Study of volatile compounds of defective virgin olive oils and sensory evaluation: a chemometric approach

It is well known that olive oils are the only foods whose legal control must also involve sensory evaluation, and that a harmonised protocol is used for this purpose: EEC regulation 2568/91 and an IOOC trade norm of the 1990s introduced a standard method among those used to assess the quality of virgin oils, after which a modified method known as the 'panel test' was developed and adopted, firstly by the IOOC and later by the EEC. One problem in applying the panel method often depends on the lack of reference standards for training judges, in addition to, in some cases, a lack of exact knowledge of the origin of some defects; for these reasons, several judges have suggested the unification of some defects, even when these originate from different kinds of problems. In this paper we have applied headspace analyses to a number of samples of oils that were also characterised by a panel. Besides the samples, standard defective oils obtained by the IOOC and used for training sensory judges were also analysed, with the aim of obtaining a model for use in method validation. Seventy-six peaks were detected and most of them identified by gas chromatography/mass spectrometry; their distribution was different in the samples characterised by different defects as assessed by the panel test. The well-known compounds of virgin olive oils were detected, including the series of C6 compounds, whose importance in defining positive ('green' flavour) and negative (rancid) characteristics of olive oils is well known. No samples classified as extra virgin ever present peaks with magnitudes as great as those found in defective oils. Chemometric data evaluation was carried out and samples were clustered on the basis of the headspace composition; the results were found to agree with those of the panel test, so a number of compounds were related to the presence of particular defects.