Name(s): ___________________________________ Period: _________ Group: ________
Lab: DENATURING PROTEINS—Group 4
Objective: To experiment with different methods of denaturing the protein found in
egg white (albumin) and milk (casein)
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.
PROTEIN DENATURATION or WHAT HAPPENS WHEN YOU FRY AN EGG?
In the egg whites the albumin will change from clear to white. We will explore how the
following denature egg albumin as well as milk casein. When egg white is heated above a certain
temperature (i.e. 60 °C) bonds in the protein molecules break and reform in different ways. This
causes the protein molecules to denature or lose their characteristic three-dimensional
structure. As the proteins uncoil, they tend to interact with each other to form a solid mass or
coagulum (the process called coagulation). This explains the changes that we observe as we
watch an egg being cooked. However, factors other than high temperature may also produce
this denaturation phenomenon.




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 for Denaturation Labs:
Group 4 – Denaturation by ACID (Lemon Juice)
Materials
 1 glass dish
 1 paper cup
 1 egg
 50 ml beaker of Lemon Juice (5ml)
 2 –50 ml beakers of milk (15 ml each)
 50 ml beaker of Lemon juice (5 ml)
 2- Stirring rods
1
Egg Albumin Procedure:
1. Separate 1 egg white, placing the egg whites in a large glass dish. Discard the egg yolk
into the paper cup.
Note: The clarity of the egg white this is your baseline or control, record your
observations in Data Table 1 below.
2. Pour (5 ml) lemon juice into the dish containing an egg white and stir.
3. Record your observation in the Egg Albumin Data Table (Data Table 1) below, and for
Group 4 and on the front board.
4. Now Do Milk (Casein) Denaturation.
Procedure for Milk (Casein) Denaturation:
1. Pour the 5 ml of Lemon juice into one of the beakers of milk and stir.
2. Compare the beaker with lemon juice and milk to the beaker with only milk. Look for any
changes in color, texture, etc…
3. Record Observations in Data Table 2 on page 3, and on the front board next to your
group number.
DATA TABLE 1~ Egg Albumin Data Table
Group
ALL
GROUPS
1
Added
Nothing—initial
observation
Heat
2
3
NaCl – Ionic
Compound (heavy
metal)
NaHCO3 – Base
4
Lemon Juice – Acid
5
Rubbing Alcohol –
Organic Liquid
6
Pine Apple JuiceAcid
Observations
2
DATA TABLE 2~ Milk Casein Data Table
Group
Added
Your group Lemon Juice – Acid
Other
groups
Observations
Lemon Juice – Acid
Post Lab Questions:
1. Copy and record all the Data on the front board into your data tables.
2. What three factors have caused denaturation of the egg albumin in this lab?
3. What common result occurred in all of the experiments with the egg albumin?
4. What results did you get with the milk casein?
3
5. Was the milk casein denatured?
6. Did all of the groups get the same results with the milk casein? If not list the differences.
7. Explain the changes that you observed in terms of change in protein structure at the
molecular level (be very specific). You may want to get a copy of an article called
‘Denaturation’ from your instructor to help you answer this question.
4