Optimization of olive leaf extract obtained by ultrasound-assisted extraction with response surface methodology

In the present article, ultrasound-assisted extraction (UAE) of polyphenols from agricultural and industrial waste of olive oil and table oil productions, olive tree (Olea europaea) leaves were investigated. The aim of the study is to examine the extraction parameters such as solvent concentration (0–100% ethanol (EtOH), v/v), the ratio of solid to solvent (25–50 mg/mL) and extraction time (20–60 min), and to obtain the best possible combinations of these parameters through response surface methodology (RSM). The extract yield was stated as mg extract per g of dried leaf (DL). Total phenolic content was expressed in gallic acid equivalent (GAE) per g of dried leaf. Free radical scavenging activity for the antioxidant capacity was tested by 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical. The second order polynomial model gave a satisfactory description of the experimental data. 201.2158 mg extract/g DL, 25.0626 mg GAE/g DL, and 95.5610% in respect to inhibition of DPPH radical were predicted at the optimum operating conditions (500 mg solid to 10 mL solvent ratio, 60 min of extraction time and 50% EtOH composition), respectively.

► UAE is an alternative method as requiring less time and solvent consumption for extracting high added value compounds.
► Acquiring the optimal operating conditions for an extraction method is a must for commercial applications of the process.
► This research aims to be a useful engineering tool to develop an extraction process from olive leaves.