30863 the science of eggs

SCIENCE OF EGGS
Page 1
How can a simple egg be transformed into so many wonderful foods? Let’s find out by
reading about the science of eggs.
Egg proteins change when you heat them, beat them, or mix them with other ingredients.
Understanding these changes can help you understand the roles that eggs play in cooking.
Proteins are made of long chains of amino acids. The proteins in an egg white are globular proteins,
which means that the long protein molecule is twisted and folded and curled up into a more or less
spherical shape. A variety of weak chemical bonds keep the protein curled up tight as it drifts
placidly in the water that surrounds it.
Heat ’em
When you apply heat, you agitate those placidly drifting egg-white proteins, bouncing them around.
They slam into the surrounding water molecules; they bash into each other. All this bashing about
breaks the weak bonds that kept the protein curled up. The egg proteins uncurl and bump into other
proteins that have also uncurled. New chemical bonds form—but rather than binding the protein to
itself, these bonds connect one protein to another.
After enough of this bashing and bonding, the solitary egg proteins are solitary no longer. They’ve
formed a network of interconnected proteins. The water in which the proteins once floated is
captured and held in the protein web. If you leave the eggs at a high temperature too long, too
many bonds form and the egg white becomes rubbery.
Beat ’em
When you beat raw egg whites to make a soufflé or a meringue, you incorporate air bubbles into the
water-protein solution. Adding air bubbles to egg whites unfolds those egg proteins just as certainly
as heating them.
To understand why introducing air bubbles makes egg proteins uncurl, you need to know a basic fact
about the amino acids that make up proteins. Some amino acids are attracted to water; they’re
hydrophilic, or water-loving. Other amino acids are repelled by water; they’re hydrophobic, or waterfearing.
Egg-white proteins contain both hydrophilic and hydrophobic amino acids. When the protein is curled
up, the hydrophobic amino acids are packed in the center away from the water and the hydrophilic
ones are on the outside closer to the water.
When an egg protein is up against an air bubble, part of that protein is exposed to air and part is still

in water. The protein uncurls so that its water-loving parts can be immersed in the water—and its
water-fearing parts can stick into the air. Once the proteins uncurl, they bond with each other—just
as they did when heated—creating a network that can hold the air bubbles in place.
When you heat these captured air bubbles, they expand as the gas inside them heats up. Treated
properly, the network surrounding bubbles solidifies in the heat, and the structure doesn’t collapse
when the bubbles burst.


SCIENCE OF EGGS
Page 2

Mix ’em up
Everyone knows that, left to their own devices, oil and water don’t mix. But for many recipes, you
mix oil-based and water-based liquids—and want them to stay that way. Often, egg yolks come to
your rescue by creating an emulsion.
Most food emulsions are known as the oil-in-water type, which means that oil (or fat) droplets are
dispersed throughout the water. Put oil and water in a jar, shake it vigorously, and you’ll disperse
the oil. To prevent the oil droplets from coalescing, however, a substance known as an emulsifier is
required. Egg yolk contains a number of emulsifiers, which is why egg yolks are so important in
making foods such as hollandaise and mayonnaise.
Many proteins in egg yolk can act as emulsifiers because they have some amino acids that repel
water and some amino acids that attract water. Mix egg proteins thoroughly with oil and water, and
one part of the protein will stick to the water and another part will stick to the oil.
Lecithin is another important emulsifier found in egg yolk. Known as a phospholipid, it’s a fatlike
molecule with a water-loving “head” and a long, water-fearing “tail.” The tail gets buried in the fat
droplets, and its head sticks out of the droplet surface into the surrounding water. This establishes a
barrier that prevents the surface of the fat droplet from coming into contact with the surface of
another fat droplet.
1.

Define the following words. Write a sentence using each word.
globular
placidly
captured
rubbery
incorporate
network
collapse
emulsion
disbursed
coalescing
emulsifier
barrier

2.
3.
4.
5.
6.
7.
8.

What does ‘em mean?
Name 3 synonyms for the word “agitate” from the reading.
Attracted to water--give the scientific name for this.
Water loving--give the scientific name for this.
Left to their own devices--What does this phrase mean?
What word is the opposite of repel?
Name 4 foods from your culture that are made with eggs. Using the information you
learned from the reading, explain how the eggs change form as they are used to

make these foods.

Reading taken from:

Q’s by Jann VM