An eco-friendly and sustainable system for monitoring the oleuropein-rich extract from olive tree (Olea europaea) leaves

Abstract

In this study, different combinations (1/1, 1/2, and 2/1 of molar ratio) of deep eutectic solvents were designed by combining a hydrogen bond acceptor (carboxylic acids such as citric and lactic acids) and a hydrogen bond donor (glycerol, ethylene glycol, ammonium and sodium acetates). Their performance was measured with respect to their success in extracting oleuropein-rich extract from olive leaves via homogenizer-assisted extraction. Lactic acid/glycerol (1/1) has been observed to be the most successful deep eutectic solvent. A split-plot central composite design was employed to observe the effects of the process parameters (water addition, speed and extraction time) on the total phenolic and oleuropein levels in the extract as well as modelling and optimization of the homogenizer-assisted extraction process. The most significant process parameter was found to be water addition (P < 0.0001). The optimum conditions were calculated as 90 s of extraction time under 14000 rpm with 50% water in the selected solvent system to achieve the highest total phenolic (39.41 mg-GAE/g-DL) and oleuropein (14, 06 mg/g-DL) yields. The proposed green solvent has been also monitored to be a sustainable extraction media depending on the stability test outcome, where the samples were kept stable for almost 2 months at 25°C, while 6 months were observed to be the storage time without degradation in colder environments.