Substituting for Rosewood Oil Aniba rosaeodora var. amazonica Ducke – a look at other high linalol containing oils.

  Copyright Tony Burfield MIBiol CIBiol ABP MIFST FLC and Sylla Sheppard-Hanger June 2003.

[Adapted and modified from an article  for Aromatherapy Today Vol 26, June 2003 pp30-37, and reproduced by kind permission of the editor, John Kerr].

  Introduction

The demise of the natural Rosewood populations (from Aniba spp. Aublet Fam. Lauraceae)* in Brazil is well known, due to over-exploitation for essential oil-producing purposes to supply the perfumery trade. Wild stands of trees still exist in deep forest areas, but poor or absence of regeneration in exploited areas, and disappointing silviculture growth trials, fuel continuing concerns. Leaf oil trials offer a hope of future sustainable oil production policy (FAO 2002) but are probably a long way from commercial reality, and anyway have been very a long time coming, being mentioned forty years previously by Arctander (1960). Loss of germplasm diversity and a narrowing of the genetic base are now being addressed for Aniba spp. with moves to establish a germplasm collection; an ‘Adopt a tree’ campaign has been instigated by Dr. Manuel Limas of Manaus University, details of which can be viewed on www.ifaroma.org. The latter, although commendable, may prove an ineffective gesture in the light of deforestation information obtained by satellite monitoring from the Brazilian National Institute of Space Research which shows a 40% rise in Amazonian tree felling in the past year (The Independent 2003).

Part of a proposal by the Botanical Medicinal Academy (BMA) recommends investigation of the use of substitute plants for endangered or threatened plants (Yarnell E. & Abascal K. 2001). In the absence of any lead in this direction from any professional alternative health organisation, and with the BMA’s policy in mind, the properties of Brazilian rosewood oil (Aniba spp.) are now considered, and possible suitable replacement oils are examined.

*Do not confuse with Dalbergia nigra, which is also called Brazilian Rosewood, but is a hardwood used (amongst other things) for musical instrument manufacture. Rosewood oil from Aniba species is also known as bois de rose oil, or bois de rose femelle.

Historical sketch

The quest for sources of fragrant raw perfumery materials such as the monoterpene alcohols geraniol, citronellol and nerol, originally prompted essential oil distillers to derive them from common essential oils, either because there was no alternative economic synthetic route, or the available synthetics were of inferior odour value to the derived materials. When the author (TB) first entered the aroma business, one of my first experiences in the trade was to prepare the perfumery raw material “rhodinol” from the saponification of terpeneless Geranium oil Bourbon fractions (Pelargonium graveolens), to produce the mixture of natural alcohols which include geraniol and laevo-citronellol, and which typically had a “red rose” note.

Linalol was another sought after perfumery ingredient, and to satisfy market demand, companies would saponify essential oils containing linalyl esters, such as Bergamot (Citrus aurantium subsp. bergamia) & Petitgrain (Citrus aurantium subsp. aurantium). Linalol ex Lavender oil (Lavandula angustifolia) is still available commercially to this day, from certain selected producers. Linaloe oils (Bursera spp. see below) from Mexico and India were also used for linalol production, but poor attention to quality by overseas producers resulted in market buyers looking elsewhere. The preferred linalol source quickly became the distillation product of the comminuted wood of the felled Amazonian tree Pau-rosa (“rosewood” or “bois de rose”) from species of A. rosaeodora A. Ducke, A. rosaeodora var. amazonica Ducke and other Aniba spp. such as A. amazonica A. Ducke and A. parviflora Meissner Mez (Fam. Lauraceae).

All about Linalol

If you’ve ever smelled commercial synthetic 97% pure or 98% coeur grades of linalol, or moreover, have compared them with a 99.99% ultra-pure synthetic grade of linalol, you will have noticed the detracting smell of traces of impurities such as dehydrolinalol, tetrahydrolinalol and perhaps linalol oxides etc. Additionally, the enantiomeric purity of linalol has an effect on the odour profile. Pure laevo-linalol is woody and lavender like, whereas pure dextro-linalol is sweet coriander-like; pure (synthetic) racemic linalol is somewhere in the middle of the two. Further, linalol isolated from an essential oil e.g. linalol ex bois de rose, may have traces of other oil components, which add to and colour its odour profile, such as para-methyl acetophenone, 3-octanol, methyl heptenone etc. These trace items help to modify the profile of pure linalool, giving to a more “authentic” rosewood note. The linalol contents of some common linalool-containing oils are shown below (Table 1) with the enantiomeric purities of the contained linalol set out in Table 2.

Oil

% Linalol content

Coriander

60-80

Kuromoji

50-70

Ho Wood

 50-75*

Linaloe Mexican

60-70

Linaloe Indian

40-75

Rosewood Brazil

65-90

Sweet Basil

45-62

Mentha citrata

20-50

Lavender

30-35

Petitgrain

20-30

Bergamot

10-30

Skimmia laureola

      17.5% **

Table 1. Linalol content of selected essential oils.

*Zhu et al. (1994)  ** Misra PN et al. 2000

SD Oil

Enantiomeric excess

 

R

S

Bergamot

100

0

Ho China

97.6

2.4

Petitgrain

72.2

27.8

Lavender French

96

4

Coriander

10

90

Rosewood

50-51

49-50

Table 2. Enantiomeric ratio figures for linalol in selected essential oils.

[Adapted from Casiabanca H. et al. (1998)]

Brazilian Rosewood Oil

When cheap synthetic racemic linalol became more commonplace in the 1960’s, linalol-containing oils could be used in their own right for their unique odour profiles. It is widely reported that Rosewood oil has a history of use in upmarket fragrances - Chanel No. 5 (Chanel 1921), Aromatics Elixir (Clinique 1972), Ungaro Pour Homme III (Ungaro 1993) all contain rosewood oil, as more recently, does Sensi by G. Armani – these upmarket uses now perhaps contrast with its former use in cheap soap perfumes.

To produce rosewood oil, slow-growing rosewood trees (which reach 30m.) are felled, and after cutting into 1m. sections are transported down-river, or larger sections are floated there. On arrival at the distillery the wood is chipped and distilled (usually in a 1000 Kg chip capacity mobile still) – the yield is typically in the region of 1%. Over-exploitation has meant that rosewood stands are now becoming more remote from established distilleries. Mors & Rizzini (1966) report that rosewood trees were found in the areas of Juriti Velho and Maués, and along the Jamundá and Oyapoc rivers, estimating actual annual production at 300-400 tons (twice the quoted official figure), although its range includes the countries of Peru, Colombia, Ecuador, Suriname and French Guiana, as well as areas of Brazil. Now (2003) it is estimated at less than one tenth of this figure, at 20-30 tons.

Ohashi S.T. et al. (1999) report on the scope for sustainable production of rosewood oil from Curua Una in Brazil, and present analyses of the wood and leaf oil compositions found in their trials, and contrast them with commercial wood oils. The authors were able to show that the enantiomeric composition of oil from different trees varied according to inherited genetic factors. Some GC/MS analysts take the eremophilene content as an index of quality of the wood oil, but since rosewood leaf oil contains relatively higher amounts of this compound, maybe this offers a possible ‘adulterers charter’ to mix the leaf oil with synthetic linalol, and pass it off as Rosewood oil. Wholesale adulteration of the wood oil occurs already however, adulterated oils being termed “US quality” in the trade, as the only unadulterated oil is shipped directly from Manaus, Brazil. 

Ho leaf oil (Cinnamomum spp.)

(Ohashi et al. 1997)

Rosewood Curua Una leaf oil (Ohashi et al. 1997)

 

0.10% cis-b-ocimene

0.08% b-pinene

0.03% myrcene

0.04% limonene

0.16% 1,8-cineole

0.04% trans-b-ocimene

0.02% p-cymene

0.25% cis-linalol oxide

0.47% trans-linalol oxide

0.57% camphor

97.47% linalol

0.05% terpinen-4-ol

0.33% hotrienol

 

0.06% cis-b-ocimene

0.03% b-pinene

0.06-0.10% myrcene

0.10-0.15% limonene

0.03-0.04% 1,8-cineole

0.03-0.05% trans-b-ocimene

0.03% p-cymene

1.20-1.80% cis-linalol oxide

1.00 to 1.54% trans-linalol oxide

1.40-2.70% cyclosatirine

73.00-78.00% linalol

0.14-0.53% terpinen-4-ol

0.40-0.54% hotrienol

0.10-0.50% g-selinene

4.50-6.00% eremophilene

3.10-4.40% unknown

0.13-0.25% epoxy-linalol

0.04% linalol oxide D-pyranoid

0.80-0.95% caryophyllene oxide

0.35-0.62% spathulenol

0.62-0.79% benzyl benzoate

Table 3. Leaf oil analysis of Ho and Rosewood leaf oils. From (Ohashi et al. 1997).

  Other South American Rosewood oils

Schultes & Raffauf (1990) review the Lauraceae in S. America, noting synonymy between Aniba, Nectandra and Ocotea species, and the rich occurrence of alkaloids in the group. Gottlieb & Kubitzki (1981) have reviewed the chemistry of the forty Aniba spp. Interesting to the authors is the statement by Arctander’s Perfumery and Flavour Chemicals Vol. II where the toxic compound nitro-benzene is described as having a odour similar to “certain lots of poor grade Bois de Rose.” Arctander claims analysis of these oils reveals nitro-compounds closely related to nitrobenzene. In particular Arctander speculates that 1-nitro-2-phenylethane might be responsible for an “unattractive shoe-polish top note”, speculating further that it might be as a result of contaminated drums or from co-gathering the leaves of Aniba caniella. [Aniba caniella has a scented bark described as smelling of cinnamon & roses]. But we digress…

Cayenne bois-de-rose oil from French Guiana is now rarely seen, but samples analysed in the 1990-1995 period by the author were found to contain 80-97% linalol, and bear some resemblance to oils now traded as S. American Ocotea caudata, especially in respect of isovaleraldehyde and furfural contents.

Peruvian Ocotea caudata samples seen by the author (TB) seem to be dominated by a clean pine disinfectant note that seems to be related to the presence of a-terpineol, an artefact probably arising from the cyclisation of linalol at low pH during distillation. Casiabanca et al. (1998) additionally notes that the pH of rosewood drops to 3.8 at the end of steam distillation, and suggests that pH drop will lead to the partial racemisation of linalol enantiomers. This is of importance for analysts deliberating on authenticity criteria for such oils. 

Ocotea caudata commercial (T. Burfield unpublished data)

Aniba rosaedora Brazil (T. Burfield unpublished data)

0.79% isovaleraldehyde 

0.59% furfural

0.24% camphene

0.20% b-pinene

---      myrcene

0.64% limonene

0.98% 1,8-cineole

0.02% cis-ocimene

0.03% tr-ocimene

tr        n-octanol

tr.        3-octanol

0.16% camphor

tr.       para-methyl acetophenone

1.01% cis-linalol oxide

1.21% tr-linalol oxide

87.5% linalol

0.08% terpinen-4-ol

2.84% a-terpineol

0.13% hotrienol

0.18% nerol*

0.40% caryophyllene oxide

0.23% spathulenol

0.98% benzyl benzoate

0.26% b-pinene

---      myrcene

0.16% limonene

0.80% 1,8-cineole

tr.        cis-ocimene

tr.        tr-ocimene

tr.        methyl heptenone tr

----      methyl heptenol

tr.        3-octanol

tr.       camphor

1.59% cis-linalol oxide

1.39% tr-linalol oxide

0.35% a-selinene

0.30% a-copaene

89.86% linalol

0.02% E,Z-2,6-dimethyl, 5,7-octadien-2-ol

0.02% linalol epoxides

0.21% terpinen-4-ol

2.61% a-terpineol

0.10% hotrienol

0.72% nerol*

0.16% geraniol

0.22% eremophilene

0.08% nerolidol

0.23% spathulenol

0.28% benzyl benzoate

Table 4 South American Rosewood Oils

(Tony Burfield – unpublished data)

* the geraniol isomer was expected to dominate in these analyses, in accordance with the literature, with only traces of nerol present, but was not found in these cases.

Mexican Linaloe oil

Mexican linaloe oil was produced from the wood and possibly the seed of Bursera aloexylon and B. delpechiana species – perhaps also other inferior species (the EOA standards also mention B. fagaroides var. ventrocosa when setting the specification criteria for Linaloe wood oil, but this has been subsequently questioned). Producing centers were in the states of Puebla and Colima. Adulteration with inferior species, and with linaloe seed oil (giving a more positive optical rotation), and which kept less well than the wood oil, lead to a quality decline in the years after 1920 which in turn lead an increased preference for Brazilian Rosewood Oil. The high yield (over 10% in direct steam fired stills), the presence of 60-70% laevo-linalol and up to 10% of linalyl acetate (and absence of camphor), together with methyl heptenol and linalol oxides give a pleasing profile to the oil, which has a lily-of-the-valley like quality, and was highly regarded by (Western) perfumers of the day (Burfield 2003).     

Indian Linaloe Oil

Bursera delphechiana, and other Bursera spp. including B. simaruba L. and B. aloexylon are used to prepare linaloe oil. In India it is more often from the air-dried husks or pericarp of the ­fruiting berries, which are collected from the ground, occasionally from the leaves; the fruit oil is not sold separately as it keeps poorly, but is mixed with the wood oil. Cultivation occurs in Karnataka, Maharastra & Andrah Pradesh, where there is up to 800 hectares under cultivation.

Indian linaloe oil is colourless or pale yellow oil, the odour strongly reminding of linalol and freshly ground coriander, with much radiance. Rosewood oil is flatter in comparison (Burfield 2000). The oil reportedly contains >75% linalol, with geraniol and a-terpineol which heavily contribute to its odour (giving a slight rosaceous-lilac aspect), although other analyses suggest 35-45% linalyl acetate and up to 48% linalol. Whereas total production volume per annum of the Mexican oil is believed to be approx. 300Kg; 50-60 tons of the Indian oil is produced: which is totally consumed by India’s internal perfumery trade (Shiva et al. 2002).

Kuromoji Oil

Kuromoji oil is obtained by steam distillation of the ovate-oblong leaves of the evergreen trees Lindera umbellata Thumb., L. membranacea Maxim and L. sericea Blume, which have with grayish-green bark native to the mountain ranges in Japan, specifically Honshu, Shikoku, Kyushu and also China. The oil was produced in Izu as a linalol source during the Second World War. The oil itself is seen as yellow liquid with a fresh odour reminiscent of linalol, one of the principle components, with a hint of orange (Burfield 2000). The dry-out is lavandaceous, slightly wood-herby, soapy. The oil typically has a negative optical rotation of –11° to -12°; the fresh odour is due to the relatively large amount of 1,8-cineol in the oil; it is not available in the quantities that would be required to substitute for Rosewood oil.

Ho Oils

Ho wood oil is often a blend of essential oils produced by the ­steam distillation of the wood of Cinnamomum species such as Cinnamomum camphora L. var. linaloolifera and Cinnamomum camphora Sieb var. glavescens Hayata (Zhu et al. 1994) from China, and also Formosa & Taiwan. The more sweet camphoraceous leaf and branch oils of these species which have linalol content as low as 15% may have to be fractionated and rectified to produce oils with a high laevo-linalol and negligible camphor content, although in a different publication Zhu et al. (1993) report on leaf oils from species containing 90% linalol. Leaf oils have competed with wood oils in the last several decades, although the exact distinction can be obscure. ­And so rectification, or double rectification of these oils, produces products often marketed as rectified ho­ oils in qualities containing from 95% to 99.5%+ linalol content; these are sometimes simply traded as ‘laevo-linalol ex Ho’. Leaf and stem oils containing 97% laevo-linalol from Cinnamomum tenuipulis found throughout S. Yunnan are also mentioned as potentially exploitable by Zhu et al. A few months ago I would have said that ho wood and leaf oils have a bright future. In recent times double rectified ho oil qualities offering over 99.5% laevo-linalol and <0.02% camphor and optical rotation values of up to –17.0° have been cheaper industrially at times than synthetic linalol coeur on the open market. Acetylation of ho wood oil to produce acetylated ho oils (mainly consisting of linalyl acetate, with some rearrangement minor amounts of other esters), together with ho oil itself as a linalol source, has been known to find its way into commercial lavender and bergamot oils from many sources.

 

                                    

At the time of writing, with the Chinese authorities introducing a ban on tree-felling of certain species including Cinnamomum  because of climatic concerns, ho oils have shot up in price. Zhu et al. (1994) had already previously warned of potential problems of exhaustion of Cinnamomum species reserves as no policy of tree replanting currently existed. To the authors, the future sustainability of this commodity is unforeseeable at present.

Coriander Oil

Coriander seed oil, CO2 extract and oleoresin from the ripe seeds of Coriandrum sativa L., are familiar spicy food flavouring ingredients. Coriander seed oil was originally important as one of the few richer sources of natural dextro-linalol (aka coriandrol), but its’ price­ has collapsed in recent years, and has, on occasion, even dipped­ below the price of synthetic linalol. Post 2000, and especially in 2002, coriander oil prices rose again and adulteration with synthetic linalol (and even ho oil (!), which has a deleterious effect on the aroma profile) once again becomes widespread and economic.

Petitgrain oil Terpeneless

Petitgrain oil terpeneless from Citrus aurantium subsp. aurantium by fractionation has been passed off as Rosewood oil to unsophisticated oil consumers in the past, but the distinctive odour of linalyl acetate should give away its’ true identity to the more discerning nose. Although terpeneless oils were favoured by the “father of Aromatherapy”, Gattefossé, fractions of essential oil oils do not find favour in mainstream aromatherapy practice, and so this matter is not pursued further. For completeness, the enantiomeric distribution of linalool in authentic petitgrain oil was determined as (3R)-(-)-linalol: 53.4-64.9% : (3S)-(+)-linalol (35.1-46.6%) by Bernreuther and Schrier (1991), in contrast to the high enantiomeric excess for (3R)-(-)-linalyl acetate (97%) : (3S)-(+)-linalyl acetate (3%) Mosandl and Juchelka (1997).

 

Other Oils

The odour of oil from the leaves of Skimmea laureola Sieb. & Zucc. ex Walp., often grown as an ornamental in European gardens, has been likened to that of Petitgrain oil. The oil does contain a modest proportion of linalol, but is dominated by high linalyl acetate content.

The well-promoted Australian oil known as “Rosalina”, is steam or water distilled from the terminal branches of wild­-harvested material of Melaleuca ericifolia Smith, an evergreen shrub with a cork-like bark found growing in an area stretching from Tasmania to New South Wales. Two chemotypes are known, a 1,8-cineole chemotype in the Southern parts of its natural range, and a linalol type, which contains up to 55% linalool, to the North of the range. The composition of the oil has been compared to tea tree oil excepting the major constituent is linalol (Brophy et al. 1998), who gave the linalol content as from 23-40%, with cineol (5-26%) and terpinolene (5-25%) also present in major proportions. The oil inevitably also contains a-terpineol from the rearrangement of linalol during distillation, and small amounts of terpinen-4-ol. The odour of the linalol chemotype is camphoraceous and linalolic with a medicinal ­quality and with some suggestion of the cleaner notes of tea-tree oil. Realistic sustainability data for the species following any potential large volume production of this oil is not clearly known, as far as the authors can establish.

Background: the Physiological effects of differing linalol enantiomers.

Are we able to foretell the physiological properties of high linalol-containing oils from considering the physiological properties of linalol enantiomers?

Peana et al. (2002) noted the occurrence of various isomers of linalol and linalyl acetate in various essential oils, and investigated the anti-inflammatory properties of pure (-)-linalol, racemic linalol and linalyl acetate, using carrageenan induced edema in rats as an inflammation model - unfortunately (+)-linalol isomers were not included in the study. [It is a great shame that we continue to see, and have to report on, unethical testing procedures, considering the current global climate against animal testing, and the moves to bring this to an eventual end within the EU - authors]. Although both forms caused edema reduction, at low levels of administration (25mg/Kg), (-)-linalol delayed odema onset and reduced its effect, whereas the racemate only reduced the effect. At higher levels no difference in effect was seen between types. The effect of linalyl acetate on edema was delayed and typical of pro-drug behaviour.

Further work by Peana et al (2003) involved studies on the antinociceptive activity of (-)-linalol in mice using two pain model techniques, acetic acid induced writhing and the hot plate test. In addition the effect of applied concentrations of (-)-linalol @ 25, 50, 75 and 100 mg/kg on spontaneous locomotor activity was evaluated – here a dose dependent increase in motility was observed eliminating a sedative effect, and superficially at least, making an interesting comparison with Buchbauer’s earlier findings (see below). Better performance of (-)-linalol administration in the  writhing test over the hot plate test is consistent with the previous findings that (-)-linalol possesses anti-inflammatory activity.  The authors suggested that (-)-linalol-induced antinociception crucially involved participation of opioidergic and cholinergic systems.

Earlier Atanassova-Shopova et al. (1973) had shown that linalol and terpineol (no isomers stated for either compound) possessed CNS depressive effects and the depressive effects of lavender oil  were partly at least but not totally due to these compounds. It should be stated that the lavender oil used in the experiments had an unusual high (15.2%) “terpineol” content. Much other work, too extensive to comprehensively review, has been done on CNS effects of lavender e.g. neurosedative tests on mice fed lavender oil in olive oil 1:60 (Guillemain et al. 1989), anti-convulsive effects in mice inhaling lavender oil vapour (Yamada 1994), and my favourite, stress reduction caused by lavender straw as indicated by reduction of travel sickness in pigs (Bradshaw et al 1998)! Buchbauer et al. (1993) looked at the effect of inhaled compounds on the motility of normal and intraperitoneally applied caffeine agitated mice. Most effective at decreasing motility in normal mice were lavender and neroli oils (details of botanical origins missing throughout), and the fragrance chemicals linalol*, linalyl acetate* and citronellal*. Caffeine agitated mice were compensated best by lavender oil, isoeugenol*, linalol*, linalyl acetate*, maltol, methyl salicylate and carvone*, but linden blossom and neroli essential oils, methyl anthranilate and farnesol* increased the agitation level and were perceived as stimulating. Mount Blanc lavender oil was noted as being the most soporific of all substances tested. Overall, relatively low concentrations of fragrance chemicals in blood caused sedative effects, effects being achieved via direct action on cell membrane lipids in the cortex. Buchbauer maintains that esters (such as linalyl acetate) are more lipophilic than monoterpenols (such as linalol) and more easily pass the blood-brain barrier and shows a table showing figures for inhaled esters and corresponding monoterpeneols, some of which confirm this view.

* isomeric composition not given

Manley (1993) had in the same year, investigated a number of oils (basil, bergamot, rosewood, chamomile, clove, geranium, lemon, lemongrass, marjoram, neroli, patchouli, peppermint, rose, sage, sandalwood and valerian) by contingent negative variation and found that their effects (sedative, stimulant or neutral) largely corresponded to their traditional aromatherapeutic labelling.

Sugawara (1997) produced what appears to be a seminal study in methodology for evaluation of the physiological consequences of fragrance (essential oils) inhalation, relating odour effectiveness to work type. Fragrance impression was scored under thirteen impression adjectives, and scores of impression were taken on inhalation before and after work, and subsequently statistically examined for significance of difference. Work could either be a mental, physical or auditory experience (“hearing environmental sound”). Effectiveness of fragrance for work was statistically evaluated in terms of numbers of significant items as shown by student’s t-test examination.

Lavender, rosemary, peppermint, marjoram, cardamom, sandalwood, basil, lime essential oils and linalol gave a more favourable impression after, rather than before, work. Linalol, peppermint and lime performed unfavourably after being compared with impression before work. Basil, linalol, peppermint and sandalwood after hearing environmental sound gave a more favourable impression.  Basil gave a more favourable impression with mental work. 

Part of the study was involved with measuring forehead electroencephalographic measurements after inhalation, where it was noted that linalol caused a greater decrease of beta-waves after work, whereas mental work with agitated inclination increased beta-waves. Experiments showing the sedative properties of linalol using optically active R-(+)-, S-(-)- and RS-(+/-)-* [i.e. racemic] grades of linalol showed that RS-(+/-)-linalol and (S)-(-)-linalol caused a decrease, whereas (S)-(+)-linalol with agitated inclination was associated with an increase of magnitude of beta waves.  

Re L. et al. (2000) have considered further the linalol containing oils which affect the CNS, including hypnotic, anticonvulsant and hypothermic properties ascribed to these oils, which the authors relate to a local anaesthetic effect of linalol (Ghelardini et al. 1999 had previously demonstrated this in vitro and in vivo for linalol and linalyl acetate, speculating on a antimuscarinic explanation or Na+ or Ca2+ blocking effect). Re et al. speculate on an inhibitory effect of linalol on the acetylcholine (ACh) release and on the channel open time in the mouse neuromuscular junction, which they were able to demonstrate (isomeric linalol composition not stated).

Cavanaugh & Wilkinson (2002) produced an interesting review of some 67 published papers on the biological activity of lavender oil, pointing out that poor attention to methodology, botanical origin and chemical analysis of the oils often hampers meaningful evaluation of published evidence. Tisserand’s suggestion that neurological effects of lavender are effected by enhancing GABA mediated effects in the amygdala, are considered, as well as Re’s work on linalol above. Relaxant effects of lavender are discussed in relation to Lis-Balchin and Hart’s anti-spasmodic (1999) on animal smooth muscle, although the latter authors postulated an intracellular cAMP mechanism rather than action via adrenergic or cholinergic receptors, or yet any action via involvement of calcium or potassium ion channels. The review seems to be on weaker ground when discussing analytical and safety issues, but discussion of the anti-microbial activity of lavender oils adequately covers many criticisms of poor methodology in essential oil microbiology studies. Studies by Lis-Balchins et al. (1998) are cited as examples by Cavanaugh & Wilkinson of current failure to find a relationship between the anti-microbial activity and the major constituents of lavender oil (such as linalol and linalyl acetate). It has to be remembered however that these studies were made on commercial oils - no authenticity indicators (a-santalene concentration, optical purity of linalyl acetate etc. etc.) are cited, and so it may be that oil purity is an important variable, amongst others, in anti-microbial efficacy. The authors conclude that from consideration of in vitro MIC values – not too dissimilar to those of tea tree oil – that lavender oil may be useful against topical infections and as a modulating agent for general healing and post-infection recovery mechanisms.

The Aromatherapeutic properties of Rosewood and certain other high linalol-containing oils.

Odour quality. The Western perfumery industry has never considered ho oils a satisfactorily performing substitute ingredient for rosewood oil in high-class perfumery, but may, at least, have used the oil in low cost perfumes. Zhu (1994) confirms the use of ho oil in Chinese perfumery. Additionally Western perfumers have often preferred rectified ho oil qualities for specific application to synthetic linalol. It is perhaps pertinent to remind readers that fragranced retail products labelled as “aromatherapy perfumes”, and constructed by classically trained perfumers rather that aromatherapists, turned over £611 million sales in the UK the three years during 1999-2002.    

General properties

In aromatherapy education, rosewood oil does not feature heavily in EU & US taught syllabuses. Although it is listed in ITEC courses (see below) it is absent, for example, from the list of essential oils in the UK National Occupational Standards for Aromatherapy Database list http://www.skillsforhealth.org.uk/db/default.asp# . Ho and linaloe oils do not feature in many aromatherapy texts, and in the US aromatherapists only became familiar with these oils as possible “substitute” for the “endangered rosewood” (SSH).

(a) Rosewood. The standard text book for the ITEC aromatherapy courses (Tucker 2000) describes Rosewood’s therapeutic actions as analgesic, antidepressant, antiseptic, bactericidal, cytophylactic, cephalic, deodorant, stimulant & tonic, but the author offers nothing in the way of direct clinical or medical proof of any of these actions, but directly refers to Patricia Davis’s popular high-street book (Davis 1999). Franchomme & Peneol (1990) cite, for the oils of A. parviflora and A. rosaedora var. amazonica: anti-infectious, anti-bacterial, anti-fungal, anti-viral, anti-parasitic, tonic and stimulant properties, suggesting use in oral & bronchial infections of adults, children and babies, vaginal candidosis, nervous depression, fatigue, and note its’ non-aggressive properties towards the skin and mucous membranes. Although some 796 references are included at the end of latter authors’ work, it is unclear which, if any, specifically refer to these stated therapeutic claims. Balz (1966) gives a list of properties very similar to that of Franchomme & Penoel above, whilst Lawless (1995) manages to find a conference quote from 1906 in support of skin care properties. Valnet (1980) does not offer a monograph on Rosewood oil.

Opdyke (1975) summarised the literature indicating that Rosewood oil was reported to have anti-convulsant activity in mice & rats, spasmolytic activity on isolated guinea pig ileum, and anti-microbial properties amongst other properties. It was also reported as non-toxic, non-irritating and non-sensitising.

Regarding in vitro microbiological studies on Rosewood oil: Lis-Balchin (1994) found no anti-oxidant action for Rosewood, found it potently active against 24/25 bacteria, but only 12 out of 20 Listeria monocytogenes varieties. It was described as moderately active against three out of three fungi; Maruzella (1958) previously found good action against five out of five fungi. Lobato et al. (1989) examined a number of Amazonian oils against Pseudomonas aeruginosa, Proteus mirabilis, Escherichia coli, Edwardsiela tarda, Klebsiella pneumoniae, Enterobacter aerogenes and Salmonella spp, however Aniba rosaedora oil was only active against five of the above.

(b) Ho. Franchomme & Penoel (1990) list for Cinnamomum camphora Sieb var. glavescens Hayata: powerful anti-infectious, anti-bacterial, anti-viral and anti-fungal; tonic, general stimulant, useful, against respiratory, digestive and genital infections, asthenias.

Hili (2000) showed that ho leaf oil had a high activity (as demonstrated by the inhibition zone technique for cultured organisms) against the yeasts Saccharomyces pombe, S. cerevisiae, and moderate activity against Candida albicans, Torula utilis, and the bacteria E. coli and Staphylococcus aureus, and low activity against Ps. aeruginosa. It should be noted that linalol and linalyl acetate were already known to possess antibacterial and anti-fungal properties according to Knobloch et al. (1989). In a further experiment Hili carried out broth dilution assays on thirteen oils in DMSO including coriander and ho leaf oils against the same micro-organisms above, noting some variation between inhibition assay and broth assay. Coriander oil was slightly more inhibitory than Ho leaf oil at a range of concentrations at concentrations from 100-500mg/ml, and was more markedly anti-fungal than ho leaf, apart from against S. pombe. Finally, and somewhat intriguingly, Hili also examined the anti-microbial activity of 1,8-cineol, thymol, eugenol and linalol (no isomer stated). Whilst the reduction in bacterial growth at 500mg/ml against the same test organisms in broth culture was closely similar between linalol and coriander oil, coriander was markedly more active against the yeasts S. pombe, S. cerevisae and T. utilis.

(c) Coriander seed oil. Considering likely deodorant properties of essential oils, Hili (2001) summarises the literature in noting that cinnamon, clove, coriander and lemongrass are active against the Corynbacterium, Propionibacterium and Streptococcal classes of bacteria associated with body odour (although from a practical point of view, it should be noted that skin safety was not taken into account). A number of studies investigate the anti-microbial properties of coriander oil e.g. in vitro anti-fungal activity: Garg et al. (1992).

Valnet (1980) lists coriander seed oil as having internal uses as a carminative, stomachic, stimulant, formerly being held to be an aphrodisiac and a memory aide, as well as external use as an analgesic.

Considerations & Recommendations

It has been very difficult in this short study to be able to adequately cover all the papers relating to the alleged beneficial properties of linalolic oils. Extrapolating the findings of the findings of the work of Pena & Sugawara, to our way of thinking, may give credence to the view that the widespread practice of oil adulteration by the deliberate addition of synthetics may change the expected physiological outcomes of aromatherapy interventions using these oils (- excluding other influential factors such as the therapist-patient relationship, patient expectations following intervention etc.). Ironically however, in the case of rosewood, the addition of synthetic racemic linalol to make ‘US quality’ rosewood oil may not actually detract from its expected effects – as an analgesic, antidepressant, antiseptic, and anti-bactericide! Addition of laevo-linalol (as ho oil) or racemic linalol to the dextro-linalol rich coriander oil on the other hand would be expected to make more substantial changes to its’ otherwise expected therapeutic actions.

In terms of finding direct substitutes for rosewood oil, high linalyl acetate containing oils such as French lavender or bergamot (not considered here) would appear not to offer odour similarity; the possibilities raised by the pro-drug effects of linalyl acetate are intriguing, however. The widespread recommendations of using ho oil as a substitute for rosewood oil are partly endorsed for anti-inflammatory, antinociceptive and anti-bacterial purposes, but some misgivings are perceived for anti-fungal purposes. We are in agreement with some points raised by Cavanaugh & Wilkinson, viz. that in-vitro microbiological testing results are not necessarily valid indicators for human microbiological infections in client intervention scenarios, and that the small quantity of literature reviewed on this subject is not necessarily truly representative of properties of the oils examined. Further, the mechanistic basis for microbial kill effects of linalol-containing oils has not been considered here. In terms of volumes required to satisfy market demands for high linalol containing oils, if it true that ho oils face an uncertain future, and if rosewood leaf oil fails to become an important production volume item, then there is a market opportunity to be filled! Many of the high-linalol oils such as Indian linaloe, are presently produced in insufficient quantity to presently provide heavy export tonnage potential – unless it was prepared to pay more and lure sales away from the internal home market. In addition Bursera species providing these linaloe oils cannot be economically distilled until trees are between twenty and forty years old, a situation not presently lending itself to sustainable short-term rapid increases in production. It may be that persuading growers to produce high linalol, low camphor containing strain of lavender, and perhaps blending this 50-50 with coriander oil, may be the nearest approach to susbstituting for rosewood oil, if ho and rosewood continue to decline in annual production volume. Alternatively Rosalina oil from high linalol-containing Melaleuca species may provide an alternative, although it remains to be seen whether the detracting typical earthy-spicy note of tea tree oil can be bred out of the aroma profiles of these oils, and whether the oil can be sustainably produced on the scale required.

Finally, a cloud hangs over the continued unfettered use of linalol containing essential oils in retailed products in Europe at least, as linalol is listed as one of the 26 skin sensitisers in the 7th Amendment to the EU Cosmetic Act, and is required to be labelled if present above certain concentrations in cosmetic products (these may include certain aromatherapy products – consult your professional AT organisation for guidance). Essential oils commonly contain 16 of these 26 sensitisers, but as a group, are not, apparently, to be treated as a special case in the regulations. Although workers in the aroma field have maintained that there is a lack of scientific rigour in published dermatological research in this area which has directly provided the basis for the SCCNFP opinion underpinning this legislation (see relevant sections of www.aroma-science.com) the passing of the Act has already had a substantial negative effect on the perfumery, natural perfumery and essential oil industries. Some industrial customers have shied away from using natural raw products that necessitate obligatory labelling warnings to customers, resulting in a sales decline for certain sectors of the aroma business. This situation is a double blow for natural raw material end-users – as we have seen Rosewood oil is threatened both by genetic erosion in its natural habitat, and its substitutes are under a legislative threat of erosion of unfettered freedom of use. 

References:

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Glossary

Coeur: A term describing a “heart cut” fraction from a fractional distillation

DMSO: dimethyl sulphoxide

EOA: Essential Oils Association

Pro-drug: A substance which only has a perceivable physiological effect after modification or bio-tranformation by the body e.g. for linalyl acetate, after trandformation into linalool by body esterases.

MIC: minumum inhibitory concentration

Racemic: an equal mixture of enantiomers resulting in zero optical activity.

Saponification: The alkaline hydrolysis of fatty acid esters, (such as citronellyl acetate) to produce alcohols (such as citronellol).

Silviculture: A branch of forestry related to the growing and tending of trees.

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