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Phycoerythrin (PE) is a phycobiliprotein holding great potential as a high-value food colorant and medicine. Deep eutectic solvent (DES)-based ultrasound-assisted extraction (UAE) was applied to extract B-PE by disrupting the resistant polysaccharide cell wall of Porphyridium purpureum. The solubility of cell wall monomers in 31 DESs was predicted using COSMO-RS. Five glycerol-based DESs were tested for extraction, all of which showed significantly higher B-PE yields by up to 13.5 folds than water. The DES-dependent B-PE extraction efficiencies were proposedly associated with different cell disrupting capabilities and protein stabilizing effects of DESs. The DES-based UAE method could be considered green according to a metric assessment tool, AGREEprep. The crude extract containing DES was further subjected to aqueous two-phase system, two-step ammonium sulfate precipitation, and ultrafiltration processes. The final purified B-PE had a PE purity ratio of 3.60 and a PC purity ratio of 0.08, comparable to the purity of commercial products., Competing Interests: Declaration of competing interest Jeongmi Lee reports financial support was provided by National Research Foundation of Korea. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Microalgae are booming as a sustainable protein source for human nutrition and animal feed. Nevertheless, certain strains were reported to have robust cell walls limiting protein digestibility. There are several disruption approaches to break down the cell integrity and increase digestive enzyme accessibility. This review's intent is to discuss the digestibility of microalgae proteins in intact cells and after their disruption. In intact single cells, the extent of protein digestibility is chiefly related to cell wall structural properties (differing among strains) as well as digestion method and when added to food or feed protein digestibility changes depending on the matrix's composition. The degree of effectiveness of the disruption method varies among studies, and it is complicated to compare them due to variabilities in digestibility models, strains, disruption method/conditions and their consequent impact on the microalgae cell structure. More exhaustive studies are still required to fill knowledge gaps on the structure of microalgal cell walls and to find efficient and cost-effective disruption technologies to increase proteins availability without hindering their quality.

In the modern era, macro-microalgae attract a strong interest across scientific disciplines, owing to the wide application of these cost-effective valuable bioresources in food, fuel, nutraceuticals, and pharmaceuticals etc. The practice of eco-friendly extraction techniques has led scientists to create alternative processes to the conventional methods, to enhance the extraction of the key valuable compounds from macro-microalgae. This review narrates the possible use of novel cell disruption techniques, including use of ionic liquid, deep eutectic solvent, surfactant, switchable solvents, high voltage electrical discharge, explosive decompression, compressional-puffing, plasma, and ozonation, which can enable the recovery of value added substances from macro-microalgae, complying with the principles of green chemistry and sustainability. The above-mentioned innovative techniques are reviewed with respect to their working principles, benefits, and possible applications for macro-microalgae bioactive compound recovery and biofuel. The benefits of these techniques compared to conventional extraction methods include shorter extraction time, improved yield, and reduced cost. Furthermore, various combinations of these innovative technologies are used for the extraction of thermolabile bioactive compounds. The challenges and prospects of the innovative extraction processes for the forthcoming improvement of environmentally and cost-effective macro-microalgal biorefineries are also explained in this review.

Chlorella is a promising microalga for CO 2 -neutral biorefinery that co-produces drop-in biofuels and multiple biochemicals. Cell disruption and selective lipid extraction steps are major technical bottlenecks in biorefinement because of the inherent robustness and complexity of algal cell walls. This review focuses on the state-of-the-art achievements in cell disruption and lipid extraction methods for Chlorella species within the last five years. Various chemical, physical, and biological approaches have been detailed theoretically, compared, and discussed in terms of the degree of cell wall disruption, lipid extractability, chemical toxicity, cost-effectiveness, energy use, scalability, customer preferences, environment friendliness, and synergistic combinations of different methods. Future challenges and prospects of environmental-friendly and efficient extraction technologies are also outlined for practical applications in sustainable Chlorella biorefineries. Given the diverse industrial applications of Chlorella, this review may provide useful information for downstream processing of the advanced biorefineries of other algae genera., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The global demand for protein ingredients is continuously increasing owing to the growing population, rising incomes, increased urbanization, and aging population. Conventionally, animal-derived products (dairy, egg, and meat) satisfy the major dietary protein requirements of humans. With the global population set to reach 9.6 billion by 2050, there would be a huge deficit in meeting dietary protein requirements. Therefore, it is necessary to identify sustainable alternative protein sources that could complement high-quality animal proteins. In recent years, microalgae have been advocated as a potential industrial source of edible proteins owing to their wide and excellent ecological adaptation. Microalgae can grow in marginal areas utilizing non-potable wastewaters with high photosynthetic efficiency. Previously microalgae species such as Arthospira, and Chlorella have been used as single-cell proteins (SCP) with limited application in pharmaceutical industries. In recent years, the demand for innovative and sustainable functional ingredients for food applications has renewed the interest worldwide in microalgae proteins. The present review aims to provide a holistic view of various aspects related to the production and processing of edible proteins from microalgae biomass. A critical review of available literature on the nutritional quality, techno-functional properties, applications in food and feed sectors, and biological activities is presented. Further, challenges associated with each stage of processing are discussed. From the literature review, it can be summarized that microalgae proteins are comparable to reference proteins both in terms of amino acid (AA) quality and techno-functional properties. However recalcitrant cell wall poses a challenge in digestibility and effective utilization of the microalgae proteins. Further, poor sensory scores and palatability of microalgae biomass limit its applications in the food and feed sector. Novel applications of microalgae proteins include meat analogues, emulsifying agents, and bioactive peptides. Development of low-cost cultivation strategies, wet biomass-based downstream processing along with the bio-refinery approach of complete biomass volarization would enhance the sustainability quotient for human food applications., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Microalgae are a promising feedstock for the production of biofuels, nutraceuticals, pharmaceuticals and cosmetics, due to their superior capability of converting solar energy and CO 2 into lipids, proteins, and other valuable bioactive compounds. To facilitate the release of these important biomolecules from microalgae, effective cell disruption is usually necessary, where the use of ultrasound has gained tremendous interests as an alternative to traditional methods. This review not only summarizes the mechanisms of and operation parameters affecting cell disruption, but also takes an insight into measuring techniques, synergistic integration with other disruption methods, and challenges of ultrasonication for microalgal biorefining. Optimal conditions including ultrasonic frequency, intensity, and duration, and liquid viscosity and sonochemical reactor are the key factors for maximizing the disruption and extraction efficiency. A combination of ultrasound with other disruption methods such as ozonation, microwave, homogenization, enzymatic lysis, and solvents facilitates cell disruption and release of target compounds, thus provides powerful solutions to commercial scale-up of ultrasound extraction for microalgal biorefining. It is concluded that ultrasonication is a sustainable "green" process, but more research and work are needed to upscale this process without sacrificing performance or consuming more energy., (Copyright © 2022. Published by Elsevier B.V.)

Microalgae have evolved into a promising sustainable source of a wide range of compounds, including protein, carbohydrates, biomass, vitamins, animal feed, and cosmetic products. The process of extraction of intracellular composites in the microalgae industry is largely determined by the microalgal species, cultivation methods, cell wall disruption techniques, and extraction strategies. Various techniques have been applied to disrupt the cell wall and recover the intracellular molecules from microalgae, including non-mechanical, mechanical, and combined methods. A comprehensive understanding of the cell disruption processes in each method is essential to improve the efficiency of current technologies and further development of new methods in this field. In this review, an overview of microalgal cell disruption techniques and an analysis of their performance and challenges are provided. A number of studies on cell disruption and microalgae extraction are examined in order to highlight the key challenges facing the field of microalgae and their future prospects. In addition, the amount of product recovery for each species of microalgae and the important parameters for each technique are discussed. Finally, pulsed electric field (PEF)-assisted treatments, which are becoming an attractive option due to their simplicity and effectiveness in extracting microalgae compounds, are discussed in detail.

Novel cell-disruption combinations (autolytic incubation and hypotonic osmotic shock combined with HPH or pH12) were used to investigate the fundamental mass transfer of lipids and proteins from Nannochloropsis slurries (140 mg biomass/g slurry). Since neutral lipids exist as cytosolic globules, their mass transfer was directly dependent on disintegration of cell walls. Complete recovery was obtained with complete physical disruption. HPH combinations exerted more physical disruption and led to higher yields than pH12. In contrast, proteins exist as both cytosolic water-soluble fractions and cell-wall/membrane structural fractions and have a complex extraction behaviour. Mass transfer of cytosolic proteins was dependent on cell-wall disintegration, while that of structural proteins was governed by cell-wall disintegration and severance of protein linkage from the wall/membrane. HPH combinations exerted only physical disruption and were limited to releasing soluble proteins. pH12 combinations hydrolysed chemical linkages in addition to exerting physical disruption, releasing both soluble and structural proteins., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Electro-Fenton process (EFP) was studied as a potential cell disruption technique for recovery of lipids from wet biomass of the microalga Chlorella homosphaera. A novel approach of electrochemical dissolution of a sacrificial steel anode was used to provide Fe 2+ required to initiate EFP and microalgae cell disruption. Response surface methodology (RSM) was employed to optimize the process parameters and maximize the lipid yield of EFP. The RSM model (R 2  = 90.66%, Adj.R 2  = 87.71%) showed that a maximum lipid yield of 18.29% could be obtained at 40 min reaction time and 4.38 g/L biomass concentration. Experimental validation resulted in a lipid yield of 19.99 ± 1.33%, which was significantly higher than wet lipid extraction without cell disruption. However, the lipid yield of EFP should be further improved to achieve comparable results to mechanical cell disruption methods. Nonetheless, biodiesel synthesized from lipids obtained via EFP conformed to the ASTM D6751-12 standard., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The commercial feasibility of energy-efficient conversion of highly concentrated microalgal suspensions to produce high-titer biofuels is a major bottleneck due to high energy consumption. Herein, high-titer biofuels (bioethanol, higher-alcohols, and biodiesel) were generated from carbohydrate-rich Chlamydomonas mexicana and lipid-rich Chlamydomonas pitschmannii biomass through energy-saving microwave pretreatment, successive fermentation, and transesterification. Microwave pretreatment needed low specific energy (4.2 MJ/kg) for 100 g/L of microalgal suspension. Proposed sustainable integrated pretreatments method achieved unprecedented total conversion efficiency (67%) and highest biomass utilization (87%) of C. pitschmannii (100 g/L) with high yields of bioethanol (0.48 g-ethanol/g-carbohydrates), higher-alcohols (0.44 g-higher-alcohols/g-proteins), and biodiesel (0.90 g-biodiesel/g-lipids). Transmission electron microscopy showed the changes in the microalgal cellular integrity before and after sequential fermentations. Energy-efficient integrated pretreatments enhanced the extraction efficiency and whole utilization of high-concentration microalgae to generate high-titer biofuels with minimum waste production., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Subcritical dimethyl ether, a green solvent, was used to extract lipids from microalgae. The effect of the water content on the process was firstly investigated. Secondly, microalgal samples were subjected to five cell disruptions, and the effects on raw lipid and fatty acid methyl ester, and its profile were evaluated. Among them, heating, microwave, and ultrasonic treatments greatly improved extraction. Mechanism analysis revealed the improvements by the three treatments were due to increased cell wall permeability rather than to complete cell disruption. After the extraction, microalgal cells with lipid being well-extracted were shriveled with extensive surface folds, indicating a loss of intracellular substances, but the cell structure was undamaged. As for dewatering performance, extraction process removed almost all of the free water but left bound water. Finally, the potential of the residues after lipid extraction to serve as solid fuel was evaluated by combustion characteristics and heating value calculation., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Switchable solvent N, N, N', N'-tetraethyl-1,3-propanediamine (TEPDA) was proposed to extract lipids from wet Nannochloropsis oceanica with a 5% higher extraction efficiency than chloroform-methanol. It was found that TEPDA acted mainly as an organic solvent to soften and dissolve lipids, while a small amount of TEPDA was dissociated into tertiary amine ion, i.e.,(C 2 H 5 ) 2 N-(CH 2 ) 3 -NH + (C 2 H 5 ) 2 . This cation acted as a surfactant to promote cell disruption and lipid separation. With moisture increasing from 0 to 84 wt%, more TEPDA was dissociated into cationic surfactant to induce local rearrangement of phospholipid bilayers in cell membranes through electrostatic interaction, resulting in the fractal dimension of disrupted cells increased from 1.49 to 1.66. Accordingly, the yield of fatty acid methyl ester (FAME) through transesterification of lipids extracted with TEPDA increased by 9%, while FAME yield from lipids extracted with chloroform and n-hexane decreased by 41% and 65%, respectively., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The yield and quality of lipids extracted from microalgal biomass are critical factors in the production of microalgae-based biodiesel. The green microalga Chlorella homosphaera, isolated from Beira Lake, Colombo, Sri Lanka was employed in the present study to identify the effect of chlorophyll removal and cell disruption methods on lipid extraction yield, fatty acid methyl ester (FAME) profile and quality parameters of biodiesel; including cetane number (CN), iodine value (IV), degree of unsaturation (DU) and high heating value (HHV). In the first section of this study, chlorophyll was removed from dry microalgae biomass prior to lipid extraction. Through the analysis of FAME profiles, it was observed that chlorophyll removal yielded biodiesel of enhanced quality, albeit with a lipid loss of 44.2% relative to the control. In the second section of the study, mechanical cell disruption strategies including grinding, autoclaving, water bath heating and microwaving were employed to identify the most effective method to improve lipid recovery from chlorophyll-removed microalgae biomass. Autoclaving (121 °C, 20 min sterilization time, total time 2 h) was the most effective cell disruption technique of the methods tested, in terms of lipid extraction yield (39.80%) and also biodiesel quality. Moreover, it was observed that employing cell disruption subsequent to chlorophyll removal has a significant impact on the FAME profile of microalgae-based biodiesel, and consequently served to increase HHV and CN although IV and DU did not vary significantly., (Copyright © 2020 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.)

Industrial scale microalgal cell disruption requires low cost, high efficiency and structural conservation of biomolecules for biorefinery. Many cultivated microalgae have thick walls and these walls are barriers for efficient cell disruption. Until recently, despite the high biodiversity of microalgae, little attention has been paid to thin-wall microalgal species in the natural environment for the production and recovery of valuable biomolecules. Instead of developing high power cell disruption devices, utilization of thin-wall species would be a better approach. The present paper describes a simple device that was assembled to evaluate the viability and effectiveness of biomolecule extraction from both thin- and thick-wall species as a proof of concept. This device was tested with high-pressure gases including N 2 , CO 2 plus N 2 , and air as the disruption force. The highest nitrogen pressure, 110 bar, was not able to disrupt the thick-wall microalgal cells. On the other hand, the thin-wall species was disrupted to different degrees using different pressures and treatment durations. In the same treatment duration, higher nitrogen pressure gave better cell disruption efficiency than the lower pressure. However, in the same pressure, longer treatment duration did not give better efficiency than the shorter duration. High pressure CO 2 treatments resulted in low soluble protein levels in the media. The best conditions to disrupt the thin-wall microalgal cells were 110 bar N 2 or air for 1 min among these tests. In these conditions, not only were the disruption efficiencies high, but also the biomolecules were well preserved., (Copyright © 2019 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.)

Microalgae are sources of nutritional products and biofuels. However, their economical processing is challenging, because of (i) the inherently low concentration of biomass in algal cultures, below 0.5%, (ii) the high-water content in the harvested biomass, above 70%; and (iii) the variable intracellular content and composition. Cell wall structure and strength vary enormously among microalgae, from naked Dunaliella cells to robust Haematococcus cysts. High-value products justify using fast and energy-intensive processes, ranging from 0.23 kWh/kg dry biomass in high-pressure homogenization, to 6 kWh/kg dry biomass in sonication. However, in biofuels production, the energy input must be minimized, requiring slower, thermal or chemical pretreatments. Whichever the primary fraction of interest, the spent biomass can be processed into valuable by-products. This review discusses microalgal cell structure and composition, how it affects pretreatment, focusing on technologies tested for large scale or promising for industrial processes, and how these can be integrated into algal biorefineries., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this study, Anabaena PCC 7120 microalgae is used as feedstock for biodiesel synthesis. Anabaena 7120 was cultivated in a closed photobioreactor. Oil was extracted by cell disruption process and purified by degumming process. Anabaena oil was characterized by GCMS spectroscopy. Barium titanium oxide (Ba 2 TiO 4 ) heterogeneous catalyst was prepared by wet impregnation process and characterized through various techniques such as TGA, XRD, FTIR, HR-SEM, EDX and surface area analyzer. Basicity of synthesized catalyst was calculated by Hammett indicator titration method. The synthesized Ba 2 TiO 4 was used in transesterification of Anabaena oil for biodiesel production and it was reused up to six cycles. The highest FAME conversion from anabaena oil was found to be 98.41% under optimized condition of 1:18 M ratio (oil:methanol), 3.5 wt% of catalyst loading and 180 min of reaction time at 65 °C temperature and 400 rpm stirring speed., (Copyright © 2019. Published by Elsevier Ltd.)

Background: Algal biofuel has a potential for reducing dependence on fossil fuel while curbing CO 2 emissions. Despite these potential benefits, a scalable, sustainable, and commercially viable system has not yet been developed. One of the key barriers is the lack of viable methods for disrupting algal biomass for the separation and extraction of bioproducts. This study experimentally investigated the feasibility of using chlorine as an agent for algal biomass disruption., Results: Chlorine was an effective agent for disrupting algal cell, as demonstrated with cell viability and SEM analyses. For disruption studies conducted using algal suspension at 0.02% solids (0.2 g/L), 90% of the algal cells were disrupted in 6 min at 10 mg/L chlorine dose. Moreover, the results demonstrated that the estimated specific energy requirement, specific cost, and GWP for chlorine were lower than those of the existing methods. The energy requirement for chlorine was 3.73 MJ/ kg of dry algae disrupted, while the requirements for the existing methods ranged from 33 to 860 MJ/ kg of dry algae. The GWP for chlorine was 0.3 kg CO 2 -eq./kg dry algae, while for the existing methods it varied from 5.9 to 369.8 CO 2 -eq./kg dry algae. Despite these advantages, it was observed that residual chlorine reacted with and mineralized the cell contents, which is undesirable., Conclusions: Future research efforts must be focused on eliminating or reducing the reaction of residual chlorine with cell contents. If this challenge is addressed, chlorine has a potential to be developed into an energy-efficient, cost-effective, and sustainable method for algal biomass disruption. This will in turn will overcome one of the technical bottlenecks, and ultimately increase algal biofuel production and reduce dependence on fossil fuel and curb CO 2 emissions.

Considering the phosphorus (P) reserve state and its value, recovery of P from microalgae has become a popular topic. In this study, an integrated system of a hydrothermal process for microalgae cell disruption to release P and magnesium modified hydrochar adsorption to capture P was set up. Emission scanning electron microscopy with Energy Dispersive X-ray spectroscopy and Three-Dimensional Excitation Emission matrix spectroscopy with parallel factor analysis were applied to evaluate the P release process from microalgae and found the optimal breaking-wall condition (P release 90.5%, hydrothermal digestion mixture of H 2 O 2 and NaOH at 348 K). Parallel factor analysis showed there was a close relationship between P and humic-like substance. Hydrochar loaded with magnesium exhibited a strong affinity for P, with maximum capacity 89.61 mg/g at 318 K. The P adsorption fitted pseudo-second-order kinetic and Langmuir models. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were applied to reveal the mechanism of hydrochar modification and adsorption. It showed that Mg is loaded on the surface of hydrochar by electrostatic attraction and electron transfer with the carboxylic acid. P absorption was reached through anion exchange., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Microalgae are considered to be one of the most promising next generation bio-based/food feedstocks with a unique lipid composition, high protein content, and an almost unlimited amount of other bio-active molecules. High-value components such as the soluble proteins, (poly) unsaturated fatty acids, pigments, and carbohydrates can be used as an important ingredient for several markets, such as the food/feed/chemical/cosmetics and health industries. Although cultivation costs have decreased significantly in the last few decades, large microalgae production processes become economically viable if all complex compounds are optimally valorized in their functional state. To isolate these functional compounds from the biomass, cost-effective, mild, and energy-efficient biorefinery techniques need to be developed and applied. In this review we describe current microalgae biorefinery strategies and the derived products, followed by new technological developments and an outlook toward future products and the biorefinery philosophy.

Lipid extraction directly from the wet oleaginous microorganisms for biodiesel production is preferred as it reduces the energy input for traditional processes which require extensive drying of the biomass prior to the extraction. The high water content (≥80% on cell dry weight) in the wet biomass hinders the extraction efficiency due to the mass transfer limitation. This limitation can be overcome by pretreating wet biomass prior to the lipid extraction using pressurized gas that can be used alone or combined with other pretreatments to disrupt the cell wall. In this review, an extensive discussion on different pretreatments and the subsequent lipid extraction using these pretreatments is presented. Furthermore, a detailed account of the cell disruption using pressurized gas (e.g., CO 2 ) treatment for microbial cell lysing is also presented. Finally, a new technique on lipid extraction directly from wet biomass using the combination of pressurized CO 2 and microwave pretreatment is proposed., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

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.

The microalgae-based biorefinement process has attracted much attention from academic and industrial researchers attracted to its biofuel, food and nutraceutical applications. In this paper, recent developments in cell-disruption and lipid-extraction methods, focusing on four biotechnologically important microalgal species (namely, Chlamydomonas, Haematococcus, Chlorella, and Nannochloropsis spp.), are reviewed. The structural diversity and rigidity of microalgal cell walls complicate the development of efficient downstream processing methods for cell-disruption and subsequent recovery of intracellular lipid and pigment components. Various mechanical, chemical and biological cell-disruption methods are discussed in detail and compared based on microalgal species and status (wet/dried), scale, energy consumption, efficiency, solvent extraction, and synergistic combinations. The challenges and prospects of the downstream processes for the future development of eco-friendly and economical microalgal biorefineries also are outlined herein., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Spirulina platensis is considered an alternative and excellent source of protein [46-63% dry basis (DB)], having protein levels comparable to meat and soybeans. Thus, it can be considered an adequate ingredient to supply the necessity of this compound in the food industry. Its carbohydrates (8-14% DB) may also be a useful food ingredient or a potential source of bioenergy. Thus, extracting these compounds from the microalgae biomass will maximize its exploitation. Sonication can completely or partially degrade the microalgal cell wall, providing a useful technique to extract the protein and carbohydrate. This study used a sequential strategy of experimental design (fractional factorial design and central composite rotatable design) to evaluate the protein and carbohydrate extraction from S. platensis defatted biomass using ultrasonic waves and mechanical agitation, under alkaline conditions. The optimal conditions for protein and carbohydrate co-extraction were established by selecting and maximizing the variables that significantly influenced the extraction. The optimized percentages recovery from the extraction process yielded 75.76% protein and 41.52% carbohydrate at 33-40min sonication and 40-55min agitation. The protein fraction may be further concentrated and purified for use in food formulations, and the carbohydrates may be a useful feedstock for bioethanol production., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In this study, the microalga Nannochloropsis gaditana was subjected to acid catalysed steam explosion treatment and the resulting exploded material was subsequently fractionated to separate the different fractions (lipids, sugars and solids). Conventional and vibrational membrane setups were used with several polymeric commercial membranes. Two different routes were followed: 1) filtration+lipid solvent extraction and 2) lipid solvent extraction+filtration. Route 1 revealed to be much better since the used membrane for filtration was able to permeate the sugar aqueous phase and retained the fraction containing lipids; after this, an extraction required a much lower amount of solvent and a better recovering yield. Filtration allowed complete lipid rejection. Dynamic filtration improved permeability compared to the tangential cross-flow filtration. Best membrane performance was achieved using a 5000Da membrane with the dynamic system, obtaining a permeability of 6L/h/m 2 /bar., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A simultaneous cell disruption and lipid extraction method is developed for microalgal biodiesel production using a triethylamine/methanol solvent system. Individually, the pure solvents, i.e. triethylamine and methanol, do not exhibit significant enhancement in lipid extraction, but a 3:7 (v/v) triethylamine/methanol mixture exhibits the highest lipid extraction, corresponding to 150% of the conventional chloroform/methanol (2:1, v/v) solvent extraction. This extraction is equivalent to 92.5% of the total lipids, even when extracted from a wet microalgal biomass with a water content of 80%. The cell surfaces of the microalgae are significantly disrupted without using additional cell disruption reagents and without requiring energy-intensive equipment. The lipid mass transfer coefficient is 1.6 times greater than that of the chloroform/methanol solvent system. It is clearly demonstrated that triethylamine and methanol cooperate well for the cell disruption and lipid extraction., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A mild biorefinery process was investigated on the microalga Nannochloropsis gaditana, to obtain an enriched fraction of water soluble proteins free from chlorophyll. After harvesting, a 100g.L -1 solution of cells was first subjected to cell disruption by either high-pressure homogenization (HPH) or enzymatic treatment (ENZ). HPH resulted in a larger release of proteins (49%) in the aqueous phase compared to the Alcalase incubation (35%). In both cases, an ultrafiltration/diafiltration (UF/DF) was then performed on the supernatant obtained from cell disruption by testing different membrane cut-off (1000kDa, 500kDa and 300kDa). After optimising the process conditions, the combination of ENZ→UF/DF ended in a larger overall yield of water soluble proteins (24.8%) in the permeate compared to the combination of HPH→UF/DF (17.4%). A gel polarization model was implemented to assess the maximum achievable concentration factor during ultrafiltration and the mass transfer coefficient related to the theoretical permeation flux rate., (Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Carotenoids have been receiving increasing attention due to their potential health benefits. Microalgae are recognized as a natural source of carotenoids and other beneficial byproducts. However, the production of micro-algal carotenoids is not yet sufficiently cost-effective to compete with traditional chemical synthetic methods and other technologies such as extraction from plant based sources. This review presents the recent biotechnological developments in microalgal carotenoid production. The current technologies involved in their bioprocessing including cultivation, harvesting, extraction, and purification are discussed with a specific focus on downstream processing. The recent advances in chemical and biochemical synthesis of carotenoids are also reviewed for a better understanding of suitable and economically feasible biotechnological strategies. Some possible future directions are also proposed., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Microalgae biodiesel is considered one of the most promising renewable fuels. However, the high cost of the downstream process is a major barrier to large-scale microalgal lipid production. In this study, a novel approach based on nickel oxide nanoparticles (NiO NPs) was developed and its effectiveness for simultaneous harvesting and cell disruption in microalgal lipid production was determined. NiO NPs exhibited a microalgal harvesting efficiency of 98.75% in 1min at pH 7. Moreover, after treating with NiO NPs for 96h, the lipid extraction efficiency of microalgae (with 80% water content) reached 91.08% and was 208.37% compared to that without NiO treatment. This approach is simple and does not necessitate drying; furthermore, no equipment with high energy consumption was required., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Cell disruption by bead milling of Neochloris oleoabundans grown under nitrogen repleted (NR) and nitrogen depleted (ND) conditions was evaluated based on the release of biochemicals and biomass to the supernatant. Additionally, energy consumption for cell disruption was calculated per kg of released component. Bead milling of NR cells resulted on average in 34% (w/w) release of biochemicals into the supernatant, with a similar composition as the untreated microalgal biomass. With ND cells, the release was higher and more selective, i.e. 57%, 59%, 68% and 56% (w/w) of respectively biomass, proteins, carbohydrates and lipids whereof 92%, 57% and 46% (w/w) respectively of phospho-, glyco- and neutral lipids., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

High moisture content in wet algal biomass hinders effective performance of current lipid extraction methods. An improved aqueous extraction method combing thermal and enzymatic lysis was proposed and performed in algal slurry of Nannochloropsis oceanica (96.0% moisture) in this study. In general, cell-wall of N. oceanica was disrupted via thermal lysis and enzymatic lysis and lipid extraction was performed using aqueous surfactant solution. At the optimal conditions, high extraction efficiencies for both lipid (88.3%) and protein (62.4%) were obtained, which were significantly higher than those of traditional hexane extraction and other methods for wet algal biomass. Furthermore, an excessive extraction of polar lipid was found for wet biomass compared with dry biomass. The advantage of this method is to efficiently extract lipids from high moisture content algal biomass and avoid using organic solvent, indicating immense potential for commercial microalgae-based biofuel production., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The three-dimensional distribution (x, y, and z) of ultrasound-induced microalgal cell disruption in a sonochemical reactor was predicted by solving the Helmholtz equation using a three-dimensional acoustic module in the COMSOL Multiphysics software. The simulated local ultrasound pressure at any given location (x, y, and z) was found to correlate with cell disruption of a freshwater alga, Scenedesmus dimorphus, represented by the change of algal cell particle/debris concentration, chlorophyll-a fluorescence density (CAFD), and Nile red stained lipid fluorescence density (LFD), which was also validated by the model reaction of potassium iodide oxidation (the Weissler reaction). Furthermore, the effect of ultrasound power intensity and processing duration on algal cell disruption was examined to address the limitation of the model.

Marine microalgae present a renewable alternative source for sustainable production of omega-3 fatty acids, as compared to conventional sources such as krill oil and fish oil. In this study, we optimised a method for lipid extraction from marine thraustochytrids using a bead mill and enzymatic concentration of omega-3 fatty acids from the thraustochytrid oil. The optimised lipid extraction conditions were, bead size 0.4-0.6μm, 4500rpm, 4min of processing time at 5g biomass concentration. The maximum lipid yield (% dry weight basis) achieved at optimum conditions were 40.5% for Schizochytrium sp. S31 (ATCC) and 49.4% for Schizochytrium sp. DT3 (in-house isolate). DT3 oil contained 39.8% docosahexaenoic acid (DHA) as a percentage of lipid, a higher DHA percentage than S31. Partial hydrolysis of DT3 oil using Candida rugosa lipase was performed to enrich omega-3 polyunsaturated fatty acids (PUFAs) in the glyceride portion. Total omega-3 fatty acid content was increased to 88.7%., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Microalgal cell disruption induced by acoustic cavitation was simulated through solving the bubble dynamics in an acoustical field and their radial kinetics (chemical kinetics of radical species) occurring in the bubble during its oscillation, as well as calculating the bubble wall pressure at the collapse point. Modeling results indicated that increasing ultrasonic intensity led to a substantial increase in the number of bubbles formed during acoustic cavitation, however, the pressure generated when the bubbles collapsed decreased. Therefore, cumulative collapse pressure (CCP) of bubbles was used to quantify acoustic disruption of a freshwater alga, Scenedesmus dimorphus, and a marine alga, Nannochloropsis oculata and compare with experimental results. The strong correlations between CCP and the intracellular lipid fluorescence density, chlorophyll-a fluorescence density, and cell particle/debris concentration were found, which suggests that the developed models could accurately predict acoustic cell disruption, and can be utilized in the scale up and optimization of the process., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Cell disruption is one of the most critical steps affecting the economy and yields of biotechnological processes for producing biofuels from microalgae. Enzymatic cell disruption has shown competitive results compared to mechanical or chemical methods. However, the addition of enzymes implies an associated cost in the overall production process. Recent studies have employed algicidal microorganisms to perform enzymatic cell disruption and degradation of microalgae biomass in order to reduce this associated cost. Algicidal microorganisms induce microalgae growth inhibition, death and subsequent lysis. Secreted algicidal molecules and enzymes produced by bacteria, cyanobacteria, viruses and the microalga themselves that are capable of inducing algal death are classified, and the known modes of action are described along with insights into cell-to-cell interaction and communication. This review aims to provide information regarding microalgae degradation by microorganisms and secreted algicidal substances that would be useful for microalgae cell breakdown in biofuels production processes. A better understanding of algae-to-algae communication and the specific mechanisms of algal cell lysis is expected to be an important breakthrough for the broader application of algicidal microorganisms in biological cell disruption and the production of biofuels from microalgae biomass., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Ultrasonication is a cell disruption process of low energy efficiency. This study dosed K(+), Ca(2+) and Al(3+) to Chlorella vulgaris cultured in Bold's Basal Medium at 25°C and measured the degree of cell disruption under ultrasonication. Adding these metal ions yielded less negatively charged surfaces of cells, while with the latter two ions large and compact cell aggregates were formed. The degree of cell disruption followed: control=K(+)>Ca(2+)>Al(3+) samples. Surface charges of cells and microbubbles have minimal effects on the microbubble number in the proximity of the microalgal cells. Conversely, cell aggregates with large size and compact interior resist cell disruption under ultrasonication. Staining tests revealed high diffusional resistance of stains over the aggregate interior. Microbubbles may not be effective generated and collapsed inside the compact aggregates, hence leading to low cell disruption efficiencies. Effective coagulation/flocculation in cell harvesting may lead to adverse effect on subsequent cell disruption efficiency., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

A study of cell disruption by bead milling for two microalgae, Nannochloropsis oculata and Porphyridium cruentum, was performed. Strains robustness was quantified by high-pressure disruption assays. The hydrodynamics in the bead mill grinding chamber was studied by Residence Time Distribution modeling. Operating parameters effects were analyzed and modeled in terms of stress intensities and stress number. RTD corresponded to a 2 CSTR in series model. First order kinetics cell disruption was modeled in consequence. Continuous bead milling was efficient for both strains disruption. SI-SN modeling was successfully adapted to microalgae. As predicted by high pressure assays, N. oculata was more resistant than P. cruentum. The critical stress intensity was twice more important for N. oculata than for P. cruentum. SI-SN modeling allows the determination of operating parameters minimizing energy consumption and gives a scalable approach to develop and optimize microalgal disruption by bead milling., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

A 2-kW continuous ultrasonic flow system (UFS) was found effective in the disruption of two microalgal strains: Scenedesmus dimorphus and Nannochloropsis oculata. Compared to the control, cell debris concentration of UFS treatments increased up to 202% for S. dimorphus and 112% for N. oculata. Similarly, Nile red stained lipid fluorescence density (NRSLD) increased up to 59.5% and 56.3% for S. dimorphus and N. oculata, respectively. It was also found that increasing ultrasound intensity improved cell disruption efficiency indicated by up to 54% increase in NRSLFD of the two strains. Increasing sonication-processing time to 3-min resulted in 33.0% increase for S. dimorphus and 45.7% increase for N. oculata in NRSLFD compared to the control. Cell recirculation was found beneficial to cell disruption, however, higher initial cell concentration significantly reduced cell disruption efficiency, indicated by 98.2% decrease in NRSLFD per cell when initial cell concentration increased from 4.25 × 10(6) to 1.7 × 10(7)cells ml(-1)., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Instant catapult steam explosion (ICSE) was employed to disrupt wet microalgal cells for efficient lipid extraction. Physicochemical properties of exploded cells were investigated through SEM, TEM, FTIR, and TGA. The exploded cells increased in fractal dimension (1.53-1.65) when preheat time was prolonged from 0 min to 5 min and in surface pore area when steam pressure was increased. Meanwhile, the exploded cells decreased in mean size (1.69-1.44 μm) when the filling ratio of wet microalgal biomass in the preheat chamber decreased (75-12.5%). Flash evaporation and volume expansion exploded the cell walls and released the cytoplasm of the microalgal cells. These phenomena decreased the carbohydrate content and increased the lipid content in the exploded biomass. However, ICSE treatment did not change the lipid compositions in the microalgal cells. Using isopropanol as a cosolvent significantly increased the yield of lipids extracted with hexane from the exploded wet microalgal biomass., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

In this study, a simultaneous process of harvesting biomass and extracting crude bio-oil was attempted from wet microalgae biomass using FeCl3 and Fe2(SO4)3 as both coagulant and cell-disrupting agent. A culture solution of Chlorella sp. KR-1 was firstly concentrated to 20 g/L and then proceeded for cell disruption with the addition of H2O2. Optimal dosage were 560 and 1060 mg/L for FeCl3 and Fe2(SO4)3, showing harvesting efficiencies of more than 99%. Optimal extraction conditions were identified via the response surface method (RSM), and the extraction yield was almost the same at 120 °C for both iron salts but FAME compositions after transesterification was found to be quite different. Given iron salts were a reference coagulant in water treatment in general and microalgae harvesting in particular, the present approach of using it for harvesting and oil-extraction in a simultaneous manner can serve as a practical route for the microalgae-derived biodiesel production., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Hydrothermal acid treatment, was adopted to extract eicosapentaenoic acid (EPA) from wet biomass of Nannochloropsis salina. It was found that sulfuric acid-based treatment increased EPA yield from 11.8 to 58.1 mg/g cell in a way that was nearly proportional to its concentration. Nitric acid exhibited the same pattern at low concentrations, but unlike sulfuric acid its effectiveness unexpectedly dropped from 0.5% to 2.0%. The optimal and minimal conditions for hydrothermal acid pretreatment were determined using a statistical approach; its maximum EPA yield (predicted: 43.69 mg/g cell; experimental: 43.93 mg/g cell) was established at a condition of 1.27% of sulfuric acid, 113.34 °C of temperature, and 36.71 min of reaction time. Our work demonstrated that the acid-catalyzed cell disruption, accompanied by heat, can be one potentially promising option for ω-3 fatty acids extraction., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Simultaneous treatment (combining with cell disruption and lipid extraction) using hydrodynamic cavitation (HC) was applied to Nannochloropsis salina to demonstrate a simple and integrated way to produce oil from wet microalgae. A high lipid yield from the HC (25.9-99.0%) was observed compared with autoclave (16.2-66.5%) and ultrasonication (5.4-26.9%) in terms of the specific energy input (500-10,000 kJ/kg). The optimal conditions for the simultaneous treatment were established using a statistical approach. The efficiency of the simultaneous method was also demonstrated by comparing each separate treatment. The maximum lipid yield (predicted: 45.9% and experimental: 45.5%) was obtained using 0.89% sulfuric acid with a cavitation number of 1.17 for a reaction time of 25.05 min via response surface methodology. Considering its comparable extractability, energy-efficiency, and potential for scale-up, HC may be a promising method to achieve industrial-scale microalgae operation., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The energy consumption of high pressure homogenisation (HPH) was analysed to determine the feasibility of rupturing algal cells for biodiesel production. Experimentally, the processing capacity (i.e. flow rate), power draw and cell disruption efficiency of HPH were independent of feed concentration (for Nannochloropsis sp. up to 25%w/w solids). Depending on the homogenisation pressure (60-150 MPa), the solids concentration (0.25-25%w/w), and triacylglyceride (TAG) content of the harvested algal biomass (10-30%), the energy consumed by HPH represented between 6% and 110-times the energy density of the resulting biodiesel. Provided the right species (weak cell wall and high TAG content) is selected and the biomass is processed at a sufficiently high solids concentration, HPH can consume a small fraction of the energy content of the biodiesel produced. This study demonstrates the feasibility of process-scale algal cell disruption by HPH based on its energy requirement., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Challenges with mid-stream fractionation steps in proposed microalgae biofuel pathways arise from the typically dilute cell density in growth media, micron scale cell sizes, and often durable cell walls. For microalgae to be a sustainable source of biofuels and co-products, efficient fractionation by some method will be necessary. This study evaluates ultrasonic cell disruption as a processing step that fractionates microalgae. A range of species types with different sizes and cell wall compositions were treated. The initial seconds of sonication offered the most significant disruption, even for the more durable Nannochloropsis cells. Following this initial period, diminishing effectiveness was attributed, by acoustic measurements, to attenuation of the ultrasound in the ensuing cloud of cavitating bubbles. At longer exposure times, differences between species were more pronounced. Processing higher concentrations of Isochrysis slowed cell disintegration only marginally, making the expenditure of energy more worthwhile., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Microalgae are a potential source for various valuable chemicals for commercial applications ranging from nutraceuticals to fuels. Objective in a biorefinery is to utilize biomass ingredients efficiently similarly to petroleum refineries in which oil is fractionated in fuels and a variety of products with higher value. Downstream processes in microalgae biorefineries consist of different steps whereof cell disruption is the most crucial part. To maintain the functionality of algae biochemicals during cell disruption while obtaining high disruption yields is an important challenge. Despite this need, studies on mild disruption of microalgae cells are limited. This review article focuses on the evaluation of conventional and emerging cell disruption technologies, and a comparison thereof with respect to their potential for the future microalgae biorefineries. The discussed techniques are bead milling, high pressure homogenization, high speed homogenization, ultrasonication, microwave treatment, pulsed electric field treatment, non-mechanical cell disruption and some emerging technologies., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Hydrothermal acid (combined with autoclaving and nitric acid) pretreatment was applied to Nannochloropsis salina as a cost-effective yet efficient way of lipid extraction from wet biomass. The optimal conditions for this pretreatment were determined using a statistical approach, and the roles of nitric acid were also determined. The maximum lipid yield (predicted: 24.6%; experimental: 24.4%) was obtained using 0.57% nitric acid at 120°C for 30min through response surface methodology. A relatively lower lipid yield (18.4%) was obtained using 2% nitric acid; however, chlorophyll and unsaturated fatty acids, both of which adversely affect the refinery and oxidative stability of biodiesel, were found to be not co-extracted. Considering its comparable extractability even from wet biomass and ability to reduce chlorophyll and unsaturated fatty acids, the hydrothermal nitric acid pretreatment can serve as one direct and promising route of extracting microalgae oil., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Lipid extraction represents one of the main bottlenecks of the microalgal technology for the production of biofuels. A novel method based on the use of H2O2 with or without FeSO4, to disrupt the cell wall of Chlorella vulgaris and favor the subsequent extraction of lipids from wet biomass, is proposed. Experimental results show that, when disruption is performed under suitable operating conditions, the amount of lipids extracted is significantly increased with respect to the case where a classical approach is applied. Moreover, quality of lipids extracted after disruption seems to be improved in view of their exploitation for producing biofuels., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

In this study, the lipid releasing characteristics of several microalgae species through continuous ultrasonication was examined. Two marine microalgae species, Tetraselmis suecica and Nannochloropsis sp., and one freshwater species, Chlorella sp. were ultrasonicated directly after cultivation. The cell disruption efficiency and lipids releasing pattern from microalgae cells were measured under various ultrasonication conditions. It was found that cell disruption efficiency correlates well with ultrasonication energy consumption despite the ultrasonication conditions. Lipids in Chlorella sp. that has rigid cell walls were released to the aqueous phase after cell disruption. T. suecica and Nannochloropsis sp. that have flexible cell membranes tend to coil up and retain the membrane lipids after disruption. Continuous ultrasonication can be a potential method to release the lipids in rigid walled microalgae species without expensive dewatering steps., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The objective of this study was to evaluate the effectiveness of high-frequency focused ultrasound (HFFU) in microalgal cell disruption. Two microalgal species including Scenedesmus dimorphus and Nannochloropsis oculata were treated by a 3.2-MHz, 40-W focused ultrasound and a 100-W, low-frequency (20kHz) non-focused ultrasound (LFNFU). The results demonstrated that HFFU was effective in the disruption of microalgal cells, indicated by significantly increased lipid fluorescence density, the decrease of cell sizes, and the increase of chlorophyll a fluorescence density after treatments. Compared with LFNFU, HFFU treatment was more energy efficient. The combination of high and low frequency treatments was found to be even more effective than single frequency treatment at the same processing time, indicating that frequency played a critical role in cell disruption. In both HFFU and LFNFU treatments, the effectiveness of cell disruption was found to be dependent on the cell treated., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Microalgae are one of the most promising sustainable energy sources for biodiesel production. However, the high costs of the downstream process are a major bottleneck for commercial-scale production of biodiesel from a microalgal biomass. A novel approach called the cationic surfactant-based harvesting and cell disruption (CSHD) method was studied to determine its effectiveness in simultaneous microalgal biomass harvesting and cell disruption. Using CSHD, the harvesting efficiency reached more than 91% in less than 5 min and 97% in 90 min. Moreover, CSHD exhibited a powerful ability to disrupt the cells; the lipid recovery was increased 133% compared to not using CSHD. CSHD allowed the extraction of up to 100% of the total lipids from a wet microalgal biomass with 80% water content. All of these results were achieved without using energy-intensive equipment. Altogether, our results suggest that CSHD is an energy-efficient technique for the downstream process of microalgal lipid production., (Copyright © 2013 Elsevier Ltd. All rights reserved.)