Exploring the potential of advanced eco-friendly extraction techniques for a rapid recovery of oleuropein-rich extracts from “Picholine Marocaine” olive tree leaves

This study aimed to explore the use of different advanced extraction methods to obtain oleuropein-rich extracts from leaves of the predominant olive variety in Morocco: “Picholine Marocaine”, and compare them with the conventional maceration method. Initially, the solubility of oleuropein in various ethanol-water ratios was predicted using COSMO-RS software. Subsequently, a kinetic study was conducted to extract phenolic compounds using maceration for 3 h, based on the total phenolic and oleuropein contents. Advanced extraction methods, including ultrasound extraction systems (based on both bath and probe systems), bead milling, microwave-based extraction, and accelerated solvent extraction, were then applied for 5 min. The obtained results from COSMO-RS prediction indicated that ethanol-water 60:40 (v:v) was the most efficient ratio. The kinetic study revealed that the highest total phenolic and oleuropein contents were achieved after 1 h of maceration. Ultrasonic extraction, using both bath and probe systems, resulted in extraction within only 5 min, of over 92% (19.61 mg of gallic acid equivalent (GAE)/g of dry weight (DW)) and 83% (17.55 mg of GAE/g DW), respectively, of the total phenolic compound yield achieved in 1 h of maceration (21.14 mg of GAE/g DW). Moreover, the extracted amount of oleuropein using ultrasonic systems (fluctuating between 15.90 and 15.10 mg/g DW for the ultrasonic bath and probe extracts, respectively) was higher than that obtained with the conventional method during 1 h (14.31 mg/g DW). Therefore, ultrasonic assisted extraction appears to be the most efficient and rapid method for obtaining oleuropein-rich extracts from Moroccan olive leaves.