Total phenol, flavonol and
flavanol contents, levels of eight phenols and antioxidant activity [DPPH● radical scavenging and Cu (II) reducing
capacity] were measured in sun-exposed leaves at the end of four consecutive seasons. Results showed a significant
seasonal variation in the leaf content of phenols of A. unedo, with the lowest values found in spring and the
highest in autumn and/or winter. Leaf ontogenetic development and/or a possible effect of low temperatures in
autumn/winter may account for such findings. Regardless of the watering regime and the sampling date, plant
exposure to UV-B radiation decreased the total flavanol content of leaves, while it increased the leaf content in
quercitrin (the most abundant quercetin derivative identified). By contrast, UV-A radiation increased the leaf
content of theogallin, a gallic acid derivative. Other phenolic compounds (two quercetin derivatives, one of
them being avicularin, and one kaempferol derivative, juglanin), as well as the antioxidant activity of the leaves,
showed different responses to UV radiation depending on the precipitation regime. Surprisingly, reduced rainfall
significantly decreased the total amount of quantified quercetin derivatives as well as the DPPH• scavenging activity
in A. unedo leaves. To conclude, present findings indicate that leaves of A. unedo can be a good source of antioxidants
throughout the year, but especially in autumn and winter.