Osmotic shock or osmotic stress is a sudden change in the solute concentration around a cell, causing a rapid change in the movement of water across its cell membrane (Fajardo et al., 2007). This shock causes a release in the cellular contents of microalgae. The method is more applicable for the strains cultivated in marine environments (eg. Nannochloropsis sp.). Os­motic shock is also induced to release cellular components for biochemical analysis (Mario, 2010). This method is also applied for Halorubrum sp. isolated from saltern ponds. The results showed increased lipid productivities and variations in lipid compositions (Lopalco et al., 2003).

Extraction of lipids is a key aspect involved in biomass-to-biodiesel production, the method directly influences the lipid productivity potential of the process. So far, several methods have been employed for extracting the cellular contents (lipids) of microalgae. Each method has its own advantages and disadvantages for practical applicability. Among the pro­cesses described, solvent extraction is suitable for extracting lipids from mass cultures but requires large volumes of solvent. The Soxhlet extraction method is applicable only when a single solvent is used and is not suitable for binary solvent applications. However, recovery and reusability of the solvent are possible with this method. The ultrasonic extraction method can perform well when coupled with the enzymatic treatment, but both methods lack cost effectiveness and feasibility for large-scale applications. Supercritical carbon dioxide extrac­tion (SC-CO2), pulse electric field procedure, osmotic shock, hydrothermal liquefaction, and wet lipid extraction require more optimization efforts for large-scale applications. A suitable method operatable with both binary and single solvents, applicable at large scales and yield­ing higher lipid productivities, is yet to be optimized for achieving enhanced microalgae lipid yields.