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DENATURING PROTEINS
Submitted by Deb Dommel
Objective:
To experiment with different methods of denaturing the protein found in
egg white (albumin)
Materials:
•
Bunsen burner
•
Ring stand
•
400 mL beaker
•
6 test tubes
•
6 raw eggs
•
NaC1
•
NaHCO
3
•
Lemon juice
•
1% Ag NO
3
(Heavy metals are not allowed in food supply)
•
Stirring rod
Background:
Proteins are large molecules made up of small amino acids. Proteins are held in a natural
shape due to the interaction of side groups on the amino acids from one part of the
molecule to another area of the molecule. These interactions may be hydrogen bonds or
disulfide bonds. We can denature the proteins by disrupting the H-bonds that are within
the structure. When this happens the overall shape of the protein changes and new
properties can be observed. The shape of a protein is associated with food processing
properties, such as solubility, gel formation, and enzyme activity.
In the egg whites the albumin will change from clear to white. We will explore how the
following denature egg albumin.
! Heat – done by cooking
! Acids & bases – can form ions on some side groups of amino acids
! Organic compounds – form their own hydrogen bonds with the amino acids
! Heavy metals – react with disulfide bonds
Procedures:
1.
Place 300 mL of water in a 400 mL beaker, place on ring stand and heat to
boiling.
2.
Label 6 test tubes #1-6
3.
Separate 3 eggs, placing the egg white in a test tube until half filled. Discard
the egg yolk.
4.
Place test tube 1 in the boiling water and allow to “cook” till egg turns white.
5.
Add NaCl to test tube #2 and stir.
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6. Add
NaHCO
3
to test tube #3 and stir.
7.
Add lemon juice to test tube #4 and stir.
8.
Add rubbing alcohol to test tube #5 and stir.
9.
Add 1% AgNO
3
to test tube #6.
10.
Record observations on the table below:
Data Table
Test
Tube
Added Observations
1 Heat
2
NaCl – Ionic
Compound
3 NaHCO
–
Base
4
Lemon juice –
Acid
5 Rubbing
alcohol
organic liquid
6 AgNO
3
– heavy
Metal
Post Lab Questions:
1. Which method appeared to have the most dramatic denaturing affect on egg
albumin? Why do you think this method had a greater affect?
2. Of the methods you tested, which would be more likely to be used in the food
industry?