Effect of Ripening on the Phenolic and Sugar Contents in the Meso- and Epicarp of Olive Fruits (Olea europaea L.) Cultivar 'Leccino'

The study was conducted during the harvest season in the year 2020 to identify and quantify primary and secondary metabolites in olive fruit of the 'Leccino' cultivar during ripening. Sugars, individual phenolic compounds, total phenolic content and total tannin content were measured separately for the first time in the skin and pulp. Most of the studied metabolites were higher in the skin. Five sugars were identified, the most important being glucose in both tissues, although its content decreased during ripening. The highest total phenolic content was observed in the skin at the last stage of ripening, because of the accumulation of anthocyanins. Individual phenolic compounds were measured by high performance liquid chromatography with-diode array detector (HPLC-DAD) and confirmed by mass spectrometry. Thirty phenolic compounds were characterized and quantified. The main individual phenolic compound in the skin and pulp was oleuropein, which decreased during ripening. Two previously unreported anthocyanins, cyanidin-3-O-diglucoside and cyanidin-3,5-O-sophoroside, were identified for the first time in olive skin. These results will allow us to better understand the synthesis, distribution and storage of some primary and secondary metabolites in different tissues of olive fruits during ripening.

Automated summary

This study was conducted in the harvest season of 2020 to measure and quantify primary and secondary metabolites in the 'Leccino' olive fruit during ripening. Sugars, phenolic compounds, total phenolic content, and tannin content were measured separately in the skin and pulp. The majority of metabolites were found to be higher in the skin, with glucose being the most important sugar. High levels of total phenolic content were observed in the skin at the last stage of ripening, due to the accumulation of anthocyanins. Oleuropein was identified as the main phenolic compound in both the skin and pulp, decreasing during ripening. Two previously unidentified anthocyanins were also discovered in the olive skin. These findings contribute to a better understanding of the synthesis, distribution, and storage of primary and secondary metabolites in different tissues of ripening olive fruits.