Effect of Tunisian olive ripeness on endogenous enzymes and virgin olive oil phenolic composition

The aim of the present work was firstly to study the impact of olive fruit ripening on olive endogenous enzyme activities and virgin olive oil (VOO) phenolic composition and secondly to determine the key enzymes contributing to VOO phenolic content, in order to define the optimum harvesting dates for Chétoui and Chemlali olives. An increase of β-glucosidase and peroxidase (POX) activities during olive ripening, followed by a slight decrease at advanced ripening stages was observed. However, 2 peaks of polyphenoloxidase (PPO) activity were obtained during olive ripening. An increase of total phenols content reached a maximum at ripening index (RI) = 4 of Chemlali olives. However, the highest amounts of total phenols were observed at RI = 3 of Chétoui olives. VOO phenolic composition depends considerably on olive cultivar and ripening degree. On the basis of phenolic profile, results showed that the best RI is between 3 and 3.7 for Chétoui olives, and between 3 and 4 for Chemlali olives. Furthermore, the three enzymes studied contribute differently in determining VOO total phenols content according to olive cultivar. Results of the discriminative analysis showed three clusters of Chétoui and Chemlali VOOs according to olive ripeness.