Photolimitation and photoinhibition as factors determining optimal dilution rate to produce eicosapentaenoic acid from cultures of the microalga Isochrysis galbana |
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Authors: | J M Fernández Sevilla E Molina Grima F García Camacho F G Acién Fernández J A Sánchez Pérez |
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Institution: | (1) Departamento de Ingeniería Química, Facultad de Ciencias Experimentales, Universidad de Almería, E-04071 Almería, Spain e-mail: jsanchez@filabres.ualm.es Tel.: +34 950 215314 Fax: +34 950 215484, ES |
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Abstract: | Eicosapentaenoic acid (EPA) productivity from continuous cultures of the marine microalga Isochrysis galbana was studied, taking into account the irradiance on the reactor surface, that is, the photolimitation/photoinhibition regime
to which the cells are exposed. Experiments were conducted under a wide variety of operating conditions. The dilution rate
ranged from 0.005 h−1 to 0.040 h−1 at five external irradiances (820, 1620, 2050, 2450 and 3270 μmol photons m−2 s−1) covering photolimited to photoinhibited growth. Under these conditions, the specific growth rate (μ) was found to be the
main factor influencing EPA content (ranging from 2.35% to 5.23% dryweight) and productivity (up to 0.88 mg l−1 h−1). The fatty acid content was not significantly affected by the external irradiance, but was influenced by the state of growth
of the microalga, depending on whether the light regime was photolimiting or photoinhibiting. It might be suggested that light
should no longer be considered an isolated factor affecting EPA synthesis, but an indirect influence through the photolimitation/photoinhibition
regime and growth rate. At a given dilution rate, EPA content and biomass concentration are lower under photoinhibiting external
irradiances than those corresponding to photolimiting conditions, and consequently EPA productivity decays. Since the effect
of photoinhibition is less marked at high biomass concentration, a strategy to optimize EPA productivity from microalgal cultures
could consist of reducing the dilution rate when the external irradiance increases above the phoinhibition threshold.
Received: 16 January 1998 / Revised revision: 27 March 1998 / Accepted: 27 March 1998 |
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