Cell disruption for microalgae biorefineries

Algae: A promising and sustainable protein-rich food ingredient for bakery and dairy products

The consumer demand for protein rich foods urges the exploration for novel products of natural origin. Algae can be considered as a gold mine of different bioactive compounds, among which protein is distributed in significant amounts i.e., around 30% and can even reach to 55-60% in some cyanobacteria. Bakery and dairy products are extensively consumed worldwide due to product diversification and innovation. However, incorporation of algae biomass can lead to the development of green colour and fishy flavour that usually is not accepted in such products. Therefore, isolation and application of algae-derived proteins opens a new door for food industry. The present review provides a comprehensive understanding of incorporation of algae as a protein-rich ingredient in bakery and dairy products. The paper provides a deep insight for all the possible recent trends related to production and extraction of algae proteins accompanied by their incorporation in bakery and dairy foods.

Current progress and future perspective of microalgae biomass pretreatment using deep eutectic solvents

Pretreatment process is considered as the most important step for effective microalgae biomass refining and has gained more interest since last decades. However, the main obstacles to commercialize microalgae products are recalcitrant cell wall and lack of cost-effective, green, and sustainable pretreatment approaches. Till now, various microalgae pretreatment approaches have been applied prior to extraction steps to enhance the accessibility of solvent inside the cells. However, high energy consumption and the hazardousness of solvents are considerable problem for these pretreatment methods. In this regard, deep eutectic solvents are recognized as sustainable and green solvents possessing great potential for microalgae biomass processing due to their low toxicity, low cost, biodegradability, easy recycling, and reuse. This article provides the fundamentals of DES composition, synthesis, properties, and the current advances in the application of microalgae biomass process.

Potential use of yeast protein in terms of biorefinery, functionality, and sustainability in food industry

A growing demand for sustainable, alternative protein sources that are nutrient-dense, such as microorganisms, and insects, has gradually evolved. When paired with effective processing techniques, yeast cells contain substantial substances that could supply the population's needs for food, medicine, and fuel. This review article explores the potential of yeast proteins as a sustainable and viable alternative to animal and plant-based protein sources. It highlights the various yeast protein extraction methods including both mechanical and non-mechanical methods. The application of nanoparticles is one example of the fast-evolving technology used to damage microbial cells. SiO2 or Al2O3 nanoparticles break yeast cell walls and disrupt membranes, releasing intracellular bioactive compounds. Succinylation of yeast protein during extraction can increase yeast protein extraction rate, lower RNA concentration, raise yeast protein solubility, increase amino acid content, and improve yeast protein emulsification and foaming capabilities. Combining physical and enzymatic extraction methods generates the most representative pool of mannose proteins from yeast cell walls. Ethanol or isoelectric precipitation purifies mannose proteins. Mannoproteins can be used as foamy replacement for animal-derived components like egg whites due to their emulsification, stability, and foaming capabilities. Yeast bioactive peptide was separated by ultrafiltration after enzymatic hydrolysis of yeast protein and has shown hypoglycemic, hypotensive, and oxidative action in vitro studies. Additionally, the review delves into the physicochemical properties and stability of yeast-derived peptides as well as their applications in the food industry. The article infers that yeast proteins are among the promising sources of sustainable protein, with a wide range of potential applications in the food industry.

Seaweed-derived phenolic compounds as diverse bioactive molecules: A review on identification, application, extraction and purification strategies

Seaweed, a diverse group of marine macroalgae, has emerged as a rich source of bioactive compounds with numerous health-promoting properties. Among these, phenolic compounds have garnered significant attention for their diverse therapeutic applications. This review examines the methodologies employed in the extraction and purification of phenolic compounds from seaweed, emphasizing their importance in unlocking the full potential of these oceanic treasures. The article provides a comprehensive overview of the structural diversity and biological activities of seaweed-derived phenolics, elucidating their antioxidant, anti-inflammatory, and anticancer properties. Furthermore, it explores the impact of extraction techniques, including conventional methods and modern green technologies, on the yield and quality of phenolic extracts. The purification strategies for isolating specific phenolic compounds are also discussed, shedding light on the challenges and advancements in this field. Additionally, the review highlights the potential applications of seaweed-derived phenolics in various industries, such as pharmaceuticals, cosmetics, and functional foods, underscoring the economic value of these compounds. Finally, future perspectives and research directions are proposed to encourage continued exploration of seaweed phenolics, fostering a deeper understanding of their therapeutic potential and promoting sustainable practices in the extraction and purification processes. This comprehensive review serves as a valuable resource for researchers, industry professionals, and policymakers interested in harnessing the untapped potential of phenolic compounds from seaweed for the betterment of human health and environmental sustainability.

Optimization and Characterization of Spirulina and Chlorella Hydrolysates for Industrial Application

Chlorella and Spirulina are the most used microalgae mainly as powder, tablets, or capsules. However, the recent change in lifestyle of modern society encouraged the emergence of liquid food supplements. The current work evaluated the efficiency of several hydrolysis methods (ultrasound-assisted hydrolysis UAH, acid hydrolysis AH, autoclave-assisted hydrolysis AAH, and enzymatic hydrolysis EH) in order to develop liquid dietary supplements from Chlorella and Spirulina biomasses. Results showed that, EH gave the highest proteins content (78% and 31% for Spirulina and Chlorella, respectively) and also increased pigments content (4.5 mg/mL of phycocyanin and 12 µg/mL of carotenoids). Hydrolysates obtained with EH showed the highest scavenging activity (95-91%), allowing us, with the other above features, to propose this method as convenient for liquid food supplements development. Nevertheless, it has been shown that the choice of hydrolysis method depended on the vocation of the product to be prepared.

Integrating wet stirred-bead milling for Tetraselmis suecica biorefinery: Operating parameters influence and specific energy efficiency

Stirred bead milling proved to be an efficient cell destruction technique in a biorefinery unit for the extraction of over 95 % of proteins and 60 % of carbohydrates from the green marine microalga Tetraselmis suecica. Optimum conditions, expressed in terms of metabolite yield and energy consumption, were found for average values of bead size and agitator rotation speed. The higher the microalgae concentration, up to 100 g.L-1, which is adequate for biofilm algae growth in an industrial unit, the more efficient the cell destruction process. Cell destruction rates and metabolite extraction yields are similar in pendular and recycling modes, but the pendular configuration reduces the residence time of the suspension in the grinding chamber, which is less costly. With regard to the cell destruction mechanism, it was concluded that bead shocks first damage cells by permeabilizing them, and that after a longer period, all cells are shredded and destroyed, forming elongated debris.

A review on pretreatment methods for lipid extraction from microalgae biomass

Microalgal lipids are promising and sustainable sources for the production of third-generation biofuels, foods, and medicines. A high lipid yield during the extraction process in microalgae could be influenced by the suitable pretreatment and lipid extraction methods. The extraction method itself could be attributed to the economic and environmental impacts on the industry. This review summarizes the pretreatment methods including mechanical and non-mechanical techniques for cell lysis strategy before lipid extraction in microalgae biomass. The multiple strategies to achieve high lipid yields via cell disruption techniques are discussed. These strategies include mechanical (shear forces, pulse electric forces, waves, and temperature shock) and non-mechanical (chemicals, osmotic pressure, and biological) methods. At present, two techniques of the pretreatment method can be combined to increase lipid extraction from microalgae. Therefore, the extraction strategy for a large-scale application could be further strengthened to optimize lipid recovery by microalgae.

Discovery of plant chemical defence mediated by a two-component system involving β-glucosidase in Panax species

Plants usually produce defence metabolites in non-active forms to minimize the risk of harm to themselves and spatiotemporally activate these defence metabolites upon pathogen attack. This so-called two-component system plays a decisive role in the chemical defence of various plants. Here, we discovered that Panax notoginseng, a valuable medicinal plant, has evolved a two-component chemical defence system composed of a chloroplast-localized β-glucosidase, denominated PnGH1, and its substrates 20(S)-protopanaxadiol ginsenosides. The β-glucosidase and its substrates are spatially separated in cells under physiological conditions, and ginsenoside hydrolysis is therefore activated only upon chloroplast disruption, which is caused by the induced exoenzymes of pathogenic fungi upon exposure to plant leaves. This activation of PnGH1-mediated hydrolysis results in the production of a series of less-polar ginsenosides by selective hydrolysis of an outer glucose at the C-3 site, with a broader spectrum and more potent antifungal activity in vitro and in vivo than the precursor molecules. Furthermore, such β-glucosidase-mediated hydrolysis upon fungal infection was also found in the congeneric species P. quinquefolium and P. ginseng. Our findings reveal a two-component chemical defence system in Panax species and offer insights for developing botanical pesticides for disease management in Panax species.

Production of chemicals and utilities in-house improves the environmental sustainability of phytoplankton-based biorefinery

Life cycle assessment was used to evaluate the environmental impacts of phytoplanktonic biofuels as possible sustainable alternatives to fossil fuels. Three scenarios were examined for converting planktonic biomass into higher-value commodities and energy streams using the alga Scenedesmus sp. and the cyanobacterium Arthrospira sp. as the species of interest. The first scenario (Sc-1) involved the production of biodiesel and glycerol from the planktonic biomass. In the second scenario (Sc-2), biodiesel and glycerol were generated from the planktonic biomass, and biogas was produced from the residual biomass. The process also involved using a catalyst derived from snail shells for biodiesel production. The third scenario (Sc-3) was similar to Sc-2 but converted CO2 from the biogas upgrading to methanol, which was then used in synthesizing biodiesel. The results indicated that Sc-2 and Sc-3 had a reduced potential (up to 60 % less) for damaging human health compared to Sc-1. Sc-2 and Sc-3 had up to 61 % less environmental impact than Sc-1. Sc-2 and Sc-3 reduced the total cumulative exergy demand by up to 44 % compared to Sc-1. In conclusion, producing chemicals and utilities within the biorefinery could significantly improve environmental sustainability, reduce waste, and diversify revenue streams.

Comprehensive Update on Carotenoid Colorants from Plants and Microalgae: Challenges and Advances from Research Laboratories to Industry

The substitution of synthetic food dyes with natural colorants continues to be assiduously pursued. The current list of natural carotenoid colorants consists of plant-derived annatto (bixin and norbixin), paprika (capsanthin and capsorubin), saffron (crocin), tomato and gac fruit lycopene, marigold lutein, and red palm oil (α- and β-carotene), along with microalgal Dunaliella β-carotene and Haematococcus astaxanthin and fungal Blakeslea trispora β-carotene and lycopene. Potential microalgal sources are being sought, especially in relation to lutein, for which commercial plant sources are lacking. Research efforts, manifested in numerous reviews and research papers published in the last decade, have been directed to green extraction, microencapsulation/nanoencapsulation, and valorization of processing by-products. Extraction is shifting from conventional extraction with organic solvents to supercritical CO2 extraction and different types of assisted extraction. Initially intended for the stabilization of the highly degradable carotenoids, additional benefits of encapsulation have been demonstrated, especially the improvement of carotenoid solubility and bioavailability. Instead of searching for new higher plant sources, enormous effort has been directed to the utilization of by-products of the fruit and vegetable processing industry, with the application of biorefinery and circular economy concepts. Amidst enormous research activities, however, the gap between research and industrial implementation remains wide.

Microalgae biomass as an alternative source of biocompounds: New insights and future perspectives of extraction methodologies

Microalgae have characteristics that make them unique and full of potential. Their capacity to generate interesting bioactive molecules can add value to various industrial applications. However, most of these valuable compounds are intracellular, which makes their extraction a major bottleneck. Conventional extraction methodologies have some drawbacks, such as low eco-friendly character, high costs and energy demand, long treatment times, low selectivity and reduced extraction yields, as well as degradation of extracted compounds. The gaps found for these methods demonstrate that emergent approaches, such as ohmic heating, pulsed electric fields, ionic liquids, deep eutectic solvents, or high-pressure processing, show potential to overcome the current drawbacks in the release and extraction of added-value compounds from microalgae. These new processing techniques can potentially extract a variety of compounds, making the process more profitable and applicable to large scales. This review provides an overview of the most important and promising factors to consider in the extraction methodologies applied to microalgae. Additionally, it delivers broad knowledge of the present impact of these methods on biomass and its compounds, raising the possibility of applying them in an integrated manner within a biorefinery concept.

Developing industry-scale microfluidization for cell disruption, biomolecules release and bioaccessibility improvement of Chlorella pyrenoidosa

To facilitate biomolecules extraction and bioaccessibility of Chlorella pyrenoidosa, a novel industry-scale microfluidization (ISM) was used to disrupt cells effectively. Microscope images showed ISM damaged cell integrity, disorganized cell wall structure, pulverized cell membrane and promoted the release of intracellular components. The decrease of particle size and the increase of ζ-potential also confirmed the cell disruption. The cell breakage ratio of sample treated at 120 MPa was 98%. Compared with untreated samples, total soluble solid content and protein extraction rate of the sample treated at 120 MPa increased by 2 °Brix and 12%. Protein was degraded by ISM, the release of intracellular protein and the reduction of molecular weight increased protein digestibility by 20% in in vitro gastric phase. Lipid yield and chlorophyll b content were also increased by ISM. These results provided a new solution to cell disruption of microalgae and expanded the application field of ISM.

Emerging green cell disruption techniques to obtain valuable compounds from macro and microalgae: a review

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.

Next-Generation Organic Beauty Products Obtained from Algal Secondary Metabolites: A Sustainable Development in Cosmeceutical Industries

Algae lay over most of the earth's habitats, and it is said that there are more algal cells in water than there are stars in the sky. They are among the wealthiest marine resources that are to be deemed harmless, with hardly any deleterious consequences. Recently, they have received a lot of consideration to be used in cosmeceuticals. Cosmetics encompass synthetic concoctions that are extremely toxic to the environment. Due to their higher molecular size, synthetic cosmetic items induce undesirable side effects and inadequate absorption rates. Consequently, utilizing algae or their secondary metabolites in cosmetics has won multiple votes. Various secondary metabolites synthesized from algae are known to provide skin advantages, such as ultraviolet protection and reduction of skin flaccidity, rough texture, and wrinkles. The tangent drawn here using algae reduces the inorganic/organic chemicals used in the industry that are known to accumulate and affect other organisms and thus opens a pandora's box of ways to a less-polluted environment. The alga is indeed very intriguing. According to the reported studies, algal cells provide biosorption, bio-assimilation, biotransformation, and biodegradation, making them suitable for the eradication of chronic and harmful contaminants from the environment. Another rapid innovation is the product's sustainability. While presenting and marketing new algal products, cosmetics producers have greatly highlighted that they are eco-friendly. This review thus accentuates the significance of using algae and their secondary metabolites in cosmetics to produce extensive variety of products that include sunscreens, moisturizers, anti-aging creams, colorants, and hair care items and extensive insight on the possible remedial capacities of algae species against environmentally dangerous substances in the context of cosmetic chemicals.

Microalgae: A Promising Source of Bioactive Phycobiliproteins

Phycobiliproteins are photosynthetic light-harvesting pigments isolated from microalgae with fluorescent, colorimetric and biological properties, making them a potential commodity in the pharmaceutical, cosmetic and food industries. Hence, improving their metabolic yield is of great interest. In this regard, the present review aimed, first, to provide a detailed and thorough overview of the optimization of culture media elements, as well as various physical parameters, to improve the large-scale manufacturing of such bioactive molecules. The second section of the review offers systematic, deep and detailed data about the current main features of phycobiliproteins. In the ultimate section, the health and nutritional claims related to these bioactive pigments, explaining their noticeable potential for biotechnological uses in various fields, are examined.

Sequential extraction of value-added bioproducts from three Chlorella strains using a drying-based combined disruption technique

In this study, the sequential extraction of the three types of biochemicals from microalgae is employed, which is a more realistic and practical solution for large-scale extraction of bioproducts. The drying, grinding, organic solvent treatment, and ultra-sonication were combined to disrupt cells and sequentially extract bioproducts from three microalgae strains, Chlorella sorokiniana IG-W-96, Chlorella sp. PG-96, and Chlorella vulgaris IG-R-96. As the drying is the most energy-intensive step in cell disruption and sequential extraction, the effect of this step on sequential extraction deeply explored. The results show that total ash-plus contents of biochemicals in freeze-dried samples (95.4 ± 2.8%, 89.3 ± 3.9%, and 77.5 ± 4.2 respectively) are higher than those in oven-dried samples (91.0 ± 2.8%, 89.5 ± 3.0%, 71.4 ± 4.8%, respectively) showing the superiority of freeze drying over oven drying merely for Chlorella vulgaris IG-R-96 (p-value = 0.003) and non-significant variation for Chlorella sorokiniana IG-W-96 (p-value = 0.085) and Chlorella sp. PG-96 (p-value = 0.466). Variation among biochemical contents of strains is due to the difference in cell wall strength confirmed by TEM imaging. The freeze-dried samples achieved higher lipid yields than oven-dried samples. The total carbohydrate yields followed the same pattern. The extraction yields of total protein were higher in freeze-dried samples than in oven-dried. Total mass balance revealed that drying-based sequential extraction of value-added bioproducts could better demonstrate the economic potential of sustainable and renewable algal feedstock than independent assays for each biochemical.

Cell destruction level and metabolites green-extraction of Tetraselmis suecica by low and intermediate frequency ultrasound

Low (20 kHz) and intermediate (100 kHz) frequency ultrasound (US) were studied for their efficiency on cell destruction and metabolites extraction of the microalga T. suecica. This study revealed different levels of cell destruction. Firstly, the prolonged irradiation of US at low frequency allowed the extraction of 90% of total proteins and 70% of carbohydrates by rapidly inducing at high power (100 W or 200 W) a coiling up phenomenon of the cell walls on themselves. A low power (50 W) over short times allows extracting proteins by the perforation of the cells without destroying them, opening the perspective of milking. Furthermore, the use of 100 kHz frequency, showed lower yields of metabolites as well as a low level of cell destruction, resulting in a simple deflation of the cells.

Exploring the Benefits of Phycocyanin: From Spirulina Cultivation to Its Widespread Applications

Large-scale production of microalgae and their bioactive compounds has steadily increased in response to global demand for natural compounds. Spirulina, in particular, has been used due to its high nutritional value, especially its high protein content. Promising biological functions have been associated with Spirulina extracts, mainly related to its high value added blue pigment, phycocyanin. Phycocyanin is used in several industries such as food, cosmetics, and pharmaceuticals, which increases its market value. Due to the worldwide interest and the need to replace synthetic compounds with natural ones, efforts have been made to optimize large-scale production processes and maintain phycocyanin stability, which is a highly unstable protein. The aim of this review is to update the scientific knowledge on phycocyanin applications and to describe the reported production, extraction, and purification methods, including the main physical and chemical parameters that may affect the purity, recovery, and stability of phycocyanin. By implementing different techniques such as complete cell disruption, extraction at temperatures below 45 °C and a pH of 5.5-6.0, purification through ammonium sulfate, and filtration and chromatography, both the purity and stability of phycocyanin have been significantly improved. Moreover, the use of saccharides, crosslinkers, or natural polymers as preservatives has contributed to the increased market value of phycocyanin.

Current Status and Nutritional Value of Green Leaf Protein

Green leaf biomass is one of the largest underutilized sources of nutrients worldwide. Whether it is purposely cultivated (forage crops, duckweed) or upcycled as a waste stream from the mass-produced agricultural crops (discarded leaves, offcuts, tops, peels, or pulp), the green biomass can be established as a viable alternative source of plant proteins in food and feed processing formulations. Rubisco is a major component of all green leaves, comprising up to 50% of soluble leaf protein, and offers many advantageous functional features in terms of essential amino acid profile, reduced allergenicity, enhanced gelation, foaming, emulsification, and textural properties. Nutrient profiles of green leaf biomass differ considerably from those of plant seeds in protein quality, vitamin and mineral concentration, and omega 6/3 fatty acid profiles. Emerging technological improvements in processing fractions, protein quality, and organoleptic profiles will enhance the nutritional quality of green leaf proteins as well as address scaling and sustainability challenges associated with the growing global demand for high quality nutrition.

Optimized infrared-assisted extraction to obtain total lipid from microalgae Scenedesmus obliquus: a green approach

Microalgae oil has great potential to address the growing energy demand and dependence on fossil fuels. However, the multilayered cell walls of microalgae hinder efficient extraction and enhanced lipid recovery. In this study, we develop a novel protocol based on near infrared-assisted extraction (NIRAE) technology to extract efficiently total lipids from Scenedesmus obliquus. Under a greener solvent extraction approach, the effect of nine non-polar/polar solvent systems in various ratios on lipid yield was tested, and the results were compared with Soxhlet, Folch, and Bligh–Dyer methods. The highest oil yields were NIRAE 15.43%, and Soxhlet 22.24%, using AcoEt/MeOH (1:2 v/v). For Folch and Bligh–Dyer, 9.11 and 10%, respectively. The optimized NIRAE conditions obtained using response surface methodology (RSM): 43.8 min, solvent/biomass 129.90:1 (m/v), and AcOEt/MeOH 0.57:2.43 (v/v) increased the oil yield significantly to 24.20%. In contrast to conventional methods, the overall optimized NIRAE process satisfied the requirements of a green extraction because of the simple and safe operation, less solvent toxicity, lower extraction time, and solvent and energy consumption.

Effect of Abscisic Acid on Growth, Fatty Acid Profile, and Pigment Composition of the Chlorophyte Chlorella (Chromochloris) zofingiensis and Its Co-Culture Microbiome

Microalga Chlorella (Chromochloris) zofingiensis has been gaining increasing attention of investigators as a potential competitor to Haematococcus pluvialis for astaxanthin and other xanthophylls production. Phytohormones, including abscisic acid (ABA), at concentrations relevant to that in hydroponic wastewater, have proven themselves as strong inductors of microalgae biomass productivity and biosynthesis of valuable molecules. The main goal of this research was to evaluate the influence of phytohormone ABA on the physiology of C. zofingiensis in a non-aseptic batch experiment. Exogenous ABA stimulated C. zofingiensis cell division, biomass production, as well as chlorophyll, carotenoid, and lipid biosynthesis. The relationship between exogenous ABA concentration and the magnitude of the observed effects was non-linear, with the exception of cell growth and biomass production. Fatty acid accumulation and composition depended on the concentration of ABA tested. Exogenous ABA induced spectacular changes in the major components of the culture microbiome of C. zofingiensis. Thus, the abundance of the representatives of the genus Rhodococcus increased drastically with an increase in ABA concentration, whereas the abundance of the representatives of Reyranella and Bradyrhizobium genera declined. The possibilities of exogenous ABA applications for the enhancing of the biomass, carotenoid, and fatty acid productivity of the C. zofingiensis cultures are discussed.

Microalgae biomass deconstruction using green solvents: Challenges and future opportunities

Microalgae enablefixation of CO₂into carbohydrates, lipids, and proteins through inter and intracellularly biochemical pathways. These cellular components can be extracted and transformed into renewable energy, chemicals, and materials through biochemical and thermochemical transformation processes.However, recalcitrant cell wall andlack of environmentally benign efficient pretreatment processes are key obstacles in the commercialization of microalgal biorefineries.Thus,current article describes the microalgal chemical structure, type, and structural rigidity and summarizes the traditional pretreatment methods to extract cell wall constituents. Green solvents such as ionic liquid (ILs), deep eutectic solvents (DES), and natural deep eutectic solvents (NDESs) have shown interesting solvent characteristics to pretreat biomass with selective biocomponent extraction from microalgae. Further research is needed in task-specific IL/DES design, cation-anion organization, structural activity understanding of ILs-biocomponents, environmental toxicity, biodegradability, and recyclability for deployment of carbon-neutral technologies. Additionally, coupling the microalgal industry with biorefineries may facilitate waste management, sustainability, and gross revenue.

A review on current advances in the energy and cost effective pretreatments of algal biomass: Enhancement in liquefaction and biofuel recovery

The main downside of utilizing algal biomass for biofuel production is the rigid cell wall which confines the availability of soluble organics to hydrolytic microbes during biofuel conversion. This constraint reduces the biofuel production efficiency of algal biomass. On the other hand, presenting various pretreatment methods before biofuel production affords cell wall disintegration and enhancement in biofuel generation. The potential of pretreatment methods chiefly relies on the extent of biomass liquefaction, energy, and cost demand. In this review, different pretreatments employed to disintegrate algal biomass were conferred in depth with detailed information on their efficiency in enhancing liquefaction and biofuel yield for pilot-scale implementation. Based on this review, it has been concluded that combinative and phase-separated pretreatments provide virtual input in enhancing the biofuel generation based on liquefaction potential, energy, and cost. Future studies should focus on decrement in cost and energy requirement of pretreatment in depth.

Structured population balances to support microalgae-based processes: Review of the state-of-art and perspectives analysis

Design and optimization of microalgae processes have traditionally relied on the application of unsegregated mathematical models, thus neglecting the impact of cell-to-cell heterogeneity. However, there is experimental evidence that the latter one, including but not limited to variation in mass/size, internal composition and cell cycle phase, can play a crucial role in both cultivation and downstream processes. Population balance equations (PBEs) represent a powerful approach to develop mathematical models describing the effect of cell-to-cell heterogeneity. In this work, the potential of PBEs for the analysis and design of microalgae processes are discussed. A detailed review of PBE applications to microalgae cultivation, harvesting and disruption is reported. The review is largely focused on the application of the univariate size/mass structured PBE, where the size/mass is the only internal variable used to identify the cell state. Nonetheless, the need, addressed by few studies, for additional or alternative internal variables to identify the cell cycle phase and/or provide information about the internal composition is discussed. Through the review, the limitations of previous studies are described, and areas are identified where the development of more reliable PBE models, driven by the increasing availability of single-cell experimental data, could support the understanding and purposeful exploitation of the mechanisms determining cell-to-cell heterogeneity.

Sustainable Production of Pigments from Cyanobacteria

Pigments are intensely coloured compounds used in many industries to colour other materials. The demand for naturally synthesised pigments is increasing and their production can be incorporated into circular bioeconomy approaches. Natural pigments are produced by bacteria, cyanobacteria, microalgae, macroalgae, plants and animals. There is a huge unexplored biodiversity of prokaryotic cyanobacteria which are microscopic phototrophic microorganisms that have the ability to capture solar energy and CO2 and use it to synthesise a diverse range of sugars, lipids, amino acids and biochemicals including pigments. This makes them attractive for the sustainable production of a wide range of high-value products including industrial chemicals, pharmaceuticals, nutraceuticals and animal-feed supplements. The advantages of cyanobacteria production platforms include comparatively high growth rates, their ability to use freshwater, seawater or brackish water and the ability to cultivate them on non-arable land. The pigments derived from cyanobacteria and microalgae include chlorophylls, carotenoids and phycobiliproteins that have useful properties for advanced technical and commercial products. Development and optimisation of strain-specific pigment-based cultivation strategies support the development of economically feasible pigment biorefinery scenarios with enhanced pigment yields, quality and price. Thus, this chapter discusses the origin, properties, strain selection, production techniques and market opportunities of cyanobacterial pigments.

Extraction and purification of phycobiliproteins from algae and their applications

Microalgae, macroalgae and cyanobacteria are photosynthetic microorganisms, prokaryotic or eukaryotic, living in saline or freshwater environments. These have been recognized as valuable carbon sources, able to be used for food, feed, chemicals, and biopharmaceuticals. From the range of valuable compounds produced by these cells, some of the most interesting are the pigments, including chlorophylls, carotenoids, and phycobiliproteins. Phycobiliproteins are photosynthetic light-harvesting and water-soluble proteins. In this work, the downstream processes being applied to recover fluorescent proteins from marine and freshwater biomass are reviewed. The various types of biomasses, namely macroalgae, microalgae, and cyanobacteria, are highlighted and the solvents and techniques applied in the extraction and purification of the fluorescent proteins, as well as their main applications while being fluorescent/luminescent are discussed. In the end, a critical perspective on how the phycobiliproteins business may benefit from the development of cost-effective downstream processes and their integration with the final application demands, namely regarding their stability, will be provided.

Progress on Conventional and Advanced Techniques of In Situ Transesterification of Microalgae Lipids for Biodiesel Production

Global warming and the depletion of fossil fuels have spurred many efforts in the quest for finding renewable, alternative sources of fuels, such as biodiesel. Due to its auxiliary functions in areas such as carbon dioxide sequestration and wastewater treatment, the potential of microalgae as a feedstock for biodiesel production has attracted a lot of attention from researchers all over the world. Major improvements have been made from the upstream to the downstream aspects related to microalgae processing. One of the main concerns is the high cost associated with the production of biodiesel from microalgae, which includes drying of the biomass and the subsequent lipid extraction. These two processes can be circumvented by applying direct or in situ transesterification of the wet microalgae biomass, hence substantially reducing the cost. In situ transesterification is considered as a significant improvement to commercially produce biodiesel from microalgae. This review covers the methods used to extract lipids from microalgae and various in situ transesterification methods, focusing on recent developments related to the process. Nevertheless, more studies need to be conducted to further enhance the discussed in situ transesterification methods before implementing them on a commercial scale.

Amelioration for oxidative stability and bioavailability of N-3 PUFA enriched microalgae oil: an overview

Technological improvements in dietary supplements and nutraceuticals have highlighted the significance of bioactive molecules in a healthy lifestyle. Eicosapentaenoic acid and Cervonic acid (DHA), omega-3 polyunsaturated fatty acids seem to be famed for their ability to prevent diverse physiological abnormalities. Selection of appropriate pretreatments and extraction techniques for extraction of lipids from robust microalgae cell wall are very important to retain their stability and bioactivity. Therefore, extraction techniques with optimized extraction parameters offer an excellent approach for obtaining quality oil with a high yield. Oils enriched in omega-3 are particularly imperiled to oxidation which ultimately affects customer acceptance. Bio active encapsulation could be one of the effective approaches to overcome this dilemma. This review paper aims to give insight into the cultivation methods, and downstream processes, various lipid extraction approaches, techniques for retaining oxidative stability, bioavailability and food applications based on extracted or encapsulated omega-3.

Mild acoustic processing of Tisochrysis lutea for multiproduct biorefineries

Cellular agriculture could represent a more sustainable alternative to current food and nutraceutical production processes. Tisochrysis lutea microalgae represents a rich source of antioxidants and omega-3 fatty acids essential for human health. However, current downstream technologies are limiting its use. The present work investigates mild targeted acoustic treatment of Tisochrysis lutea biomass at different growth stages and acoustic frequencies, intensities and treatment times. Significant differences have been observed in terms of the impact of these variables on the cell disruption and energy requirements. Lower frequencies of 20 kHz required a minimum of 4500 J to disrupt 90% of the cells, while only 1000 J at 1146 kHz. Comparing these results with current industry standards such as bead milling, up to six times less energy use has been identified. These mild biomass processing approaches offer a certain tunability which could suit a wide range of microorganisms with only minor adjustments.

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.

Technoeconomic Evaluation of Microalgae Oil Production: Effect of Cell Disruption Method

Microalgae have a high capacity to capture CO2. Additionally, biomass contains lipids that can be used to produce biofuels, biolubricants, and other compounds of commercial interest. This study analyzed various scenarios for microalgae lipid production by simulation. These scenarios include cultivation in raceway ponds, primary harvest with three flocculants, secondary harvest with pressure filter (and drying if necessary), and three different technologies for the cell disruption step, which facilitates lipid extraction. The impact on energy consumption and production cost was analyzed. Both energy consumption and operating cost are higher in the scenarios that consider bead milling (8.79–8.88 kWh/kg and USD 41.06–41.41/kg), followed by those that consider high-pressure homogenization (HPH, 5.39–5.46 kWh/kg and USD 34.26–34.71/kg). For the scenarios that consider pressing, the energy consumption is 5.80–5.88 kWh/kg and the operating cost is USD 27.27–27.88/kg. The consumption of CO2 in scenarios that consider pressing have a greater capture (11.23 kg of CO2/kg of lipids). Meanwhile, scenarios that consider HPH are the lowest consumers of fresh water (5.3 m3 of water/kg of lipids). This study allowed us to develop a base of multiple comparative scenarios, evaluate different aspects involved in Chlorella vulgaris lipid production, and determine the impact of various technologies in the cell disruption stage.

The role of bioprocess systems engineering in extracting chemicals and energy from microalgae

In this study, the role of process systems engineering in enhancing the algae economy is highlighted. First, basic characteristics of the various strains of microalgae are presented. In addition, the beneficial extracted bioproducts and their applications are reviewed. Then, an overview of the various technologies available in each step of biorefinery to produce added-value products and biofuels from microalgae is provided. These technologies are compared in terms of required energy and efficiency. Different perspectives of the algae industry, from molecule to enterprises scale where process systems engineering can have a role, are addressed. Subsequently, the roles of process systems engineering in process and product design, process control, and supply chain of the algae biorefinery are discussed. It is found that process systems engineering can play an important role in the biobased economy, especially by applying sustainability and economic concepts in the decision-making process for selecting the best feedstock, processing pathways, and desired products. Tools such as market analysis, techno-economic analysis, life cycle assessment (LCA), and supply chain (SC) analysis can be applied to design sustainable algae biorefinery. There are, however, several challenges such as the lack of data, the complexity of optimization, and validation that should be addressed before using these tools.

Biodiesel Production through Acid Catalyst In Situ Reactive Extraction of Chlorella vulgaris Foamate

A method of biodiesel production from the freshwater microalgae Chlorella vulgaris based on the conversion of the dewatered algal biomass from a foam column (“foamate”) was investigated. The foam column collected and concentrated the microalgae. The foam was generated by passing air through a pool of algae, to which a collector/surfactant cetyltrimethylammonium bromide (CTAB) had been added. To produce biodiesel, the resultant “foamate” was esterified in situ using sulfuric acid and methanol. The effect of reaction temperature (30–70 °C), reaction time (30–120 min) and methanol/oil molar ratio (100–1000), were examined in a single-stage extraction–transesterification experiment on biodiesel yield at concentration of the catalyst H2SO4/oil molar ratio of (8.5/1). The thermodynamics and kinetics of transesterification of the microalgae oil were also investigated. The maximum biodiesel yield (96 ± 0.2%) was obtained at a reaction temperature of 70 °C, a reaction time of 90 min and methanol/oil molar ratio of 1000/1. Reaction kinetic parameters were determined that fitted the experimental data at all temperatures. A reversible reaction with first order forward and second order backward kinetics were found to be a good match for the experimental results. The kinetic model fitted experiments well under various temperatures and methanol/oil mole ratios. Under the most suitable conditions of reaction temperature, reaction time and methanol/oil molar ratio, the apparent activation energy was found to be 18.7 kJ/mol and pre-exponential factor 51.4 min−1. The activation entropy (ΔS), change in Gibbs free energy (ΔG) and variation in activation enthalpy (ΔH) revealed that the transesterification reaction is endergonic and unspontaneous, while the endothermic nature of the reaction was confirmed by the positive value (16.6 kJ/mol) of the ΔH. The thermodynamic information and kinetic model reported here will provide valuable insight into the understanding of the in situ transesterification process from algae foamate to biodiesel.

Ultrasound for microalgal cell disruption and product extraction: A review

Microalgae are a promising feedstock for the production of biofuels, nutraceuticals, pharmaceuticals and cosmetics, due to their superior capability of converting solar energy and CO₂ 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.

Liquid wastes as a renewable feedstock for yeast biodiesel production: Opportunities and challenges

Microbial lipids (bacterial, yeast, or algal) production and its utilization as a feedstock for biodiesel production in a sustainable and economical way along with waste degradation is a promising technology. Oleaginous yeasts have demonstrated multiple advantages over algae and bacteria such as high lipid yields, lipid similarity to vegetable oil, and requirement of lesser area for cultivation. Oleaginous yeasts grown on lignocellulosic solid waste as renewable feedstocks have been widely reported and reviewed. Recently, industrial effluents and other liquid wastes have been evaluated as feedstocks for biodiesel production from oleaginous yeasts. The idea of the utilization of wastewater for the growth of oleaginous yeasts for simultaneous wastewater treatment and lipid production is gaining attention among researchers. However, the detailed knowledge on the economic aspects of different process involved during the conversion of oleaginous yeast into lipids hinders its large-scale application. Therefore, this review aims to provide an overview of yeast-derived biodiesel production by utilizing industrial effluents and other liquid wastes as feedstocks. Various technologies for biomass harvesting, lipid extraction and the economic aspects specifically focused on yeast biodiesel production were also analyzed and reported in this review. The utilization of liquid wastes and the incorporation of cost-efficient harvesting and lipid extraction strategy would facilitate large-scale commercialization of biodiesel production from oleaginous yeasts in near future.

Recovering Microalgal Bioresources: A Review of Cell Disruption Methods and Extraction Technologies

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.