Evaluation of Olive Leaves of Different Varieties and Climatic Cultivation Conditions as a Source of Bioactive Substances Using Sustainable Extraction Methods

This study investigates the impact of olive tree variety and environmental stress on the production of bioactive compounds in olive leaves, focusing on phenolic content and antioxidant capacity. Three olive varieties—Kalamata, Koroneiki, and wild olive (Olea europaea var. Silvestris)—from two climatically distinct regions in Greece (Stamna and mountainous Paravola) were analyzed. Using three sustainable extraction methods, Ultrasound-Assisted Extraction (UAE), Enzyme-Assisted Extraction (EAE), and Microwave-Assisted Extraction (MAE), the total polyphenolic content (TPC) and antioxidant activity (AA%) of the olive leaf extracts were quantified. Results revealed significant variation in polyphenolic yield depending on both extraction technique and environmental conditions. EAE consistently outperformed other methods in polyphenol recovery, especially from wild olive leaves in the higher-stress environment of Paravola, which showed the highest TPC. This work underscores the synergistic role of varietal and climatic factors in secondary metabolite accumulation and highlights the potential of green extraction technologies in valorizing olive by-products.