Sunday, February 5, 2012

Essential oils: Lemongrass essential oil

Lemongrass isn't just for flavouring your favourite Asian noodles any more! It's an essential oil, too! Lemongrass essential oil (Cymbogon citratus) is steam distilled from cultivated plants. (It can also be CO2 extracted.) It's considered to be a sedative, flavouring and fragrance agent, analgesic, anti-microbial and antiseptic, fungicidal, insecticidal, and astringent. (And you know we'll be looking to those claims over the next few days!) It can be found all over the world in more tropical climes.

Lemongrass contains limonene (4.39%), citronellol (1.32%), borneol (2.16%), neryl acetate (2.95%), and the major components neral (31.85%) and geranial (40.79%), and 4% unknown stuff (reference 1).

The main ingredients that interest us are neral (to the left) and geranial, which are isomers of citral, and make up about 65% to 85% of the compounds found in lemon grass. Citral offers some potent anti-microbial properties - click here for a study- and it seems to be the main ingredient in lemon grass that offers the active properties. (More about this tomorrow!)

Geranial is considered a stronger antimicrobial than neral and has a strong lemon odour. Neral has a less strong lemon odour, but is sweeter than geranial. Both are used as flavouring and fragrancing agents.

Geranial oxidizes to become a potential sensitizer (2), so be careful using this essential oil (as we should be careful using all essential oils!). "The autoxidation of geranial with O2 was studied both experimentally and using density functional theory...Geranial was found to autoxidize, forming 6,7-epoxygeranial as the main oxidation product. The dioxolan derivative is believed to form in an acid catalyzed closed shell reaction between 6,7-epoxygeranial and geranial. The dioxolan hydroperoxide and 6,7-epoxygeranial are strong sensitizers and are considered to be the compounds mainly responsible for the skin sensitization potency of air-exposed geranial."

If you live in the EU be aware of this (from this paper): "Citral is one of 26 fragrance materials identified as a suspected cause of allergic contact dermatitis by the European Commissions advisory committee...the directive requires that citral be listed on the ingredient label of consumer products when present at greater than 10 ppm for leave-on cosmetic products and 100 ppm for rinse-off cosmetics."

This is a really important thing to note about lemongrass essential oil - it is considered a skin irritant or sensitizer for a lot of applications. Be very careful how much you use. We will be looking at this the day after tomorrow! 

We know limonene is a potent degreaser - that's one of the reasons we use it in degreasing products in the kitchen and workshop - so it is possible to use lemongrass essential oil where you might use orange essential oil, although it contains about 1/15th the amount of limonene. Lemongrass is considered an astringent essential oil.

And, of course, lemongrass essential oil can be used as a great fragrance. It's got that high, airy lemony smell that is really great in a lot of applications.

As an aside, I have done quite a few searches to see if lemongrass is photosensitizing, and I have found nothing to say it is. If you have some information to the contrary, please let me know! 

Related posts:
The chemistry of essential oils: Terpenes
Essential oils: Processing techniques

(1) Composition: Nikos G. Tzortzakis, (., & Costas D., E. (2007). Antifungal activity of lemongrass (Cympopogon citratus L.) essential oil against key postharvest pathogens. Innovative Food Science And Emerging Technologies,

(2) Hagvall, L., Bäcktorp, C., Norrby, P., Karlberg, A., & Börje, A. (2011). Experimental and theoretical investigations of the autoxidation of geranial: a dioxolane hydroperoxide identified as a skin sensitizer. Chemical Research In Toxicology, 24(9), 1507-1515.


Sara @Osmosis said...

Thank you Thank you
I've been using it in my deodorant concoction and have not had any reaction. Hope it stays that way, because I love it!

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