Biuret Test for Proteins

Testing for the Presence of Proteins

Aim:
To test to see if a sample of food contains proteins.

Equipment:

• Test tube
• Sodium Hydroxide (0.1 mol/L)
• Copper sulfate (0.1 mol/L)
• Food sample (milk and eggs)

Method:

1. Place about 2mL of sample into a test tube.
2. Add 5 drops of sodium hydroxide
3. Add 5 drops of copper sulfate
4. Shake the test tube gently from side to side.
5. Record your observations.

Results:
The egg whites when tested with the Biuret solution turned a light blue colour and on further addition of sodium hydroxide turned a dark purple colour.

The milk did also turn a light blue colour but then stayed light blue. Due to the original colour of the milk the solution stayed a blue with a slight hint of pruple.

Conclusion:
Both the milk and eggs turned the blue biuret solution a purple colour which shows the presence of protein. Both milk and eggs are good examples of everyday foods which we expect to be high in protein and this test had confirmed that.