The technology of bread-making : including the chemistry and analytical and practical testing of wheat, flour, and other materials employed in bread-making and confectionery / by William Jago and William C. Jago.

William Jago

Date:: 1911

Credit: The technology of bread-making : including the chemistry and analytical and practical testing of wheat, flour, and other materials employed in bread-making and confectionery / by William Jago and William C. Jago. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

851/944 page 839

$those of maize are unaltered. As little as from 1 to 2 per cent, of maize can thus be detected. The test may be employed cpiantitatively by taking mixtures containing loiou'n quantities of maize starch, treating tliem in the same -way as the sample under examination, and deciding which matches it Avhen drops of similar size are microscoj)ically examined. The same method is applicable to the detection of maize in rye flour. {Zeits. f. Unter- such. Kaftr.-u Genussmittel, 1899, 2 [1] 27.) 912. Maize in Wheaten Flour, Embrey.—^Embrey has not found the foregoing process to give satisfactory results in his hands, and has therefore devised and recommends the follovdng modiflcation :—Mixtures of pure wheat and maize flours are prepared containing respectively 10, 15, 20, 25 and 30 per cent, of the maize. Weighed quantities (0-2 gram) of each of these, and of the samjAe under examination, are placed in test tubes (15 c.m. X 2 c.m.) which are fitted with paraffnied corks. To each is added a quantity of 20 c.c. of potassium hydroxide solution (18 grams per litre), and the tubes shaken uniformly for 3 minutes. Twelve drops of diluted hydro- chloric acid (HCl of specific gravity 1-16, 50 c.c. ; water, 100 c.c.) are next introduced and the tubes shaken, and then whnled in a centrifugal machine at 600 revolutions per ininute. One c.c. of the clear liquid is transferred to a Nessler tube and diluted to 50 c.c., after which 1 c.c. of an iodine solu- tion (I, 0-25 gram ; KI, 1 gram ; water to 250 c.c.) is added. The tint obtained compared Avith those of the standard tubes gives the proportion of maize within about 5 per cent. For a more exact determination, 10 c.c. of the clear liquid from each tube are boiled for 2 hours Avith 1 c.c. of dilute suljDhuric acid (1 : 7), then neutrahsed, diluted to 50 c.c. and run from a burette into a boiling mixture of Gerrard’s solution, 10 c.c., and Fehling’s solution, 2 C.C., until the colour is discharged. The percentage of maize is obtained from the standard tube of AAFich the same amount is requned to discharge the colour. Gerrard’s Solution is prepared by diluting 10 c.c. of freshly prepared Fehling’s solution AAdth 40 c.c. of water, and adding a solution (about 5 per cent.) of potassium cyanide from a burette, until the blue colour is only just perceptible. During the addition of the cyanide, the diluted Fehling’s solution is kept boiling and constantly stirred in a porcelain dish. {Analyst, 1900, 25, 315.) This process is really an estimation of the soluble starch resulting the rupture of the granules of AAdieaten starch by the action of potassium hydroxide solution. In the first method it is directly estimated as starch by a colori- metric process Avith iodine ; and in the second by conversion into glucose and then volumetricaUy by a modification of Fehlmg’s solution. An objec- tion to the method is that variations in the proportion of Avheaten starch in a flour may be due to causes other than the presence of maize. Thus a very Aveak flour may contain more starch than a very strong one, and if the former be also exceptionally dry and the other comparatively moist the difference is stiU further enhanced. Also, if even as much as 30 per cent, of maize flour is contained in the flour the actual reduction in AAdieat starch is only approximately from about 70 to 50 per cent. On the other hand the amount of maize flour Avill have been increased from zero to 30 per cent. ; obviously, therefore, a direct estimation of the maize starch is preferable if practicable. As a modification of Embrey’s method it is suggested that the solution of clear starcli sliould be decanted off, the insoluble residue thoroughly shaken up Avith Avater, and again Avhirled in the centrifugal machhie, so as to free it as far as possible from soluble starch. The residual rnaize starch may then be dissolved by heating Avith AA'ater, and estimated either colorimetrically Avith iodine, or by conversion into glucose and esti-$