Influence of water content and cell disruption on lipid extraction using subcritical dimethyl ether in wet microalgae

Recent Analytical Methodologies in Lipid Analysis

Lipids represent a large group of biomolecules that are responsible for various functions in organisms. Diseases such as diabetes, chronic inflammation, neurological disorders, or neurodegenerative and cardiovascular diseases can be caused by lipid imbalance. Due to the different stereochemical properties and composition of fatty acyl groups of molecules in most lipid classes, quantification of lipids and development of lipidomic analytical techniques are problematic. Identification of different lipid species from complex matrices is difficult, and therefore individual analytical steps, which include extraction, separation, and detection of lipids, must be chosen properly. This review critically documents recent strategies for lipid analysis from sample pretreatment to instrumental analysis and data interpretation published in the last five years (2019 to 2023). The advantages and disadvantages of various extraction methods are covered. The instrumental analysis step comprises methods for lipid identification and quantification. Mass spectrometry (MS) is the most used technique in lipid analysis, which can be performed by direct infusion MS approach or in combination with suitable separation techniques such as liquid chromatography or gas chromatography. Special attention is also given to the correct evaluation and interpretation of the data obtained from the lipid analyses. Only accurate, precise, robust and reliable analytical strategies are able to bring complex and useful lipidomic information, which may contribute to clarification of some diseases at the molecular level, and may be used as putative biomarkers and/or therapeutic targets.

Extraction and Separation of Natural Products from Microalgae and Other Natural Sources Using Liquefied Dimethyl Ether, a Green Solvent: A Review

Microalgae are a sustainable source for the production of biofuels and bioactive compounds. This review discusses significant research on innovative extraction techniques using dimethyl ether (DME) as a green subcritical fluid. DME, which is characterized by its low boiling point and safety as an organic solvent, exhibits remarkable properties that enable high extraction rates of various active compounds, including lipids and bioactive compounds, from high-water-content microalgae without the need for drying. In this review, the superiority of liquefied DME extraction technology for microalgae over conventional methods is discussed in detail. In addition, we elucidate the extraction mechanism of this technology and address its safety for human health and the environment. This review also covers aspects related to extraction equipment, various applications of different extraction processes, and the estimation and trend analysis of the Hansen solubility parameters. In addition, we anticipate a promising trajectory for the expansion of this technology for the extraction of various resources.

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.

Chemical markers in marine food web: A simple workflow based on methyl tert-butyl ether extraction for fatty acids and stable isotopes assessment in plankton samples

Fatty acids (FAs) are used, often in combination with stable isotopes (SIs), as chemical biomarkers to assess the contribution of different prey to the diet of consumers and define food web structure and dynamics. Extraction of lipids is traditionally carried out using methanol (MeOH) combined with chloroform or dichloromethane, these latter being well-known environmental pollutant and potential carcinogenic agents. Recently, extraction protocols based on methyl tert-butyl ether (MTBE) and MeOH have been proposed as an alternative to halogenated solvents in lipidomic studies. However, no specific investigation has been performed to assess MTBE suitability in marine ecological studies including FA analysis together with SI measurements. We used an analytical workflow for qualitative and quantitative analysis of FAs and SIs in field samples of phytoplankton, zooplankton and the scyphomedusa Pelagia noctiluca, applying MTBE in comparison with chloroform- and dichloromethane-based protocols for total lipid extraction. Our analysis suggested that MTBE is a reliable substitute for lipid extraction in trophic ecology studies in marine planktonic organisms.

Astaxanthin as a King of Ketocarotenoids: Structure, Synthesis, Accumulation, Bioavailability and Antioxidant Properties

Astaxanthin (3,3-dihydroxy-β, β-carotene-4,4-dione) is a ketocarotenoid synthesized by Haematococcus pluvialis/lacustris, Chromochloris zofingiensis, Chlorococcum, Bracteacoccus aggregatus, Coelastrella rubescence, Phaffia rhodozyma, some bacteria (Paracoccus carotinifaciens), yeasts, and lobsters, among others However, it is majorly synthesized by Haematococcus lacustris alone (about 4%). The richness of natural astaxanthin over synthetic astaxanthin has drawn the attention of industrialists to cultivate and extract it via two stage cultivation process. However, the cultivation in photobioreactors is expensive, and converting it in soluble form so that it can be easily assimilated by our digestive system requires downstream processing techniques which are not cost-effective. This has made the cost of astaxanthin expensive, prompting pharmaceutical and nutraceutical companies to switch over to synthetic astaxanthin. This review discusses the chemical character of astaxanthin, more inexpensive cultivating techniques, and its bioavailability. Additionally, the antioxidant character of this microalgal product against many diseases is discussed, which can make this natural compound an excellent drug to minimize inflammation and its consequences.

Extraction of lipids from microalgae using classical and innovative approaches

Microalgae, as a photosynthetic autotrophic organism, contain a variety of bioactive compounds, including lipids, proteins, polysaccharides, which have been applied in food, medicine, and fuel industries, among others. Microalgae are considered a good source of marine lipids due to their high content in unsaturated fatty acid (UFA) and can be used as a supplement/replacement for fish-based oil. The high concentration of docosahexaenoic (DHA) and eicosapentaenoic acids (EPA) in microalgae lipids, results in important physiological functions, such as antibacterial, anti-inflammatory, and immune regulation, being also a prerequisite for its development and application. In this paper, a variety of approaches for the extraction of lipids from microalgae were reviewed, including classical and innovative approaches, being the advantages and disadvantages of these methods emphasized. Further, the effects of microalgae lipids as high value bioactive compounds in human health and their use for several applications are dealt with, aiming using green(er) and effective methods to extract lipids from microalgae, as well as develop and extend their application potential.

Strategy for high-yield astaxanthin recovery directly from wet Haematococcus pluvialis without pretreatment

A novel integrated extraction technique for high recovery of natural astaxanthin from wet encysted Haematococcus pluvialis (H. pluvialis) is demonstrated. The technique can be used to effectively disrupt the cell wall and perform extraction in a one-pot system without a high-energy, cost intensive pre-drying step. The most suitable green solvent was researched in terms of high extraction yield and astaxanthin recovery. Moreover, an optimized condition for the selected green solvents was determined by varying process parameters, viz., the ball milling speed (100-300 rpm) and time (5-30 min). A high recovery of astaxanthin directly from wet H. pluvialis (30.6 mg/g based on its dry mass) and a high extraction yield (58.2 wt%) were achieved using ethyl acetate at 200 rpm after 30 min. Therefore, compared to its counterparts, the biphasic solvent system plays a key role in achieving high extraction yield and astaxanthin recovery from wet H. pluvialis.

Cell disruption and astaxanthin extraction from Haematococcus pluvialis: Recent advances

The green microalga Haematococcus pluvialis is an excellent source of astaxanthin, a powerful antioxidant widely used in cosmetics, aquaculture, health foods, and pharmaceuticals. This review explores recent developments in cell disruption and astaxanthin extraction techniques applied using H. pluvialis as a model species for large-scale algal biorefinery. Notably, this alga develops a unique cyst-like cell with a rigid three-layered cell wall during astaxanthin accumulation (∼4% of dry weight) under stress. The thick (∼2 µm), acetolysis-resistant cell wall forms the strongest barrier to astaxanthin extraction. Various physical, chemical, and biological cell disruption methods were discussed and compared based on theoretical mechanisms, biomass status (wet, dry, and live), cell-disruption efficacy, astaxanthin extractability, cost, scalability, synergistic combinations, and impact on the stress-sensitive astaxanthin content. The challenges and future prospects of the downstream processes for the sustainable and economic development of advanced H. pluvialis biorefineries are also outlined.

Algae biorefinery: a promising approach to promote microalgae industry and waste utilization

Microalgae have a number of intriguing characteristics that make them a viable raw material aimed at usage in a variety of applications when refined using a bio-refining process. They offer unique capabilities that allow them to be used in biotechnology-related applications. As a result, this review explores how to increase the extent to which microalgae may be integrated with various additional biorefinery uses in order to improve their maintainability. In this study, the use of microalgae as potential animal feed, manure, medicinal, cosmeceutical, ecological, and other biotechnological uses is examined in its entirety. It also includes information on the boundaries, openings, and improvements of microalgae and the possibilities of increasing the range of microalgae through techno-economic analysis. According to the findings of this review, financing supported research and shifting the focus of microalgal investigations from biofuels production to biorefinery co-products can help guarantee that they remain a viable resource. Furthermore, innovation collaboration is unavoidable if one wishes to avoid the high cost of microalgae biomass handling. This review is expected to be useful in identifying the possible role of microalgae in biorefinery applications in the future.

Advances in Lipid Extraction Methods-A Review

Extraction of lipids from biological tissues is a crucial step in lipid analysis. The selection of appropriate solvent is the most critical factor in the efficient extraction of lipids. A mixture of polar (to disrupt the protein-lipid complexes) and nonpolar (to dissolve the neutral lipids) solvents are precisely selected to extract lipids efficiently. In addition, the disintegration of complex and rigid cell-wall of plants, fungi, and microalgal cells by various mechanical, chemical, and enzymatic treatments facilitate the solvent penetration and extraction of lipids. This review discusses the chloroform/methanol-based classical lipid extraction methods and modern modifications of these methods in terms of using healthy and environmentally safe solvents and rapid single-step extraction. At the same time, some adaptations were made to recover the specific lipids. In addition, the high throughput lipid extraction methodologies used for liquid chromatography-mass spectrometry (LC-MS)-based plant and animal lipidomics were discussed. The advantages and disadvantages of various pretreatments and extraction methods were also illustrated. Moreover, the emerging green solvents-based lipid extraction method, including supercritical CO2 extraction (SCE), is also discussed.

Experimental and modelling studies of convective and microwave drying kinetics for microalgae

Conventional microalgal drying consumes huge time and contributes to 60-80% of downstream process costs. With the aim to develop an effective and rapid drying process, the present study evaluated the performance of microwave based drying (MWD) with a power range of 360-900 W and compared with the conventional oven drying (OD) at 40-100 °C. MWD was found to be efficient due to uniform and volumetric heating because of dipolar interaction, with an effective diffusivity of 0.47 × 10^-9-1.63 × 10^-9 m² s^-1, comparatively higher than OD. Activation and specific energy of 32.43 W g^-1 and 42.9-56.07 kWh kg^-1 was projected respectively, and a falling rate period with best fit for Newton and Henderson-Pabis model was observed for MWD. Uniform heating from internal sub-surface avoided cell distress, resulting in 14.4% higher lipid yield and significant preservation of biochemical components that can be processed into bioenergy and valuable products in microalgal biorefinery.

Surfactant-Free Decellularization of Porcine Aortic Tissue by Subcritical Dimethyl Ether

Porcine aortic tissue was decellularized by subcritical dimethyl ether (DME) used as an alternative to the surfactant sodium dodecyl sulfate. The process included three steps. For the first step, lipids were extracted from the porcine aorta using subcritical DME at 23 °C with a DME pressure of 0.56 MPa. Next, DME was evaporated from the aorta under atmospheric pressure and temperature. The second step involved DNA fragmentation by DNase, which was primarily identical to the common method. For the third step, similar to the common method, DNA fragments were removed by washing with water and ethanol. After 3 days of DNase treatment, the amount of DNA remaining in the porcine aorta was 40 ng/dry-mg, which was lower than the standard value of 50 ng/mg-dry. Hematoxylin and eosin staining showed that most cell nuclei were removed from the aorta. These results demonstrate that subcritical DME eliminates the need to utilize surfactants.