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      Continuous microalgae cultivation in a photobioreactor

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      Biotechnology and Bioengineering
      Wiley

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          Microalgae as a raw material for biofuels production.

          Biofuels demand is unquestionable in order to reduce gaseous emissions (fossil CO(2), nitrogen and sulfur oxides) and their purported greenhouse, climatic changes and global warming effects, to face the frequent oil supply crises, as a way to help non-fossil fuel producer countries to reduce energy dependence, contributing to security of supply, promoting environmental sustainability and meeting the EU target of at least of 10% biofuels in the transport sector by 2020. Biodiesel is usually produced from oleaginous crops, such as rapeseed, soybean, sunflower and palm. However, the use of microalgae can be a suitable alternative feedstock for next generation biofuels because certain species contain high amounts of oil, which could be extracted, processed and refined into transportation fuels, using currently available technology; they have fast growth rate, permit the use of non-arable land and non-potable water, use far less water and do not displace food crops cultures; their production is not seasonal and they can be harvested daily. The screening of microalgae (Chlorella vulgaris, Spirulina maxima, Nannochloropsis sp., Neochloris oleabundans, Scenedesmus obliquus and Dunaliella tertiolecta) was done in order to choose the best one(s), in terms of quantity and quality as oil source for biofuel production. Neochloris oleabundans (fresh water microalga) and Nannochloropsis sp. (marine microalga) proved to be suitable as raw materials for biofuel production, due to their high oil content (29.0 and 28.7%, respectively). Both microalgae, when grown under nitrogen shortage, show a great increase (approximately 50%) in oil quantity. If the purpose is to produce biodiesel only from one species, Scenedesmus obliquus presents the most adequate fatty acid profile, namely in terms of linolenic and other polyunsaturated fatty acids. However, the microalgae Neochloris oleabundans, Nannochloropsis sp. and Dunaliella tertiolecta can also be used if associated with other microalgal oils and/or vegetable oils.
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            Differential lipid and fatty acid profiles of photoautotrophic and heterotrophic Chlorella zofingiensis: assessment of algal oils for biodiesel production.

            The objective of this study was to document and compare the lipid class and fatty acid composition of the green microalga Chlorella zofingiensis cultivated under photoautotrophic and heterotrophic conditions. Compared with photoautotrophic cells, a 900% increase in lipid yield was achieved in heterotrophic cells fed with 30 g L(-1) of glucose. Furthermore heterotrophic cells accumulated predominantly neutral lipids (NL) that accounted for 79.5% of total lipids with 88.7% being triacylglycerol (TAG); whereas photoautotrophic cells contained mainly the membrane lipids glycolipids (GL) and phospholipids (PL). Together with the much higher content of oleic acid (C18:1) (35.2% of total fatty acids), oils from heterotrophic C. zofingiensis appear to be more feasible for biodiesel production. Our study highlights the possibility of using heterotrophic algae for producing high quality biodiesel. Copyright © 2010 Elsevier Ltd. All rights reserved.
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              Carotenoid and fatty acid metabolism in light-stressed Dunaliella salina.

              beta-Carotene is overproduced in the alga Dunaliella salina in response to high light intensities. We have studied the effects of a sudden light increase on carotenoid and fatty acid metabolism using a flat panel photobioreactor that was run in turbidostat mode to ensure a constant light regime throughout the experiments. Upon the shift to an increased light intensity, beta-carotene production commenced immediately. The first 4 h after induction were marked by constant intracellular levels of beta-carotene (2.2 g LCV(-1)), which resulted from identical increases in the production rates of cell volume and beta-carotene. Following this initial phase, beta-carotene productivity continued to increase while the cell volume productivity dropped. As a result, the intracellular beta-carotene concentration increased reaching a maximum of 17 g LCV(-1) after 2 days of light stress. Approximately 1 day before that, the maximum beta-carotene productivity of 30 pg cell(-1) day(-1) (equivalent to 37 mg LRV(-1) day(-1)) was obtained, which was about one order of magnitude larger than the average productivity reported for a commercial beta-carotene production facility, indicating a vast potential for improvement. Furthermore, by studying the light-induced changes in both beta-carotene and fatty acid metabolism, it appeared that carotenoid overproduction was associated with oil globule formation and a decrease in the degree of fatty acid unsaturation. Our results indicate that cellular beta-carotene accumulation in D. salina correlates with accumulation of specific fatty acid species (C16:0 and C18:1) rather than with total fatty acid content.
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                Author and article information

                Journal
                Biotechnology and Bioengineering
                Biotechnol. Bioeng.
                Wiley
                00063592
                October 2012
                October 2012
                May 04 2012
                : 109
                : 10
                : 2468-2474
                Article
                10.1002/bit.24516
                22488253
                490f386d-3b16-4ae9-be70-c12916c78ccd
                © 2012

                http://doi.wiley.com/10.1002/tdm_license_1.1

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