The presence of proteins can be detected by the Biuret test.
(i) Crush the food sample and put some of it into a clean test tube. Add some sodium hydroxide solution.
(ii) Cork the test tube and shake it to mix the food with the sodium hydroxide solution. Then add a little copper sulphate solution. Cork and shake it again.
If the solution turns blue, there is no protein in the food. But if it turns violet, there is protein in the food.
