How can you test presence of proteins in a given food item?

Take a small quantity of the food item. If the sample is solid, grind it. Put some part of this in a clean test tube, add 10 drops of water to it and shake the test tube. Now, with the help of a dropper, add two drops of solution of copper sulphate and 10 drops of solution of caustic soda to the test tube. Shake well and place the test tube in test tube stand for a few minutes.

Observe colour of the contents of test tube. If colour of the contents turns violet, the food item contains protein.

Note: Copper sulphate and caustic soda solutions are harmful. Handle them with care.

Food + water + copper sulphate + caustic soda → violet colour → protein is present.