Sustainable Extraction of Hydroxytyrosol from Olive Leaves Based on a Nature-Inspired Deep Eutectic Solvent (NADES)

Abstract

Within the circular economy framework, the valorisation of olive leaves as an effective source of organic compounds rather than an agricultural waste, represents a great opportunity. Olive leaves contain bioactive polyphenols, such as the health-enhancing catechol hydroxytyrosol (HT), derived primarily from oleuropein. This study establishes a novel and sustainable approach for the extraction of HT from olive leaves, utilizing eco-friendly deep eutectic solvents derived from natural sources (NADES). By optimizing the extraction process, the study highlights the efficacy of the eutectic mixture cholinium/glycerol (1:2 mol/mol) in achieving HT-rich extracts from olive leaves (0.12 ± 0.03 g HT/g of dry extract). Indeed, the method demonstrates a remarkable yield of HT, reaching 12.3 ± 0.9 g/kg of leaf powder, under optimized conditions. The antioxidant properties of the extract are thoroughly assessed, suggesting its potential health benefits. Significantly, the study underscores the scalability of the extraction method, showcasing its viability for large-scale production while maintaining excellent outcomes. Furthermore, the sustainability of the extraction method is boosted by the reuse of NADES across multiple extraction cycles, enhancing resource efficiency and reducing environmental impact. This research unlocks the potential of olive leaves as a valuable source of bioactive compounds and outlines a sustainable extraction approach aligning with the principles of the circular economy.