The Chemistry Column

Tea-time no more

Claire Gormley

Typically, in the weeks leading up to the New Year— and, often, for a few weeks after —I see a lot of messages about how things will be different and better now that the new year has come. This year, as we begin another year of the Covid-19 pandemic, I haven’t seen quite as much of this talk. People are unsure of what the year will bring, and living with this uncertainty for so long has come with a wealth of new health problems for many. Our mental health is at the top of this list and, while I understood the low feelings I had through lockdown, I wasn’t prepared to experience social anxiety when things started to return to normal, and the gastrointestinal issues that this would cause me.

In my desperation to see friends and family without experiencing discomfort, I began drinking Peppermint tea (Mentha piperita) to soothe my stomach, and found even more relief from Peppermint oil tablets. This remedy dates back to the Ancient Egyptians, who are thought to have used Peppermint leaves to aid digestion and alleviate an upset stomach (iberogast.co). The Ancient Greeks and Romans are also said to have used it to soothe the stomach (encyclopedia.com). However, Peppermint is not everyone’s cup of tea; some have reported heartburn, nausea, abdominal pain, and dry mouth as side effects to ingesting Peppermint oil (National Center for Complementary and Integrative Health).

These side effects are less likely to occur if the Peppermint oil is released slowly in the body, which can be achieved by putting the oil in an enteric-coated capsule— an outer layer designed to resist breaking down in a highly acidic pH environment (like the stomach) but readily dissolves in a more alkali pH environment (like the small intestine) (Pharmapproach, 2021). With the potential to help so many under the right conditions, researchers are now investigating Peppermint oil as a potential treatment for irritable bowel syndrome (IBS) (Thompson et al, 2013).

Mentha piperita is a naturally occurring hybrid of Mentha aquatica (Water Mint) and Mentha spicata (Spearmint). All three belong to the Lamiaceae family of flowering plants, and give off the minty aroma for which they’re named. The main chemical compounds found in Peppermint oil are menthol (40.7%) and menthone (23.4%) (Schmidt et al, 2009). Menthyl acetate, which is responsible for the minty aroma and flavor of the plant, is also found in smaller quantities (Schmidt et al, 2009). All three chemicals are organic compounds, meaning that they’re made up of carbon atoms bonded with other elements, such as hydrogen and oxygen.

Menthol

Menthol is classified as an alcohol group because it contains a hydroxyl (oxygen bound to hydrogen: OH) group in its structure (Wade, 2018). Interestingly, menthol can exist in two forms that are mirror images of one another, just like a right hand and a left hand. The mirrored structures— called enantiomers —are very similar but can have wildly different effects in the body. Some enantiomers may have one ‘hand’ that is highly effective at treating a disease or condition, while the other ‘hand’ is incredibly toxic (Smith, 2009). Luckily, L-menthol’s mirror image, D-menthol, is simply less effective at creating the ‘cooling’ effect that L-menthol is used for in products like toothpaste, cooling ointments, deodorants, and so on (basf.com; Wade, 2018).

Menthone

Menthone and menthyl acetate are both derivatives of menthol. The three compounds have very similar structures with slight differences. In menthone, the OH group has been replaced with a carbonyl group, an oxygen double-bonded to the carbon (=O), making it a part of the ketone family of organic compounds. Whereas menthyl acetate has an acetyl group (see the diagram) bound to the structure. Together these compounds give Peppermint oil its antibacterial, antiinflammatory, antioxidant, and anti-fungal properties, all of which make it such a promising therapeutic (Rostamabadi, Falsafi and Jafari, 2019; Thompson et al, 2013).

Menthyl acetate

Like many, I’m silently optimistic that this new year will bring more time spent with friends and family, and although I’m excited about the potential of Peppermint oil to treat IBS, I really hope this year brings less Peppermint tea!

Images

Menthol, by Benjah-bmm27, 2006. Own work, Public Domain, commons.wikimedia.org/wiki/File:Mentholskeletal.png

Menthone, by Edgar181. Public domain, via Wikimedia Commons commons.wikimedia.org/wiki/File:Menthone.png

Menthyl acetate, by Edgar181. Public domain, via Wikimedia Commons commons.wikimedia.org/wiki/File:Menthyl_acetat e.png

References

BASF. ‘The cool freshness of menthol.’ basf.com/gb/en/media/science-around-us/the-cool-freshness-of-menthol.html [Accessed: 10 December 2021]

Encyclopedia.com. ‘Peppermint.’ encyclopedia.com/plants-andanimals/plants/plants/peppermint [Last updated: 18 May 2018]

Iberogast.co. ‘Peppermint leaves (Menthae piperitae folium) – aromatic and medicinal.’ iberogast.co.za/power-of-nature/peppermint. [Accessed: 10 December 2021]

National Center for Complementary and Integrative Health. ‘Peppermint Oil.’ nccih.nih.gov/health/peppermint-oil [Last updated: October 2020]

Pharmapproach (2021) ‘Enteric Coating: An Overview.’ pharmapproach.com/enteric-coating-2/ [Accessed: 10 December 2021]

Rostamabadi, H., Falsafi, S.R., Jafari, S.M. (2019) ‘Nanostructures of starch for encapsulation of food ingredients’ in Jafari, S.M., Nanoencapsulation in the Food Industry. Elsevier Inc. 419-462.

Schmidt, E., Bail, S., Buchbauer, G., Stoilova, I., Atanasova, T., Stoyanova, A., Krastanov, A. and Jirovetz, L. (2009) Chemical composition, olfactory evaluation and antioxidant effects of essential oil from Mentha x piperita. National Product Communications, 4(8): 1107-12.

Smith, S.W. (2009) ‘Chiral Toxicology: It’s the Same Thing…Only Different’ in Toxicological Sciences, 110(1): 4-30.

Thompson, A., Meah, D., Ahmed, N., ConniffJenkins, R., Chileshe, E., Phillips, C.O., Claypole, T.C., Forman, D.W., and Row, P.E. (2013) ‘Comparison of the antibacterial activity of essential oils and extracts of medicinal and culinary herbs to investigate potential new treatments for irritable bowel syndrome’ in BMC Complementary Medicine and Therapies, 13:338.

Wade, L.G. (2018) ‘Menthol.’ britannica.com/science/menthol [Accessed: 10 December 2021]