Transcript Factors contributing to denaturation and coagulation

The Functional Properties of
Protein
•Denaturation
•Coagulation
•The factors contributing to denaturation and
coagulation
Denaturation
Protein denaturation is commonly defined as any change in the structure of a
protein. The strands of protein always arrange themselves in groups of 3 or 4 in a
coiled helix shape. The helix can be stretched out, this is called a fibrous protein
structure.
Under the right conditions the helix shape will change, strands separate and the
helix shape unfolds to become single strands OR the protein stands can twist into
a compact shape which is called a globular protein. When this has happened,
this protein has undergone the process of denaturation.
Fibrous protein
Coiled helix shape
(stands of protein)
(coiled helix shape
stretched out)
Globular protein
(helix shape twisting)
Coagulation
•
Once a protein has undergone the process of denaturation it will separate
from other nutrients and clump into a semi-soft, solid like substance. The
process by which a protein becomes solid is called coagulation.
•
Coagulations turns proteins into solids not through evaporation by some
kind of chemical reaction.
•
Separated strands of amino acids reform into groups of three with new
cross bonds between them.
•
Liquid can then trap in between these coagulated proteins to make a gel or
elastic solid. E.g. When gelatine turns solid on cooling.
•
If liquid is not trapped in between coagulated proteins it then forms clots that
float in a liquid. E.g. This could happen in a stirred custard if temperatures
are not controlled.
•
Proteins will denature and coagulate when one or more of the necessary
conditions exist.
•
An example of coagulation is the solidifying of the egg by the application of
heat
•
Coagulation and denaturation can make foods more pleasant to eat and
easier to digest.
Factors contributing to
denaturation and
coagulation
Temperature
• Heat causes proteins to denature
• Higher temperatures will set proteins
more quickly and cause them to
coagulate.
For example;
An egg is cracked into a frying pan, the heat
causes the protein strands in the egg to
uncoil (Denaturation)
More heat causes the proteins strands to reform in a new bond & the egg sets and
form a solid (Coagulation)
Acidity
• pH = Acidity will
cause proteins to
denature as it breaks
the bonds between
the amino acid
strands
• Alkalies also denature
the protein but aren’t
commonly found in
food, except Baking
soda.
Agitation
• Mechanical actions; (kneading dough,
whipping cream, or beating eggs) cause
protein strands to stretch
• Too much mechanical action = protein
strands to break and will denature the
protein
Example: Beating egg whites – if over
beaten the mixture will clot
Enzymes
• Enzymes will speed up the chemical
reaction time, i.e. the denaturation
process.
Example: Soaking meat in a marinade
containing enzymes will speed up the time
taken for the meat to cook when heated.
Sodium Concentration
• Salt attracts water and will help to keep
protein moist
• If too much salt it used then the bonds
between amino acids will break and
denature
Example: Meat with too much salt on the
outside, when cooked will cause meat to
toughen
Freezing
• When heat is removed
during freezing, proteins
with a high water content
can denature
• This is due to the water
being drawn out of the
cells, and salt will
concentrate. Amino acid
strands will separate and
denature.
Influence of sugar on protein
structure
• If sugar is added when a
protein is heated; it will
protect the protein structure
and allow it to tolerate higher
temperatures
• For example; the sugar
content in custard means
that more heat is necessary
to coagulate the protein in
the eggs and milk, and
thicken the custard