Extraction and partial purificiation of oleuropein from leaves of different olive varieties, determination of antioxidant and antimicrobial characteristics

Olive leaf which is one of the by-products of olive tree cultivation and olive processing industry, is a potential source of phenolic compounds. The most dominant phenolic compound in olive leaf is oleuropein. 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, partially purified oleuropein and purified oleuropein were obtained from the leaves of Domat, Edremit, Trilye olive tree varieties. The amount of oleuropein (using LC-MS/MS), total phenolic content (Folin-Ciocalteu method), antioxidant activity (ABTS and DPPH methods) of olive leaf products were determined. Antimicrobial activity of olive leaf products were determined against Escherichia coli O157:H7, Listeria monocytogenes, Salmonella Typhimurium and Staphylococcus aureus microorganisms by "96-well microtiter Plate" method. Oleuropein amount of olive leaf products ranged between 215.26-958.22 mg/g, total phenolic content in terms of gallic acid and oleuropein ranged between 102.36-325.02 mg GAE/g and 308.06-915.33 mg OE/g, respectively. Moroever, ABTS and DPPH methods and antioxidant activities of olive leaf products ranged between 104.83-456.50 mg TE/g and 109.27-456.93 mg TE/g, respectively. It was determined that MIC values for E. coli O157:H7, L. monocytogenes, S. Typhimurium and S. aureus cultures ranged between 1:1 (10%) to 1:64 (0.156%). In conclusion, the crude extracts obtained from different olive leaf varieties and oleuropein purified from these crude extracts have potential to extend shelf life of food products due to their determined antioxidant and antimicrobial activities.