CHEMICALS IN FOOD - THE WORLD AROUND US - The Handy Chemistry Answer Book (2014)

The Handy Chemistry Answer Book (2014)

THE WORLD AROUND US

CHEMICALS IN FOOD

Why do diet Coke® and Mentos® fizz like that?

In diet Coke®, and all soda, there are a lot of CO2 molecules trapped in solution. The slow release of CO2 from solution is what normally makes the calm bubbling in soda. But what if you were to put a catalyst for gas release into a bottle of diet Coke®? That’s exactly what a Mentos® does. Dissolved gases need a surface to start forming a bubble (let’s just assume that’s true, which it is), and the Mentos® candy provides a huge amount of surface area because it is a very porous material. So add a Mentos® and many, many more CO2 bubbles can form at the same time, which leads to a sugary eruption.

Is it good to drink chocolate milk after a workout?

Yes! Milk contains a significant amount of protein: roughly eight to eleven grams per cup. It is often recommended to consume fifteen to twenty-five grams of protein after a workout session, so drinking two to three cups of chocolate milk would meet this suggested quantity. In comparison to regular milk, chocolate milk has about twice as many carbohydrates, which is good for soothing sore and tired muscles. Of course, it also serves to rehydrate your body from the water lost during the workout. Moreover, milk provides you with nutrients like vitamin D and calcium.

Why don’t oil and water mix, anyway?

The simplest way to answer this is with the phrase you probably learned in high school— “like dissolves like.” Water is a polar molecule, so it prefers to interact with other polar molecules. Oil, a hydrocarbon of some type, lacks polar groups, and forms weak Van der Waals interactions with other nonpolar molecules.

This is only partially correct, and the actual situation is quite complicated. The major force at work here is the stability of the water phase due to the hydrogen bond interactions. When a molecule of a hydrocarbon is dissolved in water, some number of hydrogen bonds must be broken. This bond breaking costs energy. When oil and water don’t mix, these hydrogen bonds outweigh the entropy gained by mixing the phases so the water molecules stick together, and the oil remains separated.

What will happen to the gum I just accidentally swallowed?

When you were a kid, your parents or teachers probably told you (or at least they told us!) not to swallow your chewing gum because it would take years to digest. Actually your body can do just fine with digesting the flavor components, sugars and sweeteners, and softening ingredients in chewing gum. It’s only the gum base that you cannot digest. However, just because you cannot digest it does not mean it will stay around in your body for several years. The gum base will just typically pass through your digestive system in just a few days’ time. But please don’t try to swallow a bunch of gum at the same time, though—it can get stuck and cause all sorts of problems.

Is it true fresh eggs will sink in water, while bad ones will float? Why?

Yes. As an egg goes bad, proteins and other chemicals decompose and release volatile molecules like carbon dioxide (CO2). The shell of an egg is somewhat porous, so these gases can escape, decreasing the mass of the egg. Since the size of the egg doesn’t change (assuming you don’t break it), the density decreases as the egg ages, and it eventually becomes less dense than water. Whether it becomes buoyant exactly when it is spoiled or weeks after, we can’t say. That’s why your nose is so good at smelling that awful smell—so that you don’t eat rotten eggs!

Why does my mom put salt in the water to make it boil faster?

Probably because her mom told her to. There are actually two things that are affected when you add salt to water. First, the boiling point increases (remember boiling-point elevation from the chapter “Macroscopic Properties: The World We See”?). Second, the heat capacity, or how much energy it takes to raise the temperature, decreases. While you might think this would change how fast your pot of water boils, the amount of salt you would have to add to see a significant change is pretty large. The real reason you add salt to water for cooking? Flavor. Salt tastes good.

Why does asparagus make pee smell weird?

The compounds you smell in your pee after eating asparagus are most likely thioethers (although the literature over the last one hundred years on this subject includes some debate—no joke). That’s a sulfur atom with two carbon substituents. Asparagus, for some reason, has high levels of sulfur-containing amino acids. Your body breaks these down into chemicals that smell like rotten eggs or other foul odors.

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Asparagus has a lot of sulfur-containing amino acids, and when you urinate after eating this vegetable, the sulfur can be smelled in your waste.

Why does my chocolate turn white when I wait too long to eat it?

Chocolatiers refer to this as a bloomed chocolate, which is a wonderfully obscure and appealing way of describing the white stuff that forms on old Halloween candy. There are two processes that could be happening here, either sugar bloom or fat bloom. Sugar bloom is the candy world’s way of saying sugar crystallization. If your candy is exposed to moisture, sugar molecules dissolve out of the fat in the chocolate and once that moisture evaporates, the separated sugars have a chance to crystallize. If your candy has stayed dry but underwent a quick temperature change or was stored warm, it’s probably fat from the cocoa butter that has separated from the chocolate. In either case, it is usually still fine to eat.

What does a preservative do?

Preservatives keep food fresh by slowing the growth of mold and bacteria (antimicrobial preservatives), preventing oxidation (antioxidants), or slowing enzymes from continuing the ripening process after a fruit or vegetable was picked or cut.

What is the difference between artificial and natural flavoring?

The difference between calling a molecule artificial or natural is a legal definition, not a chemical or biological one. If a molecule of vanillin is isolated in a lab by extraction of a particular seed pod, the chemical is called “natural vanilla.” If that same molecule is made from lignin, which is a polymer found in naturally in wood, that substance is called “artificial vanilla.” The difference is that transforming lignin to vanillin requires chemical steps not covered by the legal definition of the word “natural.” To be clear, the “natural” and “artificial” versions of a molecule are exactly the same chemical species (same atoms, same bonds, same stereochemistry, etc.), but there may be other chemicals present that may differ in the natural and artificial versions of a product.

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So is natural vanilla worth the extra money?

Well, that’s a different question…. When the seed pods of the Mexican orchid Vanilla planifola are collected, they are put through an elaborate series of curing and aging steps. These steps allow additional flavor molecules to develop beyond just vanillin. While vanillin is a major flavor component of natural vanilla, there are hundreds of other tasty chemicals in “natural vanilla.” So you’re not buying exactly the same thing when you buy artificial and natural vanilla. Which one tastes better in your cookies is up to you, though.

Why does milk go sour?

Milk, even milk that has been pasteurized, contains a bacteria called lactobacillus. The first part of the word, “lacto,” refers to the sugar that these particular bacteria eat—lactose. When these bacteria process lactose, they secrete lactic acid. It’s this acid that makes milk taste sour and leads to curdling.

It actually doesn’t have to be lactic acid that curdles milk; any acid will do. Try taking a small glass of milk and adding lemon juice or vinegar to it. The milk will start to curdle just the same.

Is lactobacillus harmful?

Lactobacillus is used in the production of lots of foods, actually—cheese and yogurt, sourdough bread, pickled vegetables, and wine and beer. There are helpful strains of lactobacillus living in your digestive tract too. So, to answer the question, lactobacillus is not necessarily bad for you in appropriate quantities.

Why can’t lactose intolerant people eat dairy?

Most every dairy product contains lactose, which is a type of sugar. Specifically, lactose is a disaccharide made up of one galactose molecule and one glucose molecule. Lactase is an enzyme that breaks the bond that joins the galactose sugar to the glucose sugar to form this “double sugar.” Lactose-intolerant people lack the enzyme lactase, so they can’t metabolize this particular molecule.

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All mammals can digest lactose when they are first born, but it is very rare for adult mammals to continue to be able to absorb the sugars found in dairy products. Recent studies have suggested that humans only obtained this ability around the same time they began domesticating animals. This makes it possibly the most recent example of evolution in our species.

Does eating turkey make you sleepy?

You’ve probably heard that turkey contains a lot of tryptophan, which makes you sleepy. It’s true there is tryptophan in turkey, but not more than is contained in most meats. It’s also true that tryptophan is used to make serotonin, a neurotransmitter that makes humans sleepy. The problem with connecting these dots (“I’m sleepy after Thanksgiving” and “Tryptophan makes serotonin, which makes me sleepy”) is that there are also a bunch of other amino acids in turkey. For amino acids to get into your brain, they need to use transporters to cross the barrier. Tryptophan is competing for a ride on the transporter molecules with all of those other amino acids you just stuffed in your face.

So why are you sleepy after Thanksgiving dinner? It’s not the turkey, but the extra servings of carbohydrates. Carbohydrates, or sugars, cause your pancreas to release insulin. Insulin helps the body deal with the huge amount of sugar and amino acids you just consumed, but interestingly it has no effect on tryptophan. So other amino acids are taken out of the bloodstream, and tryp-tophan is free to use the transporters to get into your brain, making you sleepy.

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A chemical called tetrodotoxin in the fugu fish can be released into the fish if it is not prepared correctly by a trained chef.

Why is fugu toxic?

Fugu fish is toxic because of a molecule called tetrodotoxin. This molecule binds to the sodium ion channels in nerves’ cells, shutting down all communication in your nervous system. The toxin is not affected by cooking, so chefs that prepare this dangerous fish have to be highly trained to avoid serving parts that contain tetrodotoxin (the liver, ovaries, and skin can have very high levels of this poison).

How do Pop Rocks® candy work?

Pop Rocks® is a carbonated candy like soda is a carbonated beverage. The fizzing that goes on in your mouth is due to carbon dioxide (CO2) bubbles escaping from the candy. To make this unique treat, the ingredients are heated, exposed to high pressures of carbon dioxide, and then cooled to trap the CO2 inside the candy.

What is MSG, and is it really so bad to consume?

MSG stands for monosodium glutamate. It is a natural, but nonessential amino acid. It is used by food manufacturers as a flavor enhancer, and by itself has the taste of “umami”—the fifth taste sensation we mentioned in “Macroscopic Properties: The World We See.” There have been countless studies on its safety to eat, and the data overwhelmingly supports MSG as being safe to consume even in absurdly large quantities. But don’t try to disprove those studies—everything in moderation—your mother was right about that.

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How does popcorn pop?

The shell of a popcorn kernel is a hard, moisture-resistant coating protecting an interior filled with starch and some water. As the kernel gets hot, the starch inside first softens and then the water turns into steam, which raises the pressure inside the kernel. At some temperature the pressure inside the corn kernel is high enough to rupture the hard shell, and the kernel pops. The hot starch quickly cools, trapping tiny air bubbles inside and making a (delicious) solid foam.

What’s the difference between saturated and unsaturated fats?

The terms saturated and unsaturated refer directly the to the chemistry definition of unsaturation. Unsaturated fats contain carbon-carbon double bonds (units of unsaturation), while saturated fats have only completely saturated carbon chains. Saturated fats (like butter and lard) stack together well in the solid state, so they are generally solid at room temperature. The double bonds in unsaturated fats disrupt this lattice in the solid state, making these types of fats (like olive oil and vegetable oil) liquid at room temperature.

What about cis and trans fats?

The carbon-carbon double bonds along the hydrocarbon chain of fatty acids can be either the cis or trans isomers. Naturally occurring unsaturated fats have more cis fats, while manmade fats (like margarine) have a higher level of trans fats. Trans unsaturated fats turn out to be particularly bad for humans as they increase cholesterol, leading to heart disease.

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