Analytical approaches for the detailed characterization of microalgal lipid extracts for the production of biodiesel

Many species of microalgae produce significant amounts of triacylglycerides (TAGs), the key product for biodiesel production. The lipid characteristics of microalgae are known to differ between species and change with growth conditions. Increasing TAG production by microalgae through optimization of growth regimes is of great interest as it is a convenient feedstock for biofuel production. Microalgae have the ability to synthesize and accumulate high levels of TAGs in specialized lipid bodies located in the cytoplasm and to a lesser extent in the chloroplast. In this chapter we first summarize the key lipids in microalgae, that is, the saponifiable lipids including neutral glycerolipids (NL; which include mono-, di-, and triglycerides) and some membrane-associated lipids including glycerophospholipids (PL), sphingolipids, and glycolipids (GL) as well as fatty acyls (free fatty acids). Aspects on gravimetric measurements, the simplest form of lipid characterization of total lipids, are presented followed by step-by-step protocols for the extraction and separation of lipid classes (NL, PL, and GL) using solid-phase extraction. The final discussion presents the preparation of lipid extracts for total and free fatty acid analysis using gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC-MS) to determine the detailed composition of lipids within classes, also known as lipidomics. Screening microalgae for lipid species, searching those with high proportions of NL lipids, and determining strains and growth conditions that produce fatty acid profiles most suited for obtaining high quality biodiesel are also discussed. All these techniques are discussed in the content of biodiesel production.