Southwell.I,Lowe.R. - TEA TREE The Genus Melaleuca.pdf - Zioła - Gabsonik

Other volumes in preparation in Medicinal and Aromatic Plants—Industrial Profiles

Ginkgo, edited by T.van Beek

Ginseng, edited by W.Court

Hypericum, edited by K.Berger Büter and B.Büter

Illicium and Pimpinella, edited by M.Miró Jodral

Kava, edited by Y.N.Singh

Licorice, edited by L.E.Craker, L.Kapoor and N.Mamedov

Piper Nigrum, edited by P.N.Ravindran

Plantago, edited by C.Andary and S.Nishibe

Salvia, edited by S.E.Kintzios

Stevia, edited by A.D.Kinghorn

Tea, edited by Y.S.Zhen

Tilia, edited by K.P.Svoboda and J.Collins

Thymus, edited by W.Letchamo, E.Stahl-Biskup and F.Saez

Trigonella, edited by G.A.Petropoulos

Urtica, edited by G.Kavalali

This book is part of a series. The publisher will accept continuation orders which may be

cancelled at any time and which provide for automatic billing and shipping of each title in

the series upon publication. Please write for details.

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INTRODUCTION

IAN SOUTHWELL

Wollongbar Agricultural Institute, Wollongbar, NSW, Australia

The Australian flora is rich in trees and shrubs from the family Myrtaceae. Eucalyptus, is

well known for profuse oil glands which contain a diverse range of constituents, of which

1,8-cineole is the most abundant and most commercially utilized (Doran 1991). The genus

Melaleuca also contains hundreds of individual species with a myriad of oil constituents

present in the leaf (Brophy and Doran 1996). Both genera extend beyond Australia to

neighbouring regions of SE Asia and the Pacific. Eucalyptus is now grown extensively in

many parts of the world. Consequently Australia produces only about five percent of the

world’s eucalyptus oil. Although Melaleuca has not yet been as extensively dispersed,

plantings of M. alternifolia have been established in the United States, Zimbabwe, New

Zealand, China, India and other countries. Provenances of M. quinquenervia, a species

native to Australia, New Caledonia and Papua New Guinea, have been grown in Madagascar

(Ramanoelina et al. 1992, 1994) and, along with the New Caledonian provenance, have

been used as a source of niaouli oil. M. cajuputi, native to Australia, Indonesia, Papua New

Guinea, Malaysia, Thailand, Cambodia and Vietnam, along with some provenances of M.

quinquenervia have sometimes been described as M. leucadendron (Todorova and Ognyanov

1988; Motl et al. 1990). In addition, M. quinquenervia is grown elsewhere as an ornamental

species and for swamp reclamation and erosion control. In Florida this species has colonized

vast areas to the detriment of the environmentally important Everglades (Weiss 1997) but in

Hawaii, plantings of an estimated two million trees have not produced a weed problem

(Geary 1988).

Although some other uses are found for Melaleuca, this aromatic and medicinal plant

genus is best known for the production of medicinal essential oils. Non-medicinal uses

(Boland et al. 1984; Wrigley and Fagg 1993) include broom fence manufacture from the

branches, bark paintings, sealing and insulation from their many coloured barks, fuel and

construction materials from the wood and honey from the nectar.

Oil production figures indicate increasing M. alternifolia (tea tree) and M. cajuputi

(cajuput) volumes with steady but smaller outputs of M. quinquenervia (niaouli) oil.

Production estimates are shown in the Table 1 . The space allocated to each of these species

in this volume reflects their industrial significance.

The name tea tree arose when Captain James Cook, on his exploratory voyage of Australia

in 1770, encountered a myrtaceous shrub (possibly a Leptospermum ) with leaves that were

used by his sailors as a substitute for tea (Camellia sinensis). The naturalist, Sir Joseph

Banks, collected specimens of tea tree during this voyage. Subsequently these myrtaceous

shrubs, now known as the genera Leptospermum, Melaleuca., Kunzea and Baeckea, were

collectively known as “tea trees”, not to be confused with the Maori or Samoan derived “ti-

tree” or “ti-palm” names given to plants of the Cordyline genus (Weiss 1997).

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IAN SOUTHWELL

Table 1 Estimated production (tonnes per annum) for Melaleuca oils

a Industry estimate; b Guenther (1950); c Lawrence (1985).

Banks, on his 1770 voyage with Cook, also collected specimens from taller

broadleaved tea trees. The long standing tendency to treat these large leaved species

collectively as M. leucadendron was in many ways overcome when Blake (1968)

distinguished M. leucadendron, M. cajuputi, M. quinquenervia and M. viridiflora. The

first of these is now known as M. leucadendra. Both M. cajuputi and M. quinquenervia

have been distilled since last century for the production of cajuput and niaouli oils

respectively (Penfold and Morrison 1950). Both oils were used in medicinal preparations,

especially for the treatment of internal disorders, stomach and intestinal problems

including worms, and for the relief of headache, toothache, laryngitis and bronchitis.

The oils also have reputed insecticidal properties. The leaves of these plants have been

reported to have been used by the Australian aborigines for colds, influenza, fever and

congestion, by inhaling the vapour from crushed leaves in boiling water or by sipping

the infused water (Aboriginal Communities 1988).

The aboriginal use of the smaller leaved tea trees like M. alternifolia is not as easy to

confirm although it is possible that the leaves were tied as a poultice to a wound. The

resurgence of the tea tree oil industry in the 1980s has prompted statements such as

“the aborigines are sure to have used the species” which have then been repeated as

“the aborigines used the plant” and then as “when Captain Cook came to Australia he

found that tea tree oil was already in use”. With the last statement obviously erroneous

because of the absence of distillation facilities, one tends to even question the validity

of the earlier quotes. Confirmation of the aboriginal use of medicinal plants some 200

years ago is difficult in a culture where such remedies are preserved by oral and not

written tradition.

Throughout this volume, the term “tea tree oil” will be reserved for “Oil of Melaleuca —

Terpinen-4-ol Type” derived from M. alternifolia, M. linariifolia, M. dissitiflora and other

species of Melaleuca, giving comparable oils conforming to the ISO Standard

(International Standards Organisation 1996). The broad leaved tea tree oils, normally

known by their specific names of cajuput or niaouli when derived from M. cajuputi and

M. quinquenervia respectively are named as such in this volume. Non-cineole chemical

varieties of these two species will be clearly identified as being atypical of the usual

commercial varieties.

part of The Gordon and Breach Publishing Group.

INTRODUCTION

The “tea tree” oil industry based around the distillation of M. alternifolia and associated

species is at an exciting stage of development as this volume goes to print. The last ten years

have seen a ten-fold increase in production to around 300 tonnes per annum, coming from

in excess of three thousand hectares of plantations ( Plate 1 ) and natural stands. During this

time, plantation production has increased from a seemingly insignificant contribution with

respect to bush oil production, to being the predominant source of oil.

With this development have come the problems associated with a new monoculture crop.

Right from the plantation planning stage, matters like financial costing, soil suitability, site

requirements, land preparation, choice of genetic material, propagation method, nursery

establishment, transplanting, plant density and plant configuration are issues that need

addressing (Colton and Murtagh 1990). Weed and insect control, fertiliser application,

irrigation, harvest machinery, season and height of harvest all require prior planning.

Appropriate processing equipment and operating procedures must all be in place before the

first harvest and quality control methods established before market outlets can be located

and maintained. For the continuing bush industry, the operation begins with hand harvesting

of private or licensed forest lands and continues with the processing, quality assessment,

value adding and marketing aspects of the industry.

Production of tea tree oil is but one of the many areas covered by this volume. For

example, confusing aspects of the taxonomy of the commercial Melaleucas are clarified by

the botanist undertaking a complete taxonomic revision of the genus. The increasing

commercial value of the industry has initiated similar in-depth studies in all other areas of

Melaleuca oil production.

The chemistry of the oil has been thoroughly investigated by several researchers, some

of whom have discovered in situ leaf precursors which transform during distillation to the

commercial oil constituents (Southwell and Stiff 1989). Other investigators have used 13 C

nuclear magnetic resonance (NMR), chiral gas chromatography (GC) and 18 O incorporation

to add to our knowledge of the chemistry of the oil and its in vivo and in vitro formation

(Leach et al. 1993; Cornwell et al. 1995).

With leaf and oil yields of utmost importance for producer profit, much research has

gone into factors that effect biomass and oil yields. Parameters such as oil gland anatomy

and density, nutrients, temperature, irrigation, time of harvest, post-harvest drying, wind

breaks and others have been studied (Murtagh and Etherington 1990; Murtagh 1991; List et

al. 1995; Murtagh 1996; Murtagh and Smith 1996; Whish and Williams 1996).

Weeds and insects flourish in the warm regions where tea tree thrives. Both chemical

and non-chemical means of weed control have been assessed and recommendations made

available to producers (Virtue 1997; Storrie et al. 1997). Similarly, insect and pathogen

attacks on tea tree have been documented, pest species listed and control procedures

recommended (Campbell and Maddox 1997). Pesticides have been recommended and residue

carry over into the distilled oil has been monitored. The fate of the volatile oil in some

insect species has been studied by examining frass volatiles and reasons for the metabolism

of cineole advanced (Southwell et al. 1995).

Harvesting tea tree from natural stands leaves one exposed to the genetic and chemical

variation that occurs in nature. Plantation establishment provides an opportunity to eliminate

this variation by the selection of genetically improved planting stock. Although propagation

by tissue culture and cuttings have been investigated, the quantities of seedlings required

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IAN SOUTHWELL

have, for economic reasons, meant that most plantations have been established from seed.

The establishment of seed orchards to facilitate cross pollination of selected genotypes is

important for producing high quality and high oil yielding strains. Investigations selecting

for these superior trees, although long term projects, are beginning to show yield gains

(Doran et al. 1997).

Steam distillation is the preferred method for processing tea tree leaf for oil production.

The cost of alternate processes like supercritical fluid extraction or the application of

microwave extraction methods is prohibitive for such a high volume—low value product.

Based on eucalyptus distillation technology (Davis and House 1991), tea tree is distilled

either by hydro or steam distillation in plants ranging from state-of-the-art gas or oil fired

boilers, stainless steel bins and tubular horizontal condensers, to the more primitive

hydrodistillation bins with “coiled-pipe-in-the-water-tank” type condensers.

Tea tree oil gained early popularity because of strong antimicrobial activity measured in

the 1920s. It has been established that this activity is caused chiefly by terpinen-4-ol, the

major component in tea tree oil (Southwell et al. 1993). Early uses however included flavoring

applications where it was added to citrus oil to enhance the terpinen-4-ol content. Antimicrobial

zones of inhibition (ZOI) and minimum inhibitory concentration (MIC) values have been

recorded for the oil and numerous oil constituents against many bacteria, fungi and plant

pathogens (Carson and Riley 1995; Southwell et al. 1997b; Bishop 1995; Bishop and Thornton

1997). Clinical trials have determined the activity in vivo for conditions such as acne, tinea

and vaginitis (Bassett et al. 1990; Tong et al. 1992; Bélaiche 1985) and confirmed the non-

irritant nature of the oil when applied topically at less than 25% concentration (Southwell et

al. 1997a). Investigations such as these have led to improved in vivo and in vitro testing

methods for tea tree oil (Carson and Riley 1995; Mann and Markham 1998) including cell-

line testing of cytotoxicity as an alternative to animal testing (Hayes et al. 1997).

Entrepreneurs have capitalised on this bioactivity by either selling the oil neat or

formulating it into a myriad of value added products where it acts as a simple preservative,

antiseptic or antibacterial soothing agent or as an active ingredient in medicinal products.

Such products include antiseptic creams, soaps, mouthwashes, toothpastes, bath oils, body

lotions, lip balms, acne creams and washes, tinea creams and vaginitis creams and douches.

Legislation governs how, where and in what concentration tea tree oil can be used, what

claims can be made about its activity and how bottles must be sealed, stored and labelled.

Use in medicinal products is legislated in Australia, for example by the Therapeutic Goods

Administration (TGA) which either “lists” or “registers” such therapeutic goods depending

on the testing that the product and ingredients have undergone. The TGA then controls the

claims that can then be made about the product. Basic toxicological and efficacy investigations

have established the safety and effectiveness of use by accumulating toxicological data and

measuring both in vitro and in vivo activity (Altman 1991; Tisserand and Balacs 1995).

Data on LD 50 values, dermal toxicity, dermal irritation, mutagenicity etc. have been acquired

from animal testing and on skin irritation and allergy response from human panellists.

Although not a skin irritant, especially in formulations containing less than 25% of the oil,

a very small number of people react with allergy to the application of tea tree oil and tea tree

oil products (Southwell et al. 1997a). Investigations are determining which tea tree oil

constituents are the most allergenic and suggestions for their possible removal are being

made.

part of The Gordon and Breach Publishing Group.

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