Method M3
Determination of fatty acid ethyl esters in virgin olive oils by SPE-GC-FID
The M3 method was developed as part of WP4 ‘Analytical solutions addressing olive oil authentication issues’, specifically within Task 4.2 ‘Detection of illegal processing (deodorization): analytical tools and markers’. The procedure allows the isolation of the fraction containing the fatty acid ethyl esters (FAEE) present in virgin olive oil (VOO) samples. In this method, a 1 g silica cartridge is proposed for analyte isolation as a rapid alternative to the preparative phase defined by Annex XX of the EEC Reg. 2568/91 for FAEE determination, which requires a high volume of solvents and a very long and complex preparative procedure. The isolated fraction is subsequently analyzed by GC-FID using a low polarity column and cool on-column injection.
Our interest on this determination lies in the fact that the analytical evaluation of the content of FAEE is one of the quality parameters that permits to define the quality grade of a VOO and to detect fraudulent mixtures of extra virgin olive oils with lower quality oils whether they are virgin, lampante or, indirectly, some kind of soft-deodorised oils.
The scheme of the M3 method is shown in Fig. 1. The method has been in-house validated in terms of intra- and inter-day precision, recovery, linearity, robustness, limit of detection (LOD), limit of quantification (LOQ), and accuracy.
Fig. 1 Scheme of the isolation of the FAEE fraction through SPE
Determination of the closeness of agreement between results obtained applying the proposed method and those obtained with the reference procedure (Annex XX of the EEC Reg. 2568/91 for FAEE determination) demonstrated the methods’ equivalency.
According to OLEUM project procedures, the M3 method was selected for full validation, which included the participation of ten laboratories in a pre-trial study where participants received two different extra virgin olive oil samples and were asked to analyze them following the standard operation procedure (SOP) prepared by the method developers. Participants also had the opportunity to attend a knowledge transfer workshop in Seville (October 2019), in the course of which they asked questions and provided feedback about the application of the analytical SOP.
The weak points raised in the pre-trial study were addressed in the revised version of the SOP sent to the seventeen participants of the trial-proper whose, the obtained results have been collected and elaborated.
For the Instituto de la Grasa -CSIC- M3 developing team
Raquel B. Gómez-Coca, Mª del Carmen Pérez-Camino and Wenceslao Moreda