# Unconventional Extraction Methods of Oleaginous Yeast Cell Pretreatment and Disruption
## 4 Discussion
[43] compared three different extraction methods, i.e., Soxhlet lipid extraction using chloroform: methanol (2:1, \(v/v\)), accelerated solvent extraction (conducted in high temperature and pressure), and supercritical carbon dioxide extraction with ethanol as co-solvent. Moreover, the authors decided to compare permeabilization methods for the biomass of _Y. lipolytica_. The following pretreatments were applied: drying and milling; yeast atomization; methanol maceration; ethanol maceration; and supercritical disruption of yeast cells. In the case of Soxhlet and accelerated extraction, the application of ethanol \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Method Applied** & **Microorganism** & **Experimental Conditions** & **Lipid Extraction** & **Reference** \\ \hline  & & suspension with a conductivity at & & \\  & & 20 \({}^{\circ}\)C of either 10.14 \(\pm\) 0.63 or & & \\  & & 1.27 \(\pm\) 0.09 mS/cm; & & \\  & _Saitezvous podzolica_ yeast & the output impedance of generator & & \\  & & (50 \(\Omega\)); & & \\ PEF treatment & & electric field intensity was varied & & \\  & & between 1.4 and 4 MV/m & & \\  & _Yarrowia lipolytica_ yeast & 20 kV/cm of electrical field strength & 29.4 & [35] \\  & _Chlorella_ algae & max. 35 kV, the pulse width of the & & \\  & & square wave pulse from 2 to 99 \(\upmu\)s at a & & increase by 166.7\% & [36] \\  & & pulse repetition rate of 1-1 kHz. & & \\ \hline  & & Ultrasonic bath working at 520 kHz & & \\ US treatment & & with an intensity of 40 W & 43.0 & [40] \\  & _Naganishia liquefaciens_ yeast & US-assisted extraction of 0.6 W/mL of & & \\  & & US power combined with solvents & 97.1 & [41] \\ \hline  & _Yarrowia lipolytica_ yeast & 298 K, 1500 \(\times\) 10\({}^{5}\) Pa with 20 passes & 83.8 & [35] \\ HPP & _Saitezvous podzolica_ yeast & 2000 bar, 5 min, with 15 passes & 95.0 \({}^{\star}\) & [42] \\  & & & \\  & & & \\  & & & \\ \hline \hline \end{tabular} \({}^{\star}\) Disruption rate.  
\end{table} 
Table 1: Efficiency of microbial lipid extraction by application of unconventional permeabilization and cell disruption techniques. to biomass maceration proved to be the best pretreatment method, which resulted in the highest total extract yields (TAGs and polar lipids). For the former method, 29.7% lipid of total dry mass was obtained, and in the latter, it was 27.7%. The extract yield of 22.2% was obtained when the authors used the combined method, that is, wet yeast were macerated in ethanol for 20 h, and then subjected to supercritical disruption for 2 h at 40 \({}^{\circ}\)C, and 20 MPa was conducted [43]. In addition, switchable hydrophilicity solvents were applied as an alternative to conventional organic solvent extraction by [PERSON] et al. [44]. The authors used \(N\)-ethylbutylamine (EB), \(N\)-dipropylamine (DP), and \(N\),\(N\)-dimethylcyclohexylamine (DMCHA) as the lipid extraction solvents. Interestingly, EB and DMCHA allowed achieving up to 13% better results in comparison with Folch extraction. Importantly, the extraction time of 3 h was enough to obtain equal or higher lipid yields compared to the conventional method.