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Thursday, May 27, 2010

The White Stuff

Now that we've talked about eggshells and the thin membrane that lines them, let's move on to the egg white. The egg white is the clear, light yellow liquid that surrounds the darker yellow yolk (more on that later!). Wait a minute - why is it called the egg white if it's yellow? Anyone who has seen a hard-boiled egg knows the answer to that. The yellow liquid becomes a white solid when it is heated. But what's in the egg white, and why does it change in this way? And can we change the color in any other way?

The egg white is also known as albumen (pronounced al-BYU-min). Egg whites are mostly (85%) water, but some protein molecules are dissolved in it. These proteins are long, stringy molecules which normally have particular shapes when dissolved in water. When they are heated, the proteins denature, or become a big tangled mess. Imagine a bunch of long strings that are all tied into the same kind of very fancy knot - that's sort of like the original proteins. Then picture all of those knots untied, and all the strings become tangled up into a big ball - that's what denaturation does. The change in color from light yellow to white is caused by this change in shape.

We can denature albumen proteins in ways other than heating. For example, if you pour some rubbing (isopropyl) alcohol into egg whites, you'll see white streaks forming. The proteins can't keep their knotted shapes in alcohol, so they become denatured. Another way of denaturing proteins is by beating them. That will be the topic for the next post.

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