Testing for Protein - The Biuret Test

                                                    Testing for Protein  -  the Biuret Test

Aim:  To test is a sample of food contains protein.

Equipment:  test tube, sodium hydroxide (NaOH), copper sulfate (CuSO4), food sample (milk).

Method: 

1. Place about 2 mL of the sample into a test tube and add 5 drops of sodium hydroxide.

2. Add 5 drops of copper sulfate.

3. Shake the test tube gently from side to side.

Results:  If the solution remains blue, then no protein is present. If the solution changes to a purple colour then protein is present in the sample.

Discussion:  The Biuret test is based on the ability of Cu (II) ions to form a  violet-coloured protein after you heat the food.

Pictures:

Egg

Before heating:                              After heating:


Milk

Before heating:                            After putting the Biuret:           After heating:

Simple and Complex Sugar Experimnt

                                            Testing for Simple Sugars - the Benedict's Test

Aim:  To test a sample of food to determine whether it contains simple sugars.

Equipment:  Bunsen burner, test tube tongs, Benedict's Solution, a sample of food.

Method:

1. Place about 2 mL of the sample into a test tube and then add 5 drops of Benedict's Solution.

2. Heat with a Bunsen burner until it changes colour.

Results:  A positive test for a simple sugar results in the Benedict's Solution changing from a blue colour to a red/orange colour.

Discussion: The Benedict's Solution changes it colours depend on how much sugar in it.

Before:                           After heating:

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                                           Testing for Complex Sugars - the Iodine Test

Aim: To test if a sample food contains complex sugars.

Equipment: Test tube, food sample, iodine solution

Method:

1. Place about 2 ml of the sample in a test tube.

2. Add 3-5 drops of iodine and mix.

Results: If complex sugars (i.e. starch) are present the iodine solution will change to brown colour to a blue/black colour

Discussion: Even though the bread and the iodine are both carbohydrates, iodine will not change its colour when it react to sugar. It's because the starch is made up of many, many sugar molecules chained together. Only the long chains found in starch are able to interact with the iodine.