Abscisic Acid Sprayed on Olive Tree (Olea europaea L.) Affects the Phenolic Composition of Olive Fruit Cultivars

The aim of this research was to study the effect of abscisic acid pre-harvest treatment on the phenolic composition of olive fruits. To that end we applied abscisic acid (i.e., 50 mg/L and 100 mg/L) on Arbequina and Picual olive trees. Two different days of harvesting (i.e., day 3 and 6 after treatment) were also included in the study. Although the results obtained depended on the cultivar and on the day of harvesting a general trend was established. The treatment with 50 mg/L of abscisic acid resulted in higher total phenol content but significant decrease in the DPPH activity. In contrast, olives treated with 100 mg/L abscisic acid resulted in higher total phenol content, DPPH activity and contents of oleuropein, hydroxytyrosol and phenolic acids as compared with controls. The best values of total phenol content and IC50 were obtained for treated Picual olives (727.75 mg gallic kg-1 and 889.72 µg/ml, respectively) whereas the highest values of oleuropein and hydroxytyrosol were measured for treated Arbequina olives (508.94 and 559.67 mg kg-1, respectively). Phenolic acid content was also higher in Picual olives treated with 100 mg/L of abscisic acid. Particulary, values ranged from 7.26 mg kg-1 for caffeic acid to 92.38 mg kg-1 for chlorogenic acid. Exogenous abscisic acid applied to olive trees is a promising agronomic practice to obtain olives enriched in antioxidants.