Characterisation and authenticity assessment of rosemary and laurel essential oils using compound specific isotope analysis

The chemical composition, antioxidant activity and authenticity of commercially available rosemary (REO) and laurel (LEO) essential oils from the Slovenian market were investigated. In both EOs, 1,8-cineole was identified as the most abundant compound. It was determined that VOCs in lower concentrations contribute more to antioxidant activity compared to more abundant compounds. Key isotopic markers for adulteration detection were determined using compound-specific isotope analysis (CSIA). The sensitivity of the developed method was evaluated, demonstrating the best sensitivity for linalool in REO and for α-pinene in LEO, which means if the sample contains more than 19% of linalool (47% for α -pinene) synthetic fraction, it is almost certain (95% probability) that falsification will be suspected. When analysing commercial EOs declared as natural, the δ 13 C VPDB values indicated possible falsification of several VOCs in EOs. The developed methodology has shown great promise in the quality control of EOs, verifying labelling claims and detecting adulteration. • Less abundant VOCs exert higher antioxidant activity than major VOCs. • The method differentiates natural vs. synthetic origin in 6 of 14 target VOCs. • Adulteration is detectable when added synthetic compounds exceed 19%. • Commercial samples exhibited isotopic patterns indicative of potential adulteration.