What we know as Tea Tree oil is the result of distilling the leaves and twigs of a tree called Melaleuca alternifolia, which is a native of the east coast of New South Wales. Australia but is nowadays successfully cultivated in many countries: South Africa, Guatemala, China, India, Vietnam...some of them produce an oil with a different chemical profile that is not considered desirable in the market, you will learn about this as the lessons progress. The best oil is, of course, grown and produced in Australia because of the care and attention they put into producing a product that the world demands without any compromise to the quality.
But, lets see.
Besides geographical diversity, most of European people don't know that Melaleuca alternifolia exists with more than one chemo-type.
The term "chemo-type" is defined as "...chemically characterized parts of a population of morphologically indistinguishable individuals..." which results for the Tea Tree in chemical distinction in a plant with differences in the composition of the oil it produces. Minor genetic changes which have no effect on morphology (the form of plant) can produce large changes in the chemical phenotype. Chemo-types are defined by the most abundant chemical produced by that individual and the concept is useful in work done by natural product chemists.
Melaleuca alternifolia has six different chemo-types in the wild each producing markedly different oil: there are three main (also known as cardinal) chemo-types which are:
- The terpinen-4-ol chemo-type which yields Tea Tree oil rich in terpinen-4-ol.
- The cineole chemo-type which yields Tea Tree oil rich in 1,8 cineole.
- The terpinolene chemo-type which yields Tea Tree oil rich in terpinolene.
The figure below shows how the composition varies between the 3 cardinal and 3 intermediate (minor) chemo-types.
A plot showing the contributions of the three biochemical groups of compounds to the monoterpene fraction of the leaf oil profile of M. alternifolia. All six chemo-types are resolved and show discontinuous distributions. The intermediate chemotypes (3, 4 and 6) are positioned between the cardinal chemo-types (1, 2 and 5), which confirms a co-dominant relationship between the genetic components involved (modified from Keszei et al.).
It is important to know that all of the early( 1924-1980) as well as all modern research into the efficacy, safety and uses of Tea Tree oil has been conducted only on the terpinen-4-ol type because it has been constantly identified as the most efficacious product with the best qualities sought by consumers.
This will be explained in more detail later in this course but we must make it clear that when we refer to Tea Tree oil, we are referring ONLY to the one with the terpinen-4-ol chemo-type: it is also worth noting that the international ISO Standard specifically refer to this in their title: "Essential oil of Melaleuca, terpinen-4-ol type ( Tea Tree oil)".
As there are several chemo-types and many countries where Melaleuca alternifolia is cultivated it is important to be able to guarantee the quality of a product once it is in the market.
This is why specific and internationally accepted Standards have been established. There are two principal standards which serve as a guide to establishing quality in this valuable oil:
- The International Standards Organization (ISO).
- The Pharmacopeia Europaea (Ph. Eur.).
The ISO Standard for Tea Tree oil is ISO 4730 which was first published in 1996 and revised in 2004. A new revision is due for release in December 2016. The ISO Standard was based on the Australian Standard AS 2782 which was first published in 1967 and revised in 1985 and 2009. The AS is identical to ISO and a revision will also be released in Dec 2016.
The Ph. Eur. Standard include Tea Tree oil for the first time in 2002. This was based on the ISO Standard revision from 2004 and has not been comprehensively reviewed and updated since then. The British Pharmacopeia (BP) Standard is identical to Ph. Eur.
It is worth noting that Tea Tree oil was first described in the BP Standard in 1949, in Martindale's Pharmacopeia in 1972 and in France in 1991.
Pure Tea Tree oil (terpinen-4-ol type) contains more than 113 components which can be identified and quantified with gas chromatographic analysis (GC). As it is not practical to base a Standard on all of its components, a carefully representative selection of components are selected by experts and these are used to identify the product in the same way that fingerprint analysis uses reference points. In Tea Tree oil 15 components and their ranges as well as some physical characteristics have been chosen either because of their importance or because they are unique to that essential oil. This section concentrates on the 15 components and is based on the latest (2016) ISO 4730 Standard.
If a sample is tested by GC and compared to the Standard the components identified must be present in the ranges given in the Standard: if this is not the case then it can't be sold or be used as 100% PURE essential Tea Tree oil. The absence of a component is just as telling as its presence in an analysis especially for the 7 minor components in which the minimum are either "traces" or less than 0,5%.
The 7 minor components in the ISO Standard 4730:2016 for Tea Tree oil are shown in the table below:
-
Component
Min % Max % Sabinene traces 3.50 1,8-Cineole traces 10.00 Aromadendrene 0.20 3.00 Ledene 0.10 3.00 δ-Cadinene 0.20 3.00 Globulol Traces 1.00 Viridiflorol traces 1.00
There are another 8 major components in the 2016 ISO Standard shown in the table below:
-
Component
Min %
Max %
α-Pinene
1.00
4.00
α-Terpinene
6.00
12.00
Limonene
0.50
1.50
р-Cymene
0.50
8.00
γ-terpinene
14.00
28.00
Terpinolene
1.50
5.00
Terpinen-4-ol
35.00
48.00
α-Terpineol
2.00
5.00
All 15 of these components must be present in the GC report in the ranges shown for it to be considered pure Tea Tree oil, terpinen-4-ol type.
It is important to known that these components have wide ranges (e.g. 13% for terpinen-4-ol) because Tea Tree oil is a natural product derived from plants and there is natural variation from plant to plant as well as from year to year so the range must take this into account.
While the presence of all 15 components in the ranges listed is important there are three of these that play a key role in Tea Tree oil:
Terpinen-4-ol: this component is the largest single component of Tea Tree oil and must have a minimum of 35% and a maximum of 48%. These percentages are selected to ensure that 1) the correct chemo-type is used when the plant is selected and 2) to ensure that adulteration (synthetic or other material added) is minimized. You can learn more about this in how_iso__as_standards_help_identify_fraudulent_tto-1. Terpinen-4-ol plays a key role in the antimicrobial activity of the oil which is why this chemo-type is selected and grown.
P-cymene: this component has been identified as a key indicator of oxidation: the higher the p-cymene level the lower the quality. You can learn more about this in stabilityofttomay2012.
1,8- cineole: While there is some controversy over the amount of 1,8 cineole in Tea Tree oil the market demands that this be at or below 4%. This is not what the ISO Standard demands but this will be explored further in depth in the next lesson.
Let's move on to the next lesson.
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