On-line HPLC-GC-FID determination of exogenous and endogenous hydrocarbons in olive oils of different cultivars milled under different conditions

Olive oils may be contaminated with mineral oil hydrocarbons (MOH) from different sources (on average 10-20 mg/kg), but only few researchers [1] investigated the presence of trace amounts (<2 mg/kg) of saturated hydrocarbons (MOSH) in oils obtained by olives directly hand-pickled from the tree. On the other hand, olive oils also contain endogenous n-alkanes which may provide information related to the olive’s variety, geographical origin, presence of leaves in the milling phase, etc. [2] Different from endogenous n-alkanes, which show a typical distribution from n-C21 to n-C35, with the prevalence of odd terms over even ones, mineral oils give GC-FID traces characterized by humps of unresolved peaks, sometimes dominated by linear alkanes with an equal distribution of even and odd terms. On-line HPLC-GC-FID represents the reference method for mineral oil determination in edible oils and, by simply adjusting the amount of sample injected, it can also be used to investigate on endogenous n-alkanes. When analysing MOSH amounts in the range between 0.5- 2.0 mg/kg, the analytical determination must be preceded by sample enrichment and a purification step to eliminate the interference by endogenous n-alkanes. The first aim of this contribution was to propose simple and low solvent consumption protocols to investigate the distribution of endogenous and exogenous hydrocarbons in extra virgin olive oils. Subsequently, the optimized protocols were used to analyse oils from selected olive samples (2 different cultivars, Leccino and Bjelica) collected in Croatia and Italy. For the first time, the impact of the presence of leaves and the absence of stones during the milling phase, on both exogenous and endogenous hydrocarbons, was evaluated. The results obtained showed the presence of traces of MOSH in all the samples analysed and confirmed the great potential of endogenous n-alkanes in discriminating the cultivar and the different milling conditions. [1] L. Menegoz Ursol, C. Conchione, A. Srbinovska, S. Moret, Food Chem. 370 (2022) 130966. [2] A. Srbinovska, C. Conchione, L. Menegoz Ursol, P. Lucci, S. Moret , Foods 9 (2020) 1546.