Green Extraction Methods for Extraction of Polyphenolic Compounds from Blueberry Pomace

In this study, green extraction methods—high voltage electrical discharges (HVED), pulsed electric field (PEF), and ultrasound-assisted extraction (UAE)—were compared in terms of extraction yield of total and individual polyphenolic compounds, as well as the antioxidant capacity of blueberry pomace extracts. All extractions were performed with methanol- and ethanol-based solvents. The highest total polyphenols content (TPC) (10.52 mg of gallic acid equivalent (GAE) per g of dry weight (dw)) and antioxidant activity (AA) (0.83 mmol TE/g dw) were obtained by PEF-assisted extraction in the ethanol-based solvent after 100 pulses and 20 kV/cm, which corresponds to an energy input of 41.03 kJ/kg. A total of eighteen individual polyphenols were identified in all investigated blueberry pomace extracts by high-performance liquid chromatography with the diode-array detector (HPLC-DAD) and liquid chromatography electrospray ionization tandem mass spectrometric (LC-(HESI)-MS/MS). The highest anthocyanin (1757.32 µg/g of dw) and flavanol (297.86 µg/g of dw) yields were obtained in the methanol-based solvent, while the highest phenolic acid (625.47 µg/g of dw) and flavonol (157.54 µg/g of dw) yields were obtained in the ethanol-based solvent by PEF-assisted extraction at the energy input of 41.03 kJ/kg. These results indicated that PEF is a promising green extraction method which can improve the blueberry pomace’s polyphenol extraction yield.


Introduction
Blueberries are very popular fruit due to their numerous health benefits, nutritional value, and excellent sensory evaluation. They belong to the group of highly perishable soft fruits with a short shelf life [1]. To prolong the consumption of blueberries throughout the year, they can be preserved or processed into different products. More than 50% of fresh blueberries are processed into some kind of final fruit product; the most important commercial product is juice [2]. During juice production, waste generation may be up to 20% of the initial fruit weight [3]. Blueberries contain high amounts of anthocyanins, phenolic acids, flavanols, and flavonols [4], and the evident fact is that these Figure 1. Example of processing chambers, pulse shapes used, and mechanism of action of used extraction techniques. PEF-pulsed electric field; HVED-high-voltage electrical discharge; UAEultrasound-assisted extraction.

Pulsed Electric Field-Assisted Extraction (PEF)
The PEF experiments were performed in a laboratory treatment chamber containing parallel stainless steel electrodes (5 × 2 cm), shown in Figure 1. The electrode area was 10 cm 2 and the distance between the electrodes was 1 cm. The treatment chamber was connected to a high-voltage pulse generator, providing up to 25 kV discharges in a 10 mL chamber. The energy was stored in a set of low inductance capacitors, which were charged by the power supply; a spark gape was used as a switch. The pomace was treated by an exponentially decaying pulse with a pulse duration of 2 µs. Example of processing chambers, pulse shapes used, and mechanism of action of used extraction techniques. PEF-pulsed electric field; HVED-high-voltage electrical discharge; UAE-ultrasound-assisted extraction.

Pulsed Electric Field-Assisted Extraction (PEF)
The PEF experiments were performed in a laboratory treatment chamber containing parallel stainless steel electrodes (5 × 2 cm), shown in Figure 1. The electrode area was 10 cm 2 and the distance between the electrodes was 1 cm. The treatment chamber was connected to a high-voltage pulse generator, providing up to 25 kV discharges in a 10 mL chamber. The energy was stored in a set Foods 2020, 9, 1521 5 of 22 of low inductance capacitors, which were charged by the power supply; a spark gape was used as a switch. The pomace was treated by an exponentially decaying pulse with a pulse duration of 2 µs. The oscilloscope indicated the voltage, waveform, and current. The specific energy input for both HVED (W HVED ) and PEF (W PEF ) was obtained from Equation (1): where W is the energy input (kJ/kg), Ep is the energy of one pulse (kJ), and m is the mass of suspension (kg). The energy of one pulse (Ep HVED and Ep PEF ) was obtained from Equation (2): where U is the voltage (V) and I is the current (A). Electric field intensity (E HVED and E PEF ) was obtained from Equation (3) where E is the electric field intensity (kV/cm); V is the peak voltage (kV); d is the distance between electrodes (cm).

Determination of Total Polyphenolic Content and Antiradical Activity
The total polyphenolic content (TPC) was determined by employing Folin-Ciocalteu reagent (FC) according to a procedure described by Singleton and Rossi [33]. Briefly, 0.2 mL of extract was mixed with 1.8 mL of deionised water, 10 mL of FC (1:10), and 8 mL of 7.5% of sodium carbonate in a test tube. The development of blue colour was monitored at 765 nm after 120 min. The TPC was quantified from the gallic acid calibration curve (1-20 mg/L, R 2 = 0.9929). The TPC was calculated and expressed as mg gallic acid equivalent (GAE) per g of dry weight of blueberry pomace.
The antiradical activity (AA) was measured using a DPPH radical according to the methodology described by Brand-Williams [34]. The reaction mixture consisted of 0.2 mL of the extract and 3 mL of DPPH radical solution with 0.5 mM in ethanol. The changes in the colour of the radical from deep violet to light yellow were measured at 517 nm using a UV-vis spectrophotometer (Jenway 6300, Bibby Scientific, UK). The antiradical activity (AA) was quantified from the Trolox ® calibration curve (0.1-1.5 mmol TE/g, y = 0.9548x + 0.0294; R 2 = 0.9937). The AA was calculated and expressed as millimoles of Trolox ® equivalents (TE) per gram of dry blueberry pomace (mmol TE/g dw).

Phenolic Identification by LC-MS-MS
Identification of the major polyphonic compounds was performed by LC-MS/MS, employing a Thermo Scientific (San Jose, CA, USA) instrument based on TSQ Quantum Ultra TM triple quadrupole mass spectrometer equipped with a heated electrospray ionisation (HESI-II) source and an Accela Open autosampler with 20 µL loop. The chromatographic separation was achieved on a Kinetex C18 column (2.6 µm, 100 × 2.1 mm) (Phenomenex) at 50 °C. The mobile phase was composed of A-water with 0.1% of formic acid; B-methanol, with 0.1% of formic acid. The gradient program started with 5% B (held 5 min); it was increased to 90% of B in 11 min and kept constant for 3 min. Finally, the initial conditions were reached in 9 min. The injection volume was 10 µL, and the mobile phase flow rated was 0.2 mL/min. Selected Reaction Monitoring (SRM) acquisition mode was employed, monitoring 2 or 3 MS/MS transitions per compound (Table 1). Polyphenols were detected in the negative mode (ESI-NI) and thus, producing mainly the [M − H] − molecular ions (Table 1)

Phenolic Identification by LC-MS-MS
Identification of the major polyphonic compounds was performed by LC-MS/MS, employing a Thermo Scientific (San Jose, CA, USA) instrument based on TSQ Quantum Ultra TM triple quadrupole mass spectrometer equipped with a heated electrospray ionisation (HESI-II) source and an Accela Open autosampler with 20 µL loop. The chromatographic separation was achieved on a Kinetex C18 column (2.6 µm, 100 × 2.1 mm) (Phenomenex) at 50 • C. The mobile phase was composed of A-water with 0.1% of formic acid; B-methanol, with 0.1% of formic acid. The gradient program started with 5% B (held 5 min); it was increased to 90% of B in 11 min and kept constant for 3 min. Finally, the initial conditions were reached in 9 min. The injection volume was 10 µL, and the mobile phase flow rated was 0.2 mL/min. Selected Reaction Monitoring (SRM) acquisition mode was employed, monitoring 2 or 3 MS/MS transitions per compound (Table 1). Polyphenols were detected in the negative mode (ESI-NI) and thus, producing mainly the [M − H] − molecular ions (Table 1) except myricetin, quercetin, and anthocyanins which were detected in positive mode. For optimisation of the MS/MS transitions, the standard of the target polyphenol was introduced into the mass spectrometer by direct flow injection, and the collision energies of the SRM transitions were optimised for each polyphenol. The system was operated by Xcalibur 2.2. (Thermo Fisher Scientific Inc., San Jose, CA, USA) and Trace Finder 3.2. (Thermo Fisher Scientific Inc., San Jose, CA, USA) software.        Del-3-ara-delphinidin-3-arabinoside; Pet-3-glu-petunidin 3-glucoside; Cya-3-aracyanidin-3-arabinoside; Peo-3-glu-peonidin 3-glucoside; Peo-3-ara-peonidin 3-arabinoside; Mal-3glu-malvidin 3-glucoside.

Statistical Analysis
All extractions were performed in triplicate. Significant differences between the results were evaluated by analysis of variance (ANOVA) using Statgraphics XV Centurion software package (Manugistics Inc., Rockville, MD, USA). Differences at p-value < 0.05 were considered statistically significant at a 95% the confident level. The Least Significant Difference (LSD) test was applied to indicate the samples between which there were differences. For drawing of the Sankey diagram, Flourish studio was used (Flourish Studio, Kiln Enterprises Ltd., London, UK).

Total Polyphenolic Content and Antioxidant Activity of Extracts
The first objective of this study was to evaluate the impact of HVED, PEF, and UAE on the total polyphenol content and the antiradical activity of blueberry pomace extracts. The obtained results are presented in Figures 3 and 4. hand, different trends were observed for AA, where only time and frequency had a significant effect (p < 0.05) on the antioxidant activity of obtained extracts. The highest AA (0.41 mmol TE/g dw) was achieved in ethanol-based solvent after 15 min of treatment time and at the frequency of 100 Hz. Three-way ANOVA analysis of PEF-assisted extraction showed that all investigated factors (solvent, electric field intensity, and number of pulses) had a significant effect (p < 0.05) on the extraction of TPC and AA of extract. The highest TPC (10.52 mg GAE/g dw) and AA (0.83 mmol TE/g dw) was obtained in ethanol-based solvent after 100 pulses and 20 kV/cm, which corresponds to the energy input of 41.03 kJ/kg. Considering UAE, the three-way ANOVA analysis showed that also all investigated factors (solvent, temperature, and time) had a significant effect (p < 0.05) on the TPC and AA of extract. The highest TPC (5.46 mg GAE/g dw) was obtained in ethanol-based solvent after 15 min at 80 °C and AA (0.25 mmol TE/ g dw) in methanol-based solvent after 15 min at 80 °C. Rajha et al. [36] also demonstrated the higher efficiency of electrical treatments over ultrasound, however, giving the advantage to HVED over PEF. In their study, for the same energy input, HVED enhanced the recovery of polyphenols by ≈3 and ≈1.3 times as compared with UAE and PEF, respectively. This may explain the higher yield of polyphenols obtained by PEF in this study, since the energy input of PEF was almost twice higher comparing to the energy input of HVED.  Three-way ANOVA analysis (solvent, time, and frequency) of HVED-assisted extraction showed that all investigated factors had a significant effect (p < 0.05) on the extraction of TPC. The highest yield (6.58 mg GAE/g dw) was obtained in methanol-based solvent after 15 min of treatment time and at the frequency of 50 Hz, which corresponds to an energy input of 22.27 kJ/kg. On the other hand, different trends were observed for AA, where only time and frequency had a significant effect (p < 0.05) on the antioxidant activity of obtained extracts. The highest AA (0.41 mmol TE/g dw) was achieved in ethanol-based solvent after 15 min of treatment time and at the frequency of 100 Hz. Three-way ANOVA analysis of PEF-assisted extraction showed that all investigated factors (solvent, electric field intensity, and number of pulses) had a significant effect (p < 0.05) on the extraction of TPC and AA of extract. The highest TPC (10.52 mg GAE/g dw) and AA (0.83 mmol TE/g dw) was obtained in ethanol-based solvent after 100 pulses and 20 kV/cm, which corresponds to the energy input of 41.03 kJ/kg. Considering UAE, the three-way ANOVA analysis showed that also all investigated factors (solvent, temperature, and time) had a significant effect (p < 0.05) on the TPC and AA of extract. The highest TPC (5.46 mg GAE/g dw) was obtained in ethanol-based solvent after 15 min at 80 • C and AA (0.25 mmol TE/ g dw) in methanol-based solvent after 15 min at 80 • C. Rajha et al. [36] also demonstrated the higher efficiency of electrical treatments over ultrasound, however, giving the advantage to HVED over PEF. In their study, for the same energy input, HVED enhanced the recovery of polyphenols by ≈3 and ≈1.3 times as compared with UAE and PEF, respectively. This may explain the higher yield of polyphenols obtained by PEF in this study, since the energy input of PEF was almost twice higher comparing to the energy input of HVED.
Tables 2-5 present the results of individual polyphenols content determined in the blueberry extracts by HPLC-DAD and confirmed by LC-MS/MS.

Extraction of Anthocyanins
Anthocyanins were the most abundant polyphenolic group of compounds (Table 2) detected in the blueberry extract. Seven anthocyanins were identified in all extracts obtained in this study, regardless of the method and conditions investigated. They are delphinidin 3-glucoside, delphinidin-3-arabinoside, petunidin 3-glucoside, cyanidin-3-arabinoside, peonidin 3-glucoside, peonidin 3arabinoside, and malvidin 3-glucoside. These anthocyanins have been previously detected in blueberries [4,37,38]. Peonidin 3-glucoside was the most abundant anthocyanin in the blueberry extract obtained in this study. The total anthocyanin content ranged from 285.73 to 1757.32 µg/g of dw, depending on the extraction solvent, extraction method, and method parameters. Three-way ANOVA analysis showed that all investigated factors (HVED-solvent, time, and frequency; PEFsolvent, electric field intensity, and number of pulses; UAE-solvent, temperature, and time) had a significant effect (p < 0.05) on the extraction of anthocyanins. Regarding the extraction solvent, the methanol-based solvent proved as a better extraction solvent for anthocyanin extraction regardless of the applied method. Considering extraction methods, for HVED, the highest extraction yields of anthocyanins were achieved at a frequency of 50 Hz for 15 min and for UAE at 80 °C after 15 min (1221.28 and 953.91 µg/g of dw, respectively). However, the highest total anthocyanin content (1757. 32 µg/g of dw) compared to the other two methods was observed in the extract obtained with PEFassisted extraction in methanol-based solvent after 100 pulses and 20 kV/cm. These results are in  Table 2. The anthocyanins content (µg/g of dw) in extracts obtained after high voltage electrical discharges (HVED), pulsed electric field (PEF), and ultrasound-assisted extraction (UAE) of blueberry pomace.

Extraction of Anthocyanins
Anthocyanins were the most abundant polyphenolic group of compounds (Table 2) detected in the blueberry extract. Seven anthocyanins were identified in all extracts obtained in this study, regardless of the method and conditions investigated. They are delphinidin 3-glucoside, delphinidin-3-arabinoside, petunidin 3-glucoside, cyanidin-3-arabinoside, peonidin 3-glucoside, peonidin 3-arabinoside, and malvidin 3-glucoside. These anthocyanins have been previously detected in blueberries [4,37,38]. Peonidin 3-glucoside was the most abundant anthocyanin in the blueberry extract obtained in this study. The total anthocyanin content ranged from 285.73 to 1757.32 µg/g of dw, depending on the extraction solvent, extraction method, and method parameters. Three-way ANOVA analysis showed that all investigated factors (HVED-solvent, time, and frequency; PEF-solvent, electric field intensity, and number of pulses; UAE-solvent, temperature, and time) had a significant effect (p < 0.05) on the extraction of anthocyanins. Regarding the extraction solvent, the methanol-based solvent proved as a better extraction solvent for anthocyanin extraction regardless of the applied method. Considering extraction methods, for HVED, the highest extraction yields of anthocyanins were achieved at a frequency of 50 Hz for 15 min and for UAE at 80 • C after 15 min (1221.28 and 953.91 µg/g of dw, respectively). However, the highest total anthocyanin content (1757. 32 µg/g of dw) compared to the other two methods was observed in the extract obtained with PEF-assisted extraction in methanol-based solvent after 100 pulses and 20 kV/cm. These results are in agreement with Zhou and Huang [14], who also noticed that increasing the electric field intensity up to 20 kV/cm leads to an increase in the content of anthocyanins in the extract. The most optimal conditions for the extraction of anthocyanins by PEF in their case were at an electric field intensity of 20 kV/cm, acidified (0.1% of hydrochloric acid) 60% ethanol, and a liquid to liquid ratio of 1:6 (mL/mL). Under these conditions, the recovery of anthocyanins was 223.13 mg/L [14]. An increase in electric field intensity enhances the potential difference between the inside and outside of the cell membrane, causing a rupture of cell walls and improvement in the dissolution rate of cells [14]. Other studies on the extraction of anthocyanins showed that electrical treatments (HVED or PEF) were more effective when compared with ultrasound [14,39,40]. The study conducted by Barba et al. [15] on the extraction of anthocyanins from grape pomace showed that HVED (40 kV) was more effective compared with PEF (13.3 kV/cm). However, they also showed that PEF treatment allowed the selective recovery of extracts with an amount of anthocyanins 22 and 55% higher than with UAE and HVED, respectively [15].

Extraction of Phenolic Acids
Phenolic acids (Table 3) were the second most abundant polyphenolic group of compounds detected in blueberry pomace extract. In this study, three phenolic acids were identified: chlorogenic acid, caffeic acid, and 4-hydroxycinnamic acid. Chlorogenic and caffeic acids have been previously detected in blueberries. However, rather than 4-hydroxycinnamic acid, other phenolic acids were marked as dominant such as p-hydroxybenzoic acid, vanillic acid, or p-hydroxybenzoic acid [41,42]. In this study, phenolic acids content ranged from 119.21.73 to 625.47 µg/g of dw, and chlorogenic acid was the most abundant one found in blueberry pomace extract. Three-way ANOVA analysis showed that all investigated factors (HVED-solvent, time, and frequency; PEF-solvent, electric field intensity, and number of pulses; UAE-solvent, temperature, and time) had a significant effect (p < 0.05) on the extraction of phenolic acids. The highest extraction yields of phenolic acids with HVED were achieved in ethanol-based solvent at the frequency of 50 Hz for 15 min (442.90 µg/g of dw), while UAE showed to be more efficient in methanol-based solvent after 15 min at 80 • C (561.26 µg/g of dw). However, the highest TPC (625.47 µg/g of dw) compared with the other two methods, was observed in the extract obtained with PEF-assisted extraction in ethanol-based solvent after 100 pulses and 20 kV/cm. Other studies also showed promising results in PEF-assisted extraction of phenolic acids from different food by-products. In a study dealing with polyphenols extraction from peach by-products, Redondo et al. [43] showed that PEF application resulted in an increase in chlorogenic acid (16.3 mg/100 g), coumaric acid (0.8 mg/100 g), and chlorogenic acid (9.8mg/100 g) compared to the amounts extracted without the application of PEF (4.5, 0.2, and 2.5 and mg/100 g, respectively). Furthermore, Martín-García et al. [44], studying PEF-assisted extraction of polyphenols from brewery by-products, showed improvement in the p-coumaric acid and ferulic acid recovery from brewers spent grain compared with the conventional method.

Extraction of Flavanols
The third most abundant polyphenolic group of compounds was flavanols (Table 4). In this study, four flavanols were identified: catechin, epicatechin procyanidin B1, and procyanidin B2. Catechin, epicatechin, and only B-type procyanidins were previously identified in cultivated and wild diploid blueberry species by Wang et al. [45]. In this study, flavanols content in blueberry pomace extract ranged from 53.34 to 297.86 µg/g of dw and the most represented flavanol was procyanidin B2. Three-way ANOVA analysis showed that all investigated factors (HVED-solvent, time, and frequency; PEF-solvent, electric field intensity, and number of pulses; UAE-solvent, temperature, and time) had a significant effect (p < 0.05) on the extraction of flavanols. As for anthocyanins, methanol-based solvent proved as a better extraction solvent for flavanols extraction, regardless of the applied method. The highest total phenolic acid content (297.86 µg/g of dw) was observed in the extract obtained with PEF-assisted extraction in methanol-based solvent after 100 pulses and 20 kV/cm. For HVED, the highest extraction yields were achieved at the frequency of 50 Hz for 15 min and for UAE, at 80 • C for 15 min (182.47 and 156.04 µg/g of dw, respectively). Boussetta et al. [46] studied the HVED-assisted extraction of flavanols from grape pomace, showing an increase in the amount of extracted catechin and epicatechin. They also observed a negative effect of HVED at higher energy inputs (>80 kJ/kg) corresponding to the decrease in polyphenols content. In our study, the highest flavanol content was achieved at 22.27 kJ/kg; higher energy input (42.54 kJ/kg) resulted in a lower amount of flavanols. Interestingly, the highest amount of extracted flavanols was achieved with PEF-assisted extraction at 41.03 kJ/kg. This could be explained by the difference in the extraction mechanism of these two methods, where the HVED mechanism, among others, includes the generation of ozone, atomic hydrogen, and hydroxyl radicals during water photodissociation. The resulting oxidative chemical reactions could negatively affect the extracted polyphenols causing their damage. For example, formed ozone could react with water molecules to form hydrogen peroxide, which then decomposes to form hydroxyl radicals [46]. In particular, for high energy input, the quantity of produced oxidising species is increased and that may oxidise polyphenols. Furthermore, in the case of ethanol-based solvent, this can lead to the oxidation of ethanol in ethanal and in the formation of a flavanol-anthocyanin adduct with or without CH 3 −CH bridges originating from ethanal [47].

Extraction of Flavonols
The least abundant polyphenolic group of compounds found in the extract was flavonols (Table 5), among which myricetin was the most represented flavonol. Four flavonols were detected in blueberry pomace extract: myricetin, quercetin, kaempferol, and quercetin derivatives. These flavonols have been previously detected in blueberries [48]. In this study, flavonols content ranged from 44.53 to 157.54 µg/g of dw. Three-way ANOVA analysis showed that all investigated factors (HVED-solvent, time, and frequency; PEF-solvent, electric field intensity, and number of pulses; UAE-solvent, temperature, and time) had a significant effect (p < 0.05) on the extraction of flavonols. The highest total flavonols content (157.54 µg/g of dw) was observed in the extract obtained with PEF-assisted extraction in ethanol-based solvent after 100 pulses and 20 kV/cm. Bansal et al. [49] also showed that PEF extraction of quercetin from Emblica Officinalis is an effective treatment for the extraction of flavonols compared to conventional methods. Furthermore, Teherani et al. [50] proposed PEF (4.1 kV) as a very effective method for extraction of quercetin from onion by-products. Concerning the other two methods, higher extraction yields of flavonols with HVED were achieved in ethanol-based solvent at the frequency of 50 Hz for 15 min, while US-assisted extraction showed to be more efficient in methanol-based solvent after 15 min at 80 • C (121.90 and 98.63 µg/g of dw, respectively).
This has been shown also in other studies, which found that flavonols dissolve better in ethanol-water mixtures compared to methanol-water mixtures [51]. Numerous studies have found a significant effect of solvent type and extraction method on polyphenol yield from certain plant materials. The type of extraction solvent as well as the extraction method have a significant impact on the extraction yield of individual polyphenols from each individual plant material. There are some reports concerning optimisation of extraction conditions of phenolic compound content and antioxidant activities of some plant foods but some research works indicated the optimal procedure to usually be different for different plant matrices and different extraction methods [52,53].
Previous research has also shown that electrotechnologies (PEF or HVED) promote polyphenol extraction and that better yields can be achieved compared to other methods, including the US-assisted extraction method [14]. When applying PEF or HVED for the enhancement of the extraction of polyphenols from various raw materials, the main operating parameter is the treatment's energy input [54]. In the present study, it was shown that HVED-assisted extraction had better extraction yield at 22.27 kJ/kg. Increasing energy input results in a decrease in extraction yield. As we already mentioned, the HVED mechanism of action includes generation of hydroxyl radicals during water photodissociation, atomic hydrogen and ozone, and for high energy input, the quantity of produced oxidising species is increased, which may cause oxidation of polyphenols. This may be the reason for obtaining a lower extraction yield compared to PEF-assisted extraction.
Higher extraction yields using PEF-assisted extraction at higher energy inputs (41.03 kJ/kg) can also be explained by a different mechanism of action of PEF, followed by which is the increasing diffusivity of the intracellular substances caused by permeabilisation of cell membranes, which ultimately improve extraction efficiency by increased mass transfer rate [55]. This process increases the extraction rates and yields of different active ingredients without affecting the quality of the extracted products [14]. Furthermore, higher extraction yields may be attributed to the ability of PEF to selectively induce the extraction of specific compounds. In fact, it has been reported that the specific group of polyphenols, their relative location in the plant tissue, their bounding capacity to the plant matrix, and their chemical structure and stability during processing at different conditions [15,28] might be crucial in obtaining extracts with specific biochemical profiles.

Conclusions
The results of this study have demonstrated that the extraction yield of phenolic compounds from blueberry pomace using HVED, PEF, and UAE is dependent on all investigated factors (HVED-solvent, time, and frequency; PEF-solvent, electric field intensity, and number of pulses; UAE-solvent, temperature, and time). Comparing the different extraction methods, it can be observed that both TPC and AA of extracts obtained by PEF were higher than those obtained employing HVED and UAE. Eighteen polyphenols have been positively identified by LC-MS/MS and quantified by HPLC-DAD. The highest anthocyanin (1757.32 µg/g of dw) and flavanol (297.86 µg/g of dw) yields were obtained in methanol-based solvent, while the highest phenolic acid (625.47 µg/g of dw) and flavonol (157.54 µg/g of dw) yields were obtained in ethanol-based solvent by PEF-assisted extraction at the energy input of 41.03 kJ/kg. These results indicated that PEF can improve the extraction yield of polyphenols from blueberry pomace and that it is a promising green extraction method.