Testing for Organic
Compounds in Foods:
Protein
1.
2.
Using Biuret to Identify Presence of a Protein
Learning the Chemical Structure of an Amino Acid
Protein Testing
1. Involves an indicator, Biruet Solution
2. Biuret reacts with the amino acids in the protein
3. Solution color goes from blue to violet
4. Color change indicates a chemical reaction between the
biuret and the bonds between the amino acids of a protein
Chemistry of the Biuret Test
The Protein Test Uses Controls
Positive Control
The experiment has the
variable. The variable is
Protein. Is there protein
present?
Negative Control
Experiment
A control is a setup that yields the desired result. In the negative control, biuret is
Mixed with distilled water. Distilled water has no proteins so the color should not
change as seen in the picture. Because there is not change, this is a negative result and
therefore, the setup is a negative control. A positive control has protein and changes.
Proteins
• Are organic polymers composed of monomers called amino acids.
• Strands of amino acids are called polypeptide chains. Where are
the peptide bonds?
Proteins are many chained structures.
Amino Acids
Polypeptide Chain
Protein with two
Polypeptide chains
Where is the complete protein?
Parts of an Amino Acid
Lab Safety & Cleanup
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Test tubes are glass.
Biruet Solution is a base. Wash hands with water.
Goggles on at all times
Use special glassware soap and water with test tube brush to
wash all test tube
• Return all materials to appropriate location
• Complete data table.
• On back of lab, construct (5) observation statements and then
write a conclusion.