Different studies have reported varied concentrations of oleuropein in olive oil leaves; for example El and Karakaya found the amount of oleuropein in dry olive leaves to be between 6 and 14 %, and others found 17 to 23 % depending on the time of year at which the leaves are collected . Le Tutour found that oleuropein in dry olive oil leaves ranged from 6-9 %, while another study by Topuz and Bayram found oleuropein content to be between 6 and 16% . Medina et al reported that oleuropein showed high variability in a range of 44 to 108 mg/g, and that it constituted more than 88-94% of total phenolic Figure Oleuropein compounds in leaves . Parameters such as climate and time of harvest determine the concentration of oleuropein and other biophenols ; Romani et al reported differences in oleuropein amounts depending on cultivar, production area, sampling time, and state of leaves (fresh, dried, frozen or lyophilized) .