Acid-catalyzed hot-water extraction of docosahexaenoic acid (DHA)-rich lipids from Aurantiochytrium sp. KRS101

Acid-assisted oil extraction directly from thraustochytrids fermentation broth and its energy assessment for docosahexaenoic acid-enriched oil production

Thraustochytrids are the most prominent source of polyunsaturated fatty acids, specifically docosahexaenoic acid (DHA). Downstream processing constitutes a significant fraction of total production cost and thus needs judicious optimization. Currently, hazardous solvent-based extraction methods are used to extract oil from the dry or wet thraustochytrids cell mass. The process is also highly energy-intensive due to involvement of dewatering and drying as unit operations. Current work devised an energy-efficient acid-assisted extraction (AAE) methodology to overcome dry and wet biomass-based extraction limitations. AAE recovered 91 % of total oil with 35-40 % PUFA from the direct fermentation broth, eliminating the need for dewatering and drying of fermentation broth/cell biomass. The current work also presents an all-inclusive comparison of the energy assessment of oil extraction from dry and AAE method. AAE produced PUFA enriched oil with a total energy consumption of 210 MJ/kg, which was four times lower than that of conventional dry cell extraction methodology.

Comparative studies on biomass productivity and lipid content of a novel blue-green algae during autotrophic and heterotrophic growth

Algae have long been acclaimed as the attractive renewable source for generating third-generation biofuels, particularly biodiesel. Under the present investigation, the trends of production of biomass and lipid during the autotrophic and heterotrophic growth of newly isolated blue-green algae, Leptolyngbya subtilis JUCHE1, were compared and correlated with the variation in C-sources. In the autotrophic and heterotrophic growth studies, CO₂ and glycerol were respectively used as the inorganic and organic C-sources maintaining equivalence in the initial amount of carbon. Light was used as the source of energy in both cases. The concentration of CO₂ in the feed gas stream was varied from 5 to 20% (% v/v). Equivalent quantity of carbon was supplied through glycerol during heterotrophic growth. Small-scale closed algal bioreactors were used for growing the algae at 37 °C and 2.5 kLux light illumination in batch mode for 0-4 days. Primarily, higher biomass production from glycerol compared with CO₂ was observed. In case of photoautotrophic growth, the maximum values of biomass and lipid productivity, obtained at 15% CO₂, were 0.1857 g/L/d and of 0.020 g/L/d respectively. The maximum biomass productivity of 0.2733 g/L/d was obtained for photoheterotrophic growth at a glycerol concentration equivalent to 15% CO₂ (v/v). Under photoheterotrophic growth of Leptolyngbya subtilis JUCHE1, lipid productivity of 0.0702 g/L/d was obtained at glycerol concentration equivalent to 5% (v/v) CO₂, which is 4.66-fold higher than that obtained under corresponding photoautotrophic condition. The "switch-over" from the autotrophy to the photoheterotrophy instigated the oleaginous anabolism and consequent lipid enrichment in L. subtilis JUCHE1, which can be extracted and converted to biodiesel.

Comparative Transcriptomic Analysis Uncovers Genes Responsible for the DHA Enhancement in the Mutant Aurantiochytrium sp

Docosahexaenoic acid (DHA), a n-3 long-chain polyunsaturated fatty acid, is critical for physiological activities of the human body. Marine eukaryote Aurantiochytrium sp. is considered a promising source for DHA production. Mutational studies have shown that ultraviolet (UV) irradiation (50 W, 30 s) could be utilized as a breeding strategy for obtaining high-yield DHA-producing Aurantiochytrium sp. After UV irradiation (50 W, 30 s), the mutant strain X2 which shows enhanced lipid (1.79-fold, 1417.37 mg/L) and DHA (1.90-fold, 624.93 mg/L) production, was selected from the wild Aurantiochytrium sp. Instead of eicosapentaenoic acid (EPA), 9.07% of docosapentaenoic acid (DPA) was observed in the mutant strain X2. The comparative transcriptomic analysis showed that in both wild type and mutant strain, the fatty acid synthesis (FAS) pathway was incomplete with key desaturases, but genes related to the polyketide synthase (PKS) pathway were observed. Results presented that mRNA expression levels of CoAT, AT, ER, DH, and MT down-regulated in wild type but up-regulated in mutant strain X2, corresponding to the increased intercellular DHA accumulation. These findings indicated that CoAT, AT, ER, DH, and MT can be exploited for high DHA yields in Aurantiochytrium.

Recovery of Astaxanthin-Containing Oil from Haematococcus pluvialis by Nano-dispersion and Oil Partitioning

The feasibilities of cell disruption by homogenization-assisted high-pressure nano-dispersion and recovery of astaxanthin-containing oil by oil partitioning in oil-acetone-water solution were examined. The total fatty acid content of Haematococcus pluvialis was 414.6 mg/g cell, and the astaxanthin content was 4.4% of oil. Extra oil was added to the solution in order to recover oil through instability of dispersion status instead of solvent evaporation. A total amount of energy of 0.34 kWh/L was consumed for acetone evaporation at 50 °C, whereas fully 1.86 kWh/L of energy for water evaporation was consumed. When soybean oil was added to the solution after partial acetone evaporation, the oil-recovery yield was 97.8%, while the yield after full evaporation was 97.6% in 10-g/L solution. However, the energy consumed for partial evaporation (0.29 kWh/L) was much lower than that for full evaporation (0.40 kWh/L). When H. pluvialis oil was added to the solution after partial evaporation, the oil-recovery yield decreased to 90.6% due to the impurity of crude H. pluvialis oil in 10-g/L solution. Methods such as refining of H. pluvialis oil, increase of microalgae dosage for cell disruption, and increase of the injection amount of extra oil can help to enhance oil recovery.

An Overview of Current Pretreatment Methods Used to Improve Lipid Extraction from Oleaginous Micro-Organisms

Microbial oils, obtained from oleaginous microorganisms are an emerging source of commercially valuable chemicals ranging from pharmaceuticals to the petroleum industry. In petroleum biorefineries, the microbial biomass has become a sustainable source of renewable biofuels. Biodiesel is mainly produced from oils obtained from oleaginous microorganisms involving various upstream and downstream processes, such as cultivation, harvesting, lipid extraction, and transesterification. Among them, lipid extraction is a crucial step for the process and it represents an important bottleneck for the commercial scale production of biodiesel. Lipids are synthesized in the cellular compartment of oleaginous microorganisms in the form of lipid droplets, so it is necessary to disrupt the cells prior to lipid extraction in order to improve the extraction yields. Various mechanical, chemical and physicochemical pretreatment methods are employed to disintegrate the cellular membrane of oleaginous microorganisms. The objective of the present review article is to evaluate the various pretreatment methods for efficient lipid extraction from the oleaginous cellular biomass available to date, as well as to discuss their advantages and disadvantages, including their effect on the lipid yield. The discussed mechanical pretreatment methods are oil expeller, bead milling, ultrasonication, microwave, high-speed and high-pressure homogenizer, laser, autoclaving, pulsed electric field, and non-mechanical methods, such as enzymatic treatment, including various emerging cell disruption techniques.

Pressurized Liquid Extraction (PLE) as an Innovative Green Technology for the Effective Enrichment of Galician Algae Extracts with High Quality Fatty Acids and Antimicrobial and Antioxidant Properties

Marine organisms are potentially prolific sources of high qualify fatty acids that represent useful leads in the development of new nutraceutical agents. In this work, we investigated the lipid composition of six algae species from the Northwest of Spain (Ulva intestinalis, Ulva lactuca, Fucus vesiculosus,Dictyota dichotoma, Cystoseira baccata and Himanthalia elongata) and compared the antioxidant and antibacterial activity of ethanolic extracts obtained by pressurized liquid extraction (PLE). Furthermore, Fucus vesiculosus (F. vesiculosus) PLE using five solvents of different polarities (hexane, ethyl acetate, acetone, ethanol and ethanol:water 50:50) at three temperatures (80 °C, 120 °C and 160 °C) was investigated. F. vesiculosus ethanolic PLE extract presents considerably higher capacity of inhibiting 50% of DPPH (1,1-diphenyl-2-picryl hydrazyl) (IC50 = 7.17 μg/mL) in comparison with the rest of macroalgae studied. Moreover, the potential antimicrobial activity tested on E. coli and S. aureus shows that F. vesiculosus extract produced the best inhibition (IC50 was 2.24 mg/mL (E. coli) and 1.27 mg/mL (S. aureus)). Furthermore, regarding the different solvents and temperatures used to investigate F. vesiculosus PLE, results showed that this technique using ethyl acetate is a selective method to enrich long chain fatty acids (oleic acid, arachidonic acid and eicosapentaenoic acid) with ω-6/ω-3 ratios close to 2.7.

One-step production of biodiesel from wet and unbroken microalgae biomass using deep eutectic solvent

One-step and Two-step methods were studied for lipid extraction from wet and unbroken (water content is 65-67%) Chlorella sp. and Chlorococcum sp. (GN38) using deep eutectic solvent (DES) treated microalgae cells. Further we optimized the extraction process and studied on its underlying mechanism. Among all DES, Choline chloride-Acetic acid (Ch-Aa) DES treatment showed optimal conditions at the mass ratio of DES: methanol-H₂SO₄ (2.00%) mixture: algae biomass was 60:40:3 with reaction time was 60min, and the optimum temperature was 110°C (Chlorococcum sp.) and 130°C (Chlorella sp.) respectively. The total content of FAME by One-step method with DES treatment was improved by 30% compared with Two-step method. This process is effective on wet and unbroken paste of microalgae biomass, so the FAME extracted using one-step with DES process is feasible for microalgae based biodiesel production.

Identification of optimum fatty acid extraction methods for two different microalgae Phaeodactylum tricornutum and Haematococcus pluvialis for food and biodiesel applications

Microalgae have the potential to synthesize and accumulate lipids which contain high value fatty acids intended for nutrition and biodiesel applications. Nevertheless, lipid extraction methods for microalgae cells are not well established and there is not a standard analytical methodology to extract fatty acids from lipid-producing microalgae. In this paper, current lipid extraction procedures employing organic solvents (chloroform/methanol, 2:1 and 1:2, v/v), sodium hypochlorite solution (NaClO), acid-catalysed hot-water extraction and the saponification process [2.5 M KOH/methanol (1:4, v/v)] have been evaluated with two species of microalgae with different types of cell walls. One is a marine diatom, Phaeodactylum tricornutum, and the other a freshwater green microalga, Haematococcus pluvialis. Lipids from all types of extracts were estimated gravimetrically and their fatty acids were quantified by a HPLC equipped with Q-TOF mass spectrometer. Results indicated significant differences both in lipids yield and fatty acids composition. The chloroform and methanol mixture was the most effective extraction solvent for the unsaturated fatty acids such as DPA (C22:05), DHA, (C22:06), EPA (C20:05) and ARA (C20:04). While acid treatments improved the saturated fatty acids (SFAs) yield, especially the short chain SFA, lauric acid (C12:0), whose amount was 64% higher in P. tricornutum and 156% higher in H. pluvialis compared to organic solvent extractions. Graphical abstract ᅟ.

Evaluation of various harvesting methods for high-density microalgae, Aurantiochytrium sp. KRS101

Five technologies, coagulation, electro-flotation (EF), electro-coagulation-flotation (ECF), centrifugation, and membrane filtration, were systematically assessed for their adequacy of harvesting Aurantiochytrium sp. KRS101, a heterotrophic microalgal species that has much higher biomass concentration than photoautotrophic species. Coagulation, EF, and ECF were found to have limited efficiency. Centrifugation was overly powerful to susceptible cells like Aurantiochytrium sp. KRS101, inducing cell rupture and consequently biomass loss of over 13%. Membrane filtration, in particular equipped with an anti-fouling turbulence generator, turned out to be best suited: nearly 100% of harvesting efficiency and low water content in harvested biomass were achieved. With rotation rate increased, high permeate fluxes could be attained even with extremely concentrated biomass: e.g., 219.0 and 135.0 L/m(2)/h at 150.0 and 203.0 g/L, respectively. Dynamic filtration appears to be indeed a suitable means especially to obtain highly concentrated biomass that have no need of dewatering and can be directly processed.

Advances in direct transesterification of algal oils from wet biomass

An interest in biodiesel as an alternative fuel for diesel engines has been increasing because of the issue of petroleum depletion and environmental concerns related to massive carbon dioxide emissions. Researchers are strongly driven to pursue the next generation of vegetable oil-based biodiesel. Oleaginous microalgae are considered to be a promising alternative oil source. To commercialize microalgal biodiesel, cost reductions in oil extraction and downstream biodiesel conversion are stressed. Herein, starting from an investigation of oil extraction from wet microalgae, a review is conducted of transesterification using enzymes, homogeneous and heterogeneous catalysts, and yield enhancement by ultrasound, microwave, and supercritical process. In particular, there is a focus on direct transesterification as a simple and energy efficient process that omits a separate oil extraction step and utilizes wet microalgal biomass; however, it is still necessary to consider issues such as the purification of microalgal oils and upgrading of biodiesel properties.

Continuous extraction of lipids from Schizochytrium sp. by CO2-expanded ethanol

CO2-expanded ethanol (CXE) was used to extract DHA-containing lipids from Schizochytrium sp. with a 35.7 wt% lipid content of dry biomass in a continuous mode. The effects of operation variables such as temperature, pressure, ethanol flow rate and CO2 flow rate on extraction performance were investigated. Based on a 2(4)-central composite design and response surface methodology, the optimal operating conditions were determined to be a pressure of 6.9 MPa, a temperature of 313 K, an ethanol flow rate of 1 mL/min and a CO2 flow rate of 6.0 mL/min, providing an extracted lipid yield of 87 wt% over an extraction period of 30 min. Not only the lipid yield obtained using CXE was observed to be significantly greater than those using ethanol and pressurized ethanol as the solvents, but also a lower amount of ethanol and less time were required to achieve the same extraction yield by using CXE.

Combined enzymatic and mechanical cell disruption and lipid extraction of green alga Neochloris oleoabundans

Microalgal biodiesel is one of the most promising renewable fuels. The wet technique for lipids extraction has advantages over the dry method, such as energy-saving and shorter procedure. The cell disruption is a key factor in wet oil extraction to facilitate the intracellular oil release. Ultrasonication, high-pressure homogenization, enzymatic hydrolysis and the combination of enzymatic hydrolysis with high-pressure homogenization and ultrasonication were employed in this study to disrupt the cells of the microalga Neochloris oleoabundans. The cell disruption degree was investigated. The cell morphology before and after disruption was assessed with scanning and transmission electron microscopy. The energy requirements and the operation cost for wet cell disruption were also estimated. The highest disruption degree, up to 95.41%, assessed by accounting method was achieved by the combination of enzymatic hydrolysis and high-pressure homogenization. A lipid recovery of 92.6% was also obtained by the combined process. The combined process was found to be more efficient and economical compared with the individual process.