# Extraction of Pigments from Microalgae and Cyanobacteria--A Review on Current Methodologies
## 5 Wave-Energy-Based Cell Disruption  
Two wave-based extractions--microwave-assisted extraction (MAE) and ultrasound assisted extraction (UAE)--have been studied and optimized for the extraction of high-value compounds from microalgae and cyanobacteria. Regarding the extraction of pigments, both methods have been suggested, although only a few studies have been carried out regarding their optimization. The effects of wave-based extraction processes in the cell are represented in Figure 4.  
Figure 4: Schematic representation of microwave (MAE) and ultrasound assisted extraction (UAE) effects in microalgae and cyanobacteria cells.  
MAE occurs due to the heat shock caused when the radiation is applied to the solution, causing cell wall degradation. As a thermal process, the main limitation of its use is the limited thermostability of pigments. The main benefits of MAE are the reduced extraction time and low solvent consumption, making it a green extraction method [30]. Furthermore, because of the short extraction time, this extraction method is not restricted to thermoresistant molecules. Also, low temperatures can be used when performing MAE under vacuum conditions, although this option significantly increases the cost of the extraction process [40].  
[PERSON] et al. [40] used MAE to obtain phycobiliproteins from _Porphyridium purpureum_. Optimal phycoerythrin extraction was achieved at 40 \({}^{\circ}\)C in 10 s of microwave application. On the other hand, phycoyanin and allophycocyanin were extracted more effectively at a temperature of 100 \({}^{\circ}\)C. The temperature was controlled by oscillating the power applied [40]. In another study, [PERSON] et al. [41] also suggest microwave extraction for the obtention of carotenoids and chlorophylls from _Cylindotheca clostrium_, with an optimal condition at 5 min and 50 W, at 56 \({}^{\circ}\)C, with a higher extraction rate when compared with classic thermal extraction and UAE.  
Regarding UAE, the process is based in the use of acoustic cavitation for producing cavitation bubbles, that locally increase the pressure when they collapse. The consequent disruption of the cell wall allows the penetration of the solvent, and higher extraction rates are achieved [42]. UAE thus increases extraction yield, reducing the time and energy for processing, while ensuring good reproducibility, low solvent consumption and low temperature ranges (<70 \({}^{\circ}\)C), allowing UAE to be associated as a green extraction approach [42; 43].  
[PERSON] and [PERSON] [42] optimized the use of UAE for the extraction of \(\beta\)-carotene from _A. platensis_. Optimal conditions were found by using heptane at a temperature of 30 \({}^{\circ}\)C and an electrical acoustic intensity of 167 W.cm\({}^{-2}\), over 8 min [42]. The use of a UAE continuous system has been proposed by [PERSON] et al. [44] for the extraction of lipids from _Chlorella_ sp., pointing at a possible scaling up of UAE processes. Finally, [PERSON] et al. [17] optimized astaxanthin extraction from _H. pluvialis_ using UAE using a response surface methodology, and the optimal condition was set at an ultrasound power of 200 W and frequency of 40 kHz at 41.1 \({}^{\circ}\)C, during 16 min, with a yield 35% higher than classical solvent extraction.