Optimization and validation of microwave assisted saponification (MAS) followed by epoxidation for high-sensitivity determination of mineral oil aromatic hydrocarbons (MOAH) in extra virgin olive oil

A rapid and solvent-saving method, based on microwave-assisted saponification (MAS) followed by epoxidation and on-line liquid chromatography (LC) - gas chromatography (GC) - flame ionization detection (FID), was optimized and validated for high-sensitivity MOAH determination in extra virgin olive oils. Quantitative recoveries and good repeatability were obtained even at concentrations of added mineral oils close to the LOQ (0.5 mg/kg for the total hump, 0.2 mg/kg for each single C-fraction). The validated method, also applied for MOSH determination (C-fraction LOQ: 0.5 mg/kg), was used to analyse 18 extra virgin olive oils from the Italian market or oil mills, and 10 additional samples extracted in the laboratory (with an Abencor apparatus) from hand-picked olives. The former resulted contaminated with variable amounts of MOSH and MOAH (on average 19.0 mg/kg and 2.5 mg/kg, respectively), while the latter showed no detectable MOAH, and low and rather constant MOSH (generally below 2.0 mg/kg).

Automated summary

A rapid and solvent-saving method based on microwave-assisted saponification (MAS) followed by epoxidation and on-line LC-GC-FID has been optimized and validated for high-sensitivity determination of MOAH in extra virgin olive oils. The method was also applied for MOSH determination and showed that olive oils from the Italian market or oil mills were contaminated with variable amounts of MOSH and MOAH, while laboratory-extracted oils had low and rather constant levels of MOSH and no detectable MOAH.