Food and nutrients

Illustrating the presence of proteins

Illustrating the presence of proteins


Illustrating the presence of proteins


Illustrating that egg white contains protein:

  • Cut up pieces of cooked egg white.
  • Place them in a test tube.
  • Add some distilled water, several drops of biuret reagent and several drops of NaOH 10%.
  • Leave it to react for 15 minutes.


Be careful! NaOH causes severe burns and eye injuries. Wear suitable protective clothing, gloves and eye protection. Should it come into contact with your eyes, carefully rinse them with water for several minutes and immediately contact a hazardous products information centre or your doctor.


The result:

Proteins are made up of amino acids linked by peptide bonds.

The biuret reagent turns violet when more than 2 peptide bonds are present.