Revision of Backhousia citriodora Essential Oil Standard
RIRDC Publication No. 11/137
RIRDCInnovation for rural Australia
Revision of Backhousia citriodora Essential Oil Standard
by E. V. Lassak
February 2012
RIRDC Publication No. 11/137 RIRDC Project No. PRJ-005404
© 2012 Rural Industries Research and Development Corporation. All rights reserved.
ISBN 978-1-74254-316-1 ISSN 1440-6845
Revision of Backhousia citriodora Essential Oil Standard Publication No. 11/137 Project No. PRJ-005404
The information contained in this publication is intended for general use to assist public knowledge and discussion and to help improve the development of sustainable regions. You must not rely on any information contained in this publication without taking specialist advice relevant to your particular circumstances.
While reasonable care has been taken in preparing this publication to ensure that information is true and correct, the Commonwealth of Australia gives no assurance as to the accuracy of any information in this publication.
The Commonwealth of Australia, the Rural Industries Research and Development Corporation (RIRDC), the authors or contributors expressly disclaim, to the maximum extent permitted by law, all responsibility and liability to any person, arising directly or indirectly from any act or omission, or for any consequences of any such act or omission, made in reliance on the contents of this publication, whether or not caused by any negligence on the part of the Commonwealth of Australia, RIRDC, the authors or contributors.
The Commonwealth of Australia does not necessarily endorse the views in this publication.
This publication is copyright. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. However, wide dissemination is encouraged. Requests and inquiries concerning reproduction and rights should be addressed to the RIRDC Publications Manager on phone 02 6271 4165.
Researcher Contact Details
Dr Erich V Lassak Phytochemical Services 254 Quarter Sessions Rd Westleigh NSW 2120
Phone: (02) 9875 1894
In submitting this report, the researcher has agreed to RIRDC publishing this material in its edited form.
RIRDC Contact Details
Rural Industries Research and Development Corporation Level 2, 15 National Circuit BARTON ACT 2600
PO Box 4776 KINGSTON ACT 2604
Phone: 02 6271 4100 Fax: 02 6271 4199 Email: [email protected]. Web: http://www.rirdc.gov.au
Electronically published by RIRDC in February 2012 Print-on-demand by Union Offset Printing, Canberra at www.rirdc.gov.au or phone 1300 634 313
ii
Foreword
Backhousia citriodora F. Muell., also known as ‘lemon myrtle’, ‘lemon-scented myrtle’ or ‘lemon ironwood’, is a medium-sized tree endemic to rainforest areas of coastal Queensland. The lemon- scented volatile leaf oil of Backhousia citriodora is used in the compounding of flavours and fragrances as well as in aromatherapy.
The present Australian Backhousia citriodora essential oil standard AS 4941, first published in 2001, requires significant revision in order to reflect the improved quality of presently produced oils. The reasons for the revision are both to reflect the current commercial quality of the oil and also to tighten the present standard to prevent adulterations. This work should benefit not only Australian producers of lemon myrtle oil, but also the wider essential oils industry.
The project tested and analysed samples from a representative number of genuine Backhousia citriodora oils and combined these data with historical and recently published data to verify a proposed amendment of AS 4941–2001. To help define the chemical composition of Backhousia citriodora oil more accurately, it is recommended that the range of geraniol in the amended Australian standard to be set at 0.6 to 2.5 per cent.
In addition, the revision of the standard should allow for the ready identification of adulterants in Backhousia citriodora oil. Three adulterants in question, i.e. aldehydes C8 (n-octyl aldehyde), C9 (n- nonyl aldehyde) and C10 (n-decyl aldehyde), have citrus-like odours and are not naturally present in genuine Backhousia citriodora oil but their exact positions on gas chromatographic traces are relatively easy to identify. A note to this effect must be added to the ‘Typical Gas Chromatograms’ (on both polar and non-polar columns) in the Appendices of the amended standard together with an indication of the position where these aldehydes would elute under the gas chromatography conditions used.
This report is an addition to RIRDC’s diverse range of over 2000 research publications and it forms part of our Essential Oils and Plant Extracts R&D program, that aims to provide the knowledge and skills base for industry to provide high, consistent and known qualities in their essential oils and plant extracts products that respond to market opportunities and enhance profitability.
Most of RIRDC’s publications are available for viewing, free downloading or purchasing online at www.rirdc.gov.au. Purchases can also be made by phoning 1300 634 313.
Craig Burns Managing Director Rural Industries Research and Development Corporation
iii
Acknowledgments
The author acknowledges support from a Rural Industries Research and Development Corporation grant with industry collaboration from the lemon myrtle industry. The author thanks Mr Gary Mazzorana for assistance with the collection of oil samples and for providing essential information about previous work on lemon myrtle oils. Thanks are also due to Mr J Fergeus and Dr J Brophy for analyses of lemon myrtle oil samples, to Mr R Davis for providing samples of commercial C8, C9 and C10 aldehydes and for letting me use his laboratory facilities for the determination of optical rotations, Mr J Lambeth for samples of the three aldehydes, C8, C9 and C10, Mrs Patricia Carreto for advice on the new rules introduced by Standards Australia, and finally Mrs S Hess-Buschmann for her enthusiastic assistance in getting this project going, despite being terminally ill with cancer.
Abbreviations
ATTORI Australian Tea Tree Oil Research Institute
FID flame ionisation detector
GC gas chromatography
GC-MS gas chromatography–mass spectrometry
ISO International Organization for Standardization
MS mass spectrometry
iv
Contents
Foreword ...... iii Acknowledgments ...... iv Abbreviations ...... iv Executive Summary...... vii Introduction ...... 1 Objectives ...... 3 Methodology and Results ...... 4 Discussion and Recommendations ...... 15 References ...... 16
v
Tables
Table 1. Chemical analyses of unacceptable ‘Backhousia citriodora’ oils of overseas provenance provided by the German buyer ...... 2
Table 2. Sources of essential oil samples ...... 4
Table 3. Backhousia citriodora – chemical composition (%) ...... 5
Table 4. GC chromatograms and analysis for Backhousia citriodora oil, a mixture of aldehydes, and a combination of oil and aldehydes ...... 8
Figures
Figure 1. Backhousia citriodora B-Wax column (polar) ...... 6
Figure 2. Backhousia citriodora oil (non-polar phase) ...... 9
Figure 3. Mixture of aldehydes C8, C9 and C10 (non-polar phase) ...... 10
Figure 4. Backhousia citriodora oil + mixture of aldehydes C8, C9 and C10 (non-polar phase) .... 11
Figure 5. Backhousia citriodora oil (polar phase)...... 12
Figure 6. Mixture of aldehydes C8, C9 and C10 (polar phase) ...... 13
Figure 7. Backhousia citriodora oil + mixture of aldehydes C8, C9 and C10 (polar phase) ...... 14
vi
Executive Summary
What the report is about
The lemon-scented volatile leaf oil of Backhousia citriodora is used in the compounding of flavours and fragrances as well as in aromatherapy. The present Australian Backhousia citriodora essential oil standard AS 4941, first published in 2001, requires significant revision in order to reflect the improved quality of presently produced oils. The reasons for the revision are not only to reflect the greater chemical uniformity of presently produced oils but also to tighten the present standard in order to prevent adulteration.
Who is the report targeted at?
This report will be particularly useful for producers of Backhousia citriodora essential oils, but it is also relevant to producers of essential oils from other native plant species. It is also addressed to Standards Australia, as it presents information to be used in amending AS 4941–2001.
Where are the relevant industries located in Australia
Backhousia citriodora F. Muell. is endemic to rainforest areas of coastal Queensland, between Brisbane and Rockhampton. The citral chemotype of the plant is grown commercially in Queensland as well as in the Lismore area of northern New South Wales.
Background
Backhousia citriodora, also known as ‘lemon-scented myrtle’ ‘lemon myrtle’ or ‘lemon ironwood’, is a small to medium-sized tree belonging to the family Myrtaceae. The species exists in two chemotypes: a citral chemotype and a laevo-citronellal chemotype. The leaf essential oil of the citral chemotype, arguably the richest natural source of citral, possesses a rich, fresh lemon odour.
In 2001, as demand and production of this oil increased, Standards Australia elaborated (at the industry’s request) an Australian standard for this oil (AS 49441–2001); particularly as some oil was being exported overseas, mainly to Germany. More recently (in 2009), a buyer reported that some Backhousia citriodora oils were not genuine – the oils appeared to have been adulterated. Specifically, there appeared to be an abnormally high amount of geraniol in one oil and significant amounts of three aliphatic aldehydes in other oils.
Aims/objectives
The Australian standard for Backhousia citriodora essential oil, AS 4941–2001, needs to be urgently revised and strengthened in order to define the chemical composition of the oil more accurately and reveal more readily, and thus help to discourage, any attempts at adulteration. The project tested and analysed Backhousia citriodora essential oils from different sources. It also analysed Backhousia citriodora oil without and with added aldehydes.
Methods used
Thirteen commercial oil samples from the Northern Rivers district of New South Wales and one laboratory-distilled sample were analysed by means of combined gas-chromatography-mass spectrometry. A comparison of these analyses with other recent Backhousia citriodora investigations was made. Refractive indices and optical rotation of all samples were also undertaken to determine if samples conformed to the values specified in AS 4941–2001.
In addition, a mixture of the three aliphatic aldehydes, i.e. C8 (n-octyl aldehyde), C9 (n-nonyl aldehyde) and C10 (n-decyl aldehyde) with Backhousia citriodora oil was analysed using gas
vii
chromatographic columns. All of these aldehydes have citrus-like odours but are not naturally found in Backhousia citriodora oil.
Results/key findings
The revision of the standard involved the gas chromatographic determination of the geraniol content of a representative number of genuine Backhousia citriodora oils. This study found the mean geraniol content and standard deviation were 1.55 per cent and 0.8 per cent respectively. These values are within the range reported by other workers. The refractive indices and optical rotation of all samples complied with the values specified in AS 4941–2001.
Co-injections of the three aldehydes (C8, C9 and C10) with Backhousia citriodora oil showed that the aldehydes are relatively easy to identify in the mixture using gas chromatographic traces, and thus the traces may be used to reveal adulteration of Backhousia citriodora oil.
Recommendations
Owing to the amount of variation in geraniol content in Backhousia citriodora oils, and since the values are quite low and gas chromatography operating conditions could vary slightly from one laboratory to another, it is recommended that the range of geraniol in the amended Australian standard be set at 0.6 per cent to 2.5 per cent.
In addition, the three aldehydes C8, C9 and C10 must be absent from Backhousia citriodora oil. A note to this effect must be added to the ‘Typical Gas Chromatograms’ (on both polar and non-polar columns) in the Appendices of the amended standard together with an indication of the position where these aldehydes would elute under the gas chromatography conditions used.
viii
Introduction
Backhousia citriodora F. Muell., also known as ‘lemon-scented myrtle’ or ‘lemon ironwood’ (owing to its lemon-scented leaves and very hard wood respectively), belongs to the family Myrtaceae. It is a small to medium-sized tree endemic to rainforest areas of coastal Queensland between Brisbane and Rockhampton. The species exists in two chemical forms: a variety characterised by an essential oil very rich in citral; and a comparatively rare variety characterised by an essential oil rich in laevo- citronellal. The citral chemotype is grown commercially in Queensland as well as in the Lismore area of northern New South Wales.
The leaf essential oil of the citral chemotype, arguably the richest natural source of citral, possesses a rich, fresh lemon odour. It is used, albeit on a small scale, in the food industry as a flavour additive and in the cosmetics industry as a perfumery ingredient.
In 2001, as demand and production of this oil were on the increase, Standards Australia elaborated (at the industry’s request) an Australian standard for this oil, particularly as some oil was being exported overseas, mainly to Germany.
Recently (early 2009), a German buyer of Australian Backhousia citriodora oil (who has been importing this oil directly from an Australian producer), complained that the quality of several batches of oil, claimed to be genuine, received from overseas suppliers was unacceptable. The German buyer identified abnormally high amounts of geraniol, not found in genuine Backhousia citriodora oil in one oil and significant amounts of three aliphatic aldehydes used in the compounding of synthetic, mainly citrus-like essential oils, in several other oils labelled Backhousia citriodora.
These three aldehydes, referred to by perfumers and flavourists as aldehydes C8, C9 and C10 (based on their number of carbon atoms), are caprylic aldehyde (n-octyl aldehyde), pelargonic aldehyde (n- nonyl aldehyde) and caprinic aldehyde (n-decyl aldehyde). All of these aldehydes exhibit citrus-like odours. Apart from being available in commercial quantities from suppliers of fragrances, they are also fairly widely distributed in nature, particularly in many naturally occurring (and in some cases commercially important) essential oils such as various Citrus oils (belonging to the family Rutaceae). The composition of some of these has been defined by the International Organization for Standardization (ISO) in commercial standards, such as the peel oils of ‘bitter orange’ [Citrus aurantium L.] ISO 9844; the extremely cheap oil of ‘sweet orange’ [Citrus sinensis (L.) Osbeck] ISO 3140; ‘mandarin’ Italian type [Citrus reticulata Blanco]; ‘cold pressed lime’ Mexican type [Citrus aurantifolia (Christm.) Swingle]; etc. However, none of these aldehydes have ever been found in the leaf oils of Backhousia citriodora, or any other myrtaceous oils.
It thus appears that these abnormal Backhousia citriodora oils are not genuine. In other words, they have been adulterated (see Table 1).
As a result of this the German firm decided to terminate its purchases of Backhousia citriodora oils altogether. This not only harms the Australian producers of lemon myrtle oil, but also reflects badly on the Australian essential oil industry as a whole.
1
Table 1. Chemical analyses of unacceptable ‘Backhousia citriodora’ oils of overseas provenance provided by the German buyer Oil component Sample 1a Sample 2b Sample 3c AS 4941–2001d Neral 39% 44% 44.3% 32% minimum Geranial 46% 50% 50.7% 44% minimum Geraniol 9% n.d. n.d. Present in small amounts only; not as yet included in AS 4941–2001
Aldehyde C8 n.d. 0.61% 0.56% These three aldehydes do not occur in Aldehyde C9 n.d. 0.66% 0.86% genuine oils of B. citriodora Aldehyde C10 n.d. 0.73% 0.67% a Sample 1: labelled ‘Lemon Myrtle Oil; 18766’; b Sample 2: labelled ‘Lemon Myrtle Oil Premium – Backhousia citriodora’; c Sample 3: labelled ‘Lemon Myrtle Oil Premium’; d AS 4941–2001: Australian standard: ‘Oil of Backhousia citriodora, citral type (lemon myrtle oil)’.
2
Objectives
In order to restore the good reputation of the Australian Backhousia citriodora oil industry, the existing standard AS 4941–2001 shall be revised and strengthened in order to define the chemical composition of the oil more accurately and reveal more readily and thus help to discourage, any attempts at adulteration.
The revision of the standard involves the determination via gas chromatography (GC) of the geraniol content of a representative number of genuine Backhousia citriodora oils, commercial as well as laboratory-distilled. Historical records of GC analyses of ‘lemon myrtle’ oils carried out at the Australian Tea Tree Oil Research Institute (ATTORI), Southern Cross University, Lismore, commissioned some 11 years ago by the Lemon Myrtle Growers’ Group operating at that time in the Northern Rivers district, as well as recent data published in scientific journals are used in this project.
The three adulterants in question, i.e. aldehydes C8, C9 and C10, have been identified and their exact position shown on GC traces under the operating conditions stipulated in the Appendix of the amended Australian standard for both non-polar as well as polar GC columns.
3
Methodology and Results
Acquisition of essential oil samples
Commercial oil samples produced by lemon myrtle distillers from the Northern Rivers district of New South Wales were collected and supplied by Mr Gary Mazzorana (Director of Australian Rainforest Products P/L, 106 The Channon Road, Lismore NSW 2480). Table 2 lists growers and producers whose product was sampled.
All samples are from New South Wales sources as an enquiry about obtaining oils from Queensland had not been answered.
All essential oil samples were dried with anhydrous sodium sulphate and stored in the refrigerator at about 5°C prior to analysis.
Table 2. Sources of essential oil samples Sample no. Grower/producer 1 Bruce Jobson 2 Paul Tait 3 Mark Duffy 4 Steve Law 5 LM Co-Op 6 Roger Bird; Lemon Myrtle Fragrances 7 Barry Daley; Rainforest Remedies 8 Gary Mazzorana; Limpinwood 9 Robert Santin 10 Gary Mazzorana; Road Side 11 Australian Rainforest Products 12 Blend ARP – Robert Santin 13 Blend ARP – Bruce Jobson 14 Single cultivated tree growing at Gordon (Sydney); laboratory distilled
Chemical composition of the oils
The oils were analysed by means of a combination of capillary gas chromatography-mass spectrometry (GC-MS) using two different columns (a non-polar one; and a polar one), in compliance with the requirements of the Australian standard. The results of the analyses are shown in Table 3. Figure 1 shows the GC trace of Backhousia citriodora oil obtained using a polar column.
4
Table 3. Backhousia citriodora – chemical composition (%) Constituent Sample no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 6-methyl-5-hepten-2-one 0.7 0.4 1.1 0.7 1.3 0.6 0.8 0.4 0.5 0.4 0.7 0.5 1.1 0.3 0.6 0.5 1.0 0.7 0.9 0.5 0.1 0.4 0.4 0.3 0.5 0.4 0.9 0.2 myrcene 0.2 0.1 0.3 0.4 0.1 0.2 0.3 0.2 0.1 0.2 0.2 0.2 0.2 0.1 2,3-dehydro-1,8-cineole 0.4 0.6 0.5 0.3 0.1 0.3 0.2 0.4 0.4 0.2 0.3 0.4 0.2 0.1 myrcene+dehydrocineole 0.9 0.7 0.8 0.7 0.5 0.6 0.6 0.7 0.7 0.6 1.0 0.7 0.5 0.2 linalool 0.7 0.2 0.7 0.5 0.6 0.5 0.6 0.5 0.4 0.4 0.6 0.5 0.6 0.3 cis-isocitral 1.5 1.3 1.4 1.5 0.8 1.4 1.2 1.6 1.4 0.8 1.4 1.6 1.1 0.7 linalool+ cis-isocitral 2.5 1.9 2.4 2.5 1.7 2.4 2.2 2.5 2.2 1.6 2.3 2.5 1.9 1.4 exo-citral 0.3 0.2 0.3 0.3 0.2 0.3 0.2 0.3 0.3 0.1 0.3 0.3 0.2 0.2 0.4 0.3 0.3 0.4 0.3 0.1 0.3 0.4 0.3 0.1 0.3 0.4 0.3 0.1 citronellal 0.2 tr 0.1 0.2 0.1 0.1 0.1 0.2 0.1 0.1 0.1 0.2 0.2 0.1 0.1 - 0.1 0.1 0.2 0.1 0.2 0.1 0.1 0.1 0.1 0.2 0.1 0.1 trans-isocitral 2.5 2.2 2.5 2.4 1.5 2.3 2.1 2.6 2.3 1.4 2.3 2.6 1.9 1.0 3.0 3.3 3.0 3.0 2.3 3.2 2.6 3.2 3.1 2.0 2.8 3.2 2.5 1.5 neral 39 37 39 40 41 40 40 40 39 39 39 40 41 39 38 38 38 40 40 40 39 40 39 39 38 40 40 40 geranial 49 48 48 51 51 50 49 51 50 53 49 51 51 54 48 48 48 50 51 49 49 50 49 51 49 50 50 54 geraniol 2.1 1.9 2.1 0.8 0.6 1.1 1.9 0.7 2.3 2.1 2.6 0.9 1.2 0.3 2.4 2.1 2.2 0.8 0.7 1.2 2.0 0.8 2.6 2.3 3.0 0.9 1.4 0.5 Non-polar phase; polar phase
5
Figure 1. Backhousia citriodora B-Wax column (polar)
6
Non-polar GC-MS/FID method
The analyses have been performed by Australian Botanical Products P/L (Hallam, VIC 3803; Managing Director: Mr John Fergeus).
GC analyses were performed on a Varian chromatograph, model CP-3800, with a flame ionisation detector (FID) using split injection 20:1 on a pair of 30 m x 0.25 mm i.d. fused silica columns coated with 0.25 µm DB-5 stationary phase (J&W Scientific) linked to the middle GC injector with temperature set at 250°C. Injections were performed using a Varian CP-8400 auto-sampler. One column terminates at the Varian Saturn 2000 mass spectrometer while the other column terminates at the front FID. Helium was used as the carrier gas and was programmed from 11.9 psi for 4 min at 0.05 psi/min to 13.3 psi then –0.01 psi/min to 13.0 psi. The column temperature was programmed from 60°C to 240°C at 3°C/min and held at 240°C for 2 min.
For identification of the oil components, samples were analysed using Varian Saturn 2200 gas chromatograph-mass spectrometer with transfer line temperature set at 280°C. Auto electron ionisation mode was used with a scan rate of 1 scan/sec and filament delay for 2 min; the mass spectrometry (MS) scan commenced at 2 min to 62 min at a mass range of 39–399 m/z.
The identities of the peaks on the DB-5 analysis are based upon the Adams library and libraries (the ‘C’ library and for sesquiterpenes the ‘K’ library, which is based, in part on the data presented by Joulain & König 1998).
Polar GC-MS method
Analytical GC was carried out by Dr J Brophy (Department of Chemistry, University of New South Wales) on a Shimadzu GC17A gas chromatograph with a Megabore column of B-Wax (60 m x 0.5 mm x 1 µm), programmed from 50°C to 220°C at 3°C/min with helium as the carrier gas. Injector and detector were both programmed at 220°C. GC integrations were performed on a SMAD electronic integrator.
GC-MS was carried out on a Shimadzu GCMS-QP5000 mass spectrometer operating at 70 eV ionisation energy. The GC column used was a DB-Wax (30 m x 0.25 mm x 0.25 µm) programmed from 35°C to 220°C at 3°C/min with helium as the carrier gas. Injector temperature was 250°C. MS were recorded in EI mode at 70 eV, scanning in the 41–350 m/z range. Interface and source temperatures were 250°C and 220°C respectively, with 1 scan/sec cycle time. Compounds were identified by their GC retention time and Retention Indices relative to n-alkanes and by comparison of their MS with either known compounds or published spectra (Adams 2007; Heller & Milne 1978, 1980; Heller et al. 1983; Joulain & König 1998; Stenhagen et al. 1974).
The data presented in Table 3 show that myrcene and dehydrocineole do not separate satisfactorily on the non-polar column whilst linalool and cis-isocitral do not separate on the polar column. More importantly, geraniol separates equally well on both columns. Geraniol values for the 14 samples varied from 0.3 to 2.6 per cent on the non-polar column and from 0.5 to 3.0 per cent on the polar column. The reason for these discrepancies is not clear.
Mean values for geraniol, rounded off to one decimal, were 1.5 per cent and 1.6 per cent for the non- polar and polar columns respectively. The standard deviation was 0.8 per cent for both columns. The mean value for geraniol was therefore set as 1.55 per cent.
It may be noteworthy that the laboratory-distilled lemon myrtle oil sample from Gordon (Sydney) (sample number 14), has the lowest geraniol content amongst the oils analysed.
7
Physico-chemical characteristics
The refractive indices and optical rotations of all 14 oil samples were determined in order to see whether they conformed to the values specified in AS 4941–2001. The ranges are as follows:
• refractive index at 20°C: n20: 1.4862–1.4879 [AS 4941–2001: 1.4840–1.4910]
• optical rotation at 20°C: αD: –0.08° to +0.48° [AS 4941–2001: –1.5° to +1.5°]
All oils comply with the requirements of the present Australian standard.
Comparison with other recent Backhousia citriodora investigations
A study of Backhousia citriodora essential oils commissioned by the Lemon Myrtle Growers’ Group was carried out in 1999 by L Doimo (Doimo 1999, 2001). The project included 29 samples of oils steam-distilled by Dr Doimo from foliage supplied to ATTORI (Lismore). The oils were analysed by capillary GC using a non-polar column. The identification of individual oil constituents has been carried out using a method developed by ATTORI specifically for this purpose (1-ISOTTO and BACKSHT) but not described in the final report. Since the peak labelled ‘geraniol’ (in the gas chromatogram of the oil attached to the report) fits in well with the position of geraniol in the gas chromatograms produced in this report, Dr Doimo’g geraniol figures are undoubtedly correct (despite the fact that he mistakenly labelled his chromatogram ‘Tea Tree Oil’!). The range of geraniol in these 29 oils was 0.55 to 1.65 per cent. The mean value of geraniol content was calculated as 0.96 per cent with a standard deviation of 0.22 per cent.
The geraniol content of a sample of Backhousia citriodora analysed by Brophy et al. (1995) was 0.39 per cent.
Southwell et al. (2000) studied 68 samples of steam-distilled Backhousia citriodora oils. Unfortunately, in their publication the geraniol content of only one oil sample is noted: 0.8 per cent.
Hayes and Markovic (2002) found 0.7 per cent of geraniol in a Queensland Backhousia citriodora oil sample.
Identification of aldehydes C8, C9 and C10
Co-injections of a mixture of the three aldehydes C8, C9 and C10 with Backhousia citriodora oil, on a non-polar as well as on a polar GC column, show that they are relatively easy to identify; the aldehyde peaks do not superimpose on any of the Backhousia peaks.
The three aldehydes were commercial-grade samples and contain very small amounts of impurities. As these aldehydes are unlikely to occur in any adulterated oils in large amounts, the small amounts of impurities present do not affect the quality of the gas chromatograms and thus the detection of eventual adulteration. Table 4 lists the contents of Figures 2 to 7.
Table 4. GC chromatograms and analysis for Backhousia citriodora oil, a mixture of aldehydes, and a combination of oil and aldehydes Figure no. Sample Non-polar or polar phase 2 Backhousia citriodora oil non-polar 3 mixture of aldehydes C8, C9, C10 non-polar 4 Backhousia citriodora oil + mixture of aldehydes C8, C9, C10 non-polar 5 Backhousia citriodora oil polar 6 mixture of aldehydes C8, C9, C10 polar 7 Backhousia citriodora oil + mixture of aldehydes C8, C9, C10 polar
8
Figure 2. Backhousia citriodora oil (non-polar phase)
9
Figure 3. Mixture of aldehydes C8, C9 and C10 (non-polar phase)
10
Figure 4. Backhousia citriodora oil + mixture of aldehydes C8, C9 and C10 (non-polar phase)
11
Figure 5. Backhousia citriodora oil (polar phase)
12
Figure 6. Mixture of aldehydes C8, C9 and C10 (polar phase)
13
Figure 7. Backhousia citriodora oil + mixture of aldehydes C8, C9 and C10 (polar phase)
14
Discussion and Recommendations
The geraniol contents determined in this study are somewhat higher and more variable than those reported in Doimo’s report. The mean geraniol content and standard deviation determined in this study are 1.55 per cent and 0.8 per cent whereas Doimo’s mean content and standard deviation were determined as 0.96 per cent and 0.22 per cent respectively. The geraniol values reported by other workers fell within the ranges reported by Doimo as well as this project.
Owing to the significant variations in the geraniol contents of Backhousia citriodora oils, with only one figure reported as high as 3.0 per cent, it would be justifiable to set the per cent geraniol limits to within ± the standard deviation, e.g. 1.55 ± 0.8, that is, 0.7 to 2.35 per cent. Since the values are quite low and GC operating conditions could vary slightly from one laboratory to another, with the age of the column as well as its polarity etc., it is recommended that the range of geraniol in the amended Australian standard be set slightly wider, e.g. 0.6 to 2.5 per cent.
The three aldehydes C8, C9 and C10 must be absent. Consequently their retention time, e.g. their position on the GC trace, must be indicated should the need arise. A note to this effect must be added to the ‘Typical Gas Chromatograms’ (on both polar and non-polar columns) in the Appendices of the amended standard together with an indication of the position where these aldehydes would elute under the GC conditions used.
15
References
Adams, RP 2007, Identification of Essential Oil Components by Gas Chromatography/Quadrupole Mass Spectrometry, Allured Publishing Corporation.
Brophy, JJ, Goldsack, RJ, Fookes, CJR & Forster, PI 1995, ‘Leaf oils of the genus Backhousia (Myrtaceae)’, Journal of Essential Oil Research, vol. 7, issue 3, pp. 237–254.
Doimo, L 1999, Lemon Myrtle Growers’ Group: Analyses of Growers’ Samples, a confidential report.
Domio, L 2001, ‘Iso-citrals and iso-geranials in lemon myrtle (Backhousia citriodora F. Muell.) essential oils’, Journal of Essential Oil Research, vol. 13, issue 4, pp. 236–237.
Hayes, AJ & Markovic, B 2002, ‘Toxicity of Australian essential oil of Backhousia citriodora (lemon myrtle). Part 1. Antimicrobial activity and in vitro cytotoxicity’, Food and Chemical Toxicology, vol. 40, pp. 535–543.
Heller, SR & Milne, GWA 1978, EPA/NIH Mass Spectral Data Base, in five volumes, part of the NBS National Standard Reference Data Series of Critical Data Compilations (GPO# SN 003-003-01987-9, #NSRDS-NBS 63), US Government Printing Office.
Heller, SR & Milne, GWA 1980, EPA/NIH Mass Spectral Data Base, Supplement Number One, in two volumes, part of the NBS National Standard Reference Data Series of Critical Data Compilations, (GPO # SN 003-003-02268-3, NSRDS-NBS 63, Suppl. 1), US Government Printing Office.
Heller, SR, Milne, GWA & Gevantman, LH 1983, EPA/NIH Mass Spectral Data Base, Supplement Number Two, in two volumes, part of the NBS National Standard Reference Data Series of Critical Data Compilations, (GPO # SN 003-003-02268-3, NSRDS-NBS 63, Suppl. 2), US Government Printing Office.
Joulain, D & König, WA 1998, The Atlas of Spectral Data of Sesquiterpene Hydrocarbons, EB Verlag, Hamburg.
Southwell, IA, Russell, M, Smith, RL & Archer, DW 2000, ‘Backhousia citriodora F. Muell. (Myrtaceae), a superior source of citral’, Journal of Essential Oil Research, vol. 12, pp. 735–741.
Stenhagen, E, Abrahamsson, S & McLafferty, FW 1974, Registry of Mass Spectral Data, Wiley, New York.
16
Revision of Backhousia citriodora Essential Oil Standard
by EV Lassak
Publication No. 11/137
The lemon-scented volatile leaf oil of Backhousia citriodora is RIRDC is a partnership between government and industry used in the compounding of flavours and fragrances as well as to invest in R&D for more productive and sustainable rural in aromatherapy. The present Australian Backhousia citriodora industries. We invest in new and emerging rural industries, a essential oil standard AS 4941, first published in 2001, requires suite of established rural industries and national rural issues. significant revision in order to reflect the improved quality of presently produced oils. The reasons for the revision are not only Most of the information we produce can be downloaded for free to reflect the greater chemical uniformity of presently produced or purchased from our website
Contact RIRDC: Level 2 15 National Circuit Ph: 02 6271 4100 Most RIRDC publications can be viewed and purchased at Barton ACT 2600 Fax: 02 6271 4199 our website: Email: [email protected] PO Box 4776 web: www.rirdc.gov.au www.rirdc.gov.au Kingston ACT 2604 Bookshop: 1300 634 313
RIRDCInnovation for rural Australia