Exploring the performance of vacuum-HS-SPME for volatile profiling of olive oil

Headspace solid-phase microextraction (HS-SPME) is an easy, effective and selective technique for the analysis of volatiles and semi-volatiles compounds. For the latter, long equilibration times are needed, which are typically shortened by e.g. applying agitation or heating the sample. A recent and less explored way to improve the extraction kinetics of analytes with a low-affinity for the headspace is to sample the headspace under vacuum conditions. The methodology was termed vacuum-assisted HS-SPME (Vac-HS-SPME) and was always found higher extraction efficiencies in much shorter sampling times. This sampling strategy has been formulated and thoroughly investigated for water-based samples. However, the applicability and behaviour of Vac-HS-SPME sampling of non-aqueous sample has never been studied before.
The aim of this work was to compare Vac-HS-SPME and regular HS-SPME sampling from non-aqueous samples. Extra virgin olive oil was selected being an important ingredient of the Mediterranean diet with peculiar health benefits and sensory qualities. Extra virgin olive oil has a complex volatile aroma profile, which depends on several parameters (i.e., cultivar, geographical origin, fruit ripeness, processing practices, and storage). Past and current research efforts focus on unravelling the composition of this informative volatile fraction, so as to understand correlations with quality attributes. In the present work, the effects of extraction temperature and sampling time were investigated using traditional one variable at a time approach. Then, to better optimize the final extraction conditions and evaluate the temperature-time interaction, a two-variable central component design (CCD) was applied. A polydimethylsiloxane/carboxen/divinylbenzene (DVB/CAR/PDMS) fiber was used followed by gas chromatography-mass spectrometer (GC-MS). The results showed a great improvement in the extraction of semi-volatile compounds using Vac-HS-SPME leading to an enhancement in the information gained by the olive oil aroma fingerprint. The inherent complexity of the system requests further research to correlate thermodynamic conditions to the significant improvement in extraction conditions under non-equilibrium conditions.