Oleuropein extraction from leaves of three olive varieties ( Olea europaea L.): Antioxidant and antimicrobial properties of purified oleuropein and oleuropein extracts

In this study, it was aimed to extract, purify oleuropein from leaves of different olive varieties and determine antioxidant and antimicrobial activity. For this purpose, olive leaf crude extract (CE), partially purified oleuropein, and purified oleuropein were obtained from leaves of Domat, Edremit, and Trilye varieties. Oleuropein amount of olive leaf products ranged between 215.26 and 958.22 mg/g. Total phenolic content in terms of gallic acid and oleuropein ranged between 102.36 and 325.02 mg gallic acid equivalent (GAE)/g and 308.06 and 915.33 mg oleuropein equivalent (OE)/g, respectively. Antioxidant activities of olive leaf products ranged between 104.83 and 456.50 mg TE/g (ABTS) and 109.27 and 456.93 mg TE/g (DPPH), respectively. MIC values ranged between 50 and 0.781 mg/ml for tested microorganism cultures. Among the microorganisms, Staphylococcus aureus is the most sensitive to oleuropein extracts, while Escherichia coli O1577:H7 is the most resistant. In conclusion, CEs and oleuropein purified from these CEs have potential to extend shelf life of food products due to their determined antioxidant and antimicrobial activities. Novelty impact statement This study focused on the extraction and purification of oleuropein compound from leaves of different olive varieties due to limited studies on purification of oleuropein in literature. A simple, cheap, and fast method was devoloped, and high purity oleuropein was obtained by applying purification processes. Also, it was determined that CEs obtained from different olive cultivar leaves and oleuropein purified from these extracts have potential to improve functional properties and extend the shelf life of food products due to their antioxidant and antimicrobial activity.