Comprehensive two-dimensional gas chromatography for fingerprint pattern recognition in olive oils produced by two different techniques in Portuguese olive varieties Galega Vulgar, Cobrançosa e Carrasquenha

Abstract

a b s t r a c tFor 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 Cobranç 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 treatment, 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 analysis 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 tentatively 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.

Olive Oil Composition: Volatile Compounds

“…Few applications are still reported for olive oil analysis, nevertheless, they already showed its potential. GC × GC techniques allowed identification of olive oil key flavour compounds, present in very low concentrations (Adahchour et al 2005); it has also been used as a flexible technique for the screening of flavours and other classes of (semi-)polar compounds, using the conventional orthogonal approach and the reverse, non-orthogonal approach in order to obtain ordered structures that can simplify the identification task (Adahchour et al 2004); finally this separation technique can allow easy fingerprint analysis of several olive oil matrices directly, or using image processing statistics (Vaz-Freire et al, 2009). …”

“…Together with 2D-GC systems the advantage is clear, since, instead of a time consuming trial to determine which variables should be considered for the statistical classification method, the selection may now become as simple as inspecting the 2D contour plots obtained (Cardeal et al 2008, de Koning et al, 2008. Also the use of statistical image treatment, of 2D-GC generated contour plots, can be applied for fingerprint recognitions, precluding the alignment of the contour plots obtained, which already allowed the identification of varieties as well as extraction technologies used to produce high quality Portuguese olive oils (Vaz Freire et al, 2009). …”

Gas Chromatography in the Analysis of Compounds Released from Wood into Wine

“…2D analysis offers a genuine opportunity to characterize individual components based on retention time data alone, provided that high reproducibility of retention times can be achieved, reducing and eventually precluding, the requirement of MS detection for many samples. The reliability of peak position co-ordinates opens the possibility of fingerprinting comparison or statistical treatment in order to characterize the effects of distinct types of wood, the same wood from different origins, or even aging time (Cardeal et al, 2008;Vaz-Freire, 2009;Schmarr et al, 2010 b;Schmarr & Bernhardt, 2010).…”

Sensorial analysis and electronic aroma detection to compare olive oils produced by different extraction methods

“…It has already been shown that the vulgar volatile composition of the Galega cultivar (Vaz Freire and al, 2009) is characterized by a reduced number of compounds which include an intense peak of hexen-2-al as well as other compounds with 6 carbon atoms, like Z-2-hexenol, E-3-hexenol, Z-3-hexenol when analysis is made by SPME/ GCMS. This small number of compounds might explain the low discrimination obtained and can help understand which were the discarded sensors, SyG, SyGH, SyGCTI, which are mainly related to the detection of ammonia and ammonia derivatives, sulphur, amines and amine containing compounds.…”