Food Composition and Taste

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All About Soda

Every once in a while we all like to take a sip of our favorite beverages to quench our thirsts. One of the most famous types of beverages would be the fizzy drink known as soda. This fizzy bubbly sensation is produced by adding pressurized carbon dioxide gas into the beverage. Therefore sodas are also known as carbonate water.

Soda water is basically created by adding pressurized carbon dioxide through water. As we know from Henry’s law, high pressure increases the solubility of a certain solute. Therefore high pressure allows an abnormally high amount of carbon dioxide to be dissolved in the water, causing the water to be supersaturated with carbon dioxide. This is also why when you open up can of soda pop, all of the gas would rise to the top and try to escape. Therefore if you build up more pressure in the can by shaking it, the soda will blast out of the can when you open it.

The biting texture of soda is due to the result of effervescence. Effervescence is the escape of gas from an aqueous solution. The pressurized dilute solution of carbonic acid in water releases gaseous carbon dioxide during decompression, the lowering of pressure, when one opens the can of soda. The carbon dioxide escaping the water also creates the fizzy sounds and bubbling in the soda.

A common question concerning sodas might be: Why is soda harmful to the body aside from the artificial ingredients and sugar? The answer is: When carbon dioxide is introduced to the water, carbonic acid is created H2O + CO2–>H2CO3(figure1). Salts like sodium bicarbonate (NaHCO3) are needed in order to reduce the acidity.  And other metallic salts are introduced to the solution to neutralize the acidic flavor. Despite all of these salty cover ups of soda’s acidity, soda is still acidic, therefore over consumption is detrimental to the body.

figure 1

Here deep explanation of how the process of carbonation works:

Author: David Zhang

Sources:

http://humantouchofchemistry.com/the-science-behind-soda-water.htm

http://chemistry.wikia.com/wiki/Carbonation


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What makes bread become stale?

Rock-hard cookies are not only hard to eat, but are usually associated with staleness. While cookies can be intentionally baked to be harder than usual, a cookie that has lost its original softness is likely to be stale. Stale bread gives similar tell-tale signs. What makes bread go stale though? It’s not mold or oxidation, which are common suspects of food gone bad.

The staleness of bread actually arises from the presence, or rather the lack of the presence of water. Bread is mostly made up of starch molecules, hence it being a significant source of carbohydrates. When you bake bread, the starch molecules weaken and allow moisture to enter the complex of chemical structures that make up bread. Water molecules are able to squeeze between the starch molecules. Starch granules weaken, giving most bread a soft and fluffy texture.

Once the bread is taken out of the oven, the slow journey to staleness begins, although it won’t be noticed for a while yet. The most significant factor in staleness is the recrystallization, also called retrogradation, of starch molecules; once cooling begins, which is the moment you take the bread out of the oven, the process that was used to bake the bread essentially reverses itself. The bread slowly drys itself out; as water molecules detach themselves from the network of starch molecules, the starch begins to recrystallize into their original shape.

Let’s go into a more detailed analysis of the chemistry behind all of this. Amylose and amylopecton are the two types of starch that are found in bread. When bread is baked in the oven, a process called gelatinization occurs. This occurs when starch is heated in water; hydrogen bonds in the starch granules break, allowing water to enter the granule and causing the granule to swell. Amylose molecules leave the starch granules, while the water molecules form hydrogen bonds with the amylopectin molecules. The swelling of the starch granules is the reason why bread “rises” in the oven.

Let’s see this in action: (the swelling becomes visible at around the 00:12 mark)

However, as stated before, this entire process begins to reverse itself once the bread is taken out of the oven. First, synersis causes amylose molecules to pull back together into the starch granule, squeezing out the water molecules previously inside. Then, retrogradation allows the amylose molecules to realign in a linear-chain pattern. This structure is kept rigid because hydrogen bonding occurs between the chains of amylose. As a result, the bread feels hard and is now stale. The following diagram should help in visualizing all this chemistry.

Figure 1: Gelatinization and Retrogradation of Starch Molecules

On a less chemistry-intense note, there is something pretty surprising about preventing bread from becoming stale: bread goes stale about 6 times faster in the refrigerator than at room temperature. You might ask – Isn’t the fridge supposed to keep things from going bad? Well, for most things, yes. However, the temperature inside the fridge is actually near the optimal temperature for retrogradation of starch molecules. So how you keep bread from going stale? If you do leave it on the kitchen counter at room temperature, mold growth will occur extremely fast, as you probably already know. What you can actually do is put the bread in the freezer. Freezing temperatures are too low for starch molecules to want to recrystallize, and mold growth is basically nonexistent. Just reheat the bread when you want to eat it, and it’ll be good as new!

So should you throw out any stale slices of bread you already have? No! Unless the bread feels like a piece of rock, it is highly likely that you can make it edible again.  Just bake the bread in the oven again with water, and the effects of retrogradation should be almost completely reversed. Enjoy!

Author: Jonathan Yu

Sources:

http://www.thaiscience.info/Article%20for%20ThaiScience/Article/1/Ts-1%20a%20fresh%20perspective%20on%20staling%20the%20significance%20of%20starch%20recrystallization%20on%20the%20firming%20of%20bread.pdf

http://pubs.acs.org/doi/abs/10.1021/ma00158a016

http://www.todayifoundout.com/index.php/2011/08/bread-goes-stale-about-six-times-faster-in-the-refrigerator-than-at-room-temperature/


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More to Sweets?

Scientists have known from years ago that the T1r2 + T1r3 receptor within our taste cells on our tongues is the main mechanism by which we are able to detect sweet compounds. However, this commonly held belief that the way we are able to taste sweetness is from certain receptors in our tongue may not be the whole truth.

With the color coordinators, we can see where these T1R2 and T1R3 receptors are located on our tongues.

After researching, scientists have found that there’s much more to the taste for sweets and that its far more complex than we knew. Several other sensors that contributed to the detection of sweetness were found within our taste cells. These included those that are existent in our intestine and pancreas.

The various sugar taste sensors discovered are found to have different roles. For example, the sensor that is also found in the intestine is known as SGLT1, and it helps transport glucose into sweet taste cells, but only when sodium is present. This may explain why a pinch of salt added to baked goods, may enhance the sweetness of it.

This diagram basically shows the process of the SGLT1. You can see that glucose and Na+ go into the SGLT1 and out comes a Glut-2 along with an Na+ and K+

The sensor also found in the pancreas, a digestive organ, is known as the KATP channel and it is responsible for triggering the release of insulin when glucose levels rise.  The stu­dy’s au­thors spec­u­late that KATP may func­tion in sweet taste cells to mod­u­late taste cell sen­si­ti­vity to sugars according to met­a­bol­ic needs.

KATP channel structure

As one of the investigators of this research said “Sweet taste cells have turned out to be quite com­plex,” indeed it has. It’s really interesting to see how much more there is to tasting sweetness.

Author: Jennifer Lee


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The Unpopping Popcorn Kernels

Have you ever wondered why at the end of every bowl or bag of popcorn, you always have kernels that are left unpopped? You are then left behind with something of worthless value since eating these would only leave you with the possibility of breaking your teeth or choking from trying. But fear no further!

Scientists have discovered the secret behind unpoppable popcorn. According to the research done, the key factor that contributes to the popping quality is the chemical structure of the pericarp, the outer hull of the kernel. This covering is composed of a crystalline structure of cellulose, a carbohydrate made of glucose units, in which enables the pericarp to lock moisture and build pressure within the kernel. Eventually, the pressure results in the kernel to rupture, forming the popcorn that we eat.

Scientists identified that those in which have a stronger, more highly ordered crystalline arrangement of the cellulose molecules have the best results in popping. This is because the stronger form of the cellulose structure maximizes the moisture retention/pressure within the kernel, thus resulting in a higher chance of it completely rupturing.

Cellulose structure

This video can help visualize what’s happening inside the popcorn and why it pops.

So there may come a day when we begin to see all of our popcorn popped in our bowls/bags. It’s just a matter of time to find the perfect technique to engineer the kernels to have the optimal crystalline structure.

Author: Jennifer Lee


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What’s Wrong With Burnt Food?

Almost everyone has accidentally burnt food before, and many of them still eat the burnt areas either because they especially enjoy the crispy parts or because it is just unavoidable. However, people are often warned against doing so and are told that burnt food is carcinogenic. What’s the truth behind this? Does burnt food actually increase cancer risk? In order to have a better understanding, we need to consider the chemistry in burnt food.

Carcinogenic Compounds

One solid reason to not eat burnt food is that it contains polycyclic aromatic hydrocarbons (PAHs), which are a class of air pollutants. Some of these chemicals have been proven to be carcinogenic, and some are even found in coal tar and cigarette smoke. The toxicity of PAHs depends heavily on its structure; while many PAHs may have the same chemical formula and same number of rings, different isomers can vary from being nontoxic to being extremely toxic.

The most well-known of PAHs is benzo(a)pyrene (shown below in Figure 1), which damages DNA, which in turn can possibly cause cancer. Cooked meat products contain up to 4 ng/g of benzo(a)pyrenes and up to 5.5 ng/g in fried chicken. However, in overcooked beef, the amount of benzo(a)pyrene can reach over 60 ng/g.

The mechanism of action of DNA damage from benzo(a)pyrenes is relatively simple. The benzo(a)pyrene molecules (shown in Figure 1) intercalate themselves into DNA strands. This means that they fit between base pairs, as shown in the Figure 2, thereby interfering with transcription and possibly causing mutations.

Figure 1. Molecule of benzo(a)pyrene

Figure 2: Benzopyrenes intercalated into DNA.

The smell of smoke from burning food is not only acrid, but also contains these benzo(a)pyrenes. Therefore, in addition to avoiding eating burnt food, we should avoid burning food in the first place. While accidentally leaving the bread in the toaster for too long is sometimes hard to avoid during the morning rush, at least we now have a good reason to not eat burnt food.

Author: Jonathan Yu

Sources:

http://www.healthy-food-site.com/burnt-food.html

http://www.abc.net.au/health/talkinghealth/factbuster/stories/2011/01/25/3093063.htm#.UICQSsXyp8F


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Garlic and Wasabi

Few people would ever think of eating raw garlic, and likewise, few people will try wasabi after hearing stories about its sharp taste. However, even fewer people understand the chemistry behind the extremely pungent taste and smell of garlic and wasabi. Although garlic and wasabi certainly look nothing alike on the outside, they share various similarities in their chemical composition and chemical properties.

Garlic belongs to a genus of plants called Allicin. Many plants of this genus, such as garlic, produce sulfur compounds, which are often associated with foul odors. One of these organic compounds is allicin, which is only released when garlic is crushed or eaten raw, but not after the garlic has been cooked. Wasabi, and other mustard plants, produces another organosulfur compound called allyl isothiocyanate (AITC) that is responsible for its pungent taste.

Allicin and AITC are not only both organosulfur compounds, but also share structural similarities. AITC has been known to activate TRPA1 ion channels, which are found on sensory neurons that release pain signals. A study in 2005 found that allicin also activates a subset of these AITC-sensitive neurons due to a few structural similarities with AITC. Because both chemicals induce activation of the primary pain-pathway, it is not surprising that many people are deterred from eating garlic or wasabi.

Author: Jonathan Yu


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Hello world!

This is Jennifer, Jonathan, and David!

Our very first post! This is just an introductory message to our blog. We will be discussing the chemical composition behind our favorite thing on earth, food! Do you like our play on the word “food” in our title? For those who do not get it, it’s the lewis dot structure of O2. Hope you enjoyed that.

Happy blogging and remember to visit frequently for more interesting posts!