Characterization and seasonal variation of the quality of virgin olive oil of the Throumbolia and Koroneiki varieties from southern Greece

Extra virgin olive oil was produced from olives of the two main varieties cultivated in the region of Rethymnon in the Greek island of Crete named “Throumbolia”, and “Koroneiki”. The former is very famous due to the natural way of fruit debittering, while the latter is the most common olive variety cultivated in Northern Greece. The olives were harvested at three successive stages of ripening according to their skin color and the extra virgin olive oil was extracted using an experimental olive oil extraction mill at 30ºC. Peroxide value, UV absorption, acidity, fatty acid content and total polyphenols were measured and the contents of tyrosol, hydroxytyrosol 3,4- DHPEA-EDA, p-HPEA-EDA and 3,4-DHPEA-EA were determined by HPLC. The sterol fraction and the volatile component profile were determined by GC and SPME GC/MS, respectively. Throumbolia olive oil presented an extremely higher content of β-sitosterol and linoleic acid (n6) in comparison to the Koroneiki variety. The concentration of linoleic acid decreased in olive oils produced from both varieties in contrast to oleic acid which increased at the same time. Furthermore, the content of OH-tyrosol was higher, while the content of 3, 4-DHPEA-EDA and the total polyphenols was lower in Throumbolia olive oil than in olive oil produced from the Koroneiki variety. In general, significant differences were observed in all parameters between the olive oils produced from the two varieties during different stages of maturation.