Abstract
The olive orchard cultivation in Mediterranean countries results in huge amounts of lignocellulosic biomass residues. One of the main residues are olive leaves. Olive leaves contain high concentrations of bioactive antioxidant compounds like oleuropein and luteolin-7-glucoside. The production of biactive compounds from olive leaves requires treatments capable of breaking the lignocellulosic structure. Current research focuses on use of inexpensive, quick, and not harmful to the environment treatments, searching a more simplified large-scale operation approach. Recently, advances in applied chemistry have led to possible new emerging industrial techniques like ultrasound-assisted extraction (UAE). This technology is a promising candidate as a green treatment solution for olive leaves utilization in a biorefinery. However, this application goes through prior optimization of technique and operating conditions. The goal of this study was to optimize the extraction of oleuropein and luteolin-7-glucoside from olive leaves through an investigation of the influence of key factors of ultrasound-assisted extraction using an experimental central composite design, in comparison with conventional Soxhlet extraction. The highest extraction efficiency and antioxidant capacity were obtained under optimal increment of temperature and amplitude conditions (40 °C and 30%, respectively). Values for oleuropein, luteolin-7-glucoside were 69.91 g/kg and 1.82 g/kg, respectively.
Highlights
The activity of the olive oil industry generates enormous quantities of solid wastes; among them olive leaves represent 10% of the total weight of the olives harvested
The interest in the recovery of bioactive polyphenols from olive leaves has increased in the industry and the scientific community
Oleuropein and luteolin-7-glucoside extraction from olive leaves could add value to this by-product of the olive oil industry if they are recovered by applying efficient extraction technologies
Summary
The activity of the olive oil industry generates enormous quantities of solid wastes; among them olive leaves represent 10% of the total weight of the olives harvested. They are generated in high amounts during olive tree pruning (25 kg per olive tree annually) [1]. Olive leaves contain high amounts of a large variety of phenolic and flavonoid compounds (hydroxytyrosol, verbascoside, apigenin-7-glucoside, rutin, and ligstroside, among others), similar to those present in olives and their derived products [3,4]. There is a great interest by the scientific community in the valorization of these residues to achieve extracts enriched in these compounds that
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