Olive Leaves for Functional Herbal Infusions: Effects of Post-Harvest Processing on Bioactive Properties, α-Amylase Inhibition Activity and Consumer Safety

Olive leaves (OL; Olea europaea L.) are an abundant by-product of olive production with functional and nutraceutical potential. This study evaluated the effects of post-harvest treatments using fresh, air-dried, and lyophilized OL of cv. ‘Frantoio’, which were infused in water at 85 °C for 10 min. The antioxidant capacity (AC; DPPH method), total phenolic content (TPC; Folin–Ciocalteu assay), and α-amylase inhibition activity of the herbal infusions were assessed. Macro- and trace elements were determined directly in air-dried and lyophilized OL by inductively coupled plasma optical emission spectrometry (ICP-OES). Potential non-carcinogenic health risks were assessed using estimated daily intake (EDI), target hazard quotient (THQ), and total THQ (TTHQ). Lyophilized OL herbal infusions exhibited the highest AC (15.32 ± 0.85%), TPC (65.61 ± 1.15 mg GAE/g DW), and α-amylase inhibition activity (23.34%). The mineral analysis identified Ca and K as the predominant macroelements, whereas Cd and Pb were below the analytical limit of detection. All individual THQ and cumulative TTHQ values remained below 1, indicating no appreciable non-carcinogenic health risk under the modeled exposure conditions. These results identify lyophilization as a favorable processing option for preserving the functional potential of OL and support their potential use as raw material for functional infusions and other food applications.