# Extraction of Pigments from Microalgae and Cyanobacteria--A Review on Current Methodologies
## 6 Electroextraction  
Electric field technologies have been developed and used in food processing since the 1970s, more specifically the pulsed electric fields (PEF), that are based in the application of an electric current through the biomass in contact with a solvent for a certain period of time, in order to induce an electroporation effect [45]. The electric field can be applied continuously or in pulses, applying a charge to the cell membrane and inducing a destabilization of its structure, eventually leading to an electroporation effect by opening pores in the cell (reversibly or irreversibly), allowing solvent penetration and thus facilitating the extraction of intracellular compounds [46]. The effects of electroextraction processes on the cell are depicted in Figure 5.  
In microalgae and cyanobacteria, electrotechnologies can be used for bioproduct extraction, but also for harvesting and for production, by inducing stress for the production of secondary metabolites (including carotenoids and total antioxidant compounds) [47,48]. Changes in the intensity, shape of the electrical wave, frequency, temperature, time of extraction, number of pulses, and pulse duration can influence the efficiency of the extraction, which is dependent on the matrix biomass and the desired product or effect [48]. Electro-based methods, in special PEF, have been proposed as suitable extraction methods for several microalgae and cyanobacteria pigments. [PERSON] et al. [49,50] optimized PEF for the extraction of chlorophylls and carotenoids from _C. vulgaris_ using pulse duration values between microseconds and milliseconds. The optimized treatment (25 pulses of 3 \(\upmu\)s at an electric field strength of 20 kV.cm\({}^{-1}\)) was efficient for both cell permeabilization, cell inactivation, and extraction of pigments. In another study, [PERSON] et al. [51] suggest the use of a controlled temperature between 25 to 30 \({}^{\circ}\)C for the extraction of lutein from _C. vulgaris_. The temperature range is the same used in the production of the microalgae, thus avoiding extra costs for heating. In the case of _A. platensis_, PEF have been suggested by [PERSON] et al. [52] for the extraction of phycocyanin. The minimum electric field required was 15 kV.cm\({}^{-1}\), being the optimal 25 kV.cm\({}^{-1}\) associated with a treatment of 50 pulses of 3 \(\upmu\)s at temperature of 40 \({}^{\circ}\)C. In another study, a higher purity of phycocyanin extracted from _Nostoc commune_ was achieved by using PEF, although at a lower concentration than freeze thawing extraction, using an electric field of 5 kV.cm\({}^{-1}\), a frequency of 2 Hz, and 1500 pulses of 1 \(\upmu\)s each, at 40 \({}^{\circ}\)C [53]. [PERSON] et al. [53] also suggest that the PEF methodology seems to be not suitable for some organisms, as in the case of _Oscillatoria dexii_, where the cell wall is much more resistant. Moreover, for the extraction of phycerythrin from the red microalgae _Porphyidium cruentum_, the optimized conditions of PEF were an electric field of 10 kV.cm\({}^{-1}\), a frequency of 0.5 Hz, and 50 pulses of 3 \(\upmu\)s each with temperature kept between 20 and 30 \({}^{\circ}\)C [54]. As a pre-treatment, PEF was used for the extraction of pigments from _Nannochloropsis_ spp, using a two-stage solvent extraction process: the first stage with water as the solvent and the second one with an organic solvent mixture. The PEF treatment (20 kV.cm\({}^{-1}\), 400 pulses of 10 \(\upmu\)s) is applied only in the first stage and pigments are recovered in the second stage [55]. In addition, PEF pre-treatment was also suggested for the extraction of astaxanthin in _H. pluvialis_, with a treatment of 1 kV.cm\({}^{-1}\), 10 pulses of 5 ms, at 20 \({}^{\circ}\)C providing an extraction 1.2-fold more efficient than other disruption methods [56]. As the main advantages, electrotechnologies require much lower energy input, shorter extraction times, and lower amounts of solvent than classical, enzymatic, and wave-based methods [27].