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, microwavebased 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.