Table 2.

Extraction processes potentially applicable for milking of microorganisms.

Milking Process	Microorganism	Advantages	Disadvantages	Ability to Keep Cells Alive
Biocompatible organic solvents	Microalgae [67,100]	Improvement of lipid production Positive effect on growth	Not environmentally friendly Possible toxic mechanism	Yes, when using hydrophobic solvents
Pulsed electric field (PEF)	Yeast [103] Microalgae [104,105,106,107] Cyanobacteria [108]	High extraction yield Adjustable PEF parameters Not an energy-intensive process Large-scale process demonstrated Continuous process	Effect of electric pulsation is size dependent	Yes, but depends on the PEF parameters
Spontaneous oozing	Microalgae [109] Bacteria [110,111,112] Cyanobacteria [113,114,115]	Not an energy-intensive process Possibility of scaling up Application in solar panels	Slow oozing of HVM	Yes, it is a natural mechanism
Mechanical methods
-sonication	Microalgae [116,117] Cyanobacteria [118,119,120]	Improvement of lipid recovery	Cellular damage apoptosis Thickness of the cell wall	No
-pressure	Microalgae [this work]	Not an energy-intensive process Weak pressure to be used (below 750 µN)	Large-scale process not demonstrated Process needs to be improved	Yeswhen using low pressure (< 750 µN)
-centrifugation	Diatoms [work in progress]	Continuous process Application in solar panels	Requires energy	Not yet tested
Membrane-bound protein pumps	Bacteria [121,122]	Oozing of HVM Lower toxicity of overexpressed HVM High rate growth Possibility of scaling up	Metabolism engineering Organic phase needed for solubilization of water insoluble HVM	Yes