Olive Leaf Powder as a Potential Functional Component of Food Innovation: An In Vitro Study Evaluating Its Total Antioxidant Capacity and Phenolic Content

Olive leaves (Olea europaea) are the most abundant agricultural by-product of olive tree cultivation, generating substantial waste each year. Their disposal is deemed an environmental challenge, particularly in Mediterranean countries that dominate the olive oil sector, yet their rich bioactive profile makes them promising candidates for functional food development. This study aimed to determine the total antioxidant capacity (TAC) and total phenolic content (TPC) of olive leaf powder extracts using different extraction solvents and methods to identify the most efficient strategy for possible incorporation into functional food systems. Extractions were performed with distilled water, 70% ethanol, 80% methanol, and 50% acetone using three methods: stirring, soaking, and ultrasound-assisted extraction (UAE). TAC and TPC were quantified using the FRAP and Folin–Ciocalteu assays, respectively. Among solvents, acetone consistently yielded the highest values across most methods (TAC: 19.02 mmol Fe2+/L, TPC: 1289.95 mg GA/L), while ethanol also showed strong extraction performance (TAC: 15.35 mmol Fe2+/L; TPC: 1214.76 mg GA/L), offering a safer and more scalable option for food applications. Method-wise, UAE achieved the greatest phenolic recovery, while both UAE and stirring proved effective for antioxidant extraction. Overall, these findings provide quantitative evidence supporting possible incorporation of olive leaf powder as a valuable ingredient in functional foods and other sustainable applications, while also contributing to the circular economy through the sustainable valorization of agricultural waste.