‘Please pass the myoglobin,’ or the science of Thanksgiving

Is turkey gravy a colloid or an emulsion? I’ve always wondered about that. But I only remember to think about it at Thanksgiving when I am too sleepy to think straight. Because turkey gravy has particles imbedded in a liquid, it must be a colloid. But because it has water suspended in oil, a liquid in a liquid, it must be an emulsion.

To avoid the question, we sometimes barbecue steak for Thanksgiving. I know it’s not conventional, and for some it would be a disappointment. But having steak means I avoid having to make the hard decisions between dark and light meat. Hey, that’s another thing. What makes meat dark and light anyway?

The color of meat comes from an oxygen-storing compound called myoglobin. Muscles have to have oxygen to provide energy. Oxygen is brought to the muscle by the blood, which carries the oxygen with hemoglobin. There isn’t any hemoglobin in the muscle cell, but the muscle cell has myoglobin. The oxygen carried in the blood is handed off to the myoglobin. Myoglobin makes the meat appear dark in color the way hemoglobin makes blood appear red.

Muscles that use a lot of energy require a lot of oxygen. The more oxygen required, the more myoglobin is needed. So the darker the muscle color, the more myoglobin there is in the meat. Turkeys use their leg muscles more than their wings, so their leg muscles have more myoglobin and are darker in color. Ducks, on the other hand, have dark meat for breast muscles because they fly more than they walk. White meat is white because it is just low on myoglobin.

Want to start an argument on Thanksgiving? Just strongly state your opinion on whether or not myoglobin enhances the taste of meat, or not, and see what happens. But if you ask people to “please pass the myoglobin” you will probably not get very much to eat. They probably won’t know what you are talking about.

Myoglobin is a protein, a very large, complex molecule. They are so big and complicated that when they were first discovered as a class of compounds, early chemists called them by the technical term “glob.” That’s why a lot of proteins are called some kind of glob or another like myoglobin, hemoglobin or maybe tetra-dihydro-benzylated-chickenwire-globin.

Turkey has other suspicious compounds in it such as tryptophan. This is an amino acid that is also found in the human body. Humans can’t make tryptophan, so they have to obtain it from their food. Tryptophan is used by the human body to make serotonin, a neurotransmitter that makes fruit flies sleepy. This has led some people to think that tryptophan makes humans sleepy, also, in spite of a complete lack of evidence that fruit flies celebrate Thanksgiving. The theory is that when we eat tryptophan it causes our brains to make serotonin. The more serotonin there is, the more serotonin-activated neurons transmit.

Serotonin activated neurons are the ones that cause somnolence. It seems strange that more nerve transmission can make one feel like there is less nerve transmission.

But it may not be just tryptophan that makes you sleep through the second half of the game. Stretching the stomach and small intestine by eating a large meal causes the parasympathetic nervous system to reduce blood flow to your muscles and brain. The blood is shunted to the digestive tract that you have just overloaded. High protein and fat content in the meal tend to keep food in the stomach longer, extending the period of time that the digestive system requires extra blood flow. That leaves less blood to be delivered to the brain. Neurons do not possess myoglobin to store oxygen. So when blood flow declines, nerve activity slows.

It is not a profitable time to contemplate whether turkey gravy is a colloid or an emulsion, no matter how pressing it may seem.

Gary McCallister is professor of biology at Mesa State College.

WASHINGTON — Federal Reserve Chairman Ben Bernanke is taking some highly unusual steps to counter widespread opposition to his $600 billion plan to jump-start the economy. He’s pressing China to let its currency rise and pushing Congress to pass more stimulus aid.

Yet as he veers into these political debates, Bernanke may be putting at risk the Fed’s strongest tools — its credibility and independence.

Bernanke has been under fire since Nov. 3, when the Fed announced a bold plan to buy $600 billion in Treasury bonds. The bond purchases are intended to lower long-term interest rates, lift stock prices and encourage higher spending to energize the weak economy.


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