food test

Some useful food tests to determine if protein, sugar, or starch are present in a food stuff that has been ground up with distilled water. (1) shows the test for starch: when iodine solution is added, the solution turns blue-black if starch is present; (2) shows the test for sugar: when Benedict's reagent is added and the mixture heated, the solution turns from blue to red if glucose is present; (3) shows the test for protein: when copper sulphate and sodium hydroxide are added, the solution turns mauve if protein is present.

Any of several types of simple test, easily performed in the laboratory, used to identify the main classes of food.

Starch-iodine test Food is ground up in distilled water and iodine solution is added. A dense black colour indicates that starch is present.

Sugar-Benedict's test Food is ground up in distilled water and placed in a test tube with Benedict's reagent. The tube is then heated in a boiling water bath. If glucose is present the colour changes from blue to brick-red.

Protein-Biuret test Food is ground up in distilled water and a mixture of copper(II) sulphate and sodium hydroxide is added. If protein is present a mauve colour is seen.