Climate change effects on phytochemical compounds and antioxidant activity of Olea europaea L.

To tolerate water shortage and high temperature, olive cv. 'Meski', the main variety of table olives in Tunisia, developed several biochemical changes. The hereby study focused on the adaptation of the olive tree to the climatic conditions, considering the evaluation of phenolic compounds, chlorophylls, carotenoids, saponin and steroid synthesis, as well as the evaluation of the antioxidant activity. The analyses were made upon fresh leaves collected from three coastal areas of Tunisia (North (sub-humid), Center (higher semi-arid) and South (lower arid)) and using different leaves' extracts. The results emphasized that Southern 'Meski' trees had leaves with more polyphenols, flavonoids, o-diphenols and tannins compared with the Northern ones. From the North to the South, 'Meski' leaves showed an increase of carotenoids and a decrease of chlorophyll a and b contents. The highest level of antioxidant compounds of Southern leaves could be contributed to reduce the oxidative stress of the olive tree. The spectrophotometric analysis of the antioxidant capacity of leaves collected from Central and Southern areas, based on DPPH and ABTS radical-scavenging activity, showed a higher value of antioxidant activity than the Northern ones, at different extract concentrations. Therefore, the increase of the analyzed bioactive compounds can be considered as a response of the tree to surround aggressions and to oppose the oxidative stress that results from the severity of climatic conditions, characteristic of the Southern area.