https://www.massey.ac.nz/~ychisti/Biodiesel.pdf

Biodiesel from microalgae.

Microalgae represent an exceptionally diverse but highly specialized group of micro-organisms adapted to various ecological habitats. Many microalgae have the ability to produce substantial amounts (e.g. 20-50% dry cell weight) of triacylglycerols (TAG) as a storage lipid under photo-oxidative stress or other adverse environmental conditions. Fatty acids, the building blocks for TAGs and all other cellular lipids, are synthesized in the chloroplast using a single set of enzymes, of which acetyl CoA carboxylase (ACCase) is key in regulating fatty acid synthesis rates. However, the expression of genes involved in fatty acid synthesis is poorly understood in microalgae. Synthesis and sequestration of TAG into cytosolic lipid bodies appear to be a protective mechanism by which algal cells cope with stress conditions, but little is known about regulation of TAG formation at the molecular and cellular level. While the concept of using microalgae as an alternative and renewable source of lipid-rich biomass feedstock for biofuels has been explored over the past few decades, a scalable, commercially viable system has yet to emerge. Today, the production of algal oil is primarily confined to high-value specialty oils with nutritional value, rather than commodity oils for biofuel. This review provides a brief summary of the current knowledge on oleaginous algae and their fatty acid and TAG biosynthesis, algal model systems and genomic approaches to a better understanding of TAG production, and a historical perspective and path forward for microalgae-based biofuel research and commercialization.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1365-313X.2008.03492.x

Microalgal triacylglycerols as feedstocks for biofuel production: perspectives and advances

Thirty microalgal strains were screened in the laboratory for their biomass productivity and lipid content. Four strains (two marine and two freshwater), selected because robust, highly productive and with a relatively high lipid content, were cultivated under nitrogen deprivation in 0.6-L bubbled tubes. Only the two marine microalgae accumulated lipid under such conditions. One of them, the eustigmatophyte Nannochloropsis sp. FM102: 100–112. © 2008 Wiley Periodicals, Inc.

http://biodiesel.persiangig.com/Cultivation/(1)22033_ftp.pdf

Microalgae for oil: strain selection, induction of lipid synthesis and outdoor mass cultivation in a low-cost photobioreactor.

The use of fossil fuels is now widely accepted as unsustainable due to depleting resources and the accumulation of greenhouse gases in the environment that have already exceeded the “dangerously high” threshold of 450 ppm CO2-e. To achieve environmental and economic sustainability, fuel production processes are required that are not only renewable, but also capable of sequestering atmospheric CO2. Currently, nearly all renewable energy sources (e.g. hydroelectric, solar, wind, tidal, geothermal) target the electricity market, while fuels make up a much larger share of the global energy demand (∼66%). Biofuels are therefore rapidly being developed. Second generation microalgal systems have the advantage that they can produce a wide range of feedstocks for the production of biodiesel, bioethanol, biomethane and biohydrogen. Biodiesel is currently produced from oil synthesized by conventional fuel crops that harvest the sun’s energy and store it as chemical energy. This presents a route for renewable and carbon-neutral fuel production. However, current supplies from oil crops and animal fats account for only approximately 0.3% of the current demand for transport fuels. Increasing biofuel production on arable land could have severe consequences for global food supply. In contrast, producing biodiesel from algae is widely regarded as one of the most efficient ways of generating biofuels and also appears to represent the only current renewable source of oil that could meet the global demand for transport fuels. The main advantages of second generation microalgal systems are that they: (1) Have a higher photon conversion efficiency (as evidenced by increased biomass yields per hectare): (2) Can be harvested batch-wise nearly all-year-round, providing a reliable and continuous supply of oil: (3) Can utilize salt and waste water streams, thereby greatly reducing freshwater use: (4) Can couple CO2-neutral fuel production with CO2 sequestration: (5) Produce non-toxic and highly biodegradable biofuels. Current limitations exist mainly in the harvesting process and in the supply of CO2 for high efficiency production. This review provides a brief overview of second generation biodiesel production systems using microalgae.

https://www.springer.com/cda/content/document/cda_downloaddocument/BioEnergyResearch_Second+Generation+Biofuels+High-Efficiency+Microalgae+for+Biodiesel+Production.pdf?SGWID=0-0-45-1347846-0

Second generation biofuels: high-efficiency microalgae for biodiesel production

Biodiesel production from oleaginous microorganisms

Lipids and lipid metabolism in eukaryotic algae

The versatility of algae and their lipid metabolism

Lipids play a number of roles in living organisms and can be divided into two main groups: the nonpolar lipids (acylglycerols, sterols, free (nonesterified) fatty acids, wax, and steryl esters) and polar lipids (phosphoglycerides, glycosylglycerides). Polar lipids and sterols are important structural components of cell membranes which act as a selective permeable barrier for cells and organelles. These lipids maintain specific membrane functions providing the matrix for a very wide variety of metabolic processes and participate directly in membrane fusion events. In addition to a structural function, some polar lipids may act as key intermediates (or precursors of intermediates) in cell signalling pathways (e.g. inositol lipids, sphingolipids, oxidative products) and play a role in responding to changes in the environment. Of the nonpolar lipids, the triacylglycerols are abundant storage products, which can be easily catabolised to provide metabolic energy (Gurr et al. 2002). Waxes are common extracellular surface-covering compounds but may act (in form of wax esters) as energy stores especially in organisms from cold water habitats (Guschina and Harwood 2007). Sterols of algae have been studied extensively and a number of comprehensive reviews are already available on these nonpolar lipids (e.g., Patterson 1991; Volkman 2003; see also Chap. 3).

Algal lipids and effect of the environment on their biochemistry

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/j.febslet.2006.06.066

Mechanisms of temperature adaptation in poikilotherms.

The health benefits of increased intakes of omega-3 fatty acids are well established but palatability often presents a problem The process of emulsification is used in the food industry to provide a wider spectrum of use, often with the result of increased consumption Moreover, as emulsification is an important step in the digestion and absorption of fats, the pre-emulsification process may enhance digestion and absorption In this study the levels of plasma fatty acid and triacylglycerol (TAG) following the ingestion of either an oil mixture or an emulsified oil mixture have been compared In this randomised cross-over study, 13 volunteers received the oil mixture and 11 received the oil emulsion as part of an otherwise fat free meal Blood samples were collected at 0, 15, 3, 45, 6, 75 and 9 hours after ingestion of oil, separated and stored at -20°C Plasma triacylglycerols were assessed spectrophotometrically and fatty acids were determined by gas chromatography Following a washout period of twenty days the procedure was repeated with the assignments reversed The postprandial plasma TAG and the C18:3 (n-6), C18:3(n-3), C20:5(n-3) and C22:6 (n-3) polyunsaturated fatty acid (PUFA) levels for the emulsified oil group were increased significantly (P = 00182; P = 00493; P = 00137; P < 00001; P = 00355 respectively) compared with the non-emulsified oil group The C16:0 and C18:0 saturated fatty acids, the C18:1 (n-9) monounsaturated fatty acid and the C18:2 PUFA were not significantly different for the oil and emulsified oil groups Pre-emulsification of an oil mixture prior to ingestion increases the absorption of longer chain more highly unsaturated fatty acids (especially eicosapentaenoic acid and docosahexaenoic acid) but does not affect absorption of shorter chain less saturated fatty acids, suggesting that pre-emulsification of fish oils may be a useful means of boosting absorption of these beneficial fatty acids 
Trial registration: Current Controlled Trials ISRCTN43202606

/pdf/a-randomised-cross-over-trial-in-healthy-adults-indicating-51x6ln67gu.pdf

Irina A. Guschina

Papers

Lipids and lipid metabolism in eukaryotic algae

The versatility of algae and their lipid metabolism

Algal lipids and effect of the environment on their biochemistry

Mechanisms of temperature adaptation in poikilotherms.

A randomised cross-over trial in healthy adults indicating improved absorption of omega-3 fatty acids by pre-emulsification.