Table 1.

The advantages and disadvantages of major pretreatment methods applied to the efficient extraction of lipids.

Pretreatment Methods	Mode of Action	Advantages	Disadvantages	References
Acid-catalyzed hot-water	Release of bound lipids by uncoupling the lipid-protein and lipid-starch and intermolecular forces	Cost-effective Can be applied for wet biomass High yield of bound lipids	Degradation of thermolabile and acid-sensitive compounds	[34]
Bead beating	Mechanical compaction and shear stress	Cost-effective Continuous module of operation High disruption efficiency Mild operating temperature Suitable for lab-scale to industrial scale	High energy demand Low recovery of lipids from cells with rigid cell wall	[35,36]
Enzyme	Specific enzyme-substrateinteraction	Simple Mild temprtaure conditions No sophisticated instrument required low energy requirements Selective extraction	Long processing time and High cost of enzymes Extraction efficiency depends on the cell wall characteristics	[18,28,29,30,31,32,37]
Expeller press	Mechanical compaction and shear stress	Cost-effective and simple process Solvent-free extraction possible Microwave heating before expeller press can improve the lipid yield	High energy demand Not effective for samples of high moisture content Low recovery of lipids	[38,39,40,41]
High-pressure homogenization (HPH)	Cavitation and shear stress	Simple continuous operating system Can be applied for wet biomass Low solvent requirement Low-temperature extraction Applicable to large-scale	High capital and maintenance cost Less efficient for filamentous microorganisms Undesirable for heat-liable compounds Induced the formation of free fatty acids	[42,43]
High-speed shearing homogenization	Cavitation and shear forces	Suitable for wet and dry biomass Efficient extraction Rapid	Extensive heat generation High energy consumption	[18,44]
Hydrodynamic cavitation	Shear forces, creation, and extinction of cavities	High extraction efficiency from microalgae	High energy consumption Excess heat generation Cavitation reactor designs are at an initial stage Need optimization of critical parameters (orifice plate, inlet pressure, flow rate, cavitation number etc.)	[23,45]
Microwave Irradiation	Temperature increase, molecular energy increase	Makes membranes porous which facilitates the effective extraction of lipid Short operating time More efficient than conventional heating	High energy demand Not suitable for commercial scale High extraction temperature Generation of free radicals	[39,41,46]
Osmotic shock	osmotic pressure-induced cell disruption and the release of the intracellular lipids	Lower energy consumption Easier scale-up High yield	Generation of waste saltwater Time-consuming	[25,47]
Pulsed Electric Field (PEF)	Transient permeabilization of cell membranes	High energetic efficiency Rapid Nonthermal method	High initial capital investment-temperature extraction	[48,49,50,51]
Ultrasonication	Cavitation, acoustic streaming, and liquid shear stress	Extensively used pretreatment method Rapid High yield Energy-efficient process for optimum cell disintegration	Generation of free radicals after prolonged treatment Not investigated for large scale applications	[52,53,54,55,56]