Tryptophan, Turkey, and You

Thanksgiving. A time for family, a time for reflection, a time for gratitude, but most importantly, a time for food. Thanksgiving dinner is the one meal each year that most of us approach with reckless abandon. It may be the one  time when the goal is not to eat to fill your stomach, but to eat to fill your plate– again. Whether you are a food scientist, a biochemist, a poet, a pizza maker, or a lawyer, there is one molecule that we all seem to know about: tryptophan. Though, chances are that you don’t actually know what it is, I’m sure that you’ve heard (or even perpetuated) the common Thanksgiving rumor that it’s what causes that post-meal snooze on the couch.

Tryptophan is an essential amino acid that is non-polar and aromatic, containing a protonated –NH3+ group, a deprotonated –COO group, and an indole side chain. If that got too science-y too fast, just check out the image below.  Amino acids are the building blocks of proteins, and essential amino acids are ones that we cannot synthesize in our own bodies, and therefore must obtain from dietary sources. In addition to protein biosynthesis, tryptophan also serves as a precursor to the neurotransmitter serotonin. Serotonin produces melotonin, another molecule you’ve probably heard of if you’ve ever had trouble sleeping. These compounds work together to promote calming and relaxation. It makes sense, then, that tryptophan is the culprit of that sleepy feeling after Thanksgiving feasting. But is Tom the Turkey the one responsible?

While there are numerous common sources of tryptophan in our diets (chocolate, oats, milk, yogurt, eggs – to name a few), turkey has become infamous for its abundance.  In reality, however, the level of tryptophan in turkey is not remarkable. In 100g of turkey, there’s about 0.24g of tryptophan, similar to chicken and beef. Cheddar and Parmesan cheese have considerably higher levels (at 0.32 and 0.56, respectively). So why is it that Thanksgiving turkey puts you to sleep, but a grilled cheese doesn’t? Well, I’m not one to judge, but I’m guessing your normal grilled cheese sandwich doesn’t contain 4,500 calories. That’s the amount the average American consumes during Thanksgiving, according to the Calorie Control Council. So, while your body is metabolizing all that turkey tryptophan…it’s also doing a whole lot more. The sheer volume of food you consume is more likely the key contributor to your sleepiness than that one measly molecule.

Though tryptophan definitely gets the most attention, there’s a whole lot more science happening on your plate. Anyone who’s been charged with the important role of turkey tamer knows that the bird that goes into the oven is not the same as the one that comes out. This is, in large part, the result of one of food science’s most fundamental reactions: Maillard browning. If you’ve ever seared a steak, or drank a cup of coffee, or eaten a slice of bread, you’ve enjoyed the delicious results of this chemical reaction. For an in-depth explanation of this famous reaction, check out the earlier post on The Chemistry of Coffee. In short, it’s the reaction between amino acids (building blocks of proteins, remember) and reducing sugars that gives food desirable color and flavor.

If you’ve ever cooked a turkey, you know that the struggle is real when it comes to getting that perfect roast. To satisfy every member of the family, it needs to be brown and crispy on the outside, while still maintaining its inner moisture. If you’re adventurous (read: crazy) enough to deep fry your turkey, you’ve already found the best way to ensure rapid surface browning and maintenance of moisture throughout. For the more traditional turkey roaster, another technique might be to increase the temperature of the oven. While this does work to promote browning to a certain degree (pun intended), past the prime Maillard range (284-329˚F), another reaction starts taking over. The enemy of any meal, Thanksgiving or otherwise: pyrolysis. Pyrolysis is as bad it sounds when it comes to the centerpiece of your Thanksgiving dinner. It’s the fancy name for the reaction commonly known as burning. So, while it might be tempting to raise the temperature to speed things up a bit, it’s probably not worth the risk.

When it comes down to it, there is no validated, peer-reviewed scientific protocol behind the perfectly roasted turkey (at least in the journals I subscribe to), or much of a molecular excuse for that post-meal snooze. So in the end, whether it’s your grandma’s super secret brine, or your uncle’s perfectly engineered aluminum foil tent, or your mom’s tried-and-true basting schedule, as far as this food scientist is concerned, just go with whatever floats your (gravy) boat.

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Categories:   Celebrations, Smarts


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