Evaluation of the quality of sandalwood essential oils by gas chromatography–mass spectrometry

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Abstract

Trade and historic oils from ‘sandalwoods’, labelled as Amyris balsamifera, Eremophila mitchelli, Fusanus acuminatus (= Santalum acuminatum), Santalum album, S. austrocaledonicum, S. latifolium, S. spicatum and S. yasi, were assessed using gas chromatography–mass spectrometry (GC–MS). Using GC–MS, none of the oils assessed complied with the internationally recognised standard of a 90% santalol content, and only about half of the trade sandalwood oils met with recent International Organisation for Standardisation standards. The majority of trade oils, reportedly from S. album, contained approximately 50–70% santalols (Z-α and Z-β). Thus, the internationally recognised specification (90% santalols) for S. album requires re-evaluation by more efficient analysis methods. In view of the issues associated with the quality of sandalwood oils being traded, specifications of ≥43% Z-α-santalol and ≥18% Z-β-santalol for S. album oil estimated by GC–MS are suggested. GC–MS are recommended as it assists with authentication and quality control issues associated with sandalwood oils.

Introduction

Sandalwood oil is widely used in the cosmetic, perfumery and aromatherapy industries. The most renowned sandalwood oil is distilled from the sandalwood tree Santalum album L. (Santalaceae) and the oil is the subject of international concern regarding its sustainability and quality. There has been a serious decline in the population of S. album in India [1], [2] due to complex cultivation requirements and continuous harvesting (particularly from smuggling), combined with limited regeneration. As a result the quality of sandalwood oil entering the trade may be compromised, not only due to the declining numbers of trees with developed heartwood (trees of at least 20–25 years old), but also due to adulteration to compensate for the restricted, and thus increasingly expensive, Indian S. album oil. In view of the current issues associated with sandalwood, an investigation was conducted to develop an appropriate method to assess the quality of sandalwood essential oils being traded in the UK.

Numerous quality control issues are associated with sandalwood. At present, no standard method is available to determine adulteration of sandalwood oil, or to aid the identification of the species from which the oil was obtained. This is a particular problem as the classification of sandalwood is complex; over 100 taxon names have been published in the genus Santalum, probably representing about 25 species, also species in other families (e.g. Amyris balsamifera L., Rutaceae) are traded as ‘sandalwood’ [3]. In addition, S. album wood may be substituted with other species [2] or the oil may be adulterated with synthetic or semi-synthetic substitutes such as Sandalore® [3], [4], [5]. Substitution and/or (semi) synthetic additives would influence the chemical composition and physical properties of the oil; these factors may affect oil quality and the allergenic potential. Reported non-synthetic adulterants include castor oil, cedarwood oil and oils from ‘sandalwood’ species other than S. album [3], [6].

It is recommended that the essential oil from S. album should not contain less than 90% w/w of (free) alcohols, calculated as santalols [6], [7], [8], [9], [10], [11]. The methods described to assess the santalol content of sandalwood essential oil generally lack specificity and accuracy. For example, the acetylation methods [9], [10], [12], [13] are not specific for the santalols, which have been associated with the quality of sandalwood, and do not distinguish among the santalol isomers. Thus, adulteration of sandalwood may be undetected via these methods if some other hydroxylated compounds are amongst the adulterants. It has been suggested that sandalwood oil should be evaluated using gas chromatography (GC) by quantitation of the santalol content, with a proposed range of 40–55% for α-santalol and 17–27% for Z-β-santalol [14]. More recently the ISO (2002) has included GC analysis of S. album oil and this specifies similar proportions of Z-α- and Z-β-santalol, 41–55% and 16–24%, respectively [13]. However, these reports do not discuss potential variation in S. album oil composition, depending on origin or age, nor do they address the detection of adulterants or the evaluation of other sandalwood oils. These factors are of particular concern if we are to be able to both evaluate the quality and trace the source of the sandalwood being traded. The aim of this study was to develop and evaluate gas chromatography–mass spectrometry (GC–MS) analysis as a means to assess the quality of sandalwood, to distinguish between the different species traded as sandalwood, and to detect adulterants.

Section snippets

Samples

Thirty-eight trade samples of sandalwood essential oils were analysed, including 31 oils claimed to be from Santalum album L. from India (voucher numbers: BI 10093-6, BI 10106, BI 10132, BI 10168, BI 10172-3, BI 10179-80, BI 10183, BI 10186, BI 10190, BI 10201-2, BI 10206-7, BI 10212, BI 10270-72, BI 10275-76, BI 10279, BI 10287-89, BI 10307, BI 10579) and Indonesia (voucher number: BI 10210), as well as oils from Amyris balsamifera L. from India (voucher number: BI 10282), Eremophila mitchelli

Results and discussion

Two GC column phases were evaluated for sandalwood oil analysis. The santalols showed superior chromatographic peak shape on the polar ZB-WAX column, compared to the non-polar DB-5MS column, allowing baseline resolution of the santalols to be obtained using a shallow temperature gradient. Lengthy chromatography of the santalols produced unacceptable peak trailing on the DB-5MS column and so a steeper temperature gradient was necessary; baseline resolution of the santalols was not achieved (Fig.

Conclusion

It is evident that sandalwood oil composition may vary depending on its geographical and taxonomic origin, which may reflect current international demand and declining resources. It should also be noted that santalol composition can vary depending on the method of oil extraction [23].

From the present study, it is apparent that generally accepted specifications (90% santalol content) and analysis methods require re-evaluation. Thus, it is suggested that quality control and authentication

References (23)

  • N.W. Davies

    J. Chromatogr.

    (1990)
  • J.E.D. Fox

    Biologist

    (2000)
  • A.M. Radomiljac, H.S. Ananthapadmanabho, R.M. Welbourn, K. Satyanarayana Rao (Eds.), Sandal and Its Products, ACIAR...
  • D.P. Anonis

    Perfumer Flavorist

    (1998)
  • P. Kraft et al.

    Angew. Chem. Int. Ed.

    (2000)
  • R.E. Naipawer, in: B.M. Lawrence, B.D. Mookherjee, B.J. Willis (Eds.), Flavors and Fragrances: A World Perspective,...
  • US Dispensatory, 25th ed., Lippincott, Philadelphia, 1955, p....
  • British Pharmaceutical Codex, The Pharmaceutical Society, London, 1949, p....
  • E. Dahlian

    Hartoyo

    Buletin Penelitian Hasil Hutan.

    (1998)
  • Food Chemicals Codex, third ed., National Academy Press, Washington, DC, 1981, p....
  • International Organisation for Standardisation, first ed., ISO 3518...
  • Cited by (0)

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