LIGHT AND THERMAL DEGRADATION OF ESSENTIAL OILS

Essential oils are substances obtained from plant extraction and composed by complex mixtures of chemical compounds. The use of essential oils in therapy is due to this variety of compounds and includes physical health and mental health issues. Inhalation and topic application are the most used ways of application. Oral application is not recommended and is considered toxic, which can cause nausea, vomiting and seizures. However, it is common to see essential oil companies promoting oral consumption of their products, including the mixture of essential oil drops in food recipes. The aromatic constituents of essential oil are instable under the influence of heat, which makes this way of use innapropriate. Furthermore, the majority of commercial essential oils packages are amber glass to prevent exposure to light, but inadequate user storages can make light degradation possible. In order to evaluate light and thermal degradation, four different essential oils (lavender, lemon, peppermint and sweet orange) were exposed to ultraviolet light and crescent temperatures, separately. The samples were analyzed using Fourier-transform infrared spectroscopy (FTIR). Statistical analysis were performed using Principal Component Analysis (PCA) through software Metaboanalyst 6.0. FTIR spectra showed that alkyl groups region (2700-2990 cm⁻¹) were statistically different in both light and thermal degradation for all essential oils tested; carbonyl groups (1700-1750 cm⁻¹) showed differences for light degradation of lavender oil and both light and thermal degradation for peppermint oil; C-O bond region (1000 – 1300 cm⁻¹) and O-H  bending vibrations of phenols (1377 cm⁻¹)  showed differences in both light and thermal degradation of lemon, peppermint and sweet orange essential oils; C-H stretching vibrations of aromatics (885 cm⁻¹) showed differences for light degradation in sweet orange oil and both light and thermal degradation of lemon oil; C=C bending vibrations of alkanes (797 cm⁻¹) showed differences in light and thermal degradation of sweet orange oil; hydroxyl groups (3200-3600 cm⁻¹) showed diferences for light degradation of lavender oil only. These regions possibly correspond to different pathways of essential oils compounds degradation, such as C-C bond clevage, oxydative degradation, elimination or thermal rearregement. These results confirm that light and temperature exposure causes essential oil degradation, therefore, its storage conditions and application routes must be assesed before use.