THE PRODUCTION OF POLYUNSATURATED FATTY-ACIDS BY MICROALGAE - HORN STRAIN SELECTION TO PRODUCT PURIFICATION

A selection programme to increase the cellular eicosapentaenoic acid ( EPA) content has been carried out with the microalga Isochrysis galban a. The selection process involved two stages of single selection. EPA content continuously increased from 2.4% dry weight (d.w.) of the 'par ent' culture to an average value of 5.3% d.w. in the final stage. The proportion of total EPA variation attributable to the genetic variatio n (heritability in a broad sense) was 0.99 showing the importance of t he genome in the determination of this fatty acid. The growth and fatt y acid profile of an EPA-rich isolate grown as a chemostat in a cylind rical photobioreactor have been studied. A decrease in EPA content was observed (5.21% w/w to 2.8% w/w) at the lowest dilution rate D = 0.02 4 h(-1), up close to the maximum growth rate, D = 0.038 h(-1). At the same time, the biomass concentration also decreased from 1015 mg/litre to 202 mg/litre over the above-mentioned range of dilution rate (D). Nonetheless, the EPA productivity increases with D, with a maximum of 15.26 mg/litre/day at D = 0.0208 h(-1). Furthermore, steady-state dilu tion rates may be related to average internal light intensity. Reverse -phase, high-pressure liquid chromatography (HPLC) on octadecylsilyl s emi-preparative columns was used to separate stearidonic acid (SA), EP A and docosohexaenoic acid (DHA) in polyunsaturated fatty acid concent rate obtained by the urea complexation method from a fatty acid soluti on previously obtained by direct saponification of biomass. Isolate SA , EPA and DHA fraction purity was 94.8, 96.0 and 94.9%, respectively, with yields of 100.0, 99.6 and 94.0%.