BIOTECHNOLOGY LETTERS Volume 16 No.IO (0ct.1994) p.1035o1040 Received as revised l Oth August EFFECT OF DILUTION RATE ON EICOSAPENTAENOIC ACID PRODUCTIVITY OF PHAEODACTYLUM TRICORNUTUM UTEX 640 IN OUTDOOR CHEMOSTAT CULTURE. E. Molina Grima, J.A. S~inchez P~rez*, F. Garcia Camacho, F.G. Aci~n Fern~indez, J.M. Fern&ndez Sevilla and F. Vald6s Sanz. Departamento de Ingenieria Qufmica, Facultad de Ciencias Experimentales, Universidad de Almerfa, E-04071 ALMER[A, (SPAIN). Tel: 34-50-215032. Fax: 34-50-215070 Summary. Eicosapentaenoic acid (EPA) volumetric productivity from an outdoor chemostat culture of Phaeodactylum tricornutum UTEX 640 in a 50-1 tubular photobioreactor varies with dilution rate, reaching a maximum of 47.8 mg 1-1 d-1 at D = 0.36 d-1. Continuous culture at high dilution rates' is proposed as the most adequate operating mode to maximize polyunsaturated fatty acid production. INTRODUCTION. Microalgal biomass is being considered in contrast to fish oils, as a source of long-chain polyunsaturated fatty acids (LC-PUFAs) to be used in medicine (Radwan, 1991). These LC- PUFAs are made up primarily of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Information about culture conditions for improving the productivity of PUFAs from microalgae is scarce, and in most cases present results from cultures of a few millilitres without considering the growth and biochemical composition under mass culture conditions. In the present paper, production of EPA from an outdoor chemostat culture of Phaeodactylum tricornutum UTEX 640 in a 50-1 tubuiar photobioreactor is reported, dilution rate being the operating variable studied in order to maximize EPA productivity. MATERIALS AND METHODS. The present study was conducted uninterruptedly in July and August, 1993. The species used, Phaeodactylum tricomutum UTEX 640, was supplied by the University of Texas at Austin Collection. Growth conditions and photobioreactor description were given in a previous paper (Molina Grima et al., 1994b). Fatty acid methylation was done following the Lepage and Roy method (1984). The analysis of methyl esters was carried out by gas chromatography using a 30 m capillary column of fused silica (SP2330, Supelco, Bellefonte, Pa, USA), with an internal diameter of 0.25 mm, 0.20 IJm standard film, split ratio of 100:1, and a flame ionization detector. Supelco PUFA-1, PUFA-2 and PUFA-3 patterns were used as standards. Nonadecanoic acid was used as an internal standard to quantify fatty acid content in biomass. 1035