Monosodium glutamate (MSG)

Monosodium glutamate (IUPAC name: sodium 2-aminopentanedioate), or MSG (Figure 1), is a chemical compound found naturally but more commonly man-made to enhance flavor in food. It was first manufactured in 1908 when Japanese chemist Ikeda Kikunae sought to isolate the savory taste in many foods he called “umami” (Japanese for ‘palatable’ or ‘delicious’).6 His method involved removing the hydrogen ions from l-glutamic acid and replacing them with a sodium ion, another well-known flavor enhancer.⁶ The combination of two profoundly savory flavor enhancers boosted the umami taste of any dish and quickly spread to many cuisines around the world.⁴

Figure 2. Molecular model of monosodium glutamate

MSG is a relatively simple compound consisting of glutamic acid with a sodium cation attached instead of hydrogen. As seen in Figure 2, the molecule has a primary, four-membered carbon chain with oxygen groups attached on either end. Within the molecule, several functional groups, including an amine, two ketones, and a hydroxyl group, contribute to the rich flavor it emits when added to various food products. The molecule is mainly made up of sigma bonds, but there are also pi bonds within the two carbonyl groups.

Figure 3. Unit cell of MSG (i) and the two conformations of the glutamate ions found in the bulk (ii and iii)³

The structures of the bonds and other properties of MSG have been carefully studied by chemists, particularly in comparison to other modified glutamates such as monopotassium glutamate (MPG). Monopotassium glutamate is the same molecule as MSG but replaces the sodium cation with a larger potassium cation. However, despite the slight structural difference, MSG and MPG exhibit entirely different molecular geometries, each having several unique conformations³ (see Figure 3). The differences in metal-ligand bonding interactions have been found to relate to the difference in the size and charge of the metal cation attached to the glutamic acid.3 In addition, researchers’ analysis of the two molecular structures has revealed that there is a large sigma-bonding interaction between sodium’s 2s orbital and the glutamic acid’s oxygen atoms because they are close together in energy and space.³ By substituting the cations for one other (creating substituted MSG/MPG), chemists concluded that the large bonding interaction is primarily due to the metal cation's properties rather than the glutamic acid's structural geometry.³ The research studies on bonding have also explained previous observations regarding the structure of glutamate polypeptides, as they have revealed how cation identity can contribute to changes in molecular structure.³

Figure 4. Diagram of MSG and taste bud interactions¹

In the body, MSG can affect various aspects of human function. When consumed, the sodium ion and the glutamic acid detach from each other, allowing the acid to bind to taste receptors in the mouth and stomach to release the infamous savory flavor that the enhancer provides (as shown in Figure 4).² However, there have also been many rumors regarding the negative consequences of consuming MSG, including headaches, obesity, and other major health concerns.⁴ Although there have been research studies attempting to find the correlation between MSG and neurodegenerative disease, researchers ultimately concluded that there was an unrelated natural imbalance of glutamate in the brain.⁴

Regardless of any positive or negative rumors about MSG and its flavor-enhancing relatives, there is no controversy surrounding its chemical effects on the food many people eat. While many may continue to refer to the effects of MSG as “Chinese-Restaurant Syndrome,” it will remain a fundamental aspect of many cuisines that rely on the molecule to enhance the flavor that so many in the world savor.

Work Cited

1. Is MSG (Monosodium Glutamate) bad for your health? - Examine. examine.com. https://examine.com/articles/is-msg-bad-for-your-health/.
2. Osmosis from Elsevier. Monosodium glutamate. www.youtube.com. https://www.youtube.com/watch?v=Muym51uXNE4 (accessed 2023-07-16).
3. Ruggiero, M. T.; Sibik, J.; Erba, A.; Zeitler, J. A.; Korter, T. M. Quantification of Cation–Anion Interactions in Crystalline Monopotassium and Monosodium Glutamate Salts. Physical Chemistry Chemical Physics 2017, 19 (42), 28647–28652. https://doi.org/10.1039/c7cp05544g.
4. TED-Ed. What Is MSG, and Is It Actually Bad for You? - Sarah E. Tracy. YouTube, 2021. https://www.youtube.com/watch?v=EKgEj5asL3o (accessed 2023-07-16).
5. The Editors of Encyclopedia Britannica. monosodium glutamate | Description, Uses, & Health Impacts. Encyclopedia Britannica. https://www.britannica.com/science/monosodium-glutamate (accessed 2023-07-16).
6. Yamamoto, T.; Inui-Yamamoto, C. The Flavor-Enhancing Action of Glutamate and Its Mechanism Involving the Notion of Kokumi. npj Science of Food 2023, 7 (1). https://doi.org/10.1038/s41538-023-00178-2.