# Microwave-Assisted Extraction of Fatty Acids from Cultured and Commercial Phytoplankton Species
## 4 Discussion  
Microwave technology has enabled the development of faster, safer, and economical methods to extract and convert lipids into biofuel. The rapidly wavering electric field produced by microwaves generates heat due to frictional forces resulting from inter- and intramolecular movements of dielectric/polar material in the cell's molecules [2; 3]. Furthermore, intracellular heating generates water vapor that disrupts the cell from the inside. In turn, this can lead to the electroporation effect, i.e., a considerable increase in the electrical conductivity and permeability of cyanobacterial and microalgal cell wall as well as cytoplasmic membrane resulting from an applied external electrical field [10; 28]. The opening of cell membrane makes the extraction of intracellular metabolites efficient, because it forces out compounds from the cell matrix, producing good quality extracts [2]. In general, microwave-assisted extraction (MAE) has been considered a potential alternative to conventional extraction methods to produce biodiesel from microorganisms \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Metal**} & \multicolumn{3}{c}{**Sample**} \\ \cline{2-4}  & _Chlorella_ **sp.** & _Arthrospi_ **sp.** & _S. torques-regime_ \\ \hline Calcium & 35.79 & 22.07 & 31.25 \\ Potassium & 21.44 & 37.80 & 26.42 \\ Phosphorus & 15.35 & 10.30 & 12.03 \\ Sulfur & 11.25 & 12.69 & 11.25 \\ Iron & 11.04 & 6.25 & 8.26 \\ Chlorine & 4.54 & 10.46 & 10.25 \\ Others & 0.56 & 0.42 & 0.54 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Metal composition (%) of cyanobacterial and microalgal biomass. due to (i) reduced extraction time, (ii) reduced solvent usage, and (iii) improved transesterification yield [10; 13; 28]. An alternative to improve the efficiency of MAE would be to increase the amount of organic solvent used, but the MAE method had several advantages over the TE, due to the lower use of organic solvents as well as greater ease, speed, and efficiency, in addition to following the principles of green chemistry to produce biodiesel. In addition to the advantages, we observed that the MAE method allowed the release of more FA compounds, increased the concentration of C18:1 and C18:2, and also allowed the in-situ synthesis of biodiesel. The variety of fatty acids obtained, especially those with unsaturated chains, allows for better quality biodiesel [13; 29]. In this sense, this study provided important information on the production of biodiesel from the microcalga _Chlorella_ sp. and the cyanobacteria _Arthrospin_ sp. and _Spharospermopsis torques-regime_ using in situ transesterification assisted by microwave irradiation, an environmentally friendly methodology. As expected from the well-known prevalence of triglycerides over phosphoglycerides in eucayotic cells, the microcalga _Chlorella_ sp. had a higher concentration of lipids than the cyanobacteria prokaryotic cells. Nevertheless, it is possible to observe that the use of cyanobacterial biomass is also a clean and sustainable alternative for the production of high-quality biodiesel. Our findings on fatty acid profile from commercially available sources of _Chlorella_ sp. and _Arthrospin_ sp. as well as _S. torques-regime_ are similar to those of previous studies [28; 29; 30; 31; 32]. The observed fatty acid species are the same; however, small differences between the concentrations reported in the literature (Table S1) and those from the current study may be ascribed to different harvest and reaction procedures [10; 29; 30]. It is worth noting that the fatty acid profile of organisms can be modified not only by varying environmental conditions, but also through genetic means that could further optimize it, enabling their use as a potential biodiesel source [21; 24; 25; 26; 33]. The quality and physicochemical properties of biodiesel is considerably dependent on fatty acid composition used in the transesterification process.