Essential oils adulteration problem information

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Essential oils adulteration problem

Adulteration has been a serious problem for many years in the area of essential oils. Undoubtedly the economic incentive to blend synthetic flavourants with natural oil is too high to resist. Some essential oils naturally contain a single compound at high concentration, and often the synthetic counterpart of this major component is available at a low cost. Addition of this single compound to natural essential oils without declaration on the label amounts to adulteration.

Addition of synthetic flavourants

Synthetic flavour compounds contain impurities characteristic of the synthetic route used to prepare them. These impurities can be quantified by selected ion monitoring (SIM), gas chromatography/mass spectrometry (GC/MS) in essential oils, and their absence is an indication of the essential oil being natural (Frey 1988). For instance, the presence of impurities such as phenyl pentadienal, benzyl alcohol and eugenol in synthetic cinnamaldehyde forms the basis of its detection in natural cassia oil. These impurities could be quantified by GC/MS, and levels as low as 0.55 parts of synthetic cinnamaldehyde in natural cassia oil can be detected (Zhu et al. 1996). A mass spectrometer usually scans over a range of trace compounds in order to obtain data on every component in a mixture. The decrease in the number of masses detected using SIMresults in a 10-fold to 100-fold increase in detection sensitivity for a single compound.

Addition of edible and mineral oils

Both edible and mineral oils are often used for adulteration (Nour-el-Din et al. 1977). The mixing of expensive oils with cheaper oils can often be detected by running a GC profile of the oil. One approach is to search for components in the expensive oil which are not commercially available, and are unique to the oil. An example is beta-selinene in the oil of celery. A good quality oil should contain 7.0-7.5% beta-selinene (Straus and Wolstromer 1974). Oils containing less than 7.0% beta-selinene should be suspected of being adulterated.

Dilution with ethyl alcohol

Ethyl alcohol represents the main alcohol usually used in moderate quantities to dilute essential oils (Mostafa et al. 1990a). Dilution of essential oils with ethanol was checked using refractometric methods which were found to be unreliable (Kaminski and Dytkowska 1960). These and many other adulterations can be identified by infra-red (IR), gas chromatography (GC), and thin-layer chromatography (TLC) (Di Giacomo and Calvarano 1973). TLC has been found to be a simple method of checking adulteration in essential oils of caraway, coriander, parsley and anethum (Hoerhammer et al. 1964). Detection of nature-identical flavouring substances in high-value genuine onion oil is based on the GC/MS, or IR spectroscopy of the onion furanone, 2-n-hexyl-5-methyl- 3(2H) furanone (Losing 1999). This technique is both simple and rapid.

Iodine number for detection of adulteration

Iodine number has been suggested as a means of detecting adulteration in essential oils (Kartha and Mishra 1963), but the iodine number has not attained significance in assessing the quality of essential oils probably due to unpredictable behaviour of these oils in the presence of solutions, commonly employed for iodination. The observation that the iodine monobromide-mercuric acetate reagent brings about quantitative fission of the cyclopropane and cyclobutane rings in essential oils prompted Kumar and Madaan (1979) to make use of such iodine absorption values for this purpose. The method could detect adulteration successfully in samples considered to be unadulterated on the basis of conventional analytical procedures.

Physical methods for detection of adulteration

Physical methods such as specific gravity at 25°C, refractive index at 25°C, specific optical rotation, freezing point and chemical parameters such as ester number have been useful in detecting adulteration. Such physical properties including ester number should be considered as presumptive tests and should be confirmed by other, more specific analysis. A freezing point lower than 10.5°C is indicative of turpentine in peppermint oil (Lu 1994). Colorimetric analysis of glycerol can indicate adulteration with edible oils. TLC of the hydrocarbon fraction, GLC and IR are effective in detecting adulterant ethanol, edible oils and liquid paraffins (Mostafa et al. 1990b). The presence of cottonseed oil in different essential oils gave absorption bands characteristic of esters and unsaturated esters (at 1705-1720 cm-1), acetates (at 1245 cm-1) and the carbonyl group (at 1250-1170cm-1), while the presence of paraffin oil gave a broadened absorption band at 3000 cm-1 which characterizes the saturated and unsaturated hydrocarbons. Mineral oil in peppermint oil can be detected as turbidity, when peppermint oil is added to 60-80% ethanolic solution (Lu 1994).

Authentication of botanical and geographical origin of essential oils

Aroma constituents of essential oils such as linalool and linalyl acetate can be traced to various botanical sources such as coriander, lavender, etc. Authentication methods that could trace the botanical and even the geographical origin of such constituents are a challenge to food analytical chemists. Information of such aspects is just beginning to emerge in scientific literature. For instance, analysis of major volatile constituents has demonstrated the ratio of carvaerol/thymol to differentiate essential oils from four oregano species (Pino et al. 1993). Rosemary essential oil of different geographical origins could be differentiated on the basis of GC/MS determination of natural constituents. While Spanish oils are rich in alfa-pinene (19.4-24.7%), 1,8-cineole (19.0-21.8%) and camphor (16.3-18.9%), the French oils contain alfa-pinene (19.9-35.1%), 1,8-cineole (5.3-24.8%) and bornyl acetate (1.2-14.3%). Moroccan oils are typically rich in 1,8-cineole (43.5-57.7%) (Chalchat et al. 1993). However, chemical analysis is not always helpful in determining the geographical origin of essential oils as has been shown with sage essential oils (Lawrence 1994, 1998). The differentiation between compounds that are grown naturally, produced by fermentation or synthesized chemically is projected to reflect in legal regulations in the coming years. Hence, intensive and comprehensive basic investigations on the analytical origin assessment of flavours will gain ground.

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