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.

Simple and Complex Sugars Tests

Testing for Simple Sugars

Aim:

To test a sample of food to determine if it contains simple sugars.

Equipment:

Bunsen burner, test tube tongs, Benedict's solution, a sample of food.

Method:

1. Place about 2mL of sample (orange juice) into a test tube and then add 5 drops of Benedict's solution.
2. Heat with a Bunsen burner until it changes colour. Do not boil.

Results:

When the blue Benedict's solution was added to the orange juice a green solution was formed. However after heating the solution turned a a orange/brown colour.

Conclusion:

The Benedict's solution will turn from a blue to a yellow to a red/ orange if a simple sugar is present. When the colour of the orange juice was taken into account this colour change was observed. Hence orange juice must contain simple sugars.

Testing for Complex Sugars

Aim:

To test if a food sample contains complex sugars or not.

Equipment:

Test tube, food sample, iodine solution

Method:

1. Place about 2mL of the sample (frozen bread and water) in a test tube.
2. Add 3-5 drops of iodine solution.

Results:

When i added the brown solution to the bread it turned a black colour. 

Conclusion:

Because the iodine turned from a brown to a black colour then the bread must contain a complex sugar (starch).