Essential oils: characterisation and authenticity testing
By Eric Jamin, Eurofins Analytics France
Essential oils are high-value ingredients extracted from plants. They are not only used in cosmetics, but also in many food and feed applications for their flavouring and preservative properties. The oil's quality and its extraction from a natural source needs to be carefully checked by advanced analytical means to ensure that a product's description reflects its true composition and origin, and the value of those ingredients is in accordance with what is expected.
The analysis of essential oils by Gas-Chromatography (GC) is a well-established method for checking the composition of essential oils: ISO and AFNOR norms describe the typical GC profiles of more than 80 different oils. When combined with a Mass Spectrometer (MS) detector, this technique becomes even more discriminatory as the peak identification is further validated. Using suitable extraction procedures it is possible to perform precise and accurate quantitative analyses, and to monitor the oil's quality and stability.
Another issue is the authenticity of the main components found in essential oils: are they from the plant source they are claiming or have they been added as synthetic nature-identical compounds? The first technique available to solve this challenge is a chiral GC-MS analysis, allowing the separation of isomers of the same compound, which can provide information on the oil's natural or synthetic origin. However, not all molecules are chiral, and natural racemisation can occur for some compounds. In this case isotopic testing will help: monitoring isotope ratios in key molecules (by SNIF-NMR1 and IRMS2) allow for the detection of added synthetic or biotechnological substitutes. Examples of essential oil components for which authenticity testing using isotopic methods have proven effective are benzaldehyde, cinnamaldehyde, anethole, etc.
1 Site-Specific Natural Isotopic Fractionation determined by Nuclear Magnetic Resonance
2 Isotope Ratio Mass Spectrometry