Extraction and fractionation of microalgae-based protein products

Seaweeds-derived proteins and peptides: preparation, virtual screening, health-promoting effects, and industry applications

Seaweed, a promising source of nutritional proteins, including protein hydrolysates, bioactive peptides, phycobiliproteins, and lectins with multi-biological activities. Seaweeds-derived proteins and peptides have attracted increasing interest for their potential applications in dietary supplements, functional foods, and pharmaceuticals industries. This work aims to comprehensively review the preparation methods and virtual screening strategies for seaweed-derived functional peptides. Additionally, it elucidates their diverse biological activities, mechanisms of action, and industrial applications. Enzymatic hydrolysis appears as the most effective method for preparing functional peptides from seaweeds. Computational virtual screening has also proven to be a valuable strategy for assessing the nature of the peptides. Seaweeds-derived proteins and peptides offer numerous health benefits, including alleviation of oxidative stress, anti-diabetic, anti-hypertensive, anti-inflammatory, anti-obesity, anti-cancer, and anti-microbial activities. Studies indicate that proteins hydrolysates and peptides derived from seaweeds with low molecular weight and aromatic and/or hydrophobic amino acids are particularly significant in contributing to these diverse bio-activities. Furthermore, seaweeds-derived proteins and peptides hold great promise for industrial applications owing to the broad spectrum of bio-functional effects. They can be used as active ingredients in food products or pharmaceuticals for disease prevention and treatment, and as food preservatives, potentially with fewer side effects.

Recent trends in edible algae functional proteins: Production, bio-functional properties, and sustainable food packaging applications

In recent years, there has been a notable surge in the development and adoption of edible algae protein-based sustainable food packaging, which presents a promising alternative to traditional materials due to its biodegradability, renewability, and minimal environmental impact. Hence, this review aims to emphasize the sources, cultivation, and downstream potential of algal protein and protein complexes. Moreover, it comprehensively examines the advancements in utilizing protein complexes for smart and active packaging applications, while also addressing the challenges that must be overcome for the widespread commercial adoption of algal proteins to meet industry 4.0. The review revealed that the diversity of algae species and their sustainable cultivation methods offers a promising alternative to traditional protein sources. Being vegan source with higher photosynthetic conversion efficiency and reduced growth cycle has permitted the proposition of algae as proteins of the future. The unique combination of techno-functional combined with bio-functional properties such as antioxidant, anti-inflammatory and antimicrobial response have captured the sustainable groups to invest considerable research and promote the innovations in algal proteins. Food packaging research has increasingly benefited by the excellent gas barrier property and superior mechanical strength of algal proteins either stand alone or in synergy with other biodegradable polymers. Advanced packaging functionality such as freshness monitoring and active preservation techniques has been explored and needs considerable characterization for commercial advancement. Overall, while algal proteins show promising downstream potential in various industries aligned with Industry 4.0 principles, their broader adoption hinges on overcoming these barriers through continued innovation and strategic development.

Interfacial structure modification and enhanced emulsification stability of microalgae protein through interaction with anionic polysaccharides

Microalgae protein (MP) have emerged as a focal point of research within food processing due to its nutritional value and foaming properties. However, its isoelectric point around pH 4 leads to it susceptible to collision, binding, and precipitation. Additionally, MP has poor emulsification properties and only shows stability under strongly alkaline conditions. This study investigated the effects of food-grade anionic polysaccharides (guar gum (GG), gum arabic (GA), low acyl gellan gum (LG), and pectin (PT)) on the molecular structure and emulsification properties of MP. Results indicated that these anionic polysaccharides enhanced the UV absorption of MP near 620 nm, especially at 14 % content, while fluorescence intensity decreased due to amino acid residues masking without structural changes. The addition of polysaccharides resulted in bimodal or multimodal particle size distributions, with LG and PT showing larger particle sizes. At pH 4, negatively charged polysaccharides formed stable complexes with near-neutral MP, improving solution stability via electrostatic repulsion and diminishing turbidity. The droplet distribution analysis indicated that higher anionic polysaccharide ratios (1:4, 1:2, and 1:1) correlated with smaller droplet sizes and increased emulsion stability. Zeta-potential measurements revealed negative charges for emulsions, with LG-MP and PT-MP complexes displaying higher absolute values (15.0 to 20.7 mV) compared to GG-MP and GA-MP complexes, indicating superior stability. Storage stability analysis showed that LG-MP and PT-MP complexes stabilized emulsions had minimal delamination over two weeks. Rheological assessments showed that increasing GG and GA contents from 14 % to 50 % had negligible effects on apparent viscosity, while LG-MP (1:1) complexes stabilized emulsion displayed higher viscosity compared to PT-MP emulsions. Frequency sweep results showed that GG-MP, GA-MP, and LG-MP emulsions had greater elastic moduli (G') than viscous moduli (G"), indicating elastic behavior, whereas PT-MP emulsions transitioned from liquid-like to solid-like behavior as frequency increased. This study illustrates the advantages of high LG and PT content in preventing particle aggregation and enhancing emulsion stability, providing a theoretical and practical foundation for MP applications in food processing.

Application research and progress of microalgae as a novel protein resource in the future

Economic growth and health awareness spotlight opportunities and challenges in the food industry, particularly with decreasing arable land, climate change, dwindling freshwater resources, and pollution affecting traditional protein sources. Microalgae have emerged as a promising alternative, with higher protein content, better nutritional quality, and greater environmental resilience compared to conventional crops. They offer a protein balance comparable to meat, making them a sustainable protein source with health benefits like antioxidants, cardiovascular support, and anti-inflammatory properties. Improving the protein content of microalgae through optimized cultivation techniques is crucial to fully realize its potential as a novel food source. While there are already microalgae-based food products in the market, challenges remain in utilizing microalgal protein for widespread food production, emphasizing the need for further research. This review article explores the impact of microalgae culture conditions on protein content, the physicochemical and nutritional characteristics of microalgal protein, the health advantages of microalgal proteins and their derivatives, as well as research on separating and purifying microalgal proteins and their derivatives. It also delves into the current opportunities and obstacles of microalgal proteins and their derivatives as food, highlighting the potential for investigating the link between microalgal protein food and human health.

Utilizing proteomics to identify and optimize microalgae strains for high-quality dietary protein: a review

Algae-derived protein has immense potential to provide high-quality protein foods for the expanding human population. To meet its potential, a broad range of scientific tools are required to identify optimal algal strains from the hundreds of thousands available and identify ideal growing conditions for strains that produce high-quality protein with functional benefits. A research pipeline that includes proteomics can provide a deeper interpretation of microalgal composition and biochemistry in the pursuit of these goals. To date, proteomic investigations have largely focused on pathways that involve lipid production in selected microalgae species. Herein, we report the current state of microalgal proteome measurement and discuss promising approaches for the development of protein-containing food products derived from algae.

Research progress in microalgae nutrients: emerging extraction and purification technologies, digestive behavior, and potential effects on human gut

Microalgae contain a diverse range of high-value compounds that can be utilized directly or fractionated to obtain components with even greater value-added potential. With the use of microalgae for food and medical purposes, there is a growing interest in their digestive properties and impact on human gut health. The extraction, separation, and purification of these components are key processes in the industrial application of microalgae. Innovative technologies used to extract and purify microalgal high-added-value compounds are key for their efficient utilization and evaluation. This review's comprehensive literature review was performed to highlight the main high-added-value microalgal components. The technologies for obtaining bioactive compounds from microalgae are being developed rapidly, various innovative, efficient, green separation and purification technologies are emerging, thus helping in the scaling-up and subsequent commercialization of microalgae products. Finally, the digestive behavior of microalgae nutrients and their health effects on the human gut microbiota were discussed. Microalgal nutrients exhibit favorable digestive properties and certain components have been shown to benefit gut microbes. The reality that must be faced is that multiple processes are still required for microalgae raw materials to final usable products, involving energy, time consumption and loss of ingredients, which still face challenges.

Methods to protein and peptide extraction from microalgae: a systematic review

Currently, there is a demand for protein sources that do not use soil management or animal breeding. Among these sources we highlight the microorganisms, such cyanobacteria and microalgae, which have a simple growth using light, CO2, water and some mineral salts to generate high protein production. The extraction of these proteins depends on the method used. The most used methods for extracting bio-functional proteins are mechanical, chemical and enzymatic. The aim of this work is to analyze the protein extraction methods in microalgae using Scielo, ScienceDirect and NCBI (PubMed) electronic databases that made it possible to select original studies published in the last five years (2018-2023). A total of 2707 articles, 25 of which were selected for further analysis and subjected to risk of bias assessment. The genera Chlorella, Scenedesmus and Nannochloropsis were the most studied due to their high protein content. Mechanical methods and chemical hydrolysis are the most used methods, achieving an extraction yield of 46.0 % and 64.0 %, respectively. The best extraction results are obtained with a combination of methods, reaching up to 80.0 % yield. However, some aspects need to be observed to choose an ideal protein extraction method.

Application and prospect of microbial food Chlorella

Modern food is evolving in the direction of green, healthy, and convenient products, and developing natural products with health benefits is an important direction for the food industry. Chlorella is rich in nutrients, such as carotene and fatty acids, which provide it with a variety of health benefits, and therefore widely used in the food industry as a health or functional food. This study reviews the research progress and specific applications of Chlorella in health, functional, and other foods, and expounds on the bottlenecks faced in the use of Chlorella in food industry. This review provides a theoretical basis for the research, utilisation, and production of new food materials involving Chlorella.

Enhancing the Biological Effects of Bioactive Compounds from Microalgae through Advanced Processing Techniques: Pioneering Ingredients for Next-Generation Food Production

The heightened interest in healthy dietary practices and the preference for fresh, minimally processed foods with reduced additives have witnessed a significant surge among consumers. Within this context, bioactive compounds have garnered attention as potent agents offering beneficial biological effects when integrated into food formulations. Nevertheless, the efficacy of these bioactive compounds in product development encounters numerous challenges during various processing and storage stages due to their inherent instability. Addressing these limitations necessitates exploring novel technological approaches tailored explicitly to the application of bioactive compounds in food production. These approaches should not only focus on preserving the bioactive compounds within food matrices but also on retaining the sensory attributes (color, taste, and aroma) of the final food products. The impact of microalgae and their bioactive compounds on human health and well-being has been extensively reported in the literature. However, there is still a gap regarding the processing and stability of microalgal bioactive compounds to improve their application in the food industry. The main goal of the present work is to point out how to overcome technological challenges in enhancing the stability of bioactive compounds from microalgae for optimal food applications.

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.

Recent developments and challenges in algal protein and peptide extraction strategies, functional and technological properties, bioaccessibility, and commercial applications

The burgeoning demand for protein, exacerbated by population growth and recent disruptions in the food supply chain, has prompted a rapid exploration of sustainable protein alternatives. Among these alternatives, algae stand out for their environmental benefits, rapid growth, and rich protein content. However, the widespread adoption of algae-derived proteins faces significant challenges. These include issues related to harvesting, safety, scalability, high cost, standardization, commercialization, and regulatory hurdles. Particularly daunting is the efficient extraction of algal proteins, as their resilient cell walls contain approximately 70% of the protein content, with conventional methods accessing only a fraction of this. Overcoming this challenge necessitates the development of cost-effective, scalable, and environmentally friendly cell disruption techniques capable of breaking down these rigid cell walls, often laden with viscous polysaccharides. Various approaches, including physical, chemical, and enzymatic methods, offer potential solutions, albeit with varying efficacy depending on the specific algal strain and energy transfer efficiency. Moreover, there remains a pressing need for further research to elucidate the functional, technological, and bioaccessible properties of algal proteins and peptides, along with exploring their diverse commercial applications. Despite these obstacles, algae hold considerable promise as a sustainable protein source, offering a pathway to meet the escalating nutritional demands of a growing global population. This review highlights the nutritional, technological, and functional aspects of algal proteins and peptides while underscoring the challenges hindering their widespread adoption. It emphasizes the critical importance of establishing a sustainable trajectory for food production, with algae playing a pivotal role in this endeavor.

Microalgae Proteins as Sustainable Ingredients in Novel Foods: Recent Developments and Challenges

Microalgae are receiving increased attention in the food sector as a sustainable ingredient due to their high protein content and nutritional value. They contain up to 70% proteins with the presence of all 20 essential amino acids, thus fulfilling human dietary requirements. Microalgae are considered sustainable and environmentally friendly compared to traditional protein sources as they require less land and a reduced amount of water for cultivation. Although microalgae's potential in nutritional quality and functional properties is well documented, no reviews have considered an in-depth analysis of the pros and cons of their addition to foods. The present work discusses recent findings on microalgae with respect to their protein content and nutritional quality, placing a special focus on formulated food products containing microalgae proteins. Several challenges are encountered in the production, processing, and commercialization of foods containing microalgae proteins. Solutions presented in recent studies highlight the future research and directions necessary to provide solutions for consumer acceptability of microalgae proteins and derived products.

Challenges in Functional Food Products with the Incorporation of Some Microalgae

Much attention has been given to the use of microalgae to produce functional foods that have valuable bioactive chemicals, including essential amino acids, polyunsaturated fatty acids, vitamins, carotenoids, fiber, and minerals. Microalgal biomasses are increasingly being used to improve the nutritional values of foods because of their unique nutrient compositions that are beneficial to human health. Their protein content and amino acid composition are the most important components. The microalgal biomass used in the therapeutic supplement industry is dominated by bio-compounds like astaxanthin, β-carotene, polyunsaturated fatty acids like eicosapentaenoic acid and docosahexaenoic acid, and polysaccharides such as β-glucan. The popularity of microalgal supplements is growing because of the health benefits of their bioactive substances. Moreover, some microalgae, such as Dunaliella, Arthrospira (Spirulina), Chlorella, and Haematococcus, are commonly used microalgal species in functional food production. The incorporation of microalgal biomass leads not only to enhanced nutritional value but also to improved sensory quality of food products without altering their cooking or textural characteristics. Microalgae, because of their eco-friendly potential, have emerged as one of the most promising and novel sources of new functional foods. This study reviews some recent and relevant works, as well as the current challenges for future research, using different methods of chemical modification in foods with the addition of a few commercial algae to allow their use in nutritional and sensory areas. It can be concluded that the production of functional foods through the use of microalgae in foods has become an important issue.

Emerging revolving algae biofilm system for algal biomass production and nutrient recovery from wastewater

Toward the direction of zero‑carbon emission and green technologies for wastewater treatment, algae-based technologies are considered promising candidates to deal with the current situation of pollution and climate change. Recent developments of algae-based technologies have been introduced in previous studies in which their performances were optimized for wastewater treatment and biomass production. Among these, revolving algae biofilm (RAB) reactors have been proven to have a great potential in high biomass productivity, simple harvesting method, great CO2 transfer rate, high light-use efficiency, heavy metal capture, nutrient removal, and acid mine drainage treatment in previous studies. However, there were few articles detailing RAB performance, which concealed its enormous potential and diminished interest in the model. Hence, this review aims to reveal the major benefit of RAB reactors in simultaneous wastewater treatment and biomass cultivation. However, there is still a lack of research on aspects to upgrade this technology which requires further investigations to improve performance or fulfill the concept of circular economy.

Microalgae cultivation for treating agricultural effluent and producing value-added products

Wastewater generated within agricultural sectors such as dairies, piggeries, poultry farms, and cattle meat processing plants is expected to reach 600 million m3 yr-1 globally. Currently, the wastewater produced by these industries are primarily treated by aerobic and anaerobic methods. However, the treated effluent maintains a significant concentration of nutrients, particularly nitrogen and phosphorus. On the other hand, the valorisation of conventional microalgae biomass into bioproducts with high market value still requires expensive processing pathways such as dewatering and extraction. Consequently, cultivating microalgae using agricultural effluents shows the potential as a future technology for producing value-added products and treated water with low nutrient content. This review explores the feasibility of growing microalgae on agricultural effluents and their ability to remove nutrients, specifically nitrogen and phosphorus. In addition to evaluating the market size and value of products from wastewater-grown microalgae, we also analysed their biochemical characteristics including protein, carbohydrate, lipid, and pigment content. Furthermore, we assessed the costs of both upstream and downstream processing of biomass to gain a comprehensive understanding of the economic potential of the process. The findings from this study are expected to facilitate further techno-economic and feasibility assessments by providing insights into optimized processing pathways and ultimately leading to the reduction of costs.

Realization process of microalgal biorefinery: The optional approach toward carbon net-zero emission

Increasing carbon dioxide (CO2) emission has already become a dire threat to the human race and Earth's ecology. Microalgae are recommended to be engineered as CO2 fixers in biorefinery, which play crucial roles in responding climate change and accelerating the transition to a sustainable future. This review sorted through each segment of microalgal biorefinery to explore the potential for its practical implementation and commercialization, offering valuable insights into research trends and identifies challenges that needed to be addressed in the development process. Firstly, the known mechanisms of microalgal photosynthetic CO2 fixation and the approaches for strain improvement were summarized. The significance of process regulation for strengthening fixation efficiency and augmenting competitiveness was emphasized, with a specific focus on CO2 and light optimization strategies. Thereafter, the massive potential of microalgal refineries for various bioresource production was discussed in detail, and the integration with contaminant reclamation was mentioned for economic and ecological benefits. Subsequently, economic and environmental impacts of microalgal biorefinery were evaluated via life cycle assessment (LCA) and techno-economic analysis (TEA) to lit up commercial feasibility. Finally, the current obstacles and future perspectives were discussed objectively to offer an impartial reference for future researchers and investors.

Phycobiliprotein Peptide Extracts from Arthrospira platensis Ameliorate Nonalcoholic Fatty Liver Disease by Modulating Hepatic Lipid Profile and Strengthening Fat Mobilization

Arthrospira platensis phycobiliprotein peptide extracts (PPEs) exhibit potential mitigative effects on hepatic steatosis. However, the precise role of PPEs in addressing high-fat-induced nonalcoholic fatty liver disease (NAFLD), as well as the underlying mechanism, remains to be elucidated. In this study, NAFLD was induced in rats through a high-fat diet (HFD), and the rats were subsequently treated with PPEs for a duration of 10 weeks. The outcomes of this investigation demonstrate that PPE supplementation leads to a reduction in body weight gain, a decrease in the accumulation of lipid droplets within the liver tissues, alterations in hepatic lipid profile, regulation of lipolysis-related gene expression within white adipose tissues and modulation of intestinal metabolites. Notably, PPE supplementation exhibits a potential to alleviate liver damage by manipulating neutral lipid metabolism and phospholipid metabolism. Additionally, PPEs appear to enhance fat mobilization by up-regulating the gene expression levels of key factors such as HSL, TGL, UCP1 and UCP2. Furthermore, PPEs impact intestinal metabolites by reducing the levels of long-chain fatty acids while concurrently increasing the levels of short-chain fatty acids. The findings from this study unveil the potential of PPE intervention in ameliorating NAFLD through the modulation of hepatic lipid profile and the reinforcement of the fat mobilization of intestinal metabolites. Thus, PPEs exhibit noteworthy therapeutic effects in the context of NAFLD.

Applications of Microalgae in Foods, Pharma and Feeds and Their Use as Fertilizers and Biostimulants: Legislation and Regulatory Aspects for Consideration

Microalgae are a rich resource of lipids, proteins, carbohydrates and pigments with nutritional and health benefits. They increasingly find use as ingredients in functional foods and feeds as well as in cosmetics and agricultural products including biostimulants. One of their distinct advantages is their ability to grow on wastewaters and other waste streams, and they are considered an environmentally friendly and cheap method to recover nutrients and remove pollutants from the environment. However, there are limits concerning their applications if grown on certain waste streams. Within, we collate an overview of existing algal applications and current market scenarios for microalgal products as foods and feeds along with relevant legislative requirements concerning their use in Europe and the United States. Microalgal compounds of interest and their extraction and processing methodologies are summarized, and the benefits and caveats of microalgae cultivated in various waste streams and their applications are discussed.

Algae as a potential source of protein meat alternatives

With the rise of plant-based meat alternatives, there is a growing need for sustainable and nutritious sources of protein. Alga is a rich protein source, and initial studies show that it can be a good component in developing protein meat alternatives. However, there are certain limitations in their use as the need for efficient and optimal technical process in large-scale protein extraction and purification, as well as overcoming certain negative effects such as potentially harmful compounds, allergenicity issues, or sensorial affections, especially in color but also in textural and flavor characteristics. This review offers a vision of the fledgling research about using alga protein in the development of meat alternatives or supplementing meat products.

Microwave treatment on structure and digestibility characteristics of Spirulina platensis protein

As a novel protein resource, the low digestibility of Spirulina platensis protein (SPP) limits its large-scale application. From the perspective of food processing methods, different heating treatments were explored to improve the structure and digestibility of SPP. In this study, SPP was heated by water bath and microwave at the same heating rate and heating temperature. Microwave accelerated protein denaturation and structure unfolded as the heating intensity increases, causing more exposed hydrophobic residues and enhancing surface hydrophobicity. The data of free sulfhydryl group, particle size, and gel electrophoresis, showed that microwave treatment promoted the formation of protein aggregates. The structural changes can potentially improve the accessibility of digestive enzymes, promote the in vitro digestibility rate, and further accelerate the production of small molecular peptides and the release of free amino acids. This study provided an innovative approach to improve the digestibility and therefore the utilization efficiency of SPP.

Valorization of environmental-burden waste towards microalgal metabolites production

The present study develops a novel concept of using waste media as an algal nutrient resource compared to the usual growth media with the aid of growth kinetics study and metabolite production abilities. Food- and agri-compost wastes are compact structures with elemental compounds for microbial media. As a part of the study, environ-burden wastes (3:1) as a food source for photosynthetic algae as a substitute for the costly nutrient media were proposed. The environment-burden waste was also envisaged for macromolecule production, i.e., 99200 μg/ml lipid, 112.5 μg/ml protein, and 8.75 μg/ml carbohydrate with different dilutions of agri-waste, bold basal media (BBM), and Food waste, respectively. The fabricated growth kinetics and dynamics showcased the unstructured models of different photosynthetic algal growth phases and the depiction of productivity and kinetic parameters. The theoretical maximum biomass concentration (Xp) was found to be more (0.871) with diluted agricompost media than the usual BBM (0.697). The X_Lim values were found to be 0.362, 0.323 and 0.209 for BBM, diluted agri-compost media and diluted food waste media, respectively. Overall, the study proposes a cleaner approach of utilizing the wastes as growth media through a circular economy approach which eventually reduces the growth media cost with integrated macromolecule production capabilities.

Nutrition, allergenicity and physicochemical qualities of food-grade protein extracts from Nannochloropsis oculata

Microalgae offer an opportunity to act as a sustainable source of dietary protein. This study aimed to evaluate the impact of different protein extraction methods on the nutritional and physicochemical properties of Nannochloropsis oculata. Food-grade protein extracts were obtained by hypotonic osmotic shock using milli-Q water. Food grade (FG) and non-food grade (NFG) extraction buffers were compared along with three cell disruption methods including bead beating, probe sonication and a combination of both methods for protein extraction. Mass spectrometry was used for protein and putative allergen identification in FG extracts. Bead beating led to a slightly higher number of identifiable proteins in FG extracts compared to control condition. Putative allergenic proteins were identified in FG extracts of N. oculata using different in-silico methods. These findings support the need to further evaluate the potential allergenic proteins in microalgae including N. oculata such as immunoglobulin E (IgE) binding tests.

Microalgae-Sustainable Source for Alternative Proteins and Functional Ingredients Promoting Gut and Liver Health

Dietary proteins derived from animal sources, although containing well-balanced profiles of essential amino acids, have considerable environmental and adverse health effects associated with the intake of some animal protein-based products. Consuming foods based on animal proteins carries a higher risk of developing non-communicable diseases such as cancer, heart disease, non-alcoholic fatty liver disease (NAFLD), and inflammatory bowel disease (IBD). Moreover, dietary protein consumption is increasing due to population growth, posing a supply challenge. There is, therefore, growing interest in discovering novel alternative protein sources. In this context, microalgae have been recognized as strategic crops that can provide a sustainable source of protein. Compared to conventional high-protein crops, using microalgal biomass for protein production presents several advantages in food and feed in terms of productivity, sustainability, and nutritional value. Moreover, microalgae positively impact the environment by not exploiting land or causing water pollution. Many studies have revealed the potential of microalgae as an alternative protein source with the added value of positive effects on human health due to their anti-inflammatory, antioxidant, and anti-cancer properties. The main emphasis of this review is on the potential health-promoting applications of microalgae-based proteins, peptides, and bioactive substances for IBD and NAFLD.

Preparation and Characterization of a Multicomponent Arthrospira platensis Biomass Hydrolysate with Superior Anti-Hypertensive, Anti-Hyperlipidemic and Antioxidant Activities via Selective Proteolysis

Arthrospira platensis biomass is a sustainable source of bioactive products for the food, cosmetic, and medicine industries. As well as primary metabolites, different secondary metabolites can be obtained via distinct enzymatic degradation of biomass. In this work, different hydrophilic extracts were obtained after treating the biomass with: (i) a serine endo-peptidase (Alcalase^®), (ii) a mixture of amino-, dipeptidyl-, and endo-peptidases (Flavourzyme^®), (iii) a mixture of endo-1,3(4)-β-glucanase and an endo-1,4-xylanase, and β-glucanase (Ultraflo^®), and (iv) an exo-1,3-glucanase (Vinoflow^®) (all the enzymes from Novozymes A/S (bagsvaerd, Denmark)); with subsequent extraction of the biocomponents with an isopropanol/hexane mixture. The composition of each aqueous phase extract (in terms of amino acids, peptides, oligo-elements, carbohydrates, and phenols) and their in vitro functional properties were compared. The conditions described in this work using the enzyme Alcalase^® permits the extraction of eight distinctive peptides. This extract is 7.3 times more anti-hypertensive, 106 times more anti-hypertriglyceridemic, 26 times more hypocholesterolemic, has 4.4 times more antioxidant activities, and has 2.3 times more phenols, than the extract obtained without any prior enzyme biomass digestion. Alcalase^® extract is an advantageous product with potential application in functional food, pharmaceutics, and cosmetics.

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.

Influence of salinity and temperature on the growth, productivity, photosynthetic activity and intracellular ROS of two marine microalgae and cyanobacteria

Global Climate Change could change physical parameters in oceans, such as salinity and temperature. The impact of such changes in phytoplankton has not been well stated yet. In this study the effect of combination of three levels of temperature (20, 23, and 26 °C), and three levels of salinity (33, 36, and 39) on growth of a mixture co-cultivation of three common species from phytoplankton (one cyanobacteria, Synechococcus sp., and two microalgae, Chaetoceros gracilis, and Rhodomonas baltica), is monitored by flow cytometry under controlled cultivation conditions in a 96 h study. Chlorophyll content, enzymes activities and oxidative stress were also measured. Results demonstrate that cultures of Synechococcus sp. Exhibited a high growth at the highest temperature chosen in this study (26 °C) combined with the three selected salinity levels 33, 36, and 39. Nevertheless, Chaetoceros gracilis grew very slowly with the combination of high temperature (39 °C) and all salinities, while Rhodomonas baltica did not grow at temperatures higher than 23 °C. Maximum dry biomass and ash-free dry weight for the microalgal mixture were reached at salinity of 39 and temperature of 20 °C, the but highest chlorophyll fluorescence values were found at 30 salinity and 20 °C, decreasing as salinity and temperature increased.

Dark fermentation and microalgae cultivation coupled systems: Outlook and challenges

The implementation of a sustainable bio-based economy is considered a top priority today. There is no doubt about the necessity to produce renewable bioenergy and bio-sourced chemicals to replace fossil-derived compounds. Under this scenario, strong efforts have been devoted to efficiently use organic waste as feedstock for biohydrogen production via dark fermentation. However, the technoeconomic viability of this process needs to be enhanced by the valorization of the residual streams generated. The use of dark fermentation effluents as low-cost carbon source for microalgae cultivation arises as an innovative approach for bioproducts generation (e.g., biodiesel, bioactive compounds, pigments) that maximizes the carbon recovery. In a biorefinery context, after value-added product extraction, the spent microalgae biomass can be further valorised as feedstock for biohydrogen production. This integrated process would play a key role in the transition towards a circular economy. This review covers recent advances in microalgal cultivation on dark fermentation effluents (DFE). BioH₂ via dark fermentation processes and the involved metabolic pathways are detailed with a special focus on the main aspects affecting the effluent composition. Interesting traits of microalgae and current approaches to solve the challenges associated to the integration of dark fermentation and microalgae cultivation are also discussed.

Microalgal bioactive metabolites as promising implements in nutraceuticals and pharmaceuticals: inspiring therapy for health benefits

The rapid increase in global population and shrinkage of agricultural land necessitates the use of cost-effective renewable sources as alternative to excessive resource-demanding agricultural crops. Microalgae seem to be a potential substitute as it rapidly produces large biomass that can serve as a good source of various functional ingredients that are not produced/synthesized inside the human body and high-value nonessential bioactive compounds. Microalgae-derived bioactive metabolites possess various bioactivities including antioxidant, anti-inflammatory, antimicrobial, anti-carcinogenic, anti-hypertensive, anti-lipidemic, and anti-diabetic activities, thereof rapidly elevating their demand as interesting option in pharmaceuticals, nutraceuticals and functional foods industries for developing new products. However, their utilization in these sectors has been limited. This demands more research to explore the functionality of microalgae derived functional ingredients. Therefore, in this review, we intended to furnish up-to-date knowledge on prospects of bioactive metabolites from microalgae, their bioactivities related to health, the process of microalgae cultivation and harvesting, extraction and purification of bioactive metabolites, role as dietary supplements or functional food, their commercial applications in nutritional and pharmaceutical industries and the challenges in this area of research.

Graphical abstract

Fourier Transform Infrared Spectrometry Detection of Phaeodactylum tricornutum Biomacromolecules in Response to Environmental Changes

Environmental factors play an important role in the lipid, protein, and carbohydrate compositions of microalgae, wherein temperature and light are key influencing factors. Fourier transform infrared (FTIR) spectrometry was used in this study to detect biomacromolecules in Phaeodactylum tricornutum cells under different temperatures (10, 15, 20, and 25 °C) and different illumination conditions (1000, 2000, 3000, and 4000 lx) to study the corresponding changes in lipid, protein, and carbohydrate contents. Results indicate that the biomacromolecule content at different temperatures has different patterns. Specifically, the patterns at 15 and 25 °C are similar to each other and the contents accumulate with extended culture time. However, the pattern at 20 °C is different. The carbohydrate and protein contents peaked during the early stage of the exponential phase, whereas lipid accumulation lagged behind the former two, peaking during the middle of the culture stage and then decreasing. Lipid content was analyzed by transmission electron microscopy (TEM), which revealed that the highest lipid content was observed at 15 °C. Results also show that all of the lipid, protein, and carbohydrate contents in cells were the highest when the illumination was at 2000 lx and that the contents decreased with increasing illumination. By using FTIR, less samples were needed as compared to the traditional chemical quantitative detection methods. Moreover, the relative content changes of various biomacromolecules during the growth of P. tricornutum could be accurately determined by a single detection, thereby providing a new technique for the further study of metabolic mechanisms.

Effect of Electrofiltration on the Dewatering Kinetics of Arthrospira platensis and Biocompound Recovery

Arthrospira platensis (A. platensis) is a microalga with a wide range of commercial uses. One of the main concerns that needs to be addressed in microalgae biorefineries is the costs associated with the harvesting and concentration steps. Filtration has been shown to be an effective technique for concentrating microalgae and recent studies have attempted to enhance membrane filtration by applying an external electric field to the filtration cell. This study consisted of assessing the use of electrically assisted filtration (electrofiltration) at 60 A/m2 and 1 bar for the dewatering of A. platensis, as well as the effect of pretreating the microalgae with ultrasounds (US) on the filtration process. Untreated A. platensis exhibited better filtration kinetics than US-treated A. platensis, and electrofiltration was found to increase the cake dryness. More protein and pigments were present in the US-treated microalgae solution compared to the untreated microalgae, which led to the presence of higher concentrations of protein and pigments in the filtrate streams after pressure filtration at 1 bar without the application of an external electric field. Electrofiltration was found to consume less energy compared to traditional drying techniques used for A. platensis. However, electrofiltration degrades the biocompounds present in the filtrate and cake due to pH changes and other electrophoresis phenomena, which shows the need to optimize the process in future work.

Feasibility of membrane ultrafiltration as a single-step clarification and fractionation of microalgal protein hydrolysates

Protein hydrolysates are one of the most valuable products that can be obtained from lipid-extracted microalgae (LEA). The advantages of protein hydrolysates over other protein products encompass enhanced solubility, digestibility, and potential bioactivity. The development of an economically feasible process to produce protein hydrolysates depends on maximizing the recovery of hydrolyzed native protein from the lipid-extracted algal biomass and subsequent fractionation of hydrolyzed protein slurry. Previously, we reported a method for fractionation of enzymatically generated protein hydrolysates by acidic precipitation of algal cell debris and unhydrolyzed protein, precipitate wash, centrifugation, and depth filtration. The present study evaluates tangential flow ultrafiltration as a single-step alternative to centrifugation, precipitate wash, and depth filtration. The results demonstrate that the tangential flow ultrafiltration process has a potential that deserves further investigation. First, the membrane diafiltration process uses a single and easily scalable unit operation (tangential flow filtration) to separate and “wash out” hydrolyzed protein from the algal residue. Second, the protein recovery yield achieved with the tangential flow process was >70% compared to 64% previously achieved by centrifugation and depth filtration methods. Finally, protein hydrolysates obtained by membrane ultrafiltration exhibited slightly better heat and pH stability.

Recovery of Water-Soluble Compounds from Tisochrysis lutea

This work aims at studying the techno-economic feasibility to produce an extract, at a small industrial-production scale, from a Tisochrysis lutea's paste, in view of cosmetic applications. The paste was first thawed, diluted and centrifuged to get a crude water extract. Then, two successive stages of membrane filtration were carried out: the first one to essentially remove/retain the particles (cellular debris) by microfiltration and the second one to concentrate (ultrafiltration) the soluble compounds of the permeate from the previous step. The robustness of the processing chain has been demonstrated following the production of three similar extracts with more than 30 L input material each. Around 54% of the final extract was composed of proteins and carbohydrates. The final ingredient was assessed for genomic activity and showed multiple positive responses. Finally, an economic analysis was performed, which demonstrated that the major cost is linked to centrifugation step. The total manpower represents the highest cost of the OPEX categories.

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.

Microalgae-Based PUFAs for Food and Feed: Current Applications, Future Possibilities, and Constraints

Microalgae are currently considered an attractive source of highly valuable compounds for human and animal consumption, including polyunsaturated fatty acids (PUFAs). Several microalgae-derived compounds, such as ω-3 fatty acids, pigments, and whole dried biomasses are available on the market and are mainly produced by culturing microalgae in open ponds, which can be achieved with low setup and maintenance costs with respect to enclosed systems. However, open tanks are more susceptible to bacterial and other environmental contamination, do not guarantee a high reproducibility of algal biochemical profiles and productivities, and constrain massive cultivation to a limited number of species. Genetic engineering techniques have substantially improved over the last decade, and several model microalgae have been successfully modified to promote the accumulation of specific value-added compounds. However, transgenic strains should be cultured in closed photobioreactors (PBRs) to minimize risks of contamination of aquatic environments with allochthonous species; in addition, faster growth rates and higher yields of compounds of interest can be achieved in PBRs compared to open ponds. In this review, we present information collected about the major microalgae-derived commodities (with a special focus on PUFAs) produced at industrial scale, as well genetically-engineered microalgae to increase PUFA production. We also critically analyzed the main bottlenecks that make large-scale production of algal commodities difficult, as well as possible solutions to overcome the main problems and render the processes economically and environmentally safe.

Biochemical and Morphological Changes Triggered by Nitrogen Stress in the Oleaginous Microalga Chlorella vulgaris

Oleaginous microalgae have been considered promising sources of biodiesel due to their high lipid content. Nitrogen limitation/starvation is one of the most prominent strategies to induce lipid accumulation in microalgae. Nonetheless, despite numerous studies, the mechanism underlying this approach is not well understood. The aim of this study was to investigate the effect of nitrogen limitation and starvation on biochemical and morphological changes in the microalga Chlorella vulgaris FACHB-1068, thereby obtaining the optimal nitrogen stress strategy for maximizing the lipid productivity of microalgal biomass. The results showed that nitrogen limitation (nitrate concentration < 21.66 mg/L) and starvation enhanced the lipid content but generally decreased the biomass productivity, pigment concentration, and protein content in algal cells. Comparatively, 3-day nitrogen starvation was found to be a more suitable strategy to produce lipid-rich biomass. It resulted in an increased biomass production and satisfactory lipid content of 266 mg/L and 31.33%, respectively. Besides, nitrogen starvation caused significant changes in cell morphology, with an increase in numbers and total size of lipid droplets and starch granules. Under nitrogen starvation, saturated fatty acids (C-16:0, C-20:0, and C-18:0) accounted for the majority of the total fatty acids (~80%), making C. vulgaris FACHB-1068 a potential feedstock for biodiesel production. Our work may contribute to a better understanding of the biochemical and morphological changes in microalgae under nitrogen stress. Besides, our work may provide valuable information on increasing the lipid productivity of oleaginous microalgae by regulating nitrogen supply.

Application progress of bioactive compounds in microalgae on pharmaceutical and cosmetics

Microalgae is an autotrophic organism with fast growth, short reproduction cycle, and strong environmental adaptability. In recent years, microalgae and the bioactive ingredients extracted from microalgae are regarded as potential substitutes for raw materials in the pharmaceutical and the cosmetics industry. In this review, the characteristics and efficacy of the high-value components of microalgae are discussed in detail, along with the sources and extraction technologies of algae used to obtain high-value ingredients are reviewed. Moreover, the latest trends in biotherapy based on high-value algae extracts as materials are discussed. The excellent antioxidant properties of microalgae derivatives are regarded as an attractive replacement for safe and environmentally friendly cosmetics formulation and production. Through further studies, the mechanism of microalgae bioactive compounds can be understood better and reasonable clinical trials conducted can safely conclude the compliance of microalgae-derived drugs or cosmetics to be necessary standards to be marketed.

Microalgae Biomass as a New Potential Source of Sustainable Green Lubricants

Lubricants are materials able to reduce friction and/or wear of any type of moving surfaces facilitating smooth operations, maintaining reliable machine functions, and reducing risks of failures while contributing to energy savings. At present, most worldwide used lubricants are derived from crude oil. However, production, usage and disposal of these lubricants have significant impact on environment and health. Hence, there is a growing pressure to reduce demand of this sort of lubricants, which has fostered development and use of green lubricants, as vegetable oil-based lubricants (biolubricants). Despite the ecological benefits of producing/using biolubricants, availability of the required raw materials and agricultural land to create a reliable chain supply is still far from being established. Recently, biomass from some microalgae species has attracted attention due to their capacity to produce high-value lipids/oils for potential lubricants production. Thus, this multidisciplinary work reviews the main chemical-physical characteristics of lubricants and the main attempts and progress on microalgae biomass production for developing oils with pertinent lubricating properties. In addition, potential microalgae strains and chemical modifications to their oils to produce lubricants for different industrial applications are identified. Finally, a guide for microalgae oil selection based on its chemical composition for specific lubricant applications is provided.

The effect of cell disruption on the extraction of oil and protein from concentrated microalgae slurries

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.

A Combination of Aqueous Extraction and Ultrafiltration for the Purification of Phycocyanin from Arthrospira maxima

The purification of phycocyanin (PC) from Spirulina generally involves a combination of different techniques. Here, we report the results on PC yields from a combined aqueous extraction-ultrafiltration (UF) process of a strain of Arthrospira maxima cultivated in a farm devoted to producing PC with food-grade purity. Samples optimized from different biomass/solvent ratios were purified by using a polyethersulphone (PES) membrane with a molecular weight cut-off (MWCO) of 20 kDa. The UF system was operated at 2.0 ± 0.1 bar and at 24 ± 2 °C up to a volume concentration factor (VCF) of 5. A diafiltration (DF) process was conducted after UF in order to increase the PC recovery in the retentate. Samples were collected during both UF and DF processes in order to evaluate membrane productivity and PC purity. The average permeate fluxes of about 14.4 L/m²h were measured in the selected operating conditions and more than 96% of PC was rejected by the UF membrane independently ofthe extraction yields and times. The concentration of PC in the final retentate was 1.17 mg/mL; this confirmed the observed rejection and the final VCF of the process (about 5-fold when compared to the concentration of PC in the crude extract). In addition, the combination of UF and diafiltration allowed the removal of about 91.7% of the DNA from the crude extract, thereby improving the purity of the phycocyanin in the retentate fraction.

Production of microalgae with high lipid content and their potential as sources of nutraceuticals

In the current global scenario, the world is under a serious dilemma due to the increasing human population, industrialization, and urbanization. The ever-increasing need for fuels and increasing nutritional problems have made a serious concern on the demand for nutrients and renewable and eco-friendly fuel sources. Currently, the use of fossil fuels is creating ecological and economic problems. Microalgae have been considered as a promising candidate for high-value metabolites and alternative renewable energy sources. Microalgae offer several advantages such as rapid growth rate, efficient land utilization, carbon dioxide sequestration, ability to cultivate in wastewater, and most importantly, they do not participate in the food crop versus energy crop dilemma or debate. An efficient microalgal biorefinery system for the production of lipids and subsequent byproduct for nutraceutical applications could well satisfy the need. But, the current microalgal cultivation systems for the production of lipids and nutraceuticals do not offer techno-economic feasibility together with energy and environmental sustainability. This review article has its main focus on the production of lipids and nutraceuticals from microalgae, covering the current strategies used for lipid production and the major high-value metabolites from microalgae and their nutraceutical importance. This review also provides insights on the future strategies for enhanced microalgal lipid production and subsequent utilization of microalgal biomass.

GRAPHICAL ABSTRACT

GR15 peptide of S-adenosylmethionine synthase (SAMe) from Arthrospira platensis demonstrated antioxidant mechanism against H2O2 induced oxidative stress in in-vitro MDCK cells and in-vivo zebrafish larvae model

GR15 is a short molecule or peptide composed of aliphatic amino acids and possesses to have antioxidant properties. The GR15, ¹GGGAFSGKDPTKVDR¹⁵ was identified from the protein S-adenosylmethionine synthase (SAMe) expressed during the sulfur departed state of Arthrospira platensis (spirulina or cyanobacteria). The in-silico assessment and the structural features of GR15 showed its antioxidant potency. Real-time PCR analysis found the up-regulation of ApSAMe expression on day 15 against oxidative stress due to 10 mM H₂O₂ treatment in A. platensis (Ap). The antioxidant activity of GR15 was accessed by the cell-free antioxidant assays such as ABTS, SARS, HRAS and NO; the results showed dose-dependent antioxidant activity. The toxicity assay was performed in both in vitro and in vivo models, in which peptide does not exhibit any toxicity in MDCK cell and zebrafish embryos. The intercellular ROS reduction potential of GR15 peptide was also investigated in both in vitro and in vivo models including LDH assay, antioxidant enzymes (SOD and CAT), and fluorescent staining assay (DCFDA, Hochest and Acridine orange sting) was performed; the results showed that the GR15 peptide was effectively reduced the ROS level. Further, RT-PCR demonstrated that GR15 enhanced the antioxidant property and also up-regulated the antioxidant gene, thus reduced the ROS level in both in vitro and in vivo models. Based on the results obtained from this study, we propose that GR15 has the potential antioxidant ability; hence further research can be directed towards the therapeutic product or drug development against disease caused by oxidative stress.