Detection of hazelnut oil in extra-virgin olive oil by analysis of polar components by micro-solid phase extraction based on hydrophilic liquid chromatography and MALDI-ToF mass spectrometry.

The oil polar fraction may have a great potential for the characterization of vegetable oils and for the individuation of adulterations. In particular, adulteration of extra-virgin olive oil (EVOO) with hazelnut oil (HO) is one of the most difficult ones to detect due to the similar composition as regards triacylglycerol, total sterol and fatty acid profile. A new micro-solid phase extraction (µ-SPE) procedure based on hydrophilic liquid chromatography (HILIC) micro-columns was developed for the selective extraction and enrichment of polar compounds from EVOO and HO before matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF-MS) analysis. The method permits a simple and fast qualitative analysis of the polar fraction of the oils under study; furthermore, some peaks (such as the m/z ions 496.39, 520.46 and 522.47) were found to be present only in HO, indicating that they could be diagnostic for the presence of HO in EVOO. In order to verify the potential of the method for the individuation of this adulteration, EVOO was progressively adulterated with variable quantities of HO, subjected to the HILIC enrichment and finally to MALDI-ToF-MS analysis; the detection of adulteration was possible up to the level of 5%. Eventually, diagnostic polar compounds were identified as lysophosphatidylcholine (LPC) (16:0/0:0), LPC (18:2/0:0), LPC (18:1/0:0) by means of capillary liquid chromatography-electrospray ionization-quadrupole-ToF-MS (CapLC-ESI-Q-ToF-MS) analysis.