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Tea Tree (Melaleuca alternifolia and M. linariifolia) Oil
By Ezra Bejar,
PhD*
American
Botanical Council, PO Box 144345, Austin, TX
78714
*Corresponding author: email
Keywords: adulteration, Melaleuca
alternifolia, Melaleuca
dissitiflora, Melaleuca linariifolia,
tea tree oil, tea tree leaf oil, Melaleuca oil, essential oil of Melaleuca,
terpinen-4-ol
Goal: The goal of this bulletin is to
provide timely information and/or updates on issues of adulteration and mislabeling
of tea tree oil (TTO), in particular with Eucalyptus
oils, as well as essential oils of
other Melaleuca species not declared
in the Australian (AS 2782) and International Organization
for Standardization (ISO) 4730 norms, and those species of the closely related
genus Leptospermum.1-4
This bulletin may serve as guidance for quality control personnel, the international
herbal products industry, and the extended natural products community in
general. It is also intended to present a summary of the scientific data and
methods on the occurrence of species substitution, adulteration, the market
situation, and economic and safety consequences for the consumer and the
industry.
Scope: The ISO standards allow two species,
Melaleuca alternifolia and M. linariifolia, to be used for the
production of tea tree oil, while other standards, e.g., the monograph in the
European Pharmacopoeia, include M.
dissitiflora and other species of Melaleuca
as sources of TTO as well. Since the available data on adulteration have
been based mainly on comparison of commercial TTO with ISO standards, and M. dissitiflora oil is generally not
available in commerce, the scope of this Bulletin is limited to adulteration of
products labeled to contain the essential oil of Melaleuca alternifolia or M.
linariifolia. Since M. dissitiflora
is an acceptable species following the European Pharmacopoeia standards, the
sale of essential oils from this species as TTO should not be considered as
adulteration.
1 General
Information
1.1 Common name: Tea tree,5-7
tea tree leaf oil,8 melaleuca oil, Australian
tea tree oil9
1.2 Other common names
English:
Melaleuca
alternifolia: tea tree,5,7 paperbark tree, narrow-leaved
paperbark10-12
Melaleuca linariifolia: flax-leaved paperbark tree,
snow-in-summer12
Aboriginal Australian:
Melaleuca
alternifolia: Kimulli, Buhlam (Bundjalung
people) (Tony Larkman [Australian
Tea Tree Industry Association, Ltd (ATTIA)] oral communication to Ezra
Bejar, January 2, 2017).
Melaleuca linariifolia: Budjur12
Chinese: common name: 茶树精油 (Australian tea tree oil: 澳洲 茶树精油)
Danish: Tetræ,13 Australsk tea tree, Australsk
te-træ
Dutch: Theeboom13
French: Mélaleuca (arbre à thé),13 mélaleuque, tea tree, théier Australien4,14
German: Teebaum,13 Australischer Teebaum
Italian: Melaleuca,13 tea tree, albero del
tè
Maori: Ti Tree5,10
Norwegian: Tea tree
Spanish: Árbol de té,14 Melaleuca alternifolia13
Swedish:
Teoljebuske, teträd
International
Nomenclature of Cosmetic Ingredients (INCI): Melaleuca alternifolia (tea tree) oil15
China
INCI: 互生叶白千层 (Melaleuca alternifolia) 叶油15
1.3 Accepted Latin binomial for both
species:16,17
Melaleuca alternifolia (Maiden & Betche) Cheel
Melaleuca linariifolia Sm.
1.4 Synonyms for both species:
Melaleuca alternifolia: Melaleuca linariifolia var. alternifolia Maiden &
Betche.
Melaleuca linariifolia: Melaleuca
hyssopifolia (Cav.) Dum.Cours, Myrtoleucodendron
linariifolium (Sm.) Kuntze, and Ozandra
hyssopifolia (Cav.) Raf.18
1.5 Botanical family: Myrtaceae
1.6 Distribution: Melaleuca
alternifolia and
M. linariifolia are both native Australian species endemic to the East
coastal littoral of continental Australia from Maryborough, Queensland in the north
to Port Macquarie, New South Wales in the south and west to the Great Dividing
Range. The native habitat of M.
alternifolia is low-lying, swampy, subtropical, coastal ground.10-12 Melaleuca linariifolia has a more limited distribution range, being
endemic to the Australian states of Queensland and New South Wales. It grows in
heath and dry sclerophyll forest in moist or swampy ground; on the East coast,
Central and Southern Australia, and adjacent ranges.12
Melaleuca alternifolia has been
introduced and cultivated in Brazil, China, Indonesia, Kenya, Madagascar, Malaysia,
South Africa, Tanzania, Thailand, United States, and Zimbabwe.11,19 (Tony Larkman [ATTIA]
oral communication to Ezra Bejar, January 2, 2017)
The distribution of cultivars of M. alternifolia growing outside of
Australia is not easily determined. In China, Melaleuca species were first introduced about 100 years ago, along
with Eucalyptus. In 2004, TTO
production in the Guangxi Zhuang Autonomous Region in the South of China was 60–80
tons/year. Of these, 40–50 tons were good quality oil (defined by the authors as
40–50% terpinen-4-ol and <3% eucalyptol [1,8-cineole]) coming from forestry
plantations of selected planting stock, according to the Guangxi Forestry Research
Institute (GFRI).20
South Africa is a
significant producer of tea tree oil. Relatively small cultivations on the
African continent are in Madagascar, Kenya, Tanzania, and Zimbabwe. In Kenya, tea tree is grown by local farmers around
the small town of Naro Moro on the slopes of Mount Kenya. According to a
commercial website there are as many as four million planted trees for tea tree
oil production.21
1.7 Plant part and raw material form: Leaves
and terminal branchlets. The essential oil is obtained by steam distillation.
Melaleuca alternifolia has six different chemotypes,
with three considered the main (also known as cardinal) chemotypes:22,23
- The terpinen-4-ol chemotype which yields tea
tree oil rich in terpinen-4-ol.
- The cineol chemotype which yields tea tree oil
rich in 1,8-cineole.
- The terpinolene chemotype, which yields tea tree
oil rich in terpinolene.
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 consistently identified as
the most effective antimicrobial product with the best therapeutic qualities
sought by consumers in the treatment of acne, dental applications, and as an
aid in oral and foot infections, to name a few.24,25
While M. linariifolia is named as a source botanical
in monographs and the Australian and International Standards Organization (ISO)
norms, plantations in Australia predominantly use M. alternifolia for essential oil production, since it is easier to
grow, more abundant, and has been the subject of the most intense selective
breeding to improve essential oil yields.26
1.8 General use(s): Melaleuca
alternifolia has a long history of traditional medical use in Australia as a
topical antiseptic, antibacterial, antifungal, anti-inflammatory, and antiviral
agent.25,27
Melaleuca linariifolia traditional use information is more sparse;
however, the chemical composition of its essential oil is considered similar to
that of M. alternifolia.28 The primary indications for
TTO include minor cuts, minor burns, abrasions, pimples, athlete’s foot, insect
bites, stings and nasal and chest congestion.13,14,29
The oil is used to treat fungal infections, in particular, candidiasis and
dermatophytosis, and it is available worldwide both as neat oil and as an
active component in an array of commercial products in Australia, and many other
parts of the world.
Some specific medical uses
identified in Australian product registrations include the following: temporary
relief of cough due to bronchial irritation or bronchitis, relief of the
symptoms of catarrh, colds, cold sores, influenza/flu, sinusitis, and tinea by
topical application. Tea tree oil is also used as an aid in the maintenance or improvement
of general well-being, relief of the symptoms of allergies, in aromatherapy and
massage, and as a first-aid treatment of minor burns.30-32
The European Medicines Agency’s community herbal monograph specifies the
following indications; small superficial wounds and insect bites, small boils (furuncles
and mild acne), the relief of itching and irritation in cases of mild athlete´s
foot, and symptomatic treatment of minor inflammation of the oral mucosa. Commercial
products include gels, creams, lotions, shampoo, foot care products, soaps,
toothpastes, insect repellents, and air fresheners.25,30-33
1.9 Nomenclature considerations: The name tea tree causes much confusion. The most frequent confusion is with
the renowned tea plant (Camellia sinensis,
Theaceae), but also with other members of the Myrtaceae family growing in
Australia. Tea tree is confused with a
number of species of the genus Melaleuca,
species of the closely related genus Leptospermum,
as well as species of the genera Kunzea
and Baeckea growing in Australia and
New Zealand.7 The reason for this confusion
is that the vernacular name ‘‘tea trees’’ is referred collectively to a group
of plants which are also known as ‘‘paperbark trees’’ and both terms are still used
to refer to any member of the Melaleuca
or Leptospermum genera, of which
there are several hundred. For instance, common names for M. cajuputi include ‘‘swamp tea tree’’ and ‘‘paperbark tea tree’’,
while those for M. quinquenervia
include ‘‘broad-leaved tea tree’’ and ‘‘broad-leaved paperbark”.33-35
In Australia, many
Leptospermum species are cultivated domestically and these are often mistaken as a
source of tea tree oil. In addition, the essential oils derived from the New
Zealand plants Kunzea ericoides and Leptospermum scoparium, and known
commonly as kanuka and manuka oils, respectively, are often referred to as New
Zealand tea tree oils (also known as ti tree oils), although they have a
different chemical composition.36
2 Market
2.1 Importance in the trade: The use of
tea tree oil as an ingredient in commercial products is quite extensive. Global production rose from 200 metric tons (MT) in 1995 to
540-580 MT in 2012.33,37 In 2013, Brophy et al. estimated that world trade of
TTO was in excess of 36 million Australian dollars (AUD); with Australia being
the largest producer and exporter.23 In Australia, there were 3,000 hectares (ha) of M. alternifolia trees planted for the
production of essential oil, which produced a reported 450–500 MT of essential
oil in 2013.23
Table 1. TTO Production and Sales Survey in Australia
Yeara
|
2012 / 2013
|
2013 / 2014
|
2014 / 2015
|
2015 / 2016
|
2016 / 2017
|
Production (MT)
|
407
|
551
|
667
|
845
|
714
|
Available Supply
(MT)
|
553
|
555
|
680
|
848
|
726
|
Sales (Implied)
Demand (MT)
|
549
|
542
|
677
|
836
|
711
|
Demand change (%)b
|
33.4%
|
-1.3%
|
25.0%
|
23.4%
|
-14.9%
|
Closing Stockc
(MT)
|
4
|
13
|
3
|
12.5
|
15
|
Average Price/kg (AUD)
|
$30.33
|
$37.17
|
$43.02
|
$45.02
|
N/A
|
ABSd Export
(MT)
|
N/A
|
443
|
582
|
620
|
584
|
a The reporting period is
from April 1 to March 31, except for 2012/2013 (January 1 to March 31)
Data provided by Australian Tea Tree
Oil Association (ATTIA). All figures are given in metric tons (MT), except for Average
Price, given in Australian dollars, and the demand change. The implied sales
demand figures are derived by subtracting the closing stock amounts from the
available supply figure. The 2016/17 projected production figures are the
expected harvest figures as declared by growers to ATTIA.
b Compared to prior year
c Amount of inventory at the end of the reporting period
d Australian Bureau of Statistics
In 2015, ATTIA reported over 800 MT of TTO being produced.26,27 However, the total area planted and the total production worldwide is
potentially twice as much from plantings in several countries outside Australia,
including China.23
2.2 Supply sources:
As mentioned above, Australia is the country with the largest production
of TTO with around 800 MT produced annually. The year 2015 was a record at 845 MT,
but just exceeded 700 MT in 2016 due to adverse conditions (drought). Melaleuca
linariifolia is grown on only one plantation in Australia (approx. 3,500 plants)
with limited annual production.26
Chinese TTO production figures
are not easy to obtain, but ATTIA estimates that the country produces about 200
MT annually, derived from M. alternifolia (usually essential oil with a high
1,8-cineole content). (Tony
Larkman [ATTIA] oral communication to Ezra Bejar, December 4, 2016)
Other
TTO-producing countries are Kenya (~20 MT), Zimbabwe (~20 MT) and South Africa (unknown,
but estimated at 35 MT), which all provide essential oil that complies with ISO
standards. There are a few minor plantations in the United States (California),
New Zealand, Thailand, and Malaysia, but no data are available on any of these.
(Tony Larkman [ATTIA] oral
communication to Ezra Bejar, December 4, 2016)
2.3 Market dynamics: In Australia, over the past eight years, farm gate prices of
pure TTO from M. alternifolia have fluctuated
in the range of AUD $29.00 to AUD
$49.00 per kg, depending on the supply
and demand dynamics. Prices increased from $29 to a peak price in 2008 of AUD $49.00. After that year prices declined steadily to a low of
AUD $30.33 in 2012. In the last four years, the material has regained value (Table
1). The current estimated farm gate price for TTO is in the range of AUD $40.00-AUD $43.00
per kg, excluding packaging.11,26
The
Australian Bureau of Statistics (ABS) reported Australian TTO exports in 2016 having
a total value of AUD $25,203,914 for all regions in the world. In the first
trimester of 2016, total exports were $7,087,020, with a 62.5% share (based on dollar
value) going to North America. Europe had the second largest share (25.2%), followed
by Asia (10.7%), then Africa and the Middle East (1.6%), and South America with
no data in the first trimester.38
The price range outside Australia for materials labeled as
tea tree oil has been as low as US $20.00 per kg, which provides an economic incentive
to manufacturers for using those materials. Recent sales information from
China, as well as the other TTO producing countries, is unavailable.
3 Adulteration
3.1 Known adulterants:
Adulteration is known to be a significant problem in the essential oil industry,
driven by optimization of profits by using lower-cost synthetic material, added
to natural essential oils.39 The most common adulterants
found in the marketplace are low-cost versions of essential oils, containing
similar terpene (volatile) compounds, made, for example, with synthetic
material or essential oil components from natural sources. Another problem is
the addition of vegetable oils.39-42
In the case of TTO, adulteration involves spiking with
other essential oils or pure compounds of natural or synthetic origin.43 Added materials may include
byproducts of the eucalyptus (Eucalyptus
globulus and others species of Eucalyptus
[Myrtaceae family]) oil industry, pine (Pinus
spp, Pinaceae) oil or white camphor (Cinnamomum
camphora, Lauraceae) oil, which are frequently found in the chromatographic
analysis of so-called TTO.34,43
Eucalyptus essential oil is extracted by steam distillation of the leaves of
several Eucalyptus species cultivated
worldwide. China produces about 90% of the world trade of the medicinal cineol-rich
eucalyptus oil. However, the presence of borneol and camphene in the
chromatographic analysis of TTO samples coming from China, as tested by ATTIA,
cannot be solely explained by adulteration with eucalyptus oil and/or its
constituents. These compounds are not present in TTO or eucalyptus oil.7,44-47
Less frequently other Myrtaceae species are used as
sources for adulteration. This may include species of the genus Melaleuca not included in the ISO TTO
standards norm, as well as species of a closely related genus, Leptospermum, growing in Australia and
New Zealand. Other suggested adulterants of TTO include tea tree species known
as cajuput (Melaleuca cajuputi Powell), niaouli (Melaleuca viridiflora
Sol. ex Gaertn.), manuka (Leptospermum scoparium), or kanuka (Kunzea
ericoides (A.Rich.) Joy Thomps.) oils.34,35
However, adulteration with cajuput, niaouli, manuka, or kanuka oils does not
appear to make economic sense. The oils of these species are relatively expensive
and thus there would be minimal financial gain in using them.
ATTIA estimates that China
exports up to 1,200 MT of products labeled as tea tree oil annually, and while
reliable data are scarce, it estimates that China may be producing only up to a
maximum of 200 MT per year from M. alternifolia. This indicates that up to 1,000 MT of adulterant may be used to
extend the small (~200 MT) output of genuine material, resulting in a supply of
material that is of highly variable quality and composition.
3.2 Sources of information supporting confirmation of adulteration:
The earliest references to alleged adulteration of TTO were obtained indirectly,
in the form of adverse event reports or internal emails and faxes with
complaints to ATTIA from 1990-2000.48
In 2013, a publication suggested
that compounded and uncertified TTO coming mainly from China had been flooding
the markets, causing problems to consumers and cosmetic manufacturers. The
report indicated compounded TTO, containing the 15 main compounds, was either
blended with genuine TTO and resold as Australian TTO or re-exported as is to
suppliers in Europe and the United States.49
In 2015, Australian
researchers found consistent enantiomeric ratios for 57 samples of authentic
100% pure Australian TTOs they analyzed. The averages were: 68.5 ± 0.2% (+): 31.5
± 0.2% (–) for terpinen-4-ol and 74.2 ± 1.4% (+): 25.8 ± 1.4% (–) for α-terpineol
in oils sourced directly from different plantation sites throughout Australia. In
contrast, considerable ratio variations were observed for 43 commercial TTOs
sampled from North
America, the European Union, Asia, Australasia, and South Africa. About
50% of the samples had between 26-62% of (+)-terpinen-4-ol, differing markedly from
the 68-70% value found for Australian TTO. The TTOs sourced internationally were
from companies that mix Australian with Chinese and other foreign TTO sources,
as well as adulterating substances.50 A concern that pure Australian
TTO was being intentionally adulterated, extended (diluted), or otherwise
modified with undisclosed lower-cost ingredients was tested using
enantioselective multidimensional gas chromatography (eGC).51 Results suggested pure TTO from
Australia was free of adulteration; however, commercial samples from different
continents, all labeled as M.
alternifolia oil, showed a large variation which indicated the possibility
of adulteration.51
Occurrence of adulteration
was confirmed by Wang et al., 2015,47 using the same 100 TTO samples
(57 samples from Australian tea tree plantations & 43 commercial TTO
samples) as Wong et al.51 In addition, Wang et al.
reported that samples that were ISO4730:2004-compliant when distilled did not
meet the ISO standards when tested using conventional GC-MS analysis because of
excessive p-cymene and/or reduced α–terpinene, γ-terpinene, and terpinolene
concentrations. Autoxidation was thought to be responsible for most of the
observed deviations. Forty-nine percent of the commercial products did not meet
the ISO specifications. There was a substantial subset of commercial products
that met ISO4730: 2004 standards, but displayed unusual enantiomeric +/−
ratios.47
Evidence for the sale of
adulterated TTO is also provided by a recent investigation by the Australia’s Competition
and Consumer Commission (ACCC). The Commission eventually fined Felton Grimwade
& Bosisto’s Pty Ltd AUS $10,800 after chemical analysis showed that the
company’s tea tree oil was adulterated. The identity of the adulterant was not
detailed in the infringement notice.52
Finally, an analysis of 25
tea tree oil samples from markets in Australia, the United Kingdom, North
America, and South Africa by GC-MS and determination of (+)- and (-)-terpinen-4-ol
ratios found evidence for adulteration in eight samples (32%).43
3.3 Accidental or intentional adulteration: According to ATTIA,
adulteration was both partial (by mixing adulterating materials with TTO) and
complete (by substituting the TTO in its entirety with materials of lower
quality) in the early days of the TTO industry. Since the start of ATTIA’s
campaign about the Australian and ISO standards and the use of chiral analysis,
the nature of adulteration has changed and has become more sophisticated with
more care taken to hide the irregularities. The only conclusion that can be
made from this is that TTO adulteration is definitely intentional.43,48
3.4 Frequency of occurrence: The frequency of adulteration appears
to depend on the geographic origin of the material. ATTIA tested TTO samples
from Australian and Zimbabwe plantations, as well as commercial samples from Australia,
Canada, China, Germany, Indonesia, Italy, Korea, New Zealand, Spain, United Kingdom,
United States, and Zimbabwe. None of the Australian plantation samples were
adulterated showing a distinctive profile in Chiral Analysis. Most commercial
samples from New Zealand (2/2), Australia (13/20), and US (23/36) met the TTO
specifications, while all (10/10) commercial samples from China were considered
adulterated. Adulteration rates in European commercial samples were 7/20 (United
Kingdom), and 4/11 (Spain). (Tony Larkman [ATTIA]
oral communication to Ezra Bejar, January 2, 2017)
Wohlmuth et al. found
that one third (2/6) and two thirds (4/6), respectively, of Australian and
South African samples were adulterated. Of the four samples from the United Kingdom,
one was considered definitely adulterated and two others possibly adulterated.
One of the five samples (20%) analyzed from North America was not authentic
TTO.43
Considering all the
results together, the adulteration of TTO appears to be rather common.
3.5 Possible safety/therapeutic issues: The prevalence of contact
allergy to tea tree oil is rare, ranging from only 0.3–2.7%.53 It has been suggested that the
positive in vitro tests to TTO are either
caused by oxidized ingredients or due to the presence of an adulterant.9,35,54
Also, allergic reactions to TTO appear to occur only in predisposed individuals
and may be due to individual sensitivity, or to various oxidation products,
including peroxides, which are formed by exposure of the oil to light and/or
air.53
Methyl
eugenol, a compound that is of certain toxicological concern due to its
structural similarity to estragole and safrole (which have shown carcinogenic
effects in rodents), has been reported to occur at higher levels in M. dissitiflora than M. alternifolia. The higher methyl
eugenol concentration has been cited as one of the reasons why M. dissitiflora was eliminated as a
source material for TTO in the 2017 ISO standard.55
3.6 Analytical methods to detect
adulteration: Since the essential oil is the ingredient of commerce, microscopic
and macroscopic methods of analysis for authentication are not useful beyond
the distillation factories, and are not applicable for the identification of TTO.4,8,56
Pharmacopeial and normative methods focus on ingredient testing after steam
distillation and include organoleptic evaluation, density, refractive index,
optical rotation, thin-layer chromatography (TLC), conventional gas-chromatography
(GC), GC-mass spectrometry (MS), chiral GC-MS analysis, and subsequent chemometric
analyses.4,8,47,50,56
However, these methodologies may not be sufficient to detect all adulterations.
The European and British pharmacopeias also use a GC method for
authentication with flame-ionization as the detector system. The authentication
is based on relative percentage of 11 individual terpenes in the TTO.8,56
Many GC methods have been developed since the 1980s, including the use of
chiral columns. These methods provide a clear profile of the chemical
composition, and chemical variation of TTO, and established quality control procedures
to identify adulterants. Mass spectrometry has now become the standard
detection system for gas chromatographic separations.17,22,44,57-63
Determination of enantiomeric ratios of terpinen-4-ol, and α-terpineol using
lanthanide shift reagents has also been achieved by nuclear magnetic resonance
(NMR), but the successful application to TTO authentication has yet to be
shown.44
The GC-MS methods using chiral columns, allowing the separation of
enantiomers and the determination of enantiomeric ratios, has provided clear
criteria to identify adulterants in TTO.27,43,47,51
However, Davies et al. evaluated enantiomeric ratio test results obtained for a
set of 57 samples analyzed by GC-MS in three laboratories and concluded that the
complete resolution of the terpinen-4-ol enantiomers was not always achieved,
leading to a variability in average terpinen-4-ol enantiomer ratios (63.3-69.8/30.2-36.7
(+)/(-)-terpinen-4-ol) among the laboratories. The authors suggested that
absolute ratios for terpinen-4-ol enantiomers may not be an appropriate way to
determine TTO authenticity, but that the ratios should be set by each
analytical laboratory using a reference material with a known ratio.27
However, no such reference material is available to our knowledge.
Wong et al.51 conducted chiral analysis
of three key monoterpenes (limonene, terpinen-4-ol and α-terpineol)
present in tea tree oil by a combination of enantioselective multidimensional GC
[GC − eGC] and two-dimensional gas chromatography [eGC × GC]. Ranges of TTOs
sourced directly from plantations of known provenance in Australia were
compared with commercial TTOs from different continents. Fast chiral
separations were achieved within 25 min for GC − eGC and < 20 min for eGC ×
GC. Exact enantiomeric composition of chiral markers for authentic TTOs was achieved.
Consistent enantiomeric ratios for
limonene, terpinen-4-ol, and α-terpineol
were obtained for 57 authentic Australian TTOs. In contrast, commercial samples
from different continents showed a large variation. Specifically, samples from
the United States and the United Kingdom had much higher (+) limonene and much
lower (+)- terpinen-4-ol averages. Some of the [+]-α-terpineol values were
inconsistent; they were either too low or high, which suggested adulteration.51
A large set (n = 104) of
TTOs and commercial TTO products were analyzed with a combination of conventional
GC-MS, chiral GC-MS, and chemometric techniques. Twenty terpenoids were
determined in each sample and compared with ISO standards (ISO-4730: 2004).47
The combined results and
conclusions of these reports served as the basis for a new version of ISO 4730,
which was released in February 2017. The TTO ISO4730: 2017 standard addresses
several of the issues with the older ISO 4730: 2004 in terms of tighter
requirements for the chromatographic profile of the essential oil by gas
chromatography. The new standard establishes a minimum of 35% terpinen-4-ol,
14% γ-terpinene
and 6% α-terpinene.4 The
Australian Standard (AS2782: 2009) is also being updated to be identical to the
new ISO version (it will be AS2782: 2017).
The cited reports suggest
that both chiral and chemometric analyses are needed to confirm the authenticity
of commercial products, including those that met all of the ISO4730: 2017 standards
which can be used to assess possible adulteration.
4 Conclusions
Adulteration
of TTO with synthetic terpinen-4-ol, or
industrial waste from ‘normalizing’ eucalyptus, and other essential oils such
as pine and white camphor occurs frequently by intentional dilution of
the ingredient to reduce production costs. The lack of an effective standard
were past challenges that have been overcome with the new 2017 ISO4730 norm, which
has tighter ranges for the main 15 terpenes found in authentic TTO. The most common adulteration of TTO
with eucalyptus and pine oils is readily detected using GC and chiral enantiomeric
analysis and has been incorporated into the new ISO norm (ISO4730: 2017).
Adulteration with other Melaleuca
species such
as cajuput, niaouli, manuka, or kanuka oils rarely occurs in practice, as they
are too expensive.
5 References
- Oil of Melaleuca, terpinen-4-ol type (Tea
Tree oil) AS 2782-2009; ISO 4730:2004 Sydney,
NSW, Australia: Standards Australia; 2009.
- Oil
of Melaleuca, terpinen-4-ol type (Tea Tree oil). AS 2782-2017; ISO 4730:2017 Sydney, NSW, Australia: Standards
Australia; 2017.
- Oil
of Melaleuca, terpinen-4-ol type (tea tree oil). ISO 4730:2004. Geneva, Switzerland: International Organization for
Standardization (ISO); 2004.
- Essential
oil of Melaleuca, terpinen-4-ol type (Tea Tree oil). ISO 4730:2017. Geneva, Switzerland: International Organization for
Standardization (ISO); 2017.
- McGuffin
M, Kartesz JT, Leung AY, Tucker AO. American
Herbal Products Association's Herbs of Commerce. 2nd ed. Silver Springs,
MD: American Herbal Products Association; 2000.
- Moley
T, Foster S, Awang D, Hu SY, Kartesz JT, Tucker AO. Herbs of Commerce. 1st ed. Austin, TX: American Herbal Products
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Revision summary
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