This post on grapefruit essential oil is part of our wonderful exploration into the Science and Chemistry of Grapefruit.

Why Grapefruit?

The easy answer: cause we have (or had) a buttload of it! If you’re familiar with Palm Desert (and the surrounding area), you’ll know that there are citrus trees everywhere and just about every other person is on some sort of statin medication making grapefruit verboten.

So, we have friends (and friends of friends) that have grapefruit excess… We are happy to help!

Boxes of grapefruit

200+ lbs of grapefruit

We’re happy to help because ever since we acquired our essential oil steam distillation kit, we’ve been eager to steam distill, well, everything! In our third experiment last year, we steam distilled pink grapefruit essential oil. OMG! The smell was heavenly. And it’s absolutely true that grapefruit essential oil is very “uplifting.”

Now that we have a plethora of pink grapefruit, we want to distill more essential oil. Which led to the questions, what are we going to do with all the juice and our steam distilled grapefruit essential oil?

What’s in grapefruit essential oil?

Juicy pink grapefruit

Juicy pink grapefruit

First off, what to do with the juice is easy. We drink some, freeze some, make desserts, and turn the rest into grapefruit molasses. What to do with grapefruit essential oil is a little more complicated.

For starters, we would like to test our steam distilled grapefruit essential oil, as in a gas chromatograph-mass spectrometry (GC-MS) analysis. A GC-MS analysis identifies the substances in a particular sample. Here, grapefruit essential oil. Many factors may affect the scent and quality of an essential oil such as soil conditions, water, weather, when the material was harvested, etc, not to mention how it was distilled. This is of particular interest to us.

If you look at a GC-MS report of grapefruit, expeller-pressed or steam distilled, you’ll notice a particular compound that is off the charts—like over 90%. And that’s limonene.

Limonene

What makes grapefruit a grapefruit? It’s the smell that makes it instantly recognizable. So what’s the smell? Mostly, it’s Limonene.
Limonene is a clear, colorless liquid hydrocarbon classified as a cyclic monoterpene, and is the major component in oil of citrus fruit peels.

Here’s a picture of limonene, well, technically a skeletal formula (a.k.a. line angle formula or shorthand formula) of it:

Limonene-2D-skeletal

As mentioned in the Wikipedia definition, limonene is a monoterpene. Which means it’s a class of terpenes that has two isoprene units. Ha! If you’re like me, you have no idea what that means! But bear with me.
Terpenes and terpenoids are the primary constituents of the essential oils of many types of medicinal plants and flowers.
That’s really all we need to know. Some GC-MS reports group substances by major compounds, i.e., terpenes, esters, alcohols, aldehydes, etc. Thus, it helps to know that limonene is a terpene.
After all this talk, I’m sure you’re dying to look at some examples of grapefruit essential oil GCMS reports. Here are a few:

And if you’re looking for something more ‘hands on’, check out this chemistry experiment for isolating limonene.

What else is in grapefruit?

So, getting back to grapefruit… What we smell in grapefruit and other citrus fruits is D-limonene. (The other, less common, limonene is L-limonene found in mint oils with a pine or turpentine-like scent.) Thus, whether expeller-pressed or steam distilled, D-limonene gives grapefruit essential oil it’s familiar fragrance.

grapefruit peels for essential oil distillation

Grapefruit peels for essential oil distillation

After reading this, you must be wondering how limonene ‘complicates’ the usage of grapefruit essential oil. Well, it doesn’t really. Grapefruit’s notoriety as a contraindication to statins and being phototoxic is actually attributed to another compound. Which is hard to imagine since over 90% of the peel is limonene! But we’ll explore that in our next post… Stay tuned!