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.

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.

Fοllow up with our previous study on the extraction of saffron processing waste polyphenols using deep eutectic solvents, the objective of this examination was a comparative evaluation of pressurized liquid extraction (PLE), stirred-tank extraction (STE) and stirred-tank extraction with ultrasonication pretreatment (STE/UP) with respect to the recovery of pigments and antioxidant polyphenols from saffron processing waste. Aqueous solutions of citric and lactic acids at two different concentrations were used as green solvents. The extracts obtained under the specified conditions were analyzed for total pigment and total polyphenol yields as well as for their ferric-reducing power and antiradical activity. Furthermore, each produced extract was analyzed with liquid chromatography–mass spectrometry to profile its analytical polyphenolic composition. In all cases, PLE provided inferior results compared to the two other techniques, producing extracts with lower polyphenolic concentration and weaker antioxidant properties. On the other hand, no specific pattern was detected concerning the effect of ultrasonication, acid type and acid concentration. Hierarchical cluster analysis indicated that stirred-tank extraction with 1% (w/v) lactic acid and ultrasonication pretreatment might be the highest-performing combination, providing extracts with increased polyphenol and pigment concentration; however, it also enhanced antioxidant activity. It was also concluded that the significantly shorter extraction time when using PLE might be an important element in further optimizing the process, buttressing the use of this technique for the establishment of innovative and sustainable-by-design extraction methodologies.

Polyphenols are an important class of compounds, due to their excellent antioxidant properties. Lately, much effort has been placed into developing new extraction techniques and optimizing them, so that polyphenols can be retrieved more efficiently from the plant materials. One of the most recent advances in extraction techniques is pulsed electric field extraction (PEF). This new technique is environmentally friendly and has the potential to maximize the recovery of compounds from plant tissues. Although the efficiency of PEF depends, among others, on the nature of the solvent used, up to date, there are no reports on the optimization of the PEF extraction of polyphenols, using hydroethanolic solutions of varying content in ethanol. In this study, three hydroethanolic solutions, water, and ethanol were used for the PEF-based extraction of total polyphenols from Sideritis raiseri. Results were conclusive that the 1:1 mixture of ethanol and water can increase by up to 146% the yield of polyphenols in the extract, highlighting the need to study more extensively, in the future, mixtures of solvents and not just plain water.

The present study aimed to evaluate the pulsed electric field (PEF)-assisted extraction of phytochemicals from Salvia officinalis L. leaves. The study parameters included a PEF pulse duration of 10 or 100 μs for 30 min, using different “green” extraction solvents: pure ethanol, pure water, and their mixtures at 25, 50, and 75% v/v concentrations. The resulting extracts were evaluated against reference extracts obtained without PEF. For estimation of the extraction efficiency, the content in total polyphenols, individual polyphenols, and volatile compounds, as well as the resistance to oxidation, were determined. The optimal PEF contribution on the total and individual polyphenols, rosmarinic acid, extractability (up to 73.2% and 403.1% increase, respectively) was obtained by 25% v/v aqueous ethanol solvent using a pulse duration of 100 μs. PEF was proven to also affect the final concentration and composition of volatile compounds of the extracts obtained.

The present study examines, compares, and documents the environmental impact of five extraction techniques through Life Cycle Assessment (LCA). The material used was Moringa oleifera freeze-dried leaves and the assessment was based on their polyphenol content Three out of the five examined techniques are referred to in the literature as “green” techniques, namely Pulsed Electric Field (PEF), Microwave-Assisted Extraction (MAE), and Ultrasound-Assisted Extraction (UAE). The other two examined were conventional extraction techniques and, specifically, boiling water and maceration; the latter served as a control in this study. The analysis utilized special software (SimaPro ecoinvent) for the “cradle to gate” LCA, along with a sensitivity analysis of the model examining the variation in the environmental impact based on the origin of the source of electricity (renewable sources such as photovoltaic arcs), aiming to highlight the optimal technology choice. This LCA study's Functional Unit (FU) was one gram (g) of extracted total polyphenols (dry) produced by a case-specific number of extraction cycles for each technology under assessment (considering their technical efficiency depicted as polyphenols yields), measured by the Folin–Ciocalteu method and expressed as mg Gallic Acid Equivalents per g of dry Moringa oleifera leaves. The study outcome indicates that PEF and MAE deliver the best environmental scores. The main contributing parameters are the Moringa oleifera leaves and the amount and origin of electricity used to make 1 FU. These parameters are dominant in the categories of freshwater ecotoxicity, marine ecotoxicity, human carcinogenic toxicity, and human non-carcinogenic. The better performance of these two techniques is due to the more efficient extraction with reduced electricity consumption, which can become even more environmentally friendly if replaced with renewable sources such as photovoltaic arcs.

In this study, the use of pulsed electric field (PEF) for the extraction of polyphenols from mature Elaeagnus pungens ‘Limelight’ leaves is discussed. Optimization of the main parameters that affect the extraction process was carried out. More specifically, the composition of the solvent (ethanol, water, and mixtures of the two at a 25% v/v step gradient) and the main PEF-related parameters (i.e., pulse duration, pulse period, and electric field intensity) was optimized. The obtained extracts were examined for their polyphenol content with the Folin–Ciocalteu assay and individual polyphenols were also assessed with high-performance liquid chromatography. The extracts obtained with PEF were compared to the extract compared without PEF, in terms of total polyphenols. According to the results, the optimum extraction parameters were found to be a pulse duration of 10 μs, a pulse period of 1000 μs, and an electric field intensity of 0.85 kV cm−1 after 20 min of extraction. The optimum solvent was found to be the 50% (v/v) ethanol/water mixture. The extract prepared under the optimum conditions was found to contain 58% more polyphenols compared with the extract prepared without PEF. Moreover, an increase of up to 92% was recorded for specific polyphenols. Based on the above, it was evidenced that the examined parameters influenced the recovery of polyphenols, suggesting that such parameters should be also examined in similar studies, in order to maximize the extraction yield of polyphenols.