Analytica Chimica Acta 633 (2009) 263–270 Contents lists available at ScienceDirect Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca Comprehensive two-dimensional gas chromatography for fingerprint pattern recognition in olive oils produced by two different techniques in Portuguese olive varieties Galega Vulgar, Cobranc ¸ osa e Carrasquenha L. Torres Vaz-Freire a , M.D.R. Gomes da Silva b,∗ , A.M. Costa Freitas a,∗ a ICAM (Instituto de Ciências Agrárias e Mediterrânicas), Departamento de Fitotecnia, Universidade de Évora, Apt 94, 7002-554 Évora, Portugal b REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal article info Article history: Received 11 August 2008 Received in revised form 27 October 2008 Accepted 22 November 2008 Available online 3 December 2008 Keywords: Comprehensive two-dimensional gas chromatography Olive oil Volatile organic compounds Solid phase micro extraction Fingerprinting Image treatment abstract For olive oil production a metal hammer-decanter olive processing line was compared to a traditional metal hammer-press line, a discontinuous method which, if properly used, yields high-quality virgin olive oils. Galega, Carrasquenha and Cobranc ¸ osa olives (traditional Portuguese varieties) were studied. The analysis of the aroma compounds was performed after headspace-solid phase micro extraction. The analytical results obtained after comprehensive gas chromatography in tandem with time of flight mass spectrometry (GC × GC/ToFMS) for these three different olive oil varieties, from a single year harvest and processed with two different extraction technologies, were compared using statistical image treat- ment, by means of ImageJ software, for fingerprint recognitions and compared with principal component analysis when the area data of each chromatographic spot of the contour plots were considered. The differences used to classify the olive oils studied under different groups after principal component anal- ysis were observed independently of the treatment used (peak areas or the sum of the pixels counts). When the individual peak areas were considered, more then 75.7% of the total variance is explained by the first two principal components while in the case where the data were subjected to image treatment 84.0% of the total variance is explained by the first two principal components. In both cases the first and second principal components present eigenvalues higher then 1.0. Fingerprint image monitoring of the aroma compounds of the olive oil allowed a rapid differentiation of the three varieties studied as well as the extraction methods used. The volatile compounds responsible for their characterization were tenta- tively identified in a bi-dimensional polar/non-polar column set in the GC × GC/Tof-MS apparatus. This methodology allowed the reduction of the number of compounds needed for matrices characterization, preserving the efficiency of the discrimination, when compared with the traditional methods where the identification of all peaks is needed. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Olive oil production is one of the most traditional agricultural industries in the Mediterranean region, and it is still of primary importance for rural economy, local heritage and environment of most Mediterranean countries. The European Union is the leading world producer, producing around 80% of the world’s olive oil and consuming around 70% [1,2]. Olive trees belong to the Olea europea L. family but among them different cultivars with different characteristics can be found in the world production zones. The most important cultivars used in Portugal are Galega Vulgar, Carrasquenha, Cordovil, Cobranc ¸ osa and ∗ Corresponding authors. Tel.: +351 212 948351; fax: +351 212 948550. E-mail addresses: mdr@dq.fct.unl.pt (M.D.R.G. da Silva), afreitas@uevora.pt (A.M.C. Freitas). Verdeal [3], which are also the ones responsible for the generation of olive oil under the classification of Protected Denomination Origin (DOP) [3]. The predominant variety is Galega Vulgar, representing 80% of the olive patrimony in Portugal [4]. Olive oil quality is dependent on region, variety, the degree of maturation of the olives and sanitary conditions, processing/ extraction technology as well as storage duration and conditions [5,6]. Processing is, in fact, a major factor affecting olive oil quality. Pressed oil obtained under the proper processing conditions is usu- ally of great quality. Press extraction was almost the only olive oil extraction process used for centuries. Extraction technology has, however, progressed significantly since the beginning of the seven- ties, when the centrifugation system appeared. Since than several comparisons were made between the so-called three-phase cen- trifugation system extraction with the two-phase centrifugation system [7]. When compared to the press system, these processes 0003-2670/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2008.11.057