Onions are not only a staple ingredient in many cuisines but also known for their ability to make us cry when we cut into them. This tear-inducing effect is due to specific compounds found in onions. Let's explore the chemical composition of onions and the compounds responsible for our tears.

One of the primary compounds in onions is a class of sulfur-containing compounds called thiosulfinates. The most well-known thiosulfinate in onions is allicin, which is responsible for the pungent odor and taste of onions. When an onion is cut or crushed, the enzyme alliinase converts the precursor compound alliin into allicin, releasing a volatile gas into the air.

When this gas comes into contact with the moisture in our eyes, it forms a weak sulfuric acid, which irritates the eyes and triggers tears as a protective mechanism. The more pungent the onion, the higher the concentration of thiosulfinates, and the stronger the tear-inducing effect.

Aside from thiosulfinates, onions also contain flavonoids, particularly quercetin. Quercetin is a powerful antioxidant known for its anti-inflammatory and anti-cancer properties. It is responsible for the yellow color of onions and is found in higher concentrations in the outer layers of the bulb.

Furthermore, onions are a rich source of fructans, a type of carbohydrate that is not easily digestible by humans. Fructans act as prebiotics, promoting the growth of beneficial bacteria in our gut and aiding in digestion.

References:

1. Hu, L., Zhu, M., Li, Y., Zhang, C., & Zeng, H. (2017). Chemical composition, taste compounds and antioxidant capacity of Chinese bayberry (Myrica rubra Sieb. et Zucc.) cultivars. Food Chemistry, 221, 447-453.
2. Slimestad, R., Fossen, T., & Vågen, I. M. (2007). Onions: a source of unique dietary flavonoids. Journal of Agricultural and Food Chemistry, 55(25), 10067-10080.
3. Slavin, J. (2013). Fiber and prebiotics: mechanisms and health benefits. Nutrients, 5(4), 1417-1435.

By understanding the chemical composition of onions, we can appreciate not only their culinary uses but also their potential health benefits. So, the next time you shed a tear while cutting onions, remember the fascinating compounds that make it happen!