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  • 1
    Electronic Resource
    Electronic Resource
    Photolimitation and photoinhibition as factors determining optimal dilution rate to produce eicosapentaenoic acid from cultures of the microalga Isochrysis galbana (1998)
    Springer
    Applied microbiology and biotechnology 50 (1998), S. 199-205 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002530051277
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  • 2
    Electronic Resource
    Electronic Resource
    Preservation of the marine microalga, Isochrysis galbana: influence on the fatty acid profile
    Amsterdam : Elsevier
    Aquaculture 123 (1994), S. 377-385 
    Details
    ISSN: 0044-8486
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0044-8486(94)90072-8
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  • 3
    Electronic Resource
    Electronic Resource
    n-3 PUFA productivity in chemostat cultures of microalgae (1993)
    Springer
    Applied microbiology and biotechnology 38 (1993), S. 599-605 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid productivities from chemostat cultures of an isolate of Isochrysis galbana have been studied. The productivities reached in the interval of dilution rates between 0.0295 h−1 and 0.0355 h−1 were 1.5mg·1−1·h−1 for lipids, 300 μg·1−1·h−1 for EPA and 130μg1·1−1·h−1 for DHA. Furthermore, light attenuation by mutual shading, and agitation speed influences on growth and fatty acid composition were analysed. A model relating steady-state dilution rates to internal average light intensity has been proposed, the parameter values of which obtained by non-linear regression were: maximum specific growth rate (μmax)=0.0426 h−1; the affinity of cells to light (Ik) = 10.92 W·m−2; the exponent (n) = 5.13; regression coefficient (r 2)=0.9999.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00182796
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of growth rate on the eicosapentaenoic acid and docosahexaenoic acid content of Isochrysis galbana in chemostat culture (1994)
    Springer
    Applied microbiology and biotechnology 41 (1994), S. 23-27 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Isochrysis galbana rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) has been grown as a chemostat culture at 20° C and pH 8.00 controlled by CO2 injection. From a low dilution rate (D) of 0.0024 h−1 to 0.0377 h−1, close to maximum growth, a decrease in EPA content from 5.21% dry weight (d.w.) to 2.80% d.w. was observed, although the percentage of EPA in the total fatty acids increased. Lipids were fractionated, EPA being the major fatty acid found in the glycolipid fraction, whereas in the neutral lipid fraction were mainly palmitic and palmitoleic acids. At the same time, the biomass concentration also decreased from 1015 mg·l−1 to 202 mg·l−1 over the range of Ds mentioned. Nonetheless, EPA productivity had a maximum value of 15.26 mg·l−1·day−1 at D=0.0208 h−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00166076
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of growth rate on the eicosapentaenoic acid and docosahexaenoic acid content of Isochrysis galbana in chemostat culture (1994)
    Springer
    Applied microbiology and biotechnology 41 (1994), S. 23-27 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract An isolate of Isochrysis galbana rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) has been grown as a chemostat culture at 20° C and pH 8.00 controlled by CO2 injection. From a low dilution rate (D) of 0.0024 h−1 to 0.0377 h−1, close to maximum growth, a decrease in EPA content from 5.21% dry weight (d.w.) to 2.80% d.w. was observed, although the percentage of EPA in the total fatty acids increased. Lipids were fractionated, EPA being the major fatty acid found in the glycolipid fraction, whereas in the neutral lipid fraction were mainly palmitic and palmitoleic acids. At the same time, the biomass concentration also decreased from 1015 mg·l−1 to 202 mg·l−1 over the range of Ds mentioned. Nonetheless, EPA productivity had a maximum value of 15.26 mg·l−1·day−1 at D=0.0208 h−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00166076
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  • 6
    Electronic Resource
    Electronic Resource
    Biomass and icosapentaenoic acid productivities from an outdoor batch culture of Phaeodactylum tricornutum UTEX 640 in an airlift tubular photobioreactor (1995)
    Springer
    Applied microbiology and biotechnology 42 (1995), S. 658-663 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract An outdoor tubular photobioreactor, based on an external-loop airlift, has been used to cultivate the diatom Phaeodactylum tricornutum UTEX 640, rich in icosapentaenoic acid (EPA). The system was operated in batch mode. The specific growth rate in the exponential phase, averaged over the whole day, was 0.254 day−1 · A 25 gl−1 maximum biomass concentration was obtained by the end of the culture period. The dissolved oxygen generated never rose over 210% of air saturation nor was there impediment to biomass generation or inhibition of photosynthesis. Furthermore, around 2 × 1017 quanta cm−2 s−1 light intensity seemed to saturate the photosynthetic activity. Biomass losses during the night could be reduced to less than 5% by maintaining the culture at 16°C at night. The maximum concentration and productivity of EPA were 423 mgl−1 and 13 mgl−1 day−1, respectively, at the end of the culture, although a 21-mgl−1 day−1 net EPA generation rate was obtained at the linear growth phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00171940
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  • 7
    Electronic Resource
    Electronic Resource
    Growth yield determination in a chemostat culture of the marine microalgaIsochrysis galbana (1996)
    Springer
    Journal of applied phycology 8 (1996), S. 529-534 
    Details
    ISSN: 1573-5176
    Keywords: Quantum yield ; average irradiance ; light absorption ; photobioreactor ; photosynthetic efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The growth yield of the PUFA-producing marine microalgaIsochrysis galbana ALII-4 grown in a light limited chemostat, was measured under a wide variety of conditions of incident irradiance (I O ) and dilution rates (D). The experiments were conducted under laboratory conditions at 20 °C under continuous light. D ranged from 0.0024 to 0.0410 h−1 at three intensities of Io (820, 1620 and 3270 µmol photon m−2 s−1) close to those found in outdoor cultures. A maximum efficiency Ψ max = 0.616 g mol photon−1 was obtained at I O = 820 µmol photon m−2 s−1 and D = 0.030 h−1 and the maximum capacity of the biomass to metabolize the light harvested was found to be 13.1 µmol photon g−1 s−1. Above this value, a significant drop in the system efficiency was observed. A new approach based in the averaged irradiance is used to assess the photon flux absorbed by the biomass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02186332
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  • 8
    Electronic Resource
    Electronic Resource
    Assessment of the photosynthetically active incident radiation on outdoor photobioreactors using oxalic acid/uranyl sulfate chemical actinometer (2000)
    Springer
    Journal of applied phycology 12 (2000), S. 385-394 
    Details
    ISSN: 1573-5176
    Keywords: actinometry ; incident photon flux ; photobioreactor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A simple actinometric method was evaluated formeasuring the photosynthetically active incidentphoton flux on outdoor photobioreactors. The method isbased on uranyl sulfate catalyzed photodecompositionof oxalic acid in presence of light. The uranyl–oxalate chemical actinometer absorbs radiation ofwavelengths below 535 nm. In the present work, thephotobioreactor wall material did not transmit lightenergy of wavelengths below 350 nm and the effectiveabsorptivity method was used to evaluate the photonflux between 350–535 nm. The standard solar spectrumof the American Society for Testing and Materials(ASTM) was employed for estimating the ratio betweenthe photosynthetically active radiation (400–700 nm)and the solar radiation in the 350–535 nm range. Thisratio (2.21) was taken to be equal to the quotientbetween the photosynthetically active radiation (PAR)and the incident photon flux on the photobioreactor'ssurface (for the solar radiation between 350–535 nm).PAR measurements with 4π spherical and 2πquantum sensors were used to validate the method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008153630822
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  • 9
    Electronic Resource
    Electronic Resource
    Variation of fatty acid profile with solar cycle in outdoor chemostat culture ofIsochrysis galbana ALII-4 (1995)
    Springer
    Journal of applied phycology 7 (1995), S. 129-134 
    Details
    ISSN: 1573-5176
    Keywords: chemostat culture ; Isochrysis galbana ; fatty acids ; solar cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Outdoor chemostat cultures of the marine microalgaIsochrysis galbana at constant dilution rate (0.034 h−1 ) have been carried out under different weather conditions. Steady-state biomass concentrations were 1.61±0.03 kg m−3 in May and 0.95±0.04 kg m−3 in July, resulting in biomass output rates of 0.54 kg m−3 d−1 and 0.32 kg m−3 d−1 in May and July, respectively. Two patterns of daily variation with the solar cycle were observed in the fatty acid content. Saturated and mono-unsaturated fatty acids (16:0 and 16:1n7) show significant variation with the solar cycle, associated with short-term changes in environmental factors. Palmitic and palmitoleic acids are generated during daylight and consumed during the dark period. However, polyunsaturated fatty acids do not show a significant response to the solar cycle and their changes are associated with long-term variation in environmental factors. The maximum EPA productivity was obtained in May, 14.1 g m−3 d−1, which is close to that found in the literature for indoor continuous cultures. Nonetheless, the outdoor EPA content (up to 2.61 % d.wt) was lower than the indoor EPA content from a previous study (5% d.wt).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00693058
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  • 10
    Electronic Resource
    Electronic Resource
    Mixotrophic growth of Phaeodactylum tricornutum on glycerol: growth rate and fatty acid profile (2000)
    Springer
    Journal of applied phycology 12 (2000), S. 239-248 
    Details
    ISSN: 1573-5176
    Keywords: eicosapentaenoic acid ; microalga ; mixotrophic growth ; Phaeodactylum tricornutum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mixotrophic growth of the eicosapentaenoic acid (EPA)producing diatom Phaeodactylum tricornutum UTEX640 was carried out in 1-L batch cultures under anexternal irradiance of 165 μmol photons m-2s-1 by supplementing the inorganic culture mediumwith glycerol. The effect on the growth and the fattyacid profile was studied for different initialglycerol concentrations (0–0.1 M). The optimalglycerol concentration was 0.1 M.A lag phase was observed at high glycerolconcentrations. The present study also shows thatsuccessive additions of glycerol at 0.1M concentrationand using ammonium chloride as a nitrogen sourceremarkably increased the maximum biomass concentration(16.2 g L-1) and maximum biomass productivity(61.5 mg L-1 h-1). These values wererespectively 9 and 8-fold higher than in thephotoautotrophically grown control. The level ofsaponifiable lipids in mixotrophically cultured cellswas significantly higher than in photoautotrophicallycultured cells and increased with the glycerolconcentration in the medium. The concentration ofstorage lipids, saturated and monounsaturated fattyacids, were enhanced but the EPA content did notchange significantly. The EPA content was around 2.2%of biomass dry weight. The maximum EPA yield was33.5 mg L-1 d-1 and was obtained in aculture containing 0.1 M glycerol, supplementedperiodically by ammonium chloride. This productivitywas 10-fold higher than the EPA productivity obtainedunder mixotrophic conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008123000002
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