of the room, and filter off the barium sulfate. Extract with chloroform or ether. Remove the extract and test it for salicylic acid with dilute ferric chlorid. (See first test under salicylic acid.) In this method salicylic acid must first be proven absent.

Mohler’s Test.—Treat the remainder of the second part of the above ether residue with 2 or 3 cc. of concentrated sulfuric acid. Heat till white fumes appear. Add a few crystals of potassium nitrate and when cool dilute with water. Add an excess of ammonia, then a drop or two of ammonium sulfid. If a red color appears immediately on the surface, it shows the presence of benzoic acid.

COLORING MATTER IN CATSUPS AND TOMATOES

Cochineal

Girard and Dupre Test.—Shake well a portion of the sample with water and filter, acidify with hydrochloric acid, then extract with amyl alcohol, and if cochineal is present the extract will be colored yellow or orange, the particular shade depending on the amount of cochineal present. Remove the amyl alcohol and wash with water until it is neutral. To half of this, add a very dilute solution of uranium acetate, drop by drop, and shaking well after the addition of each drop. Cochineal, if present, will produce a characteristic emerald-green color.

Confirm by adding a drop or two of ammonia to the second half of the amyl alcohol extract and a violet coloration will be produced if cochineal is present.

Coal-Tar Coloring Matter

Sostegni and Carpentieri Test.—Free from grease a piece of woolen cloth (nun’s veiling will do) by boiling first in very dilute caustic soda solution and then in water. Acidify a portion of the sample with 2 to 4 cc. of 10 per cent solution of hydrochloric acid and filter. Strips of the cleansed cloth are boiled in this filtrate for 5 or 10 minutes, then removed, washed in water and boiled with very dilute hydrochloric acid solution. Wash out the acid and dissolve the color from the cloth by boiling in a solution of ammonium hydroxid (1 to 50). (The time required will depend upon the dye present.) Remove the cloth from the solution and acidify the latter with hydrochloric acid and another piece of the cleansed cloth is immersed and again boiled. This second dyeing fixes only coal-tar colors on the cloth, hence, no fear of mistaking them for the natural color of the vegetable.

IN GREEN PICKLES, BEANS, PEAS, ETC.

Copper Salts

Burn 20 grams of the sample to an ash and wet the ash with concentrated nitric acid, dilute with water and boil. Add ammonia till strongly alkaline and filter. If the filtrate is blue, copper is present.

Confirm by acidifying the filtrate with acetic acid and adding potassium ferrocyanid. A red or brownish precipitate or coloration proves the presence of copper. The test for other heavy metals may be made by the general method given under meats.

IN MIXED PICKLES

Turmeric

Shake with alcohol to extract the color. Soak a piece of filter paper in the extract and dry in an air oven at 100° C. Wet the filter paper with a weak solution of boric acid to which a very little hydrochloric acid has been added. If turmeric is present, a cherry-red color will appear when the filter paper is dry.

“SOAKED” VEGETABLES

Peas, Beans, and Corn

There is really no chemical test for this class of foods. Certain helpful directions given in Bul. 65, p. 54, of the Bureau of Chem., will assist in identifying such goods. All or nearly all of the green color of peas and beans is destroyed by the process of “soaking.” They have the appearance of the well-matured product, and are firm and mealy with well-formed cotyledons. The process of soaking starts the growth of the caulicle of the pea. The kernel of corn is plump and hard and does not have the milky consistency of the immatured product. The characteristic succulence of the green pea, bean, and corn is absent in the soaked product.

Alum in Pickles

This is sometimes added to the pickling solution to produce hardness and crispness.

Burn to ash a sample of the pickles, and, if they are free from copper, fuse in a platinum dish with sodium carbonate. Extract with boiling water, and after filtering add ammonium chlorid solution. If alum is present, a flocculent precipitate will form.

Examination of the Can or Box in which Vegetables are Sealed

Generally when the ends of a can are convex, instead of plane or concave, it is spoiled. In the souring of canned sweet corn, it is exceptional that the ends are forced outward.

Strike the can and the spoiled cans will give a dull sound while the good ones will give a distinct tone. Some practice will be necessary to use this test.

One can judge of the amount of tin dissolved by the corrosion of the inside of the can.

Reject cans that show much rust around the cap on the inside of the head.

If more than one hole is found soldered in the cap, reject the can. Cans of salmon are the only exception that has come to the author’s notice. A second hole, in general, indicates that decomposition had set in and the can had been punctured and resealed.