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 "titree" or "ti-palm" names given to plants of the Cordyline genus (Weiss 1997).
Table 1 Estimated production (tonnes per annum) for Melaleuca oils
M, alternifolia tea tree terpinen-4-ol Australia
Ai, cajuputi cajuput 1,8-cineole Indonesia, Vietnam
M. quinquenervia niaouli 1,8-cíneole
New Caledonia, Madagascar
20b 4e 8-12a
"Industry estimate; bGuenther (1950); cLawrence (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.
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 13C nuclear magnetic resonance (NMR), chiral gas chromatography (GC) and 18O 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 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; Belaiche 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 cellline 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 LD50 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.
Over a period of ten years, the volume of production at the farm gate has increased tenfold. This oil has, in most cases, been sold with only minor delays and a minimum of stockpiling. The price has varied somewhat to reflect the supply and demand equilibrium. Prices peaked in the late eighties when demand exceeded supply. More recently however the price has fallen and stabilised gradually to reflect increasing production. The establishment of more large-scale plantations, if successful, will increase production beyond demand and consequently decrease the international price of the oil. An increasing quantity of the oil is being sold in value-added products by the smaller producers rather than being sold in bulk to commercial formulators. Some believe that markets will have to expand in existing buyer countries, spread into new territories, and be formulated into a wider range of pharmaceutical type products, for the world market to absorb the projected increase in oil volumes.
Although traditionally longer established on world markets, cajuput and niaouli oils from the large leaved M. cajuputi and M. quinquenervia respectively (Brophy and Doran 1996) have not enjoyed the surge in market popularity associated with the M. alternifolia group. These species are still popular in their local producing regions of SE Asia and New Caledonia respectively, with the latter also growing in Madagascar. The potential exists for many other Melaleuca species to be distilled and their oils traded commercially. M. stipitata, for example, combines the antimicrobially active ingredients of the M. alternifolia group with the pleasant aromatic notes of lemon grass. Higher yielding varieties of these chemotypes would be needed for their commercial production to be viable. Other large leaved varieties have potential as sources of linalool, nerolidol and viridiflorol (M. quinquenervia), methyl cinnamate and ocimene (M. viridiflora) and lemon oil (M. citrolens). Other small leaved species could also be used as sources of eudesmol (M. uncinata), methyl eugenol and methyl isoeugenol (M. brarteata).
In this volume we attempt to review the wealth of information on the commercial and potentially commercial Melaleuca species that exists in the scientific literature, in agricultural bulletins, in government legislation and in the manuals of Melaleuca oil entrepreneurs.
Aboriginal Communities of the Northern Territory. (1988) Traditional Bush Medicines. An Aboriginal
Pharmacopoeia. Greenhouse, Richmond, Victoria, pp. 160-165. Altman, P. (1991) Assessment of the skin sensitivity and irritation potential of tea tree oil. Report for Rural Industries Research and Development Corporation. Pharmaco Pty Ltd., Sydney, Australia. Bassett, I.B., Pannowitz, D.L. and Barnetson, R.St-C. (1990) A comparative study of tea-tree oil versus benzoylperoxide in the treatment of acne. Med. J. Aust., 153, 455-458. Bélaiche, P. (1985) Traitement des infections vaginales a Candida albicans par l'huile essentielle de
Melaleuca alternifolia (Cheel). Phytotherapy, 15, 13-14. Bishop, C.D. (1995) Antiviral activity of the essential oil of Melaleuca alternifolia (Maiden & Betche)
Cheel (Tea Tree) against tobacco mosaic virus. J. Essent. Oil Res., 7, 641-644. Bishop, C.D. and Thornton, I.B. (1997) Evaluation of the antifungal activity of the essential oils of Monarda citriodora var. citriodora and Melaleuca alternifolia on post-harvest pathogens. J. Essent. Oil Res., 9, 77-82.
Blake, S.T. (1968) A revision of Melaleuca leucadendron and its allies (Myrtaceae) Contr. Queensland Herb., 1,1-114.
Boland, D.J., Brooker, M.I.H., Chippendale, G.M., Hall, N., Hyland, B.P.M, Kleinig, D.A. and Turner,
J. (1984) Forest Trees of Australia, 4th edition, Nelson, Melbourne. Brophy, J.J. and Doran, J.C. (1996) Essential Oils of Tropical Asteromyrtus, Callistemon and Melaleuca Species. ACIAR Monograph No. 40, Canberra.
Campbell, A.J. and Maddox, C.D.A. (1997) Controlling insect pests in tea tree using pyrgo beetle as the basis. RIRDC Research Paper Series, 97/62, Rural Industries Research and Development Corporation, Canberra.
Carson, C.F. and Riley, T.V. (1995) Antimicrobial activity of the major components of the essential oil of Melaleuca alternifolia. J. Appl. Bact., 78, 264-269.
Colton, R.T. and Murtagh, G.J. (1990) Tea-tree oil—plantation production. Agfact P6.4.6. NSW Agriculture and Fisheries, Orange, Australia.
Cornwell, C.P., Leach, D.N. and Wyllie, S.G. (1995) Incorporation of oxygen-18 into terpinen-4-ol from the H218O steam distillates of Melaleuca alternifolia (Tea Tree). J. Essent. Oil Res., 7, 613-620.
Davis, G.R. and House, A.P.N. (1991) Still design and distillation practice. In D.J.Boland, J.J.Brophy and A.P.N.House (eds.), Eucalyptus Leaf Oils, Inkata Press, Sydney, pp. 187-194.
Doran, J.C. (1991) Commercial sources, uses, formation, and biology. In D.J.Boland, J.J.Brophy and A.P.N.House (eds.), Eucalyptus Leaf Oils, Inkata Press, Sydney.
Doran, J.C., Baker, G.R., Murtagh, G.J. and Southwell, I.A. (1997) Improving tea tree yield and quality through breeding and selection. RIRDC Research Paper Series, 97/53, Rural Industries Research and Development Corporation, Canberra.
Geary, T.F. (1988) Melaleuca quinquenervia (Cav.) S.T.Blake. In R.M.Burns and M.Mosquera (eds.), Useful Trees of Tropical North America. North American Forestry Commission Publ. No. 3, Washington DC.
Guenther, E. (1950) The Essential Oils, Van Nostrand, New York, Vol. 4, pp. 526-548.
Hayes, A.J., Leach, D.N. and Markham, J.L. (1997) In vitro cytotoxicity of Australian tea tree oil using human cell lines. J. Essent. Oil Res., 9, 575-582.
International Standards Organization (1996) Oil of Melaleuca, terpinen-4-ol type (Tea Tree Oil). International Standard ISO 4730:1996(E), International Standards Organization, Geneva.
Lawrence, B.M. (1985) A review of the world production of essential oils (1984). Perfumer and Flavorist, 10(5), 1-16.
Leach, D.N., Wyllie, S.G., Hall, J.G. and Kyratzis, I. (1993) The enantiomeric composition of the principal components of the oil of Melaleuca alternifolia. JAgric. Food Chem., 41, 1627-1632.
List, S., Brown, P.H. and Walsh, K.B. (1995) Functional anatomy of the oil glands of Melaleuca alternifolia (Myrtaceae). Austral. J. Bot., 43, 629-641.
Mann, C.M. and Markham, J.L. (1998) A new method of determining the MIC of essential oils. J. Appl. Microbiology, in press.
Motl, O., Hodacová, J. and Ubik, K. (1990) Composition of Vietnamese cajuput essential oil. Flavour and Fragrance Journal, 5, 39-42.
Murtagh, G.J. (1991) Irrigation as a management tool for production of tea tree oil. RIRDC Research Report DAN-19A. Rural Industries Research and Development Corporation, Canberra.
Murtagh, G.J, (1996) Month of harvest and yield components of tea tree. I. Biomass. Australian Journal of Agricultural Research, 47, 801-815.
Murtagh, G.J. and Etherington, R.J. (1990) Variation in oil concentration and economic return from tea tree (Melaleuca alternifolia Cheel) oil. Australian Journal of Experimental Agriculture, 30, 675-679.
Murtagh, G.J. and Smith, G.R. (1996) Month of harvest and yield components of tea tree. II Oil concentration, composition and yield. Australian Journal of Agricultural Research, 47, 817-827.
Penfold, A.R. and Morrison, F.R. (1950) Tea tree oils. In Guenther, E. (ed.), The Essential Oils, Van Nostrand Co. Inc., New York, Vol. 4, pp. 526-548.
Ramanoelina, P.A.R., Bianchini, J.P., Andriantsiferana, M., Viano, J. and Gaydou, E.M. (1992) Chemical composition of niaouli essential oils from Madagascar. J. Essent. Oil Res., 4, 657-658.
Ramanoelina, P.A.R., Viano, J., Bianchini, J.P. and Gaydou, E.M. (1994) Occurrence of variance chemotypes in niaouli (Melaleuca quinquenervia) essential oils from Madagascar using multivariate statistical analysis. J. Agric. Food Chem., 42, 1177-1182.
Southwell, I.A., Hayes, A.J., Markham, J. and Leach, D.N. (1993) The search for optimally bioactive Australian tea tree oil. Acta Horticulturae, 344, 256-265.
Southwell, I.A., Freeman, S. and Rubel, D. (1997a) Skin irritancy of tea tree oil. J. Essent. Oil Res., 9, 47-52.
Southwell, I.A., Maddox, C.D.A. and Zalucki, M.P. (1995) Metabolism of 1,8-cineole in tea tree (Melaleuca alternifolia and M.linariifolia) by pyrgo beetle (Paropsisterna tigrina). J. Chem. Ecol., 21, 439-453.
Southwell, I.A., Markham, J. and Mann, C. (1997b) Why cineole is not detrimental to tea tree oil. RIRDC Research Paper Series, 97/54, Rural Industries Research and Development Corporation, Canberra.
Southwell, I.A. and Stiff, I.A. (1989) Ontogenetical changes in monoterpenoids of Melaleuca alternifolia leaf. Phytochemistry, 28, 1047-1051. Storrie, A., Cook, T., Virtue, J., Clarke, B. and McMillan, M. (1997) Weed Management in Tea Tree.
NSW Agriculture, Orange, Australia. Tisserand, R. and Balacs, T. (1995) Essential Oil Safety—A Guide for Health Care Professionals.
Churchill Livingstone, Edinburgh, pp. 45-55, 80, 82, 150, 187, 204, 219. Todorova, M. and Ognyanov, I. (1988) Composition of Vietnamese essential oil from Melaleuca leucadendron L. Perfumer and Flavorist, 13, 17-18. Tong, M.M., Altman, P.M. and Barnetson, R.St-C. (1992) Tea tree oil in the treatment of Tinea pedis.
Australasian J. Dermatol. 33, 145-149. Virtue, J.G. (1997) Weed interference in the annual regrowth cycle of plantation tea tree (Melaleuca alternifolia). PhD Thesis. The University of Sydney. Weiss, E.A. (1997) Essential Oil Crops, CAB International, Oxford, pp. 302-319. Whish, J.P.M. and Williams, R.R. (1996) Effects of post harvest drying on the yield of tea tree oil
(Melaleuca alternifolia). J. Essent. Oil Res., 8, 47-51. Wrigley, J.W. and Fagg, M. (1993) Bottlebrushes, Paperbarks and Tea Trees and all other Plants in the Leptospermum Alliance, Angus and Robertson, Sydney.
Plate 1 Tea tree plantation in New South Wales, Australia (R.Colton)
Plate 2 Mature Melaleuca alternifolia tree in a Plate 3 Melaleuca alternifolia flower natural stand (I.Southwell) (I.H0lliday)
Plate 5 Melaleuca quinquenervia flower (B.Trilles)
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