PROTEIN AND EGGS
Denaturation changes the shape of a protein
molecule without breaking its peptide bonds.
 The result is a looser, less compact structure.

PROTEIN DENATURATION

http://www.youtube.com/watch?v=v2-iY7ZoDOc
Denaturation is the first step in the process of
coagulation.
 Coagulation changes a liquid into a soft, semisolid mass (polypeptides unfold during
denaturation, then collide and clump together
to from a solid).

EGG COAGULATION

http://www.youtube.com/watch?v=y77dNgSbrQI

Example: Beating an egg denatures its
proteins. The protein coagulates as the egg
cooks.
Heat is the most common agent in denaturing
protein.
 Other means of denaturation include freezing,
mechanical treatment (i.e. beating eggs or
kneading dough) and very high or low pH (i.e.
adding lemon juice to sour milk lowers pH and
milk proteins denature).


Before coagulation occurs, denaturation is
sometimes reversible. That’s why whipped egg
whites left to stand can turn to liquid again.
Eggs contain every vitamin and mineral for
calcium and vitamin C.
 The yolk contains all of the fat, along with most
of the other nutrients.

Proteins can act as emulsifiers.
 An emulsifier stabilizes oil and water mixtures.
 Certain proteins contain polar amino acids; one
end is attracted to water and one end is
attracted to oil (i.e. the proteins in eggs keep
mayonnaise blended).

WHAT IS AN EMULSIFIER?

http://www.youtube.com/watch?v=R7sYROUNO7g
Meringue is a foam.
 Air bubbles are incorporated and trapped in a
protein film by whipping.
 Foams add volume and lightness to products.
 Foam begins with a protein-containing liquid
(i.e. egg whites).

Remember, whipping denatures the protein
molecule; the protein molecule coagulates to
form a film around the air pockets.
 The large protein molecules in egg whites make
them ideal for foams.
 Cream of tartar lowers pH and is often added to
stabilize the protein and produce a higher
quality foam.

Fat (i.e. in egg yolks) can drastically reduce a
foam’s volume, or prevent foaming entirely.
 Cooks must be very careful to keep the yolks
out when separating whites to whip.
 Fats tend to cling to plastic so recipes often
specify using glass or metal bowls for whipping
egg whites.

WATER BOTTLE TRICK

http://www.youtube.com/watch?v=iAp8pEaWB1Y
Over-whipping can also be a problem.
 A foam is most stable just before reaching its
maximum volume.
 Past that point, the proteins unfold to the point
that they lose elasticity.

FIXING OVER-WHIPPED EGG WHITES

http://www.youtube.com/watch?v=2xJwoz5FRbg
RAINBOW ROSE MERINGUE COOKIES

http://www.youtube.com/watch?v=3ok5LHMP-R4
THE PERFECT OMELETTE

http://www.youtube.com/watch?v=OQyRuOEKfVk
LAB - BAKED ALASKA

http://www.youtube.com/watch?v=k4jZdQm1yHc