Food Adulteration and Its Detection / With photomicrographic plates and a bibliographical appendix

by Jesse P. Battershall

Among the methods which have been suggested for the detection of such accidental impurities as darnel, ergot, and mildew, are the following:—If pure flour is digested for some time with dilute alcohol, the latter either remains quite clear or it acquires a very light straw-colour; with flour contaminated with darnel, the alcohol shows a decided greenish tint, and possesses an acrid and disagreeable taste. In case the alcohol used is acidulated with about 5 per cent. of hydrochloric acid, the extract obtained exhibits a purple-red colour with flour containing mildew, and a blood-red colour with flour containing ergot. When flour contaminated with ergot or other moulds, is treated with a dilute solution of aniline violet, the dye is almost wholly absorbed by the damaged granules, which are thus rendered more noticeable in the microscopic examination.

The following test is often used for the detection of alum in flour:—A small quantity of the suspected sample is made into a paste with a little water and mixed with a few drops of an alcoholic tincture of logwood; a little ammonium carbonate solution is then added. In the presence of alum, a lavender-blue coloured lake is formed, which often becomes more apparent upon allowing the mixture to remain at rest for a few hours. The production of a brown or pink coloration is an indication of the absence of alum. A modification of this test, proposed by Blyth, consists in immersing for several hours in the cold aqueous extract of the flour a strip of gelatine, with which the alum combines; the gelatine is subsequently submitted to the action of the logwood tincture and ammonium carbonate as above.

For the quantitative estimation of alum in flour, the following processes are usually employed:—A considerable quantity of the sample is incinerated in a platinum dish, the ash is boiled with dilute hydrochloric acid and the solution filtered. The filtrate is next boiled and added to a concentrated solution of pure sodium hydroxide, the mixture being again boiled and afterwards filtered hot. A little sodium diphosphate is now added to the filtrate which is then slightly acidulated with hydrochloric acid, and finally made barely alkaline by addition of ammonium hydroxide. The resulting precipitate, which, in the presence of alum, consists of aluminium phosphate, is brought upon a filter, well washed, and then weighed.

Another method, which is a modification of that of Dupré, is as follows:—The ash obtained by the calcination of the flour (or bread), is fused, together with four times its weight of pure mixed sodium and potassium carbonates, the fused mass treated with hydrochloric acid, the solution evaporated to dryness and the separated silica collected and weighed. A few drops of sodium phosphate solution are added to the filtrate from the silica, then ammonium hydroxide in excess, by which the calcium, magnesium, ferric and aluminium phosphates are precipitated. The two latter are next separated by boiling the liquid with an excess of acetic acid (in which they are insoluble), and brought upon a filter, washed, dried, and weighed. The iron sometimes accompanying the precipitate of aluminium phosphate, can be determined by reduction with zinc and titration with potassium permanganate. If the presence of alum is indicated by the logwood test, and it is quantitatively determined by either of the preceding methods, it has been suggested that an allowance be made for the small proportion of aluminium silicate occasionally found in unadulterated flour or bread, and a deduction from the total alum present of one part of alum for every part of silica obtained is considered proper. The weight of aluminium phosphate found, multiplied by 3·873, or by 3·702, gives respectively the corresponding amounts of potash-alum or ammonia-alum contained in the sample examined.

BREAD.

Bread is usually prepared by mixing flour with water, kneading it into a uniform dough, submitting it to a process of “raising,” either by means of a ferment or by the direct incorporation of carbonic acid gas, and finally baking the resulting mass.

Unleavened bread, however, is made by simply kneading flour with water, with the addition of a little salt, and baking. The oatcake of the Scotch, the passover bread of the Israelites, and the corncakes of the Southern States are the best known varieties of unleavened bread.

The porosity peculiar to raised bread is caused by the generation of a gas, either previous to, or during the process of baking. In former times (and to some extent at present, notably in Paris), fermented bread was made by the use of leaven, which is dough in a state of incipient decomposition; but in this country, the common agent employed in raising bread is yeast, which consists of minute vegetable cells (Torula cerevisiæ) forming either the froth or deposit of fermenting worts.

By the action of these ferments, the gluten of the flour first undergoes a modification and enters into a peculiar combination with the starch-granules, which become more or less ruptured; the soluble albumen is rendered insoluble, and the starch is transformed, first into sugar, then into carbonic acid and alcohol. These changes are perfectly analogous to those which occur in the fermentation of the wort in the preparation of fermented liquors.