Diet Coke uses aspartame to provide zero calories and sweetness at the same time, but separating the optical isomers is key. The ability to remove the bitterness of aspartame and retain its sweetness is a key aspect of chemical engineering, which also plays an important role in pharmaceuticals, food, and other fields.
Diet Coke first appeared in 2005. Because of its zero calories, Diet Coke is still a favorite among many women fighting the weight war. But what if Diet Coke tasted bitter? The bitterness of Diet Coke can make women who are stressed out about their diets throw the can away in anger. In fact, if it weren”t for chemical engineering, Diet Coke would be very bitter, not sweet. The substance responsible for Diet Coke’s sweetness is aspartame, not sugar, which is why it tastes sweet despite having no calories. Aspartame is more than 200 times sweeter than sugar, which means that a small amount is enough to produce an intense sweetness, making it the closest thing to sugar among sweeteners. On the other hand, the optical isomers of aspartame, unlike aspartame, have a strong bitter taste. This is due to the different chemical reactions that occur when aspartame and its optical isomers bind to the taste buds, the organs that sense taste. Chemical engineering techniques to separate these different flavors of aspartame and its optical isomers are the secret key to Diet Coke’s sweetness.
So what are optical isomers? Optical isomers are substances that have the same three-dimensional structure but cannot be stacked on top of each other. For example, your left and right hands have the same shape, but they can’t be stacked on top of each other. You can’t put your left glove on your right hand. Optical isomers exist in pairs, and their relationship is the same as that of a left and right hand. Optical isomers are also called “enantiomers” because they are mirror images of each other, just as your right hand looks like your left hand when you hold it up to a mirror. Optical isomers look the same, but they are actually different substances. This is because no matter which way you turn, the two molecules are not completely enclosed. Two molecules that are optical isomers have the same physical properties, such as mass and boiling point, but they react completely differently in the same environment.
Optical isomers are found in nature, and often only one of the two forms exists within an organism. On the other hand, when optical isomers are synthesized artificially, a mixture of half and half of both isomers is created, which is called a racemic mixture. The technique of isolating only one of the isomers from this mixture is also applied to the process of obtaining aspartame, which is used in Diet Coke.
The Department of Chemical and Biomolecular Engineering at Seoul National University has five subdepartments: synthetic, process, polymer, nano, and environmental. Among them, the synthesis laboratory studies the properties of these optical isomers and how to separate racemic mixtures economically and efficiently. When optical isomers are essential chemicals in the process of making a product, chemical engineering skills play an absolutely crucial role. It is the role of chemical engineers to synthesize optical isomers and devise economical and efficient methods to isolate only one target isomer from a mixture in high purity. Since the separation of optical isomers is time-consuming and expensive, various research efforts are underway to improve these limitations.
The results of optical isomerism research are utilized in a variety of fields, including medicine, cosmetics, and food. In the field of medicine, more than half of all medicines are composed of optical isomers. When a drug contains two optical isomers, precise chemical engineering techniques are required because one may have the original effect while the other is ineffective or may cause serious side effects.
One example is thalidomide, which was marketed in the late 1950s and 1960s as an anti-morning sickness drug for pregnant women. It was promoted as a miracle drug because it showed few side effects in animal studies, but it caused the birth of more than 10,000 deformed babies in 46 countries around the world. One of the optical isomers of thalidomide was not toxic in animals, but was later found to cause birth defects, including limb defects, in humans who took the drug before the first 42 days of pregnancy.
Because many of the chemicals we use in the modern world are composed of optical isomers, the study of isomers provides a crucial technique in many fields. Optical isomers are pairs of very different properties that can be either medicine or poison, depending on how pure they are isolated. It’s thanks to this chemical engineering technique that we can enjoy a sweet Diet Coke without worrying about the calories. It will be interesting to see what innovative products chemical engineers will come up with in the future by studying optical isomers.
