Antioxidant, Antibacterial, and Antidiabetic Activities of Different Extracts from Wild Olive Leaves Grown in United Arab Emirates

Olive leaves (Olea europaea L.) are a source of natural bioactive compounds with various health benefits and are often considered agricultural waste. This study aimed to evaluate the antioxidant, antibacterial, and antidiabetic activities of an infused aqueous extract and ultrasonic-assisted extracts (aqueous, methanol, ethyl acetate, and hexane) from wild olive leaves grown in the United Arab Emirates (UAE). The aqueous-infused extract exhibited the highest total phenolic content (TPC; 91.9 mg GAE/g extract), the highest reducing power activity, the lowest IC50 value for diphenyl-1-picrylhydrazyl (DPPH) inhibition (97.3% and 81.1 µg/mL, respectively), and the highest α-amylase and α-glucosidase inhibition activities (77.1% and 83.3%, respectively). Meanwhile, the ultrasonic-assisted methanolic extract exhibited the highest total flavonoid content (31.2 mg RE/g extract) and significant α-amylase and α-glucosidase inhibition activities (61.8% and 77.2%, respectively). The antimicrobial activity of wild olive leaf extracts (WOLEs) at concentrations of 1, 2.5, and 5 mg, tested using the disc diffusion method against Gram-positive and Gram-negative bacterial strains, was weak or ineffective at the studied concentrations. The study concluded that WOLEs are high in total phenolic and flavonoid content and antioxidant and antidiabetic activities, suggesting the potential use of WOLE in folk medicine.