Commercial production of intracellular microalgal metabolites requires the following: (1) largescale monoseptic production of the appropriate microalgal biomass; (2) recovery of the biomass from a relatively dilute broth; (3) extraction of the metabolite from the biomass; and (4) purification of the crude extract. This review examines the options available for recovery of the biomass and the intracellular metabolites from the biomass. Economics of monoseptic production of microalgae in photobioreactors and the downstream recovery of metabolites are discussed using eicosapentaenoic acid (EPA) recovery as a representative case study. D

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The in¯uence of culture age and nitrogen concentration on the distribution of fatty acids among the dierent acyl lipid classes has been studied in continuous cultures of the microalga Phaeodactylum tricornutum. The culture age was tested in the range of 1.15±7 days, controlled by adjusting the dilution rate of fresh medium supplied. The eect of nitrogen concentration was tested from saturating conditions to starvation by modifying nitrate concentration in the fresh medium. Culture age had almost no in¯uence on the fatty acid content; 16:0, 16:3 and 20:5 increased moderately wherein the level of 16:1 decreased when the culture age decreased. Culture age had no eect on the total fatty acid content that remained around 11% of dry weight. Conversely, culture age had a greater impact on lipid classes, producing changes in amounts of triacylglycerols (TAG) which ranged between 43% and 69%, and galactolipids (GLs) that oscillated between 20% and 40%. In general, the content of polar lipids of the biomass decreased with culture age. The other factor assayed, nitrogen content, aected the fatty acid pro®le. Saturated and monounsaturated fatty acids accumulated when the nitrogen concentration was decreased. The experiments regarding the eect of nitrogen concentration on lipid species were carried out with cells of an average age of 3.5 days. A decrease of the nitrogen concentration caused the GL fraction to decrease from 21 to 12%. Conversely, both neutral lipids (NLs) and phospolipids (PLs) increased from about 73 to 79% and from 6 to 8%, respectively. In these experiments, TAG was the lipid class with the highest increase, from 69 to 75%. 7

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