Microalgae are composed of single cells surrounded by an individual cell wall, which in­cludes "unusual" lipid classes and fatty acids that differ from those in higher animals and plants (Guschina and Harwood, 2006). For extraction of lipids from microalgae, regular extraction methods may not be applicable (Eline et al., 2012). Extracting and purifying oil from algae is considered challenging due to its energy — and economically intensive nature (Fajardo et al., 2007; Lee et al., 2010; Mercer and Armenta, 2011).

8.6.2.1 Solvent Extraction

The existing procedures for the extraction of lipids from source material usually involve selective solvent extraction, and the starting material may be subjected to drying prior to ex­traction (Lee et al., 2010). Lipids are soluble in organic solvents but sparingly soluble or in­soluble in water. Solubility of lipids is an important criterion for their extraction and typically depends on the type of lipid present and the proportion of nonpolar lipids (princi­pally triacylglycerols) and polar lipids (mainly phospholipids and glycolipids) in the sample (Huang et al., 2010). Several solvent systems are used, depending on the type of sample and its components. The solvents of choice are usually hexane in the case of Soxhlet and Goldfish methods (Additions and Revisions, 2002); chloroform/methanol or chloroform/methanol/ water in the case of the Folch Method (Folch and Sloane-Stanley, 1957); or modified Bligh and Dyer Procedure (Bligh and Dyer, 1959). This method is best suited to extract nonpolar lipids because polar lipids are scarcely soluble in nonpolar solvents.