Water as a Solvent of Election for Obtaining Oleuropein-Rich Extracts from Olive (Olea europaea) Leaves

Julieta Ines Monteleone,Aldo Todaro,Laura Siracusa,Rosa Palmeri,Giovanni Spagna,Lucia Parafati,Elisa Sperlinga

doi:10.3390/agronomy11030465

Abstract

Leaves from Olea europaea represent one of the main by-products of the olive oil industry, containing a plethora of bioactive compounds with several promising activities for human health. An organic solvent-free extraction method was developed for the recovery of olive leaf phenols, which obtained an extract containing oleuropein in high amounts. A comparison of various extraction media is reported, together with the total phenolic content, DPPH (2,2-Diphenyl-1-picrylhydrazyl) content, ORAC (oxygen radical absorbance capacity), and polyphenol oxidase activity of the corresponding extracts. The polyphenol profiles and content of the most representative extracts have also been studied. Extraction solvent and temperature significantly influenced the phenolic content and antioxidant activity of the extracts, with hot water representing the solvent of election for the extraction of bioactive compounds from this matrix. All the extracts obtained showed reasonably high total phenol content (TPC) and good DPPH radical scavenging activity; among them, the water extract is characterized by desirable traits and could be used for many industrial applications and human consumption.

Highlights

The olive tree (Olea europaea L.) is an important crop in the Mediterranean area, it is considered a drought-tolerant crop and has developed physiological mechanisms to tolerate drought stress and grow under adverse climatic conditions, such as the regulation of gas exchange and an antioxidant system [1]
Oleuropein is an heterosidic ester of β-glucosylated elenolic acid and 3,4-dihydroxyphenylethanol; it belongs to the chemical class of secoiridoids, which are present in all members of the Oleaceae family [4]
The total phenol content (TPC) values found in our experiments are in accordance with what was reported by Ortega-García and Peragòn [35], who investigated the polyphenol content in leaves from different olive cultivars extracted by methanol-containing mixtures after an n-hexane pre-treatment to remove oil residues

Summary

Introduction

The olive tree (Olea europaea L.) is an important crop in the Mediterranean area, it is considered a drought-tolerant crop and has developed physiological mechanisms to tolerate drought stress and grow under adverse climatic conditions, such as the regulation of gas exchange and an antioxidant system [1]. The olive tree and its products have a relevant importance in different fields. Olive leaves are a copious by-product of the olive oil industry and of olive tree pruning. They are considered a cheap and natural source of phenolic compounds such as hydroxytyrosol, verbascoside, rutin, tyrosol, and oleuropein. Oleuropein is an heterosidic ester of β-glucosylated elenolic acid and 3,4-dihydroxyphenylethanol (hydroxytyrosol); it belongs to the chemical class of secoiridoids, which are present in all members of the Oleaceae family [4]

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Conclusion