methods for the characterization, authentication, and adulteration of essential oils

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11Essential Oils in Food Preservation, Flavor and Safety. http://dx.doi.org/10.1016/B978-0-12-416641-7.00002-X

Copyright 2016 Elsevier Inc. All rights reserved.

Chapter 2

Methods for the Characterization,Authentication, and Adulterationof Essential Oils

Tzi Bun Ng1, Evandro Fei Fang2, Alaa El-Din Ahmed Bekhit3, Jack Ho Wong11The Chinese University of Hong Kong, School of Biomedical Sciences, Faculty of Medicine, Hong Kong, China; 2National Institute on Aging, National

Institutes of Health, Laboratory of Molecular Gerontology, Baltimore, MD, USA; 3University of Otago, Department of Food Science, Dunedin, New Zealand

List of Abbreviations

GCMS Gas chromatographymass spectrometry

SSR Simple sequence repeat

RAPD Random amplified polymorphic DNA

SFE GCMS Supercritical fluid extraction GCMS

MDGC Multidimensional gas chromatography

GCCIRMS Gas chromatographycombustionisotope ratio mass spectrometry

INTRODUCTION

Essential oils extracted from plants are used in cosmetics, in many foods, and for their fragrance, flavoring, and preservative

properties. The bulk is employed for the fragrance or flavor industries, with only a small percentage for therapeutic purposes.

It is imperative that therapeutic oils are unadulterated. Completely pure natural essential oils should be obtained straightfrom the grower without intervention by a vendor. Ideally, essential oils should be clearly labeled with the botanical name,

cultivation method, country of origin, the plant tissue employed for distillation, and main constituents. However, very few

people using essential oils know that the oils they are using may be adulterated. Unscrupulous manufacturers of essential

oils may resort to adulterating the oils with the intent to make the price competitive and maximize the profit. Extraordinarily

cheap essential oils and labels such as for external use only, not for internal use, and dilute prior to topical application

should alert one to the possibility of adulteration.

The adulterants are: (1) vegetable carrier oils, alcohol, and synthetic oils used as diluents; (2) cheaper oils of the

same species but of different geographical origins; (3) cheaper essential oils extracted from another part of the plant;

(4) cheaper essential oils from related species; and (5) isolated natural, or (semi) synthetic compounds. Frankincense

may be adulterated with gum resin, alcohol, and other solvents. Many commercial samples of lavender oil are com-

posed of lavandin, camphor, linalyl acetate, propylene glycol, and petrochemicals. Synthetic oils have appeared in

products claimed to be natural oils. Noxious chemicals with health risks, including phthalates and benzyl alcohol,

have been detected in essential oils.In view of the aforementioned adulteration of plant essential oils, it is of paramount importance to examine the various

methods available for authentication and adulterant detection which are mentioned below.

METHODS OF AUTHENTICATION

Gas ChromatographyMass Spectrometry (GCMS) for Hyssopus cuspidatusEssential Oil

An investigation of the chemical composition of the essential oil of Hyssopus cuspidatus Boriss from Xinjiang,

China employing GCMS led to the identification of 50 compounds. The principal constituents comprised oxygenated


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12 PART |I General Aspects

sesquiterpenes (1.25%), octane (1.85%), monoterpenes (26.14%), and oxygenated terpenes (66.33%). The authenticity

ofH. cuspidatusmay be confirmed by the physicochemical parameters of the compounds ( Zhou et al., 2010).

Determination of Enantiomeric Composition for Essential Oils of Indian Origin

Use of 10% heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin as a chiral stationary phase to

ascertain the enantiomeric ratios of linalool in a diversity of authentic essential oils originating from India has beenreported by Chanotiya and Yadav (2009). A complete enantiomeric excess for (3S)-(+)-linalool was typical of leaf

oils from Lippia albaand Cinnamomum tamala while below 90% excess was found in Zanthoxylum armatum leaf,

Zingiberroseumroot/rhizome, and Citrus sinensisleaf oils. By contrast, an enantiomeric excess of (3R)-()-linalool

was observed in essential oils of basil (100% for Ocimum basilicum) and bergamot mint (7275% forMentha citrata).

Thus enantiomeric compositions could be used to assess the authenticity of essential oil ( Chanotiya and Yadav, 2009).

In addition, Kreis and Mosandl (1992)reported the stereoanalysis of chiral compounds present in lavandula essential

oil. An example is shown in Table 1.

Supercritical Fluid Extraction GCMS (SFE GCMS) Involving Use of Multidimensional GCto Resolve Enantiomers for Essential Oils of Lavandula

An approach based on SFE was adopted to investigate, both qualitatively and quantitatively, the compositions of the

predominant volatile aroma constituents in essential oils of different varieties of Lavandula. Under optimal condi-tions of SFE, relative standard deviations (RSDs) from three replicates below 2% and recoveries up to 59% could be

achieved. For separation of the target enantiomeric compounds, multidimensional gas chromatography was deployed.

The data disclosed an enantiomeric purity exceeding 90% for every compound in the different varieties examined,

lending credence to the natural constant enantiomeric composition of the compounds of interest. The data can be of

value in authenticity investigations and in choosing natural sources of enantiomerically homogeneous compounds

(Flores et al., 2005).

TABLE 1 Enantiomeric Distributions of Chiral Monoterpenoids From Authentic Samples of Lavandula Oils

No.

trans-Linaloloxide (2R, 5R) cis-Linalol oxide(2R, 5S) Linalyl acetate (R) Lavandulol (R) Terpinen-4-ol (S) Linalol (R)

2 3 11 13 16 17

1 86.4 88.5 >99 93.2 97.4

2 >99 98.5 97.8 94.5

3 88.6 86.0 >99 98.0 96.6

4 84.6 86.7 >99 89.8 98.0 95.1

5 90.2 91.5 >99 >99 94.2 97.5

6 96.1 91.5 >99 >99 98.2 97.3

7 95.8 92.9 >99 98.3 98.0 96.9

8 >95 >95 >99 98.7 98.3 98.2

9 85.4 90.0 >99 >99 98.1 96.1

10 87.5 95.8 >99 >99 98.4 97.1

11 >99 >99 98.1 95.2

12 76.7 82.9 98.8 >99 98.1 97.2

13 86.2 89.3 >99 96.2 89.1 95.1

Reproduced from Kreis and Mosandl (1992)with a kind permiss ion from John Wiley and Sons Publishing. Permit No 3341621103500.


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Essential Oil Authenticity Chapter |2 13

Enantioselective Capillary Gas Chromatography and Online Methods of Isotope Ratio MassSpectrometry

Mosandl (2004)wrote an excellent review on enantioselective capillary gas chromatography and online methods of isotope

ratio mass spectrometry in the authentication of food flavor and essential oil compounds, covering papers published in the

10 years preceding his review.

Enantioselective Capillary Gas Chromatography and Isotope Ratio Mass Spectrometry, CoupledOnline with Capillary Gas Chromatography on an HP5 Column for Various Essential Oils

Enantioselective capillary gas chromatography conducted using a Supelco beta-DEX 225 column heptakis(2,3-di-O-

acetyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin SPB 20poly-20% diphenyl, 80% dimethylsiloxane) and isotope ratio

mass spectrometry, coupled online with capillary gas chromatography on an HP5 column have been exploited for analysis

and authenticity investigations of essential oils. The essential oils examined included those of the following plants: lemon

(Citrus limon), lemongrass (Cymbopogon citratusand Cymbopogon flexuosus), citronella (Cymbopogon nardusL.Ceylon

type and Cymbopogon winterianusJava type),Litsea cubeba, Lippia citriodora, lemon myrtle (Backhousia citriodora),

lemon gum (Eucalyptus citriodora), and precious lemon balm oil (Melissa officinalisL.). Isotope data (13C(Pee Dee

Belemnite (PDB)) and 2H(Vienna standard mean ocean water (V-SMOW)) for citral (neral + geranial) and citronellal

from isotope ratio mass spectrometry online coupled with capillary gas chromatography (GC-Py-IRMS) and chiral data

for citronellal in these essential oils can yield information on the origin of essential oils and disclose adulterants. Principalcomponents analysis of specific compounds was carried out for discriminating essential oils from L. cubeba, C. citratus,

and C. flexuosus(Nhu-Trang et al., 2006a).

Online Gas Chromatography Pyrolysis Isotope Ratio Mass Spectrometry (HRGCPIRMS) forthe Flavor Compounds Decanal, Linalool, Linalyl Acetate, E-2-Hexenal, and E-2-Hexenol inEssential Oils

Hr et al. (2001)applied the HRGCPIRMS technique to find the 2H(SMOW) values of the aforementioned flavor

compounds in foods and essential oils. Procedures such as simultaneous distillation extraction, solvent extraction, and

liquid/liquid extraction used for preparing samples had negligible effects on the 2H values. Only the 2H data recorded for

linalool did not permit distinction between synthetic and natural products. For decanal, linalyl acetate, E-2-hexenal, and

E-2-hexenol, the data appeared to be useful for differentiation purposes (Table 2).

TABLE 2 Application of HRGCPIRMS Technique to Distinguish Between Synthetic

and Natural Flavor Compounds in Essential Oils

2H(SMOW) Values: 2H Abundance

Synthetic decanal samples From 90 to 156 per 1000

Natural decanal samples From 138 to 262 per 1000

Synthetic linalyl acetate samples From 199 to 239 per 1000

Natural linalyl acetate samples From 213 to 333 per 1000

Synthetic E-2-hexenal samples From 14 to 109 per 1000

Natural E-2-hexenal samples From 263 to 415 per 1000

Synthetic E-2-hexenol samples From 41 to 131 per 1000

Natural E-2-hexenol samples From 238 to 348 per 1000

Synthetic linalool samples From 207 to 301 per 1000

Natural linalool samples From 234 to 333 per 1000

Only the 2H data recorded for linalool did not permit distinction between synthetic and natural products.Data compiled from Hr et al. (2001).


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Isotope Ratio Mass Spectrometry Online Coupled with Capillary Gas Chromatography(GC-Py-IRMS)

GC-Py-IRMS on column INNOWAX has been exploited in studies on the authenticity of phenolic essential oils (Table 3,

Nhu-Trang et al., 2006b).

Gas ChromatographyCombustionIsotope Ratio Mass Spectrometry (GCCIRMS), inCombination with GCMS and GC Flame Ionization Detector (FID) for Rosa damasceneEssential Oil

Nineteen commercial samples of R. damascenaessential oil collected from various localities, together with an authen-

tic sample of essential oil extracted from fresh flowers, were analyzed by GCMS and GCFID. Elemental analyzer

(EA)IRMS and GCCIRMS were employed for analysis of the 13C composition of bulk samples and of some specific

components. It was discovered that essential oils from Turkey and Bulgaria contained mainly citronellol, geraniol, and

nonadecane, while Iranese essential oils were abundant in the aliphatic hydrocarbons nonadecane. The 13C values of bulk

samples fell within the range 28.1 to 26.9, characteristic of C3plants. The 13C values of specific components were

found within the range for natural aromatic substances from C3plants, with the exception of geranyl acetate, which demon-

strated elevated values (up to 18) caused by adulteration with an oil from a C4plant (Cymbopogon martinii, palmarosa)

which has a lower cost and existing in the bulk of essential oils (Pellati et al., 2013).

HeadspaceSolid Phase Microextraction Coupled to GCCIRMS for Citrus Oils

Schipilliti et al. (2010)evaluated the authenticity of some mandarin essential oils using GCCIRMS. Schipilliti et al.

(2013)examined the authenticity of Italian liqueurs, bergamot, lemon, and mandarin, by using headspacesolid phase

microextraction coupled to GCCIRMS. Their carbon isotope ratios were compared with those of genuine cold-pressed

peel oils. Direct enantioselective gas chromatography was used to determine the enantiomeric distribution of selected chiral

volatiles and GCMS was employed for qualitative analyses (Schipilliti et al., 2013).

Multi Dimensional Gas Chromatography (MDGC) and GC-C-IRMS for Bitter Orange FlowerOil (or Neroli) and Lime Oils

Five samples of Egyptian neroli oils, manufactured in 2008 and 2009 in the same factory, and claimed to be authentic,

were used in the study of Bonaccorsi et al. (2011). GCFID and GCMSlinear retention index were employed to analyze

TABLE 3 2H(V-SMOW) Values Of Various Components in Essential Oils

2H(V-SMOW)

Carvacrol 61 per 1000

Thymol From 49 to 7 per 1000

p-Cymene From 300 to 270 per 1000

-Terpinene From 285 to 248 per 1000

Thymol From 259 to 234 per 1000

Carvacrol in authentic oregano oils From 223 to 193 per 1000

p-Cymene in authentic oregano oils From 284 to 259 per 1000

Aromatic Compounds in Authentic Satureja montanasubsp. Montana Essential Oil

Carvacrol 226 per 1000 (SD = 1.7 per 1000)

p-Cymene 283 per 1000 (SD = 3.0 per 1000)

-Terpinene 273 per 1000

SD, standard deviation.Data compiled from Nhu-Trang et al. (2006b).


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the composition, and enantioselective GC utilized to investigate the enantiomeric distribution of 12 volatile compounds.

GC-C-IRMS was employed to ascertain the 13C(VPDB) values of some alcohols, esters, and monoterpene and sesquiter-

pene hydrocarbons. The variation of the composition depended on the time of manufacture. Linalool dropped while linalyl

acetate rose from March to April. The RSD for the 13C(VPDB) remained small (max. 3.89%), assuring sample authenticity

(Bonaccorsi et al., 2011).

Bonaccorsi et al. (2012)conducted an investigation on the authenticity of lime oils (Citrus aurantifoliaSwingle and

Citrus latifoliaTanaka), by employing MDGC to study the enantiomeric distribution of camphene, limonene, linalool,-phellandrene, -phellandrene, -pinene,terpinen-4-ol, -terpineol, sabinene, and -thujene. GCCIRMS was used to

ascertain the isotopic ratios of -caryophyllene, geranial, germacrene B, limonene, neral, -pinene, -pinene, -terpineol,

and trans--bergamotene. The concurrent deployment of the two techniques facilitates detection of adulteration in citrus

essential oils. In fact, in some cases detection of adulteration is possible only with one of the two techniques. The merit of

their simultaneous usage is the need to analyze only a small number of constituents hence minimizing the amount of data to

be handled. Moreover, the traditional method of analysis which relies on the assessment of the entire volatile fraction may

not be sensitive enough to disclose the oil quality when there is only a slight level of adulteration (Bonaccorsi et al., 2012).

GCFID and GCMS forZanthoxylum armatumLeaf Essential Oil

The predominant types of compounds detected in the leaf oils comprised acyclic and menthane monoterpenoids, simple

alcohols, aldehydes, and ketones. The unique composition was characterized by a richness of nonterpenic acyclic ketones,

exemplified by 2-undecanone and 2-tridecanone, and the meager content of undec-10-en-1-al and p-phellandren-8-ol.Other components encompassed oxygenated monoterpenes like 1,8-cineole, linalool, terpinen-4-ol, and alpha-terpineol.

Sesquiterpene hydrocarbons, in particular trans-caryophyllene, a-humulene, and germacrene D, were present. On the con-

trary, the oil distilled from the leaves on the second day of distillation was characterized by an abundance of 2-tridecanone

and trans-caryophyllene compared with fresh foliage. Moreover, a rich content of 2-undecanone and 2-tridecanone is char-

acteristic ofZ. armatum. Thus, the two acyclic ketones may be utilized in authenticity testing (Bisht and Chanotiya, 2011).

Ultra-High Performance Liquid ChromatographyTime-of-FlightMass Spectrometry (UHPLCTOFMS) Profiling and 1H Nuclear Magnetic Resonance (NMR) Fingerprinting for Lemon Oil

A metabolomic strategy which depends on UHPLCTOFMS profiling and 1H NMR fingerprinting to reveal variances in

metabolites has been designed for lemon oil samples that find application in the flavor and fragrance industry. Flavonoids,

furocoumarins, fatty acids, and terpenoids present in the mixtures were markers with a differentiating role. Quantitative

NMR unveiled low levels of citropten and an abundance of bergamottin in samples from Italy compared with Argentinian

samples (Marti et al., 2014).

Near Infrared (NIR) Spectroscopy for Sandalwood Oil

NIR spectroscopy in conjunction with multivariate calibration models such as principal component regression and partial

least square regression is qualitative and quantitative analytical tool for detecting adulterants in sandalwood oil with the

advantages of speed, sensitivity, and nondestructiveness. Following appropriate preprocessing of the raw near infrared data,

the models were constructed by cross-validation. To find the optimal number of factors, the smallest root mean square error

of cross-validation and calibration was utilized. The coefficient of determination and the root mean square error of predic-

tion in the prediction sets were employed as the parameters for evaluation (Kuriakose et al., 2010).

Kuriakose and Joe (2013)conducted a study that employed NIR spectroscopy to investigate the authenticity of samples

and quantitate adulteration of sandalwood oils. Quantitative analysis of data was executed using full spectrum or sequentialspectrum. The optimum number of partial least square components was procured according to the smallest root mean square

error of calibration (RMSEC = 0.00009% v/v). The smallest root mean square error of prediction (RMSEP = 0.00016% v/v)

in the test set and the largest coefficient of determination (R2= 0.99989) were employed for assessment for the best model.

Locally weighted regression was introduced to collect nonlinear information and for comparison with the linear partial least

square regression model (Kuriakose and Joe, 2013).

NIR Spectroscopy for Various Essential Oils

Cross-validation models can be used to predict with accuracy virtually all of the constituents of essential oils. In various

cinnamon (Cinnamomum zeylanicum) and clove (Syzygium aromaticum) essential oils, which demonstrated analogous


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compositions, 23 components (accounting for the bulk of the oil) were correctly predicted. Likewise, 20 components in

Cinnamomum camphora, 32 components inRavensara aromatica, and 26 components inLippia multiflorathat made up

the bulk of the oils, were also correctly predicted. For almost all of the components, the modeled and reference values

obtained by GCFID exhibited a high correlation and a variance below 5%. The model was used to disclose erroneous

commercial labeling of C. camphoraoil asR. aromaticaoil (Juliani et al., 2006).

Simple Sequence Repeat (SSR)

The certification labels protected designation of origin (PDO) and protected geographical indication (PGI) are required

by the European Commission for assuring the authenticity of food products. Regulations for labeling, production, and

commercialization of olive oil were laid down in European Economic Community Regulation No. 510/2006. Genotype is

important in the establishment of PDO and PGI labels. The analysis of 21 olive oil samples was conducted with the help

of nine nuclear and two shortened simple sequence repeats. An array of simple sequence repeat markers can be used to

accurately attribute an olive oil to a certain cultivar (Vietina et al., 2011).

Random Amplified Polymorphic DNA (RAPD) Method

A study of 84 commercial Mediterranean oregano samples collected between 2001 and 2007 disclosed the prevalence of

adulteration. Materials from plants with an oregano-like flavor (Satureja montanaand Origanum majorana), and plant

materials devoid of essential oils from Cistus incanus, Rubussp. andRhus coriaria, were added as adulterants. The RAPDmethodology devised by Marieschi et al. (2009) using 13 differentiating primers facilitated the sensitive detection of

materials from C.incanus, Rubussp., andR. oriariaadded as adulterants and expedited analysis of big batches of samples

(Marieschi et al., 2009).

Attentuated Total Reflectance (ATR)-Mid-infrared Portable Handheld Spectrometerfor Peruvian Sacha Inchi Seed Oils

Thermally regulated ZnSe ATR mid-infrared benchtop and diamond ATR midinfrared portable handheld spectrometers

were used by Maurer et al. (2012)to investigate Peruvian seed oils abundant in omega-3 fatty acids. A soft independent

model of class analogy and partial least squares regression were utilized for the analysis of the spectral data. Polyunsatu-

rated fatty acid concentrations resembling levels seen in flax oils were revealed. Partial least square regression showed

good correlation between reference tests and spectra from infrared devices with correlation coefficients exceeding 0.9,

facilitating speedy analysis of composition of fatty acids. Results indicated existence of adulteration (Maurer et al., 2012).

SUMMARY POINTS

The bulk of plant essential oils are utilized by the fragrance or flavor industries, with only a small percentage for therapeu-

tic purposes.

In order to lower the price of the essential oils and hence attract more customers, adulterants are added by the producers to

the oils.

Adulterants include diluents and cheaper oils from other plant tissues, related plant species, or plants of the same species

but from other countries. Some of the adulterants detected such as phthalates and benzyl alcohol are hazardous to health.

Various types of methodology are available for authentication and adulterant detection. They include GCMS, determina-

tion of enantiomeric composition, SFE GCMS involving use of multidimensional GC to resolve enantiomers, enantiose-

lective capillary GC, and online methods of IRMS. Other methods comprise enantioselective capillary gas chromatography and IRMS coupled online with capillary gas chro-

matography, NIR spectroscopy, SSR, RAPD, and various other methods.

DISCLAIMER

This article was written in a personal capacity (E.F.F.) and does not represent the opinions of the United States Food

and Drug Administration, the United States Department of Health and Human Services, or the United States Federal

Government.


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ACKNOWLEDGMENT

This research was supported in part by the Intramural Research Program of the NIH, National Institute on Aging, USA.

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methods for the characterization, authentication, and adulteration of essential oils

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