Phenolics and Other Structural Compounds from Leaves of Olea europaea L.: Extraction Techniques and Pharmacological Activities

The olive tree (Olea europaea L.) is a quintessential part of the Mediterranean region, providing both oil and fruit that play crucial roles in the local diet. Olives are not only a rich source of nutrition but also contain high levels of polyphenols and antioxidants, which have garnered significant attention for their health benefits. These beneficial compounds are present in various parts of the olive tree, including the fruits, leaves, and virgin olive oil. The characteristic bitter and spicy flavor of green olives and virgin olive oil can be traced back to these antioxidant derivatives with oleuropein being a prominent example. This compound undergoes enzymatic biotransformation during the fruit ripening process, essential for the olive plant’s defense mechanisms and tissue-specific functions. Beyond the fruit, olive leaves are rich in bioactive compounds that hold considerable promise for human health. This review provides a detailed examination of the historical significance of olive species and highlights the abundance of polyphenolic compounds found in olive leaves. It discusses the classification of bioactive compounds in olives, extraction techniques, and their diverse biological activities, including antimicrobial, antioxidant, anticancer, antidiabetic, anti-inflammatory, and antiatherogenic effects. This updated review emphasizes the latest findings to provide more specific and detailed insights into the characteristics and pharmacological importance of oleuropein.