Use of Pulsed Electric Field as a Low-Temperature and High-Performance “Green” Extraction Technique for the Recovery of High Added Value Compounds from Olive Leaves

Abstract

Olive leaves (OLL), an agricultural waste by-product, are considered a significant bioresource of polyphenols, known as bioactive compounds. This study evaluates the pulsed electric field (PEF) technique for the extraction of polyphenols from OLL. The study parameters included a series of “green” solvents (ethanol, water as well as mixtures of them at a 25% step gradient) and different input values for the pulse duration of PEF. The phytochemical extraction degree was evaluated using total phenol concentration (Folin–Ciocalteu method) and high-performance liquid chromatography (HPLC) analyses, while the antioxidant activity was assessed using differential scanning calorimetry (DSC). The results obtained from the PEF extracts were compared with those of the extracts produced without the PEF application. The highest PEF effect was observed for aqueous ethanol, 25% v/v, using a pulse duration of 10 μs. The increase in the total polyphenols reached 31.85%, while the increase in the specific metabolites reached 265.67%. The recovery in polyphenols was found to depend on the solvent, the pulse duration of treatment and the structure of the metabolites extracted.

Pulsed Electric Field and Salvia officinalis L. Leaves: A Successful Combination for the Extraction of High Value Added Compounds

“…For 6-hydroxy luteolin 7-O-glucoside, in our study, the change in the pulse duration from 10 to 100 µs was followed by a higher increase in the levels of the metabolite, in comparison to the increase obtained for the three other identified metabolites (Table 3, Figure 4). A similar effect was observed during another study performed by our team regarding enhanced polyphenol extraction from olive leaves using PEF [27]. As in the current study, the effect of different duration pulses, 10 and 100 µs, was tested.…”

“…An apparatus already presented by Pappas et al [27] was utilized. In brief, a system comprised of a high voltage power generator (maximum voltage up to 25 kV), a 25 MHz function/arbitrary waveform generator, an electronic switch circuit (IGBTs), and a rectangular treatment chamber made of stainless steel with dimensions: 10 cm × 10 cm × 1 cm.…”

“…The electrical conductivity of solvents, the strength of the field, the treatment time, and the energy contribution (kJ•kg −1 ) determinations were measured as we have previously described [27]. Both PEF and reference samples were extracted for 30 min.…”

“…The DSC method used was adapted from Pappas et al [27]. A Perkin Elmer Diamond DSC (PerkinElmer Inc, Shelton, CT, USA) was used.…”

“…As indicated by Batra et al [32], this technique can determine the changes in the different physicochemical properties of compounds, which are shown by changes in the heat flow, and therefore, the oxidative stability of a sample can be evaluated through this technique [27]. DSC is the most widely used analytical technique for studies of physical characteristics and thermo-oxidative degradation of fats and oils, as well as their mixtures with herbal plant extracts, according to Kozłowska and Gruczyńska [33].…”