What is a quick test for sucrose?

Iodine is a common indicator of starch's presence in a solution. What would be a common indicator of a disaccharide such as table sugar?
flightman_21 1/09/98

One simple colorimetric test for sucrose involves resorcinol (1,3-benzenediol). The test is often used to check to see if honey has been adulterated with commercial invert sugar.

The following procedure was taken from Practical Physiological Chemistry, by P. B. Hawk, and O. Bergham (7th edition, Blakiston, Philadelphia, 1943.) To make the indicator solution, dissolve 0.05 g of reagent-grade resorcinol in 100 mL of HCl solution (dilute commercial HCl 1:2 to obtain a solution of density 1.18-1.19 g/mL). Add about 5 drops of a 1% solution of the unknown carbohydrate to a test tube containing 1 mL of the freshly prepared resorcinol solution and heat the mixture to boiling. A cherry red color develops within a few minutes if fructose or sucrose is present. A yellow to salmon color has no significance. If the boiling is prolonged a red color can be obtained for other sugars.

Most analytical procedures for disaccharides exploit the optical activity of sugars (their ability to rotate plane-polarized light).

Author: Fred Senese senese@antoine.frostburg.edu



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