What is the Tauber Test?

Answer 1

A color test for identification of pentose sugars; the sugars produce a cherry-red color when heated with a solution of benzidine in glacial acetic acid. extracted from JBC Online @ http://www.jbc.org A SPECIFIC QUALITATIVE COLOR TEST FOR KETOHEXOSES BY HENRY TAUBER (From the Venereal Disease Research Laboratory, United States Public Health Service,

United States Marine Hospital, Staten Island, New York)

(Received for publication, September 23, 1949)

Ketohexoses (fructose and sorbose) or compounds which yield ketohexoses

(sucrose, raffinose, and inulin) give rise to a bright reddish purple color in the presence of aminoguanidine and sulfuric acid. The color is stable for several hours. Equivalent amounts of aldohexoses produce no color in 24 hours.

In this reaction guanidine nitrate or nitroguanidine cannot be used instead of aminoguanidine; therefore the amino group attached to the guanidine molecule probably is essential to the formation of the colored compound.

The following pentoses, aldohexoses, and aldohexose-yielding compounds

produce no color under similar conditions: arabinose, xylose, ribose, glucose, galactose, mannose, lactose, maltose, melibiose, dextrin, starch, and glycogen. No color is given by formaldehyde or by the pure proteins, crystalline pepsin, crystalline trypsin, and crystalline chymotrypsin.

Furfural gives a yellow color and furfuryl alcohol a brown color. Acetone, methylethyl ketone, and levulinic acid produce a very slight yellow color. EXPERIMENTAL Aminoguanidine Solution-2.5 gm. of aminoguanidine sulfate- Hz0

(Eastman Kodak Company, No. 4023) in 100 cc. of distilled water. This solution is very stable at room temperature. Sulfuric Acid-Concentrated sulfuric acid, C.P.

Color Test

0.5 cc. of concentrated sulfuric acid is placed in a 12 X 100 mm. testtube.

0.2 cc. of the aminoguanidine sulfate solution is added without mixing. 0.2 cc. of the test solution containing 0.4 mg. of fructose, sorbose, or inulin is added, and the contents of the tube are well mixed. A bright reddish purple color forms in about 1 minute and ncreases in intensity for some time. 0.4 mg. samples of aldohexoses gave no color in

24 hours. A color identical to that given by 0.4 mg. of fructose, sorbose, or inulin is obtained with 0.8 mg. of sucrose or 1.2 mg. of raffinose. As small an amount as 50 y of fructose may be readily detected by this test. Solutions containing as much as 2 mg. of aldohexose per test pro- 605

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606 COLOR TEST FOR KETOHEXOSES

duce a hardly noticeable light lilac color. More concentrated aldohexose solutions, however, produce a color similar to the one given by the dilute ketohexose solutions. This interference is probably caused by the conversion of a small quantity of the aldohexose into the color-forming compound by the sulfuric acid. Thus solutions which are to be tested for ketohexose should be diluted to contain not more than 3 mg. of total

carbohydrate per cc. or 0.6 mg. per test. It is important to note that the reagents and carbohydrate solutions should be exactly measured in order to eliminate possible reactions by aldohexoses. SUMMARY A convenient and rapid color reaction for ketohexoses and conditions for obtaining specificity with the test have been described.