Phenolic composition, antioxidant capacity, enzyme inhibition, and aroma composition of lyophilized olive leaves of cv. Gemlik and Kilis Yağlık

Abstract In this study, lyophilized leaves from olive varieties grown in Turkey were extracted using three different solventswith ultrasonication. Antioxidant capacity, total phenol, phenolic compounds, and enzyme inhibition of the extracts were determined. By LC-HRMS, 27 compounds among 84 different phenolic standards were determined in olive leaves, and approximately 35% of them were oleuropein. Total phenol content varied depending on solvents and variety, and antioxidant capacity varied accordingly. Kilis Yağlık ethanol and Gemlik methanol extracts showed the highest inhibition of α-glucosidase and α-amylase, respectively. The aroma compounds of the leaves were extracted by solid-phase microextraction (SPME) and identified by GC-MS. A total of 52 volatile compounds belonging to seven different classes were identified in olive leaves. Considering the obtained bioactive components and properties, the antidiabetic effect of olive leaves and the volatile compounds in their composition are noteworthy. Overall, this study highlights the valorization of olive leaves as an agro-industrial bio-waste within a circular economy framework, demonstrating how BioE3-driven processing strategies (bioeconomy, bioenergy, and bio-based products) can enable sustainable value addition and resource efficiency. Graphical abstract