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Chemistry of Cooking
We tend to think of cooking as an art, but much of its basis actually comes fromchemistry. Let's take, for instance, the example of cooking meat. Why do we bother withcooking meat? For one, it kills the bacteria that can live in meat and be harmful to us. Butadditionally, it makes the meat much more tender—easier to eat and easier to digest.05Typically, protein is the second-highest component of meat behind water. Proteinshave several levels of organization. A protein's primary structure is the order in whichthe amino acids are joined by their peptide bonds. A protein's secondary structure ismade up of local interactions of the primary structure. Secondary structure includesalpha helices, beta sheets, turns, and loops. Tertiary structure is formed when various10secondary structures interact, typically over long distances. Finally, quaternary structureis the interaction of different protein subunits. Proteins fold tightly in complexways that are energetically and sterically favorable. So what happens to this complexorganization when meat is heated? These interactions become weaker. Proteins denature,meaning their interactions weaken and their quaternary, tertiary, and secondary15structures break down. Instead of tightly folded proteins, they become loose andstretched out. This denaturation is what makes meat more tender. However, continuingto cook meat after this initial denaturation serves only to remove water, making themeat tougher and drier. In particular, the denaturation of collagen makes meat moretender. Collagen is the most abundant protein in animal connective tissue. Tougher20cuts of meat tend to have more connective tissue, and thus more collagen.But heating proteins isn't the only way to denature them: they can also be denaturedby adding certain denaturing substances. Many of these substances, like strongacids and bases, you wouldn't want to add to your food; however, one commondenaturing agent is salt. This is why you may want to brine a tougher cut of meat in25addition to cooking it. Brining involves soaking something in a solution of salt water.Another benefit of brining is that when the meat absorbs the salt, this draws water intothe meat to dilute the salt. Thus, brining also serves to keep meat moist. Some chefswill advise searing the outside of a cut of meat before cooking it through to lock in themoisture. However, chemistry doesn't support this approach: steam is equally capable30of escaping through a seared crust as it is through non-seared meat.If you've ever cooked red meat, you know that as it cooks, it turns brown. Red meat isred because of its high myoglobin content. Myoglobin is an oxygen-storing protein foundin muscle cells. It is associated with an iron atom. Before the meat is cooked, the ironatom is in the +2 oxidation state. Cooking it removes an electron, thus changing it to the35+3 oxidation state. This transforms the color to brown. On the other hand, white meatdoesn't turn brown because it doesn't have nearly as much myoglobin to be oxidized.We rarely pause mid-recipe to consider the chemistry of cooking, but understandingthe chemical reactions occurring in our food will help us to become better cooks.Isn't that some food for thought?
Mean Percent Yield of Meat Cooked Under Different Methods
1. It can be reasonably inferred from the passage that which of these protein structures is LEAST impacted by heating?
2. Which option gives the best evidence for the answer to the previous question?
3. The sentence in lines 12-13 ("So what . . . heated") serves to
4. As used in line 13, the word "weaker" most closely means
5. According to the passage, which of these cooking approaches would have the most negligible effect on the tenderness of meat?
6. Which option gives the best evidence for the answer to the previous question?
7. As used in line 39, the phrase "some food for thought" most closely means
8. The passage explicitly states that the substance most directly responsible for the browning of meat is
9. Based on the information in the graph and on lines 19-20 ("Collagen . . . collagen"), what type of cooking method would most likely be most appropriate for a tough cut of meat?
10. According to the graph, broiled meat's yield is about how much greater than braised meat's yield?
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