The Unique Scent of Grapefruit
Can the human nose be a better detector of fraudulent oils than a laboratory machine?
Yes it can! and here I will present the case of grapefruit essential oil to demonstrate that fact.
While grapefruit oil is 86-92% d-limonene, that is not what you smell. d-Limonene, in any concentration, is experienced as a faint orange-like aroma. Amazing as it seems, one molecule in a billion of the sulfur compound in grapefruit is so strong that it overcomes the d-limonene and is easily picked up and distinguished by our sensitive noses. (strong odors are a characteristic of most sulfur compounds, which are also found in onions and garlic).
The major proportion of any essential oil (99.99%) is composed of only three elements – C (carbon), H (hydrogen) and O (oxygen) but sometimes sulfur and nitrogen contribute key roles. For example the distinctive fragrance of grapefruit oil (Citrus paradisi) is due to a sulfur compound, 1-p-menthen-8-thiol C10H18S) – also known as thioterpineol, it occurs in a tiny trace amount – less than one part per billion (ppb). 1 ppb is equivalent to five drops in an Olympic swimming pool.
In numeric form, that is an infinitesimal 0.0000001%
Yet its presence dominates the scent of grapefruit.
Check it out, if you have a bottle of grapefruit oil handy, take a whiff and experience a molecule or two of that sulfur compound. You can impress your friends by saying. ‘Hmmmm …..I believe there is a trace of 1-p-menthen-8-thiol in this oil’
The other citrus rind oils (bergamot, orange, lemon, tangerine, mandarin and lime) are all more than 50% d-limonene, like grapefruit, yet they each have a different fragrances and different therapeutic properties determined by their minor and trace constituents. Grapefruit, for example, has been shown to be effective against skin cancer. It can also dissolve fat tissue and has been used to assist in weight loss and reduce cellulite. Unlike the other citrus oils, grapefruit is also a topical anesthetic. Put a drop on your tongue and it will go numb. This is due to nootkatone (0.1-2%), a compound unique to grapefruit. These therapeutic properties are not due to its main ingredients, but come from its minor and trace compounds like 1-p-menthen-8-thiol and others.
Another fascinating property, unique to the aroma of grapefruit is its ability to make women appear younger than they are. In one study, when men were asked to estimate the ages of women wearing grapefruit scented perfume, they underestimated by an average of six years. So ladies, add six years of youth to your life by simple applying grapefruit oil. Now be careful. Grapefruit oil is phototoxic. So don’t apply it to your skin and expose yourself to sun or ultraviolet light.
Grapefruit is an illustration of why an essential oil needs to be harvested and produced as close to nature as possible without tampering with even the least of the ingredients.
Sulfur Makes Its Presence Known
Sulfur compounds probably occur in most essential oils but usually in concentrations of only one part per million (ppm) to less than one part per billion (ppb). Such low concentrations are beyond what can be detected by gas chromatography – which is the customary means of analyzing essential oils in a laboratory Hence, in trying to determine if an oil is natural or synthetic, the usual laboratory procedures may not be able to tell. If all of the major compounds are present in the synthetic version, the absence of all of the trace compounds can go undetected. Nevertheless, when present even in small quantities, sulfur compounds almost always noticeably affect the fragrance of an oil. In many cases, a little sulfur plays the distinguishing role, as in the case of grapefruit just discussed.
This is why the human nose can be a better detector of fraudulent oils than a laboratory machine.
Reference : The Chemistry of Essential Oils Made Easy by David Stewart PhD.