Protein test (Biuret test)

detects peptide bonds linking amino acids together.

Biuret solution, which is made of Sodium Hydroxide (NaOH) and Copper(II) Sulfate (CuSO_4)

Steps:

Add the food sample solution to a test tube (if it's solid, crush it and mix it with distilled water first).

Add an equal volume of Biuret solution to the sample and mix well. 

Add a few drops of copper(II) sulfate solution and gently shake.

Result:

Blue: Protein is absent (Negative result)

Violet: Protein is present (Positive result).