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Food Test – Protein

HOW DOES IT WORK?

Experiment 1: Test for Protein – Millon’s experiment
Time allocation: 45 Min

Millon’s test utilize a reagent called Millon’s test solution which is a solution of mercuric and mercurial ions in nitric and nitrous acid.  The hydroxyl group (free-OH) reacts with tyrosine (an amino acid found in nearly all proteins) changing the colour of the solution to a pink or dark red colour.

 

Experiment 2:    Test for Protein – Biuret experiment
Time allocation: 45 Min

Biuret solution is a blue liquid that changes to purple when proteins are present and to pink in the presence of short chains of polypeptides. The copper atom of the biuret solution reacts with the peptide bonds to cause the colour change.

 

Experiment: Test for Protein

EXPERIMENT 1: TEST FOR PROTEIN – MILLON’S EXPERIMENT

AIM                                                                                                  

Time allocation: 45 Min

To show if proteins are present or absent in a biological compound.

MATERIALS

  • 2 x test tubes
  • Test tube rack
  • Burner with cartridge
  • 2 x Glass beakers
  • Spatula
  • Albumin powder 50g
  • Millon’s reagent 10ml dropper bottle
  • Distilled water 250ml
  • Thermometer 150mm
  • Starch powder 50g

METHOD:

  1. Prepare a water bath, heat water in the beaker to approximately 90˚C, insert a thermometer to check the temperature.
  2. Mix a spatula full albumen / egg white with water in a beaker. Stir the contents using the spatula, save some of the solution for experiment 2.
  3. Label the test tubes T1 and T2.
  4. Quarter fill test tube T1 with the egg white solution and test tube T2 with a starch solution.
  5. Using a medicine dropper add 2-3 drops of Million’s Reagent to test tube T1 and test tube T2. Gently agitate both the test tubes to mix the contents.
  6. Place both test tubes in a water bath of approx. 90 ̊C for a few minutes.
  7. Note the colour change in the test tubes.

OBSERVATIONS/RESULTS 

  1. Starch in water is white.
  2. Egg white, boiled, changes from a solution to a gel state.
  3. Egg white in water is translucent

After heating the following is observed:

CONCLUSION:

Egg white or albumin is comprised mostly of protein.  In the Millon’s reaction the reagent will react with the protein and colour will change to a pink colour showing this.  The egg white contains protein as it is the “placenta” of the chicken embryo we know as eggs.

EXPERIMENT 2: TEST FOR PROTEIN – BIURET EXPERIMENT

AIM                                                                                       

 Time allocation: 45 Min

To show if proteins are present or absent in a biological compound.

MATERIALS

  • 2 x Test tubes
  • 2 x Glass beakers
  • Water
  • Spatula
  • Egg white
  • Starch powder 50g
  • Biuret Solution 10ml dropper bottle

METHOD:

  1. Mix a spatula full of egg white with water in a beaker. Stir the contents using a spatula.
  2. Label the test tubes T1 and T2.
  3. Quarter fill test tube T1 with the egg white solution from the previous experiment and test tube T2 with starch solution you made.
  4. Using the dropper bottle of Biuret solution add 2-3 drops of Biuret solution to test tube T1 and to test tube T2. Gently agitate both the test tubes to mix the contents.
  5. Note the colour change in the test tubes.

OBSERVATION:

PRECAUTIONS:

  • This experiment requires adult wearing safety clothing and safety goggles and it is advised that students observe from a safe distance.
  • Million’s reagent is highly toxic and corrosive, wear protective eyewear and clothes.