Thermal Stability and Photostability of Satureja montana and Lavandula angustifolia Essential Oils

Abstract

The influence of light and temperature stress conditions and oxygen availability on the chemical composition of Satureja montana and Lavandula angustifolia essential oils is reported. Photostability and thermal stability were evaluated by gas chromatography-mass spectrometry (GC‑MS) analysis, comparing composition before and after the applied regimes. In Satureja montana essential oil, the amount of thymol (13.0-11.9%) and carvacrol (10.3-9.4%) decreased at elevated temperature and in the presence of air, with a simultaneous increase of p-cymene (24.2‑26.2%) while in an inert atmosphere the composition remained the same as in fresh oil. Light caused a dehydrogenation of α-terpinene (2.1-0.9%) and γ-terpinene (5.6‑4.7%) to p-cymene (24.2-25.9%) and decrease of trans-caryophyllene (5.1-4.3%). In Lavandula angustifolia essential oil, compounds sensitive to elevated temperature and the presence of oxygen were cis‑ocimene (2.8-2.2%) and trans‑ocimene (2.6-2.0%), alloocimene (3.0-2.3%), trans‑caryophyllene (4.3-3.6%) and β-farnesene (1.7-1.2%). Irradiated samples showed a decrease in the content of cis-ocimene (2.8-1.9%), alloocimene (3.0‑2.0%), crypton (0.6-0.1%), cuminal (0.3-0.0%), trans‑caryophyllene (4.3-3.5%), β-farnesene (1.7-1.1%) and germacrene-D (0.5-0.1%) and an increase of trans-ocimene (2.6-3.5%), β-bourbonene (0.0-0.2%) and several unidentified peaks. Both oils showed an individual response to light and temperature stress. The absence of oxygen and light is the only storage regime under which the initial composition can be preserved.