Isolation of oleuropein from olive leaf by effective method and investigation of its antimicrobial properties

Natural products play an important role in the production and development of food and medicine. In olive tree cultivation and olive processing industry, vast amounts of by-products are yielded. Olive leaves constitute the major by-product of olive industry. Olive leaf is potential source of phenolic compounds. Plant polyphenols have attracted great interest due to their antimicrobial activities. It was aimed to isolate the oleuropein compound from olive leaf and to identify its antimicrobial effects in this research. In the first stage, methanol extract was obtained from the olive leaf. After then, ethyl acetate extract (including oleuropein with 93.5% purity) procured from methanol extract. Ethyl acetate extract was subjected to chromatographic technique to obtain oleuropein in high purity (97.6%). The structure of oleuropein was determined by spectroscopic method including H-1 and C-13 NMR besides comparing isolated oleuropein with the standard commercially obtained. Antimicrobial activity of methanol extract, ethyl acetate extract and oleuropein was investigated on Bacillus subtilis, Candida tropicalis, Lactobacillus brevis, Lactobacillus plantarum, Proteus vulgaris, Saccharomyces cerevisiae, Salmonella enteritidis microorganisms by 96-well microtiter plate method. It was determined that MIC (Minimum Inhibitory Concentration) values of olive leaf products ranged between 1:1 (50 mg/mL) and 1:8 (6.25 mg/mL) for tested microorganisms.