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When I think of Thanksgiving dinner, “lab experiment” is not the first, nor the most appetizing term that comes to mind. I think of a roast turkey and the family dinner table covered with bowls of stuffing, glazed yams, and pumpkin pie. But beneath all of those delicious calories lies a science of cooking that we hardly think about. With Thanksgiving approaching, I decided to delve into some of the biochemical and molecular processes that are taking place in some of my favorite foods.
Fried eggs are one of my favorite breakfast foods. If you ask me how to make them, I would have to say something like this: I crack the egg open into the pan and let it cook until the clear, gooey stuff turns white; then I flip it over, cook it for however long it takes my toast to come out of the toaster, and then I eat it all. Hardly the stuff of science. But if we take a closer look, we would understand that egg whites are made up of 90% water and 10% protein. During cooking, these proteins are agitated by the heat, causing them to collide with water molecules which break the weak chemical bonds holding the proteins in shape, a process referred to as “denaturation” in lab speak. Once the proteins are denatured, the amino acids that make up the protein form new bonds and take on a new shape and structure, resulting in a fried egg cooked to perfection.
Moving from breakfast straight to dinner, marinating meat well involves a basic understanding of acids as well as muscle structure. Chicken and fish have less dense muscle structure than beef, making them easier for your marinade to flavor. If you want some carbohydrates to go with your steak, you could cook up some delicious Mac & Cheese & Sodium Citrate. Not the recipe you were thinking? A common ingredient in boxed Mac & Cheese is often sodium citrate, which is a salt of citric acid found naturally in citrus fruits. When cheese is heated, the fat and water molecules making up the cheese tend to separate. Sodium citrate is added to act as an emulsifier that will hold the fat and the cheese together so that it melts smoothly. We owe this discovery to James L. Kraft, the man who patented the first American cheese slice in 1916. Kraft demonstrated that by adding sodium phosphate to cheese, water and fat droplets stay together as the cheese melts, giving each bite the perfect combination of taste and texture.
As it is Thanksgiving season, turkey is on everyone’s mind. But if you tend to avoid turkey for fear of falling asleep at the dinner table, think again. Tryptophan is an essential amino acid in the human diet. It is a biochemical precursor to serotonin, which can be converted to melatonin, a hormone that causes sleepiness and is associated with regulation of our circadian rhythm. We can get tryptophan from a variety of sources. While tryptophan is indeed found in turkey, turkey actually contains a fairly average amount of tryptophan. In fact, some foods eaten on a regular basis also contain tryptophan, such as chicken, soybeans, and eggs. But even these foods aren’t going to make you sleepy. For tryptophan to have the alleged effect of drowsiness, it would have to be consumed in concentrated amounts on an empty stomach, not something that is going to happen on Thanksgiving Day. In addition, even if we did take in a high amount of tryptophan, the brain-blood barrier would prevent most of it from entering our brains. Most tryptophan in our bodies is not converted to melatonin in the pineal gland of our brain, but in our intestines where it controls the movement of the gut. The classic Thanksgiving sleepiness is still a real thing; extra carbohydrates and alcohol can easily cause drowsiness. So this Thanksgiving, if you are feeling sleepy, by all means take a nap. Just don’t blame the tryptophan.
Learning more about the science behind our meals is not just academically interesting. A better understanding of the ingredients and the chemical processes behind cooking can also help improve our cooking skills. In a paper published in Nature, Yong-Yeol Ahn et al. found that certain cuisines taste a certain way due to how flavor compounds are combined. Western cuisines tend to pair flavors with similar molecular components together. East Asian and Southern European cuisines do not typically pair foods with similar molecular components together, providing a possible explanation for why new cuisines might taste so different when we first try them.
Considering the variations in taste, there remains quite a lot of subjectivity in cooking. Part of the fun of cooking is experimenting with different ingredients, flavors and cooking methods to see what works best, much like carrying out an experiment in lab. So next time you’re making a dish, remember, there is a lot of science behind even the simplest recipes.
With that, we wish everyone a Happy Thanksgiving!
Here are some fun links to learning more about the science behind cooking:
Harvad offers a free-online course: http://www.npr.org/blogs/thesalt/2013/09/30/227918426/now-you-can-go-to-harvard-and-learn-cooking-science-from-top-chefs
How to make candy and the science behind it: http://www.exploratorium.edu/cooking/candy/index.html
And just for fun, the “Periodic Table of Meat:” http://www.pleated-jeans.com/2010/07/12/the-periodic-table-of-meat-image/
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A blog for ASBMB Today by Rajendrani Mukhopadhyay