Comparison of microwave, ultrasonic and conventional techniques for extraction of bioactive compounds from olive leaves (Olea europaea L.)

The aim of this study was to evaluate the effects of different extraction parameters on total phenolic (TP) compounds and antioxidant activity (AA) from olive leaves (Olea europaea L.) using microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE) and maceration. The study also emphasized on the optimization of MAE and UAE conditions, and on the potential benefits of using MAE as a pretreatment to UAE. It was demonstrated that olive leaves were a good source of phenolic compounds with high antioxidant activity. MAE at a higher temperature (86 degrees C) was more efficient in terms of TP yield, with short extraction time (3 min). MAE performed with water as a solvent was effective in disrupting the olive leaf cells thereby promoting the release of the compounds. Under this condition, the TP yield was increased by 82% when compared to maceration. In addition, it was demonstrated that MAE used as a pretreatment to UAE was more efficient. Industrial relevance: Olive leaves are usually considered as a residue with huge potential for value addition. High added-value compounds can be obtained by recovering phytochemicals from olive leaves for valorization through food products. The extraction of the bioactive compounds requires efficient techniques, but only a few studies show good extraction yields using clean techniques. Microwave-assisted extraction is a method for the extraction of bioactive compounds, which utilizes microwave energy to produce voluminous heating and the reduction of extraction time is one of the most attractive advantages of the system. In addition, the potential benefit of using microwave-assisted extraction as a pretreatment to ultrasound-assisted extraction to improve the recovery of bioactive compounds was reported and can be used as a means of intensifying the extraction process.