Effect of Olive (Olea europaea L.) Variety on Leaf Biophenolic Profile

Olive leaves are rich in valuable biophenolic compounds, characterised by high antioxidant activity, antimicrobial properties and beneficial effects on human health. Leaf biophenols are essential for metabolic adaptation of olive to various abiotic or biotic stressors and maintenance of homeostasis. The aim of this study was to determine the influence of olive variety (‘Buža’, ‘Karbonaca’ and ‘Oblica’) on the leaf biophenols concentrations. The experiment was conducted as a completely randomised design in 3 replicates. Olive leaves were collected in three sampling periods, starting from harvest in October 2017 until pruning in March 2018. The variety ‘Buža’ differed significantly from the other cultivars with its highest content of oleuropein (5239.88 mg 100 g-1 DW) and total biophenols (5943.25 mg 100 g-1 DW). The highest levels of 4-hydroxybenzoic acid (3.92 mg 100 g-1 DW), luteolin (48.17 mg 100 g-1 DW) and apigenin (7.55 mg 100 g-1 DW) were recorded in ‘Karbonaca’ samples. Tyrosol concentrations were not significantly different between ‘Karbonaca’ (4.79 mg 100 g-1 DW) and ‘Oblica’ (4.96 mg 100 g-1 DW) cultivars, however both differed from ‘Buža’ with the highest tyrosol concentration (6.67 mg 100 g-1 DW). The obtained results showed significant differences in the content of important biophenols between the selected olive varieties. Accordingly, the highest concentration of oleuropein, the most important secoiridoid in olive leaves, in cultivar ‘Buža’ could strongly determine their metabolic response to different stressors.