Olive paste fast preheating and the quality of extra virgin olive oil: sensory and chemical markers

The virgin olive oils (EVOOs) obtained with fast preheating of the olive paste after crushing combined or not with different malaxation periods were studied by means of multivariate statistical elaboration in order to find correlations between the chemical data and the sensory attributes and oxidative stability during a storage period of 12 months. Principal Component Analysis showed that a VOO with high content of simple phenolics compared to the complex phenolics is an oil which has been subjected to oxidation, for instance due to the storage or excessive heat. Based on these results, a new chemical index of ‘normalized tyrosols’ calculated as the ratio between the sum of concentration of 3,4-dihydroxyphenylethanol (3,4-DHPEA) and 4-hydroxyphenylethanol (p-HPEA) and the sum of total phenols (determined with HPLC) was proposed for the first time. This index is highly positively correlated to primary oxidation (r=0.6941) and inversely related to the oxidative stability (r=-0.6025). In addition, the normalized tyrosols are a good marker of sensory defects of EVOOs.