Influence of harvest year, cultivar and geographical origin on Greek extra virgin olive oils composition: a study by NMR spectroscopy and biometric analysis

Abstract

Two hundred twenty-one extra virgin olive oils (EVOO) were extracted from four olive mono-cultivars (Koroneiki, Tsounati, Adramitini, and Throubolia) originated from four divisions of Greece (Peloponnesus, Crete, Zakynthos, and Lesvos) and collected in five harvesting periods (2002-2006 and 2007-2008). All samples were chemically analysed by means of (1)H and (31)P NMR spectroscopy and characterised according to their content in fatty acids, phenolic compounds, diacylglycerols, total free sterols, free acidity, and iodine number. The influence of cultivars on the compositional data of the EVOO samples according to harvest year and geographical origin was examined by means of the forward stepwise canonical discriminant analysis (CDA) and classification binary trees (CBT). The CDA, when the a priori grouping was in accordance with harvest, was high (94%), whereas the classification in terms of groups formed by inclusions of geographical origin was reduced to 85%. Inclusion of both the harvesting year and geographical origin in the CDA analysis resulted in a high classification (90%) for the EVOO samples grouped into the four cultivars. The variables that most satisfactorily classified the Greek olive oils were the phenolics p-coumaric acid, pinoresinol, 1-acetoxypinoresinol, syringaresinol, luteolin, apigenin, and the hydrolysis products of oleuropein expressed collectively by the concentration of total hydroxytyrosol. Amongst the fatty acids, linoleic acid was the predictor with the highest discriminatory power. Finally, the phylogenetic significance of the olive oil compounds as determined by NMR was investigated by estimating their support to monophyly of cultivars.