Extraction of Polyphenols from Olive Leaves Employing Deep Eutectic Solvents: The Application of Chemometrics to a Quantitative Study on Antioxidant Compounds

Abstract

The extraction of phenolic compounds from olive leaves was optimized using three glycerol-based deep eutectic solvents (DESs) with lysine, proline, and arginine. A three-level Box–Behnken design was used to examine the influence of the liquid/solid ratio, concentration of DESs, and extraction temperature on the yield of the extraction process. A second-order polynomial model was used for predicting the polyphenol extraction yield. The optimal predicted conditions were used for extractions and they provided the highest total phenol yields with the glycerol–lysine exhibiting the best performance. Quantification of tyrosol, hydroxytyrosol, oleuropein, luteolin-7-O-glucoside, and rutin in the extracts showed high content in tyrosol in all DESs, particularly with glycerol–lysine and relatively similar contents with other studies for the other phenolic compounds. Finally, a linear relationship between tyrosol content and the total phenolic content of the extracts was observed.

Antioxidant and Antimicrobial Activity of Hydroethanolic Leaf Extracts from Six Mediterranean Olive Cultivars

“…In this work, the oleuropein level in Oblica was higher than in other cultivars, especially the oleuropein isomer c (10.217 mg/g). Previous studies showed that the concentrations of oleuropein in olive leaves vary considerably due to the type of cultivar, climatic and geographical conditions, sampling and drying techniques of the plant material, and the extraction parameters [ 7 , 13 , 17 , 41 , 42 ]. Irakli et al [ 43 ] investigated the influence of UAE conditions (solvent type and concentration, extraction temperature, and time) on the extract yield of oleuropein and flavonoids from olive leaves and concluded that its yield increased significantly when the concentration of all solvents increased up to 50%.…”

“…The phenolic profile of olive leaves varies within cultivar and is influenced by the timing of sampling/harvest, climatic conditions, geographical origin, age and biological cycle of the tree, agricultural practices applied, and conditions during extraction/isolation, processing, storage, etc. [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ].…”

Extractability of oleuropein, hydroxytyrosol, tyrosol, verbascoside and flavonoid-derivatives from olive leaves using ohmic heating (a green process for value addition)

“…The diffusivity of tyrosol from olive leaf tissues is partially reliant on certain conditions of the extraction system. A recent report by Akli et al, 39 proposed an optimized extraction protocol using deep eutectic solvents mixed with different amino acids including lysine which represented 53 420.23 mg per g tyrosol in the extracts, that was signicantly higher than that obtained by using a conventional solvent with 70% ethanol (19 398.64 mg g −1 ). These authors observed that the content of tyrosol was greater than that of hydroxytyrosol and oleuropein (this is typically different from what can be expected) and explained that the probable reasons can be the high stability of tyrosol and solvent suitability for tyrosol recovery.…”

Phytochemicals Derived from Agricultural Residues and Their Valuable Properties and Applications

“…Polyphenols also occur in the leaves [ 287 ]. These compounds confer bioactive properties on olive leaf extracts, such as antioxidant, antimicrobial, and antitumor activity; the capacity to reduce the risk of coronary heart disease was also reported [ 288 ].…”