A standard batch extraction unit comprises a pretreatment chamber for PEF and essential equipment for solid–liquid extraction. The pretreatment unit of PEF contains a cylindrical vessel of polypropylene (30 mm diameter on the inner side), having two stainless steel electrodes arranged parallel to each other at a 10-millimeter distance. The processing parameters include electrical field strength, pulses width, shape, number, and frequency. Inside the cylindrical unit, the sample with a little solvent was first treated between two electrodes and connected to a PEF generator. The treated sample was removed from the cylindrical unit and stirred at different velocities using a magnetic agitator to prevent solution evaporation [22].

Using a PEF batch extraction method, various intracellular compounds such as lipid [36], red beetroot pigment [37], anthocyanin [35], betanine [22], oil [38], polyphenols [31], and cellulose [39] have been extracted. Figure 2 shows the PEF batch extraction system.

The batch extraction process of PEF gave promising results in terms of extraction; however, a significant increase in the operating time has been observed, which is due to the low capacity of batch mode systems. Therefore, it is crucial to devise a PEF extraction process to perform it in regular conditions at the industrial level. Since then, the PEF continuous extraction method has been in great focus. The continuous-flow treatment chamber was first successfully used by Yongguang et al. [35] for the extraction of polysaccharides from Rana temporaria chensinensis David in 2006 [40]. Their results depicted that the extraction yield was 55.59% with PEF (20 kV/cm, 0.5% of KOH) as compared to the traditional extraction technique. In the past few years, the continuous extraction PEF applied successfully in laboratories to obtain fishbone, broccoli juice, eggshell, tomato juice, etc. This technology has been applied in industries thus far.

A typical PEF continuous extraction system consists of a high-voltage pulse generator, a treatment chamber, a suitable product handling system, and a range of monitoring and controlling equipment. The oscilloscope can read the output voltage (up to 40 kV pulse voltage) directly, and the frequency is adjustable (40–3000 Hz). During continuous extraction PEF, the solvent mixture is pumped into the treatment chamber by a peristaltic pump at a constant fluid velocity. The cooling coil has a temperature of 25 °C in a water bath controlled by a thermostat during the extraction procedure. Coaxial and the cofield continuous PEF treatment chambers are currently widely used due to their simple configurations [22]. Figure 3 shows the PEF continuous extraction system.

Due to their nutritional value worldwide and the fact that they are rich sources of beneficial antioxidants, minerals, vitamins and fibers [50], fruits, and vegetables are the most common source of nutrition. A variety of antioxidant compounds can be present in fruits and vegetables, including phenolics, carotenoids, anthocyanins, and tocopherols [51]. PEF is a promising method to extract bioactive compounds (anthocyanins, betanines, carotenoids, etc.) from fruit and vegetables, as shown in Table 1. Several factors depend on the extraction of bioactive compounds, such as the process of extraction, the solvent used for extraction and raw materials [52]. Traditional extraction techniques such as Hydro distillation, maceration, and Soxhlet require agitation, high temperatures, and chemical or organic solvents [53]. Nevertheless, the Soxhlet method needs considerable time for extraction and significant quantities of the solvent [54].

Leong et al. [55] evaluated the extraction of anthocyanins from grape juices using PEF technology with 20 µS pulse, 50 Hz frequency and 1.5 kV/cm electric field power. PEF-assisted extraction improved the release of vitamin C and anthocyanins as well as enhanced the antioxidant activity of grape juice as compared to untreated samples. The resultant extract had good phytochemical composition and protected the cells from oxidation [55]. Similarly, the PEF treatment enhanced the antioxidant activity (1.03 times) and extraction of polyphenols (1.44 times) of green grape juice [56]. Moreover, the PEF pretreatment enhanced the recovery of red raspberry (Rubus idaeus L.) juice by 9–25% without affecting the total phenolic and anthocyanin content. Furthermore, it enhanced the red raspberry press-cake extract that involved a 20% increase in phenolic content and a 26% increase in anthocyanin content [57]. In another study, PEF (13.3 kV/cm, 0–564 kJ/kg) enhanced the extraction yields of fermented grape (Dunkelfelder) pomace up to 22 and 55%. The results showed more recovery of anthocyanins as compared to traditional grinding methods, ultrasound-assisted extraction, and high-voltage electrical discharge [58].

PEF treatment is the most suitable nonthermal technique to extract phenols and flavonoids from onions without significant quality losses. Plant tissues contain a cytomembrane, which affects the movement of intracellular substances between cells. PEF treatments altered the functionality (permeability) of cytomembrane by disintegration and improved the movement of mass through cells, providing greater yields. Compared to the control samples, the PEF treatment significantly enhanced the phenolic compounds (102.86 mg GAE/100 g) by 2.2 times and the flavonoid compounds (37.58 mg QE/100 g) by 2.7 times in onions [59]. According to Fincan [60], the disintegration index was 0.86 ± 0.02 at 99 pulses of 3 kV/cm (4102 ± 239 J/kg) in the PEF-treated sesame seed cake. The extraction yields (total phenolic, antioxidant power, and antioxidant activity) produced using microwave and heat technology was comparable with PEF-assisted extraction [60]. Further, Sarkis et al. [61] stated that the disintegration index and the proteins and polyphenols content increased until 83 kJ/kg energy inputs in the case of spearmint [61].

Xue et al. [62] showed that PEF treatment (38.4 kV/cm, 272 μs) produced higher extraction yields of polysaccharides (97.7%), protein (48.9%), and polyphenolic compounds (50.9%) in white button mushrooms compared to traditional thermal treatment (95 °C for 1 h). The traditional technique has a prolonged treatment cycle as compared to the PEF system. However, PEF exhibited a fluid residence time of less than 2.6 min [62]. In the same context, Jeya et al. [25] investigated that PEF at 7 kV/cm and 2.5 kJ/kg resulted in a 4.2-fold enhancement in the yield of betanine as compared to untreated samples. According to the authors, 90% of betanine extraction was achieved in 35 min. Frontuto et al. [63] indicated that the PEF pretreatment of potato peel tissues greatly enhanced the extraction of phenolics. Accordingly, PEF pretreatment achieved the same amount (1062 mg GAE/kg) of phenolics in 144 min as compared to untreated samples (240 min) [63]. Similarly, PEF treatment (2 kV/cm, 11.225 kJ/kg) significantly enhanced the yield (13.3%) of phenolic content in olive paste [64].

Fruit and vegetable flesh or pulp is consumed while the other components, which are not mostly consumed, such as peel and seeds, contain a significant amount of various vital nutrients and phytochemicals [9,75,76]. For example, lemon, grapes, orange peels, avocado, jackfruit, longan, and mango seeds contain more than a 15% phenolic concentration, which is higher than those contained in fruit pulp [77]. In the food industry, much of the waste being produced is marked by the demand for biological oxygen and the demand for chemical oxygen. The food waste is rich in numerous bioactive components such as phenolic acids, flavonoids (hesperetin, quercetin, genistein, and kaempferol), and carotenoids (lutein and zeaxanthin); hence, it is concerned with the benefits of using PEF to recover valuable compounds that would contribute to the notion of zero waste.

Conventionally, these compounds are extracted by different treatments such as nanoemulsions used in the nutraceutical, cosmetics, and pharmaceutical industries [75]. The traditional solvent extraction techniques are time and energy consuming. For instance, the industrial batch extraction of polyphenols from grape peels is usually carried out at 50–60 °C for 20 h. Furthermore, the bioactive is enclosed in plant cell vacuoles and membrane bilayers (insoluble structures) that are not open to solvents. The usage of high temperature to enhance mass transfer and reduction in time may have serious drawbacks since high temperature (greater than 70 °C) caused rapid degradation of heat-sensitive components such as anthocyanins [78]. Kantar et al. [79] compared the total polyphenolic content of orange, grapefruit, and lemon in both juice extract and peel (flavedo/albedo) using PEF (3–10 kV/cm) as a pretreatment followed by the traditional extraction procedure (50% ethanol for 1h). The results showed an improved flavonoid content and total phenolic contents (2200 mg GAE/100 g) of fruit peels at 10 kV/cm [79].

Herbs and spices have been widely used to strengthen or enhance the taste and preserve the quality of food along with their beneficial effects on human health. The plant essential oils contain 85% of polyphenols, terpenes, monoterpenes, and sesquiterpenes. However, essential oils (derived from herbs and spices) have 70 or more different molecules of phytochemicals such as terpenoids, polyphenols, flavonols, flavonoids, and tannins [80,81,82]. Spices have been used in traditional medicine since ancient times; however, their beneficial health effects have been experimentally recognized only in the last three decades. Recently, the antioxidant properties of black pepper (piperine), red pepper (capsaicin), turmeric (curcumin), fenugreek, ginger (gingero), garlic, clove (eugenol), and onion (quercetin) have been investigated by [83]. The antioxidants derived from spices have been evaluated for the prevention of various health-related disorders including atherogenesis.

The most common method used for extracting bioactive or essential oils from plant sources is Soxhlet extraction (hydro and steam distillation), while other traditional extraction techniques include maceration, engraving, and cohobation. However, steam distillation has been used widely for the commercial production of essential oils [84]. The traditional methods are complex multistage processes, which consumed more organic solvent, time, and energy while resulting in the loss of analytes. These factors are leading to the low selectivity of conventional extraction methods. In contrast, the modern PEF technique enhanced the extraction capacity of bioactive from metabolically active tissues via increasing osmotic dehydration with less energy input and an enhanced recovery of nutrients [85]. Furthermore, PEF extraction was facilitated by solvent diffusion and freeze-drying [11].

Phyllanthus emblica L. (Syn. Emblica officinalis) is an ancient herb well known for its functional properties. PEF (18 to 24 kV/cm, 300 to 1000 µs) treated Emblica juice showed an improved (9 times) extraction of quercetin and ellagic acid than thermally processed juice. According to the authors, 22 kV/cm was the optimum electric field power for 0.79 disintegration index within 500 µs [85]. Similarly, PEF extraction at 20 kV/cm using 70% ethanol and water increased the yield (12.69 mg/g) of ginsenosides as compared to ultrasound assisted extraction, microwave assisted extraction, heat reflux extraction, and pressurized liquid extraction. The authors stated that it took less than 1 s to complete PEF extraction, which is much lower than the other methods tested [86].

According to Segovia et al. [87], PEF treatment (300 Hz, 30 kV) increased the polyphenols from 1.3 to 6.6% and the Oxygen Radical Absorption Capacity from 2.0 to 13.7% in Borago officinalis L. leaves. Moreover, PEF-assisted extraction increased the antioxidant capacity of the extracts and reduced the extraction times [87]. Barba et al. [88] established that PEF extraction treatments (0 to 141 kJ/kg, using water as a solvent) disrupt the plant cells of Stevia rebaudiana Bertoni leaves. PEF extraction improved conductivity (≈25%) and soluble matter extraction yields (≈33%) as compared to diffusion. Furthermore, PEF enhanced the antioxidant activity (50%), total phenolic compounds activity (80%), chlorogenic acid (93%), caffeic acids (55%), ferulic acid (90%), and protocatechuic acids (45%) [88]. Table 2 summarizes the range of parameters used in PEF-assisted extraction for the release of bioactive components from Agro-Industrial waste.

The major oil crops include ground nuts, olive, linseed, cotton, hemp, castor, cottonseed, safflower, sesame oils, etc. Among them soy, rape, palm, and sunflower are the most significant oil-bearing plants [92]. Fats and oils are the most consumed items and are of much importance because of triacylglycerols [93]. Furthermore, edible oils are a major source of energy (calories) and essential vitamins. Moreover, oilseeds are placed second after grains as food reserves [94,95]. Pressing is a conventional method to extract oil from seeds, which squeezes the oil out of solid material (having more than 30% oil). After pressing, the press-cake is then subjected to solvent extraction. Traditionally, cold and hot-pressing technologies are used for the extraction of oil such as solvent extraction (Soxhlet) for flaxseed. On an industrial scale, generally, the solvent extraction step is applied by using a lot of hexane in the countercurrent extractors [96]. In contrast, PEF treatments (50 kV) were used to extract oil (including tocopherols, antioxidants, herbal cholesterol (phytosterols), and other functional compounds) from oleaginous material [15]. For instance, PEF (2 kV/cm, 11.25 kJ/kg, 25 Hz) using monopolar exponential decay pulses (0.3 µs) increased the oil yield (22.66 kg/100 kg) from olive paste as compared to the control sample (20.00 kg/100 kg) [97]. Table 3 illustrates that PEF-assisted extraction is a progressing nonthermal technique to increase the extraction yield of seed oils. PEF-assisted extraction assures higher extraction yields without a detrimental impact on the nutritional value and freshness of the product [98].

Microorganisms such as bacteria, yeast, and algae are good sources for highly valued compounds such as enzymes, pigments, and nutrients as shown in Table 4. The major portion of such compounds resides inside the cell; therefore, it is essential to extract and purify them before use [103]. Microorganisms can carry out a broad range of reactions and are adaptable to a variety of conditions. They can be moved from nature into the laboratory to produce beneficial compounds on cheap sources such as carbon and nitrogen. Due to the biological activity of secondary metabolites originating from microbes, they are greatly beneficial for our nutrition and health. Research is progressed in the screening of naturally occurring microbial products, for the development of novel therapeutic agents. The search of novel chemicals is an important way forward to study the capacity of lesser-known or novel bacterial taxa [104].

Martínez et al. [105] used PEF (15–25 kV/cm, 60–150 μs, 10–40 °C) to enhance the extraction of a selective protein called phycocyanin (a water-soluble protein) from Artrosphira platensisto’s fresh biomass. According to the authors, low molecular weight compounds move directly through the cytoplasmic membrane after electroporation, while high molecular weight compounds require that the pores produced by the PEF treatment expand over time. Hence, the resultant delay of 150 min was recorded during the extraction. [105]. Similarly, Jaeschke et al. [106] also succeeded in achieving a high protein and phycocyanin yield from Arthospira platensis after a PEF treatment of 40 kV/cm utilizing pulses of 1 μs (112 kJ/kg) [106]. Martínez et al. [107] extracted another water-soluble protein (β-phycoerythrin) from Porphyridium cruentum by applying PEF for 24 h. However, this water-soluble phycobiliprotein was unobservable in the untreated cells, even after extended periods of incubation. The results showed that the extraction of β-phycoerythrin involved not only the diffusion of the pigment through the cell membrane, but also the disassembly from the cell organization of the molecule. In this way, PEF released the P. cruentum organelles (hydrolytic enzymes) that broke the bonds between the pigment and other cell compounds; thus, the water- β-phycoerythrin complex diffused, carried by a concentration gradient, through the membrane. The enzymatic autolysis of microalgae caused by PEF must be further investigated for the industrial implementation of PEF extraction technology [108]. Table 4 further confines some of the literature on PEF that involves the extraction of other phytoconstituents.