In-situ lipid and fatty acid extraction methods to recover viable products from Nannochloropsis sp

Semi-hydrophobic eutectic solvents: Sequential extraction of lipids, proteins & carbohydrates, recycling, scalability of microalga Nannochloropsis oceanica

Semi-hydrophobic eutectic solvents (ES) possess a great potential as lipid extraction solvent from untreated microalgae. However, the low vapor pressure of these solvents and the unknown effects on other biomolecules (e.g., proteins, carbohydrates) limit their application in microalgae biorefinery. In this work, recovery of the extracted lipids was performed by addition of antisolvents and the affecting parameters (i.e., antisolvent type, amount, temperature, ES imidazole content) were studied. The highest recovery was obtained with methanol addition to ES with 15 mol% imidazole at -20 °C, where lipid crystals were formed consisting mainly of saturated fatty acids. The remaining soluble lipids under the same condition were found to be fractions with mono- and poly-unsaturated fatty acids. Furthermore, based on the iterative extractions, the regenerated solvents could create sufficient driving force for lipid extraction despite the lipid accumulation. In addition, a scale-up study of lipid extraction and solvent recycling was performed (2 mL vs 500 mL), whereby the larger scale also showed a good performance. Finally, protein and carbohydrate isolation from the defatted biomass was feasible, but the proposed ES process was not sufficiently mild to maintain native proteins. On the other hand, opportunities are discussed to create new functionalities for proteins and carbohydrates so that a multiproduct biorefinery is feasible for this ES.

Effect of hydraulic retention time and treated urban wastewater ratio on progressive adaptation of an inoculated microalgae in membrane photobioreactors

Currently, there is a growing concern about water scarcity. The rising demand for wastewater treatment systems that facilitate the reuse of wastewater has resulted in a focus on the use of microalgae in sustainable treatments. These methods not only eliminate nutrients from the wastewater but also produce biomass that can be used to obtain high-value products. This study aimed to observe the effect of different hydraulic retention times (HRTs) and treated urban wastewater (TUWW) percentages on the growth of microalgae biomass and nutrient consumption in membrane photobioreactors. Microalgae biomass growth increases with HRT regardless of the percentage of TUWW. Biomass concentration stabilises at between 40% and 60% TUWW but significantly increases when 100% TUWW is used, resulting in the highest biomass concentrations. As HRT increases, ammonium and total nitrogen consumption also rise. A positive trend in ammonium consumption was observed with increasing TUWW, reaching its peak with 100% TUWW. The optimal conditions for biomass growth and nutrient removal are achieved with a 7-day HRT and 100% TUWW as influent, which was confirmed as optimal with the response surface methodology.

Effects of nitrogen starvation on growth and biochemical composition of some microalgae species

Nitrogen is one of the most important nutrient sources for the growth of microalgae. We studied the effects of nitrogen starvation on the growth responses, biochemical composition, and fatty acid profile of Dunaliella tertiolecta, Phaeodactylum tricornutum, and Nannochloropsis oculata. The lack of nitrogen caused changes in carbohydrate, protein, lipid, and fatty acid composition in all examined microalgae. The carbohydrate content increased 59% in D. tertiolecta, while the lipid level increased 139% in P. tricornutum under nitrogen stress conditions compared to the control groups. Nitrogen starvation increased the oligosaccharide and polysaccharide contents of D. tertiolecta 4.1-fold and 3.6-fold, respectively. Furthermore, triacylglycerol (TAG) levels in N. oculata and P. tricornutum increased 2.3-fold and 7.4-fold, respectively. The dramatic increase in the amount of TAG is important for the use of these microalgae as raw materials in biodiesel. Nitrogen starvation increased the amounts of oligosaccharides and polysaccharides of D. tertiolecta, while increased eicosapentaenoic acid (EPA) in N. oculata and docosahexaenoic acid (DHA) content in P. tricornutum. The amount of polyunsaturated fatty acids (PUFAs), EPA, DHA, oligosaccharides, and polysaccharides in microalgal species can be increased without using the too costly nitrogen source in the culture conditions, which can reduce the most costly of living feeding.

Study of the polysaccharide production by the microalgae C-1509 Nannochloris sp. Naumann

Biologically active compounds, including polysaccharides isolated from microalgae, have various properties. Although Nannochloropsis spp. have the potential to produce secondary metabolites important for biotechnology, only a small part of the research on these microalgae has focused on their ability to produce polysaccharide fractions. This study aims to evaluate the physicochemical growth factors of Nannochloropsis spp. microalgae, which ensure the maximum accumulation of polysaccharides, as well as to optimize the parameters of polysaccharide extraction. The optimal nutrient medium composition was selected to maximize biomass and polysaccharide accumulation. The significance of selecting the extraction module and extraction temperature regime, as well as the cultivation conditions (temperature and active acidity value) is emphasized. Important chemical components of polysaccharides responsible for their biological activity were identified.

Extraction methods of algae oils for the production of third generation biofuels - A review

Microalgae are the main source of third-generation biofuels because they have a lipid content of 20-70%, can be abundantly produced and do not compete in the food market besides other benefits. Biofuel production from microalgae is a promising option to contribute for the resolution of the eminent crisis of fossil energy and environmental pollution specially in the transporting sector. The choice of lipid extraction method is of relevance and associated to the algae morphology (i.e., rigid cells). Therefore, it is essential to develop suitable extraction technologies for economically viable and environment-friendly lipid recovery processes with the aim of achieving a commercial production of biofuels from this biomass. This review presents an exhaustive analysis and discussion of different methods and processes of lipid extraction from microalgae for the subsequent conversion to biodiesel. Physical methods based on the use of supercritical fluids, ultrasound and microwaves were reviewed. Chemical methods using solvents with different polarities, aside from mechanical techniques such as mechanical pressure and enzymatic methods, were also analyzed. The advantages, drawbacks, challenges and future prospects of lipid extraction methods from microalgae have been summarized to provide a wide panorama of this relevant topic for the production of economic and sustainable energy worldwide.

Extraction of Nannochloropsis Fatty Acids Using Different Green Technologies: The Current Path

Nannochloropsis is a genus of microalgae widely recognized as potential sources of distinct lipids, particularly polyunsaturated fatty acids (PUFA). These may be obtained through extraction, which has conventionally been performed using hazardous organic solvents. To substitute such solvents with "greener" alternatives, several technologies have been studied to increase their extraction potential. Distinct technologies utilize different principles to achieve such objective; while some aim at disrupting the cell walls of the microalgae, others target the extraction per se. While some methods have been utilized independently, several technologies have also been combined, which has proven to be an effective strategy. The current review focuses on the technologies explored in the last five years to extract or increase extraction yields of fatty acids from Nannochloropsis microalgae. Depending on the extraction efficacy of the different technologies, distinct types of lipids and/or fatty acids are obtained accordingly. Moreover, the extraction efficiency may vary depending on the Nannochloropsis species. Hence, a case-by-case assessment must be conducted in order to ascertain the most suited technology, or tailor a specific one, to be applied to recover a particular fatty acid (or fatty acid class), namely PUFA, including eicosapentaenoic acid.

A biphasic photobioreactor system for consecutive extraction of lipids and carotenoids from pre-hydrolysed microalgae and evaluation of its biodiesel potential

A green extraction method is developed using partially hydrolysed microalgal cells grown in biocompatible solvent for simultaneous cultivation and extraction of bioproducts from a highly efficient permeabilized microalgal cell with enhanced biomass and lipid content for potential use in biodiesel production. Incomplete digestion of cell wall was achieved by regulating the incubation time of the enzymatic pretreatment of the microalgal cells. 15.77% increase in lipid content was seen when untreated cells were cultured with biocompatible solvent, while cultivation of these enzymatically pretreated cells with biocompatible solvent, the lipid content increased by 53.33% and 22% higher carotenoid content was observed as compared to conventional extraction. The total fatty acids obtained after 1st and 2nd extractions in untreated samples were 67.82%, while those in enzymatically partially digested samples were 91.94%. The untreated and partially enzymatically predigested strain showed suitable properties for quality biodiesel production as per international recommendations. The cost benefit analysis of the overall process showed the use of biocompatible solvent coupled to enzymatically predigested biomass was a favorable option as compared to conventional extraction.

Can Growth of Nannochloropsis oculata under Modulated Stress Enhance Its Lipid-Associated Biological Properties?

Nannochloropsis oculata is well-recognized as a potential microalgal source of valuable compounds such as polyunsaturated fatty acids, particularly, eicosapentaenoic acid (EPA). The content and profile of these lipids is highly dependent on the growth conditions and can, therefore, be tailored through modulation of the growth parameters, specifically, temperature. Moreover, biological activities are composition dependent. In the present work, lipid extracts obtained from N. oculata, grown under constant temperature and under modulated temperature stress (to increase EPA content; Str) were characterized by GC-FID and several bioactivities were evaluated, namely, antioxidant (L-ORAC_FL), cytotoxic (MTT), adipolytic, anti-hepatic lipid accumulation (steatosis), and anti-inflammatory properties. Both extracts exhibited antioxidant activity (c.a. 49 µmol Trolox_equivalent/mg_extract) and the absence of toxicity (up to 800 µg/mL) toward colon and hepatic cells, adipocytes, and macrophages. They also induced adipolysis and the inhibition of triglycerides hepatic accumulation, with a higher impact from Str. In addition, anti-inflammatory activity was observed in the lipopolysaccharide-induced inflammation of macrophages in the presence of either extract, since lower levels of pro-inflammatory interleukin-6 and interferon-β were obtained, specifically by Str. The results presented herein revealed that modulated temperature stress may enhance the health effects of N. oculata lipid extracts, which may be safely utilized to formulate novel food products.

In Vivo Nutritional Assessment of the Microalga Nannochloropsis gaditana and Evaluation of the Antioxidant and Antiproliferative Capacity of Its Functional Extracts

Nannochloropsis gaditana is a microalga with interesting nutritional and functional value due to its high content of protein, polyunsaturated fatty acids, and bioactive compounds. However, the hardness of its cell wall prevents accessibility to these components. This work aimed to study the effect of a treatment to increase the fragility of the cell wall on the bioavailability of its nutrients and functional compounds. The antioxidant and antiproliferative capacity of functional extracts from treated and untreated N. gaditana was assessed, and the profile of bioactive compounds was characterized. Furthermore, to study the effect of treatment on its nutrient availability and functional capacity, an in vivo experiment was carried out using a rat experimental model and a 20% dietary inclusion level of microalgae. Functional extracts from treated N. gaditana exhibited higher antioxidant activity than the untreated control. Furthermore, the treated microalga induced hypoglycemic action, higher nitrogen digestibility, and increased hepatic antioxidant activity. In conclusion, N. gaditana has interesting hepatoprotective, antioxidant, and anti-inflammatory potential, thus proving itself an ideal functional food candidate, especially if the microalga is treated to increase the fragility of its cell wall before consumption.

Assessing the prospects of Zygnema heydrichii, a filamentous Chlorophyte, as a biodiesel feedstock

This research aimed to investigate the suitability of the filamentous microalga Zygnema heydrichii as a biodiesel feedstock. Under ambient culture conditions, biomass yield, lipid content, and fatty acid composition were measured. The effects of nutrient deprivation, pH, and salinity on biomass and lipid production were also investigated. Z. heydrichii under nutrient-enriched medium showed specific growth rate (µ) 0.31 day^-1 and lipid content 14.75% DW. The most abundant fatty acids were C16:0, C18:1, C18:2 and C18:3, all of which are considered appropriate for biodiesel production. Nitrogen and phosphorus depletion from the growth medium further increased lipid content to 21.45% and 15.35% DW, respectively. The N depletion of the medium remarkably increased TAG content of the culture. Z. heydrichii possess great ability to grow in salty water (40 Mm NaCl). A low-cost, semi-continuous outdoor culture yielded biomass and lipid productivity of 0.208 g day^-1and 0.038 g L^-1 day^-1, respectively.

A review on co-culturing of microalgae: A greener strategy towards sustainable biofuels production

There is a growing global recognition that microalgae-based biofuel are environment-friendly and economically feasible options because they incur several advantages over traditional fossil fuels. Also, the microalgae can be manipulated for extraction of value-added compounds such as lipids (triacylglycerols), carbohydrates, polyunsaturated fatty acids, proteins, pigments, antioxidants, various antimicrobial compounds, etc. Recently, there is an increasing focus on the co-cultivation practices of microalgae with other microorganisms to enhance biomass and lipid productivity. In a co-cultivation strategy, microalgae grow symbiotically with other heterotrophic microbes such as bacteria, yeast, fungi, and other algae/microalgae. They exchange nutrients and metabolites; this helps to increase the productivity, therefore facilitating the commercialization of microalgal-based fuel. Co-cultivation also facilitates biomass harvesting and waste valorization, thereby help to build an algal biorefinery platform for bioenergy production along with multivariate high value bioproducts and simultaneous waste bioremediation. This article comprehensively reviews various microalgae cultivation practices utilizing co-culture approaches with other algae, fungi, bacteria, and yeast. The review mainly focuses on the impact of several binary culture strategies on biomass and lipid yield. The advantages and challenges associated with the procedure along with their respective cultivation modes have also been presented and discussed in detail.

Nannochloropsis oceanica as a Microalgal Food Intervention in Diet-Induced Metabolic Syndrome in Rats

The microalgal genus Nannochloropsis has broad applicability to produce biofuels, animal feed supplements and other value-added products including proteins, carotenoids and lipids. This study investigated a potential role of N. oceanica in the reversal of metabolic syndrome. Male Wistar rats (n = 48) were divided into four groups in a 16-week protocol. Two groups were fed either corn starch or high-carbohydrate, high-fat diets (C and H, respectively) for the full 16 weeks. The other two groups received C and H diets for eight weeks and then received 5% freeze-dried N. oceanica in these diets for the final eight weeks (CN and HN, respectively) of the protocol. The H diet was high in fructose and sucrose, together with increased saturated and trans fats. H rats developed obesity, hypertension, dyslipidaemia, fatty liver disease and left ventricular fibrosis. N. oceanica increased lean mass in CN and HN rats, possibly due to the increased protein intake, and decreased fat mass in HN rats. Intervention with N. oceanica did not change cardiovascular, liver and metabolic parameters or gut structure. The relative abundance of Oxyphotobacteria in the gut microbiota was increased. N. oceanica may be an effective functional food against metabolic syndrome as a sustainable protein source.

Perfluorooctane sulfonate (PFOS) disturbs fatty acid metabolism in Caenorhabditis elegans: Evidence from chemical analysis and molecular mechanism exploration

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant that might induce disorders in fatty acid (FA) metabolism, but the underlying mechanisms remain unresolved. Caenorhabditis elegans (C. elegans) as a model organism can synthesize polyunsaturated FAs de novo via the polyunsaturated FA synthesis pathway. In this study, synchronized L1 C. elegans were exposed to 0, 0.01, 0.1, 0.5 and 1 μM PFOS for 72 h. Gas chromatography-mass spectrometry (GC-MS) was used to establish a sensitive and reliable analysis method for PFASs in exposed nematode, the instrument detection limits of nine fatty acid methyl esters examined ranged between 1.11 and 27.6 ng/mL, with satisfactory reproducibility (RSD < 10%) observed. Methyl pentadecanoate (C15:0) was used as an internal standard, the linearity of the calibration (0.1-10 μg/mL) nine FAs from the nematode were quantitatively analyzed. Comparing with the control group, PFOS exposure caused significantly decreased levels of C18:0 while significantly increased levels of C18:3n6. A decrease in the C18:3n6: C18:2n6 ratio was observed. Consistently, expression of the FA desaturation gene fat-3 was significantly down-regulated. These findings suggest that the FA disorder is associated with decrease in mRNA expression of Δ6-desaturase genes in C. elegans. Simultaneously, the disorders in FA metabolism were found to disrupt mitochondrial function with a reduction in ATP synthesis, as determined by the luciferase method. In summary, the results of the study provide insights into the adverse effects of PFOS on FA metabolism in living organisms.

Selection of extraction solvents for edible oils from microalgae and improvement of the oxidative stability

Microalgae are natural, green raw material and could be used for the development of edible oil for its abundant polyunsaturated fatty acids, with fast growth rate. The wet mud and dry powder of Scenedesmus dimorphus were applied to compare the extraction effects of different organic solvent systems in this study. The results displayed that, by using the ethanol/n-hexane (3:2, v/v) mixed solvent, the oil extraction rate from wet algal mud was 68.31 %, with 71.65 % of neutral lipid, and 1.87 % of vitamin E; the retention rates of protein, chlorophyll, and carbohydrates in the algal residue after oil extraction were 60.56 %, 53.27 %, and 80.20 %, respectively. Through the single solvent n-hexane, the oil extraction rate from dried algal powder was 71.52 %, with 75.86 % of neutral lipids, and 1.63 % of vitamin E. The retention rates of protein, chlorophyll, and carbohydrate were 55.92 %, 61.33 % and 78.35 %, respectively, suggesting the high rate of nutrient retention. In addition, the orthogonal experiments indicated that the compound of low concentration natural antioxidants with 0.010 % of tea polyphenols, 0.005 % of vitamin E, and 0.015 % of rosemary extract had the best effects on improvement of oxidative stability.

Yogurt Enriched with Isochrysis galbana: An Innovative Functional Food

Microalgae are a valuable and innovative emerging source of natural nutrients and bioactive compounds that can be used as functional ingredients in order to increase the nutritional value of foods to improve human health and to prevent disease. The marine microalga Isochrysis galbana has great potential for the food industry as a functional ingredient, given its richness in ω3 long chain-polyunsaturated fatty acids (LC-PUFAs), with high contents of oleic, linoleic, alpha-linolenic acid (ALA), stearidonic, and docosahexaenoic (DHA) acids. This study focuses on the formulation of a functional food by the incorporation of 2% (w/w) of I. galbana freeze-dried biomass and 2% (w/w) of I. galbana ethyl acetate lipidic extract in solid natural yogurts preparation. In the functional yogurt enriched with microalgal biomass, the ω3 LC-PUFA's content increased (to 60 mg/100 g w/w), specifically the DHA content (9.6 mg/100 g ww), and the ω3/ω6 ratio (augmented to 0.8). The in vitro digestion study showed a poor bioaccessibility of essential ω3 LC-PUFAs, wherein linoleic acid (18:2 ω6) presented a bioaccessibility inferior to 10% and no DHA or eicosapentaenoic acid (EPA) was detected in the bioaccessible fraction of the functional yogurts, thus indicating a low accessibility of lipids during digestion. Notwithstanding, when compared to the original yogurt, an added value novel functional yogurt with DHA and a higher ω3 LC-PUFAs content was obtained. The functional yogurt enriched with I. galbana can be considered important from a nutritional point of view and a suitable source of essential FAs in the human diet. However, this needs further confirmation, entailing additional investigation into bioavailability through in vivo assays.