Set-up of sonotrode based extraction to recover phenolic compounds from olive leaves

Olive leaves are a waste by-product obtained during the olive oil production and pruning. They contain phenolic compounds that possess antioxidative, antimicrobial, anti-atherogenic and anti-inflammatory properties, among others. For that reason, a procedure based on ultrasound-assisted extraction via sonotrode was developed to evaluate the recovery of these phenolic compounds from olive leaves. To establish the sonotrode extraction, a Box-Behnken design based on response surface methodology (RSM) was used to optimize the effects of factors such as solvent composition (30-100% EtOH), extraction time (1-10 min) and amplitude (20-100%). Qualitative and quantitative analyses of phenolic compounds were performed using HPLC coupled to DAD and mass spectrometer detectors. The highest content of phenolic compounds was 35.52 mg/g d.w. obtained using 55:45 ethanol/water (v/v), 8 minutes and 100% of the amplitude. The optimal conditions selected for the sonotrode were compared with the result obtained by a conventional ultrasonic bath achieving similar concentrations. Therefore, sonotrode could be considered as an efficient extraction technique that allows a good recovery of phenolic substances from olive leaf that could be easily scale-up at industrial level.