Optimization of Pulsed Electric Field as Standalone “Green” Extraction Procedure for the Recovery of High Value-Added Compounds from Fresh Olive Leaves

Abstract

Olive leaves (OLL) are reported as a source of valuable antioxidants and as an agricultural by-product/waste. Thus, a twofold objective with multi-level cost and environmental benefits arises for a “green” standalone extraction technology. This study evaluates the OLL waste valorization through maximizing OLL extracts polyphenol concentration utilizing an emerging “green” non-thermal technology, Pulsed Electric Field (PEF). It also provides further insight into the PEF assistance span for static solid-liquid extraction of OLL by choosing and fine-tuning important PEF parameters such as the extraction chamber geometry, electric field strength, pulse duration, pulse period (and frequency), and extraction duration. The produced extracts were evaluated via comparison amongst them and against extracts obtained without the application of PEF. The Folin-Ciocalteu method, high-performance liquid chromatography, and differential scanning calorimetry were used to determine the extraction efficiency. The optimal PEF contribution on the total polyphenols extractability (38% increase with a 117% increase for specific metabolites) was presented for rectangular extraction chamber, 25% v/v ethanol:water solvent, pulse duration (tpulse) 2 μs, electric field strength (E) 0.85 kV cm−1, 100 μs period (Τ), and 15 min extraction duration (textraction), ascertaining a significant dependence of PEF assisting extraction performance to the parameters chosen.

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

“…Cör Andrejč et al [ 14 ] investigated the effect of drying and extraction mode on oleuropein content in olive leaves and obtained the best results for air-dried samples when alcohol was used as an extraction solvent. Recently, novel and innovative technologies, including ultrasound-assisted extraction (UAE) [ 18 , 19 , 20 ], microwave-assisted extraction (MAE) [ 19 , 21 , 22 ], supercritical fluid extraction (SFE) [ 23 , 24 ], pulsed electric field extraction (PEF) [ 25 ], superheated liquid extraction (SHLE) [ 26 , 27 ], infrared-assisted extraction (IAE) [ 28 ], and high-voltage electrical discharge (HVED) [ 29 , 30 ], have been proposed to increase the recovery of phenolics from olive leaves, to shorten the extraction time, and prevent the degradation of the valuable phytochemicals. Regarding this, extraction of bioactive components in this research was achieved using safe and food-grade solvent (ethanol-water mixture) and their yield was additionally increased by the application of UAE as an eco-friendly and green technology.…”

“…Furthermore, recently, there is a great interest in an eco-friendly and green approach to the extraction of bioactives from olive leaves and different novel extraction technologies, which result in higher extraction yield, have shorter treatment time, apply less aggressive conditions (temperature, pressure, etc. ), and are cost efficient in comparison to the conventional solvent extraction techniques that have been investigated [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ].…”

Innovative Extraction Technologies for Development of Functional Ingredients Based on Polyphenols from Olive Leaves

“…Recent studies have been published on the optimization of PEF as a standalone “green” technology for the extraction of high value-added compounds from fresh olive leaves; these showed how optimal detected PEF contributes to increasing the value (~30%) of the total polyphenols assayed by Folin-Ciocalteu method and, particularly, in increasing the recovery (~120%) of luteolin-diglucoside, quercetin-3 -O- rutinoside, luteolin-rutinoside, luteolin-7 -O- glucoside, apigenin-7 -O- rutinoside, luteolin-3′ -O- glucoside, luteolin aglycone, and oleuropein determined by HPLC, transpired using a rectangular-shaped extraction chamber and a 25% v/v aqueous ethanol solvent choice, using a pulse duration of 2 μs under 0.85 kV/cm electric field strength, and a period of 100 μs for a 15 min extraction duration [ 64 , 65 ].…”

Combination of Pulsed Electric Field and Ultrasound in the Extraction of Polyphenols and Volatile Compounds from Grape Stems

“…The equipment used for the PEF treatment is provided in detail in our previous studies [19,20,23]. In brief, the was comprised of a high voltage power generator (Leybold, LD Didactic GmbH, Huerth, Germany), a digital oscilloscope, a function/arbitrary waveform generator, and a treatment chamber made of two stainless steel plates (10 cm length and 10 cm height) and 1 cm Teflon between them for isolation purposes.…”

“…However, to the best of our knowledge, the pulsed electric field has not been employed to date. The pulsed electric field (PEF) is a green extraction technique that has been used in recent years to optimize the extraction process of precious substances [18][19][20]. PEF is an extraction technique, based on electro-permeabilization, aiming at the creation of pores in the cellular membranes, and thus, assist in the extraction of compounds.…”