Effects of geographical origin and extraction methods on total phenolic yield of olive tree (Olea europaea) leaves

Olive tree (Olea europaea) leaves were extracted with methanol by homogeniser-assisted extraction (HAE) and ultrasound-assisted extraction (UAE) methods, which are novel technologies used in this field. The leaves were hand-picked from three olive trees of the same cultivar grown in the same region. In order to observe the effect of the geographical origin, the following six different sites in Anatolia were chosen: Bursa, Mardin, Ayvalik, Kas, Tekirdag and Canakkale. The results were presented by means of the extract yields and total phenolic contents expressed in gallic acid equivalent (GAE) per gram of dried leaf. The extract yields of HAE varied from 102.27 to 443.16 mg/g-dried leaf. Total polyphenols content in leaves ranged from 10.11 to 61.66 mg-GAE/g-dried leaf. As regards UAE, the extract yield changed between 88.75 and 350.82 mg/g-dried leaf, while total phenolic content varied from 7.35 to 38.66 mg-GAE/g-dried leaf. The greatest amounts of extract and total polyphenol were observed in olive leaves cultivated in Bursa through HAE. In addition, the kinetics of the total phenolic content through UAE were described by the film theory model.

► This study was conducted to investigate differences in six cultivars of olive tree grown in Turkey but of different origin.
► A comparison of extraction methods assisted by homogeniser and ultrasonic waves has been evaluated.
► The kinetics of the total phenolic content through ultrasound-assisted extraction were described by the film theory model.