In-depth profiling of essential oils from Portuguese forest trees using GC-based methods: biogenic volatile characterization and thermal degradation relevant to fire risk

This study reports the characterization of biogenic volatile organic compounds (BVOCs) present in the essential oils (EOs) extracted from major tree species in Portugal: Eucalyptus globulus Labill., Pinus pinaster Aiton, Quercus robur L., and Quercus suber L. EOs were obtained by hydrodistillation of dried leaves and analysed using gas chromatography-quadrupole mass spectrometry (GC-qMS) and comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-ToFMS). EO yields ranged from 0.38 % to 2.37 % (w/w, dry weight basis). GC-qMS analysis identified 34 compounds in E. globulus, 36 in P. pinaster, 34 in Q. robur, and 19 in Q. suber. The major constituents were 1,8-cineole (60.1 %) in E. globulus, abietadiene (21.6 %) in P. pinaster, kaur-16-ene (17.7 %) in Q. robur, and eugenol (5.4 %) in Q. suber. GC × GC-ToFMS showed a substantially higher analytical capacity, allowing the identification of 98 compounds in E. globulus, 57 in P. pinaster, 105 in Q. robur, and 35 in Q. suber, including 25, 13, 77, and 24 compounds reported for the first time, respectively. The dominant BVOC classes were oxygenated monoterpenoids (66.9 %) in E. globulus, hydrocarbon diterpenoids (29.8 %) in P. pinaster, hydrocarbon diterpenoids (18.0 %) in Q. robur, and miscellaneous compounds (26.4 %) in Q. suber. Beyond their industrial and therapeutic relevance, these terpenoids may act as potential fuels during forest fires. Thermal carbonization experiments (100-600 °C) further identified key BVOC classes and burning compounds, highlighting their possible contribution to flammability under extreme atmospheric conditions.