This NBC Learn video, one in a 6-part "Cheeseburger Chemistry" series, uses the cooking of hamburgers to explain the structure of myoglobin, its role in making red meat red, the effects of heat on myoglobin's structure and meat's color, and the Maillard -- or browning -- reaction.
The Chemistry of Burgers
AL ROKER, reporting:
The burger part of a cheeseburger is short for hamburger, which is what Americans call a cooked patty of ground meat, usually beef. Immigrants to the U.S. in the early 1900s brought with them favorite recipes, one of which was shredded or minced cooked beef, a back-home favorite of many Germans, some of whom were from the German city of Hamburg, and known as you guessed it, Hamburgers.
Anyway, by the 1940s, the hamburger was a fully assimilated American favorite and still is, along with its cousin, the cheeseburger. U.S. meat producers estimate Americans eat 14 billion hamburgers a year. Burgers start off like this: pieces of red meat, usually less-tender cuts of beef, put through a grinder.
KENT KIRSHENBAUM (New York University): The meat itself is composed of ground muscle tissue, usually from a cow. And that will contain a large amount of protein; also contains some fats and quite a bit of water.
ROKER: The chemistry of food, especially meat, is a research focus for Kent Kirshenbaum, a chemistry professor at New York University funded by the National Science Foundation. As he says, meat contains a lot of proteins, chain molecules made up of amino acids strung together like beads on a necklace. Something like this.
KIRSHENBAUM: One of the major components of muscle, of meat, is a protein called myoglobin. That is composed almost completely of helices or coiled regions of the protein chain.
ROKER: Helices is the plural of helix, a shape like a spring, or a spiral staircase. You may be familiar with DNA: a double helix.
KIRSHENBAUM: These helices are bundled together within the protein structure, and deep inside that protein there is a component of the protein that has one iron atom tucked away right in the center of it. Myoglobin was actually the very first protein whose structure was understood or solved.
ROKER: A feat that won two British chemists, John Kendrew and Max Perutz, the Nobel prize in chemistry in 1962. Myoglobin is a major reason red meat is red.
KIRSHENBAUM: The red color that we see in meat is actually not coming from the blood. That red color is coming from that myoglobin molecule in the meat tissue.
ROKER: That is, in fresh, raw meat. Meat changes color, in a series of chemical reactions, when you apply heat: Put a burger on a grill or in a skillet, and it turns brown because of what happens to the myoglobin as you’re about to see. Julie Yu is an NSF-funded chemist at The Exploratorium in San Francisco.
JULIE YU (The Exploratorium): So we’re gonna cook some hamburger patties two different ways, and we’re gonna see how the color of the patty tells us something about the chemical reactions that took place as it cooked. I’m gonna put one patty into this boiling water. And you can see pretty instantly that the color of the meat changes, from the bright red that it was when it was raw to kind of this dull gray. And this other patty, I’m gonna put into this pot. So the sizzle that you hear when the raw meat hits the hot plate is actually the water molecules on the surface of the meat, boiling off. So the temperature of this pot is very high.
ROKER: As the burgers cook, the myoglobin proteins in the meat do what atoms and molecules generally do when heated: move, or vibrate, faster and faster, which denatures the proteins, changing their natural shape.
KIRSHENBAUM: Generally, proteins are very carefully composed into precise arrangements. When we add heat to hamburger meat to cook it, the atoms in those proteins could begin to move around, and those very careful arrangements could begin to become scrambled or unfolded.
ROKER: As the proteins change shape, or denature, particularly around the iron atoms, the color changes. The burger boiled at one temperature turns grayish brown. The burger pan-fried at a higher temperature is a richer, darker brown.
YU: And the texture of it is a little crusty, compared to the soft, boiled burger.
ROKER: That darker browning on the outside of the fried burger is due to what’s called the Maillard reaction. Louis-Camille Maillard was a French chemist in the early 1900s who studied the science of browning. In fact, the Maillard reaction is also called the browning reaction.
Maillard found that when he heated amino acids, remember the beads in the protein necklaces? Plus sugars like those in carbohydrates, which are in almost all natural foods, including meat, the substance turned brown, different shades, depending on the temperature, which you can see when Julie Yu cuts her two burgers open.
YU: When we cut inside the burgers, you’ll see that inside the color is exactly the same. The inside of the meat patty wasn’t exposed to the high temperature of the pan and so it wasn’t able to undergo the high-temperature Maillard reaction, which create these nice crusty brown bits that are very flavorful to us.
KIRSHENBAUM: The Maillard reactions result in development of rich brown colors. And they also generate an incredible variety of different flavor molecules as well. Other places where you might see a browning reaction are on a nice rich piecrust, or on a nice brown piece of toast.
ROKER: A toast, then, to meat and to heat and to the chemical reactions that turn this into this.
YU: Oh, it’s so perfect. It’s gonna be the best-tasting burger ever!
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