This blog post explores the importance of aspartame isolation technology, which enables the sweetness of diet cola, and its chemical engineering principles.
Diet cola first appeared in 2005. Because it’s zero-calorie, diet cola remains beloved by many women fighting the battle of the bulge. But what if this diet cola tasted bitter? Women stressed by dieting might get angry at the bitter taste and throw away the half-finished can without a second thought. In fact, without chemical engineering, diet cola would be bitter, not sweet. The substance responsible for its sweetness isn’t sugar but aspartame, which delivers sweetness without calories. Aspartame is over 200 times sweeter than sugar, meaning a small amount provides intense sweetness, and it replicates the taste of sugar most closely among sweeteners. In contrast, the optical isomer of aspartame produces a strong bitter taste unlike aspartame itself. This difference arises because the chemical reactions that occur when aspartame and its optical isomer bind to taste receptors, called taste buds, are distinct. The chemical engineering technology that separates aspartame and its optical isomer, which have different tastes, is the secret key enabling the sweetness of diet cola.
So what exactly are optical isomers? Optical isomers are substances with identical three-dimensional structures but cannot be superimposed on each other. For example, the left and right hands have the same shape but cannot be placed one on top of the other. It’s the same principle as not being able to put a left-hand glove on your right hand. Optical isomers exist in pairs, and this relationship is analogous to that of left and right hands. Just as your right hand appears mirrored when reflected in a mirror, optical isomers possess mirror-image structures to each other, hence they are also called ‘mirror-image isomers’. Optical isomers appear identical but are actually different substances. This is because no matter how you rotate them, the two molecules cannot perfectly overlap. While optical isomers share physical properties like mass and boiling point, they react completely differently even under identical conditions.
Optical isomers are commonly found in nature, and within living organisms, often only one form exists. Conversely, when optical isomers are synthesized artificially, a mixture containing equal parts of both isomers is produced, known as a racemic mixture. The technology used to isolate only the desired isomer from this mixture is also applied in the process of obtaining aspartame, used in diet cola.
The Department of Chemical and Biological Engineering at Seoul National University offers five specialized tracks: Synthesis, Process, Polymer, Nano, and Environmental. Within the Synthesis Laboratory, researchers investigate the properties of these optical isomers and develop methods to economically and efficiently separate racemic mixtures. When essential chemicals in manufacturing processes are optical isomers, chemical engineering technology plays an absolutely critical role. It is the role of chemical engineers to devise economical and efficient methods for synthesizing optical isomers and isolating only the desired enantiomer from mixtures with high purity. Since separating optical isomers is time-consuming and costly, various studies are underway to overcome these limitations.
The achievements of optical isomer research are utilized in diverse fields such as pharmaceuticals, cosmetics, and food. Particularly in the pharmaceutical sector, over half of all drugs are composed of optical isomers. If a drug contains both optical isomers, one may possess the intended efficacy while the other could be ineffective or cause severe side effects, necessitating precise chemical engineering techniques.
One notable example is thalidomide, marketed as an anti-nausea medication for pregnant women from the late 1950s to the 1960s. Thalidomide was promoted as a miracle drug because animal testing showed almost no side effects, yet it caused over 10,000 cases of birth defects in 46 countries worldwide. It was later discovered that while one optical isomer of thalidomide showed no toxicity in animals, it caused birth defects like limb deficiencies in humans who took the drug before the 42nd day of pregnancy.
Since many chemicals used in modern society consist of optical isomers, isomer research provides crucial technology across diverse fields. Optical isomers are a pair with vastly different properties; depending on how purely they are separated, they can become either medicine or poison. It is precisely this chemical engineering technology that allows us to enjoy sweet diet cola without calorie worries. We can look forward to what innovative products chemical engineers will unveil through their research on optical isomers.
