Food commodities from microalgae

Leveraging microalgae as a sustainable ingredient for meat analogues

As the world's population and income levels continue to rise, there is a substantial increase in the demand for meat, which poses significant environmental challenges due to large-scale livestock production. This review explores the potential of microalgae as a sustainable protein source for meat analogues. The nutritional composition, functional properties, and environmental advantages of microalgae are analyzed. Additionally, current obstacles to large-scale microalgal food production are addressed, such as strain development, contamination risks, water usage, and downstream processing. The challenges associated with creating meat-like textures and flavors using techniques like extrusion and emulsion formation with microalgae are also examined. Lastly, considerations related to consumer acceptance, marketing, and regulation are summarized. By focusing on improvements in cultivation, structure, sensory attributes, and affordability, microalgae demonstrate promise as a transformative and eco-friendly protein source to enhance the next generation of meat alternatives.

Characterization of Selected Microalgae Species as Potential Sources of Nutrients and Antioxidants

Microalgae are exceptional organisms from a nutritional perspective, boasting an array of bioactive compounds that have long justified their incorporation into human diets. In this study, we explored the potential of five microalgae species: Nannochloropsis sp., Tetraselmis chuii, Chaetoceros muelleri, Thalassiosira weissflogii, and Tisochrysis lutea. We conducted comprehensive analyses of their nutritional profiles, encompassing protein content, individual amino acid composition, mineral and trace element levels, fatty acid profiles (including saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs)), polyphenol compositions, and vitamin B content. The antioxidant activity of the ethanolic extracts was evaluated using two methods: ABTS and DPPH radical scavenging assay. The total protein content of the microalgae ranged from 34.09 ± 0.39% to 42.45 ± 0.18%, with the highest concentration observed in T. weissflogii. Essential amino acids such as histidine, threonine, lysine, valine, isoleucine, leucine, phenylalanine, and methionine were present in concentrations ranging from 0.53 ± 0.02 to 12.55 ± 2.21 g/16 g N. Glutamic acid emerged as the most abundant amino acid, with concentrations ranging from 6.73 ± 0.82 to 12.55 ± 2.21 g/16 g N. Among the microalgae species, T. chuii exhibited the highest concentrations of calcium (Ca) and manganese (Mn), while C. muelleri showed prominence in magnesium (Mg), sodium (Na), and iron (Fe). T. weissflogii stood out for its potassium (K) content, and T. lutea contained notable amounts of copper (Cu), zinc (Zn), and lead (Pb). Regarding fatty acid profiles, Nannochloropsis sp. and T. chuii were predominantly composed of SFA, while C. muelleri and T. weissflogii were rich in MUFA. PUFAs dominated the fatty acid profile of T. lutea, which also exhibited the most diverse range of polyphenolic substances. We also analyzed the B vitamin content, with T. lutea displaying the highest concentrations of niacin (B3) and riboflavin (B2). Antioxidant activity was confirmed for all microalgae tested using DPPH and ABTS radical IC50 (mg/mL) converted to Trolox equivalent (TEAC). These findings underscore the substantial potential of the examined microalgae species as sources of biologically valuable substances characterized by rapid growth and relatively undemanding cultivation conditions.

Tracing the Impact of Domestic Storage Conditions on Antioxidant Activity and Lipid Profiles in the Edible Microalgae Chlorella vulgaris and Tetraselmis chui

The microalgae Chlorella vulgaris and Tetraselmis chui are valued for their nutrient-rich content, including lipids and polyunsaturated fatty acids (PUFA). However, little is known about how storage and processing affect their lipid quality. This study aimed to assess the impact of domestic storage and cooking practices in dried biomass of C. vulgaris and T. chui. Four conditions were tested: control (newly opened package), light (storage at room temperature and daily light regimen for three weeks), frozen (storage in the freezer at -20 °C for three weeks), and heated (three cycles of 90 min at 100 °C). Lipid extracts were analyzed by GC-MS and LC-MS, and antioxidant activity through DPPH and ABTS radical scavenging assays. Tested storage conditions promoted a decrease in fatty acid content and in diacyl/lyso lipid species ratios of phospholipid (PC/LPC, PE/LPE) and betaine lipids (DGTS/MGTS). Lipid extracts from light treatment showed the lowest antioxidant activity in C. vulgaris (ABTS, IC40: 104.9; DPPH, IC20: 187.9 ± 15.0), while heat affected the antioxidant activity of T. chui (ABTS, IC40: 88.5 ± 2.8; DPPH, IC20 209.4 ± 10.9). These findings underscore the impact of managing storage and processing conditions to optimize the nutritional and functional benefits of C. vulgaris and T. chui in food and feed applications.

Lactic acid fermented microalgae and cyanobacteria as a new source of lipid reducing compounds: assessment through zebrafish Nile red fat metabolism assay and untargeted metabolomics

Obesity is one of the most important threats to human health. Besides existing pharmacological or clinical interventions, novel effective and largely available solutions are still necessary. Among diverse natural resources, microalgae are well known for their complexity in the production of novel secondary metabolites. At the same time, lactic acid bacteria (LAB) are known for their capacity to metabolize, through fermentation, different matrices, and consequently to modify or produce new compounds with potential bioactivity. This work aimed to study the production of fermented microalgae and cyanobacteria, and to analyse their extracts in the zebrafish Nile red fat metabolism assay. Three microalgal species (Chlorella vulgaris, Chlorococcum sp. and Arthrospira platensis) were fermented with seven strains of LAB from 4 species (Lacticaseibacillus rhamnosus, Lacticaseibacillus casei, Lactobacillus delbrueckii bulgaricus and Lacticaseibacillus paracasei), derived from the UPCCO - University of Parma Culture Collection, Parma, Italy). All the selected strains were able to ferment the selected species of microalgae, and the most suitable substrate for LAB growth was Arthrospira platensis. Extracts from fermented Chlorella vulgaris and Chlorococcum sp. reduced significantly the neutral lipid reservoirs, which was not observed without fermentations. The strongest lipid reducing effect was obtained with Arthrospira platensis fermented with Lactobacillus delbrueckii bulgaricus 1932. Untargeted metabolomics identified some compound families, which could be related to the observed bioactivity, namely fatty acids, fatty amides, triterpene saponins, chlorophyll derivatives and purine nucleotides. This work opens up the possibility of developing novel functional foods or food supplements based on microalgae, since lactic acid fermentation enhanced the production of bioactive compounds with lipid reducing activities.

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

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

The influence of Spirulina extract on pathogenicity, immune response, and vaccine efficacy against H9N2 avian influenza virus in specific pathogen free chickens

Avian influenza (AI) viruses pose a risk to the worldwide poultry industry. Ultimately, improving the efficiency of the H9N2 vaccine is necessary to better control low-pathogenic avian influenza-H9N2 by using natural immunostimulant. Therefore, the goal of the present study was to examine varying doses of the cyanobacterium Spirulina extract on the effectiveness of H9N2 vaccine. Thus, a total of 150 specific pathogen-free (SPF) chickens were allocated into 6 groups, 25 birds each, as follow: G1, G2, and G6 were supplemented with 200, 400, and 400 mg Spirulina extract/kg feed, respectively, whilst the feed in G3, G4, and G5 were not supplemented with Spirulina extract. At 21-days-old, only the chickens in G1, G2, and G3 were vaccinated with the H9N2 AI vaccine. After 4 wk postvaccination, the chickens in G1, G2, G3, G4, and G6 were challenged with H9N2 AI Egyptian strain. The challenged virus was selected from a recent circulating Egyptian strain during 2022, and it was related to A/quail/Hong Kong/G1/97-like virus lineage and clustered with G1-B sub-lineage EGY-2 group. It had a high amino acids identity percentage of 92.6% with the A/chicken/Iran/av1221/1998 (Boehringer Ingelheim) vaccine. The results of real-time reverse-transcriptase polymerase-chain-reaction (rRT-PCR) revealed that no shedding of the virus was reported in G1, G2, G3, and G5. The supplementation of Spirulina extract in low (200 mg/kg of feed) and high (400 mg/kg of feed) concentration with the birds vaccinated with H9N2 AI vaccine (G1 and G2) induced prominent immuno-stimulatory effect in a dose dependent manner where it strongly enhanced the phagocytic activities of broilers' peripheral blood monocytes, and lysozyme at all days postvaccination (dpv) and days postchallenge (dpc) compared to other groups with significant differences at all day of experiment and 21st dpv, 28th dpv, 7th dpc, and 14th dpc, respectively. The supplementation with Spirulina extract in G1 and G2 induced the highest hemagglutination inhibition antibody titer in a dose-dependent manner at all-time intervals. The antibody titer postvaccination was significantly increased in G1 and G2 at 14th, and 21st dpv, in comparison with G3. Furthermore, G1 and G2 showed higher significant antibody titers at 7th and 14th dpc, compared to other groups. Furthermore, Spirulina extract (200 and 400 mg/kg feed) in G1 and G2 showed anti-inflammatory effect in a dose dependant manner by downregulating nitric oxide levels at all times postchallenge with a significant difference at 3 to 7 dpc compared to G3, G4, and G6, with improved histopathological alterations in the trachea, lung, kidney, spleen, and bursa of Fabricius.  G6 supplied with 400 mg/kg Spirulina extract feed only without vaccination had a similar effect as vaccinated groups on innate immunity. However, it delayed the production of antibodies and did not prevent viral shedding as in vaccinated groups. In conclusion, vaccination in conjunction with either dose of Spirulina extract (G1, and G2) prevents viral shedding, increases the immune response, and reduces inflammation and histopathological change caused by H9N2 AI infection in a dose dependent manner. We recommend the use of 400 mg Spirulina extract/kg feed as a natural immunostimulant in conjunction with the H9N2 vaccine to achieve the highest possible level of protection against H9N2 AI infection.

Development and Application of an Automated Raman Sensor for Bioprocess Monitoring: From the Laboratory to an Algae Production Platform

Microalgae provide valuable bio-components with economic and environmental benefits. The monitoring of microalgal production is mostly performed using different sensors and analytical methods that, although very powerful, are limited to qualified users. This study proposes an automated Raman spectroscopy-based sensor for the online monitoring of microalgal production. For this purpose, an in situ system with a sampling station was made of a light-tight optical chamber connected to a Raman probe. Microalgal cultures were routed to this chamber by pipes connected to pumps and valves controlled and programmed by a computer. The developed approach was evaluated on Parachlorella kessleri under different culture conditions at a laboratory and an industrial algal platform. As a result, more than 4000 Raman spectra were generated and analysed by statistical methods. These spectra reflected the physiological state of the cells and demonstrate the ability of the developed sensor to monitor the physiology of microalgal cells and their intracellular molecules of interest in a complex production environment.

Effects of light quality on microalgae cultivation: bibliometric analysis, mini-review, and regulation approaches

The ever-increasing concern for energy shortages and greenhouse effect has triggered the development of sustainable green technologies. Microalgae have received more attention due to the characteristics of biofuel production and CO2 fixation. From the perspective of autotrophic growth, the optimization of light quality has the potential to promote biomass production and bio-component accumulation in microalgae at low cost. In this study, bibliometric analysis was used to describe the basic features, identify the hotspots, and predict future trends of the research related to the light quality on microalgae cultivation. In addition, a mini-review referring to regulation methods of light quality was provided to optimize the framework of research. Results demonstrated that China has the greatest interest in this area. The destination of most research was to obtain biofuels and high-value-added products. Both blue and red lights were identified as the crucial spectrums for microalgae cultivation. However, sunlight is the most affordable light resource, which could not be fully utilized by microalgae through the photosynthetic process. Hence, some regulation approaches (e.g., dyes, plasmonic scattering, and carbon-based quantum dots) are proposed to increase the proportion of beneficial spectrum for enhancement of photosynthetic efficiency. In summary, this review introduces state-of-the-art research and provides theoretical guidance for light quality optimization in microalgae cultivation to obtain more benefits.

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.

White and honey Chlorella vulgaris: Sustainable ingredients with the potential to improve nutritional value of pork frankfurters without compromising quality

This study aimed to evaluate the effect of the chlorophyll-deficient microalgae mutants, honey (yellow) and white Chlorella vulgaris, (3%) on the nutritional, physicochemical, microbiological, and sensory characteristics of frankfurters. The presence of microalgae resulted in increased PUFA content and higher PUFA/SFA ratio, but lower n-6/n-3 ratio and lipid indices (P < 0.05). C. vulgaris inclusion in frankfurters increased (P < 0.05) Na, K, Ca, P, and Zn and improved the Na/K ratio, but lowered Mn, and in the case of white C. vulgaris, Cu content, compared to the control. The higher protein content decreased water release from emulsions elaborated with microalgae. White C. vulgaris inclusion decreased cohesiveness and springiness of the frankfurters. Due to the presence of pigment, microalgae inclusion led to a decrease in redness and an increase in yellowness of frankfurters. The presence of microalgae resulted in lower (P < 0.05) bacterial counts and did not affect TBARs during storage. The addition of microalgae in frankfurters produced acceptable sensory characteristics but resulted in lower scores compared to reference products.

Recent developments in the production and utilization of photosynthetic microorganisms for food applications

The growing use of photosynthetic microorganisms for food and food-related applications is driving related biotechnology research forward. Increasing consumer acceptance, high sustainability, demand of eco-friendly sources for food, and considerable global economic concern are among the main factors to enhance the focus on the novel foods. In the cases of not toxic strains, photosynthetic microorganisms not only provide a source of sustainable nutrients but are also potentially healthy. Several published studies showed that microalgae are sources of accessible protein and fatty acids. More than 400 manuscripts were published per year in the last 4 years. Furthermore, industrial approaches utilizing these microorganisms are resulting in new jobs and services. This is in line with the global strategy for bioeconomy that aims to support sustainable development of bio-based sectors. Despite the recognized potential of the microalgal biomass value chain, significant knowledge gaps still exist especially regarding their optimized production and utilization. This review highlights the potential of microalgae and cyanobacteria for food and food-related applications as well as their market size. The chosen topics also include advanced production as mixed microbial communities, production of high-value biomolecules, photoproduction of terpenoid flavoring compounds, their utilization for sustainable agriculture, application as source of nutrients in space, and a comparison with heterotrophic microorganisms like yeast to better evaluate their advantages over existing nutrient sources. This comprehensive assessment should stimulate further interest in this highly relevant research topic.

Growth and fatty acid distribution over lipid classes in Nannochloropsis oceanica acclimated to different temperatures

After light, temperature is the most relevant environmental parameter in outdoors cultivation of microalgae. Suboptimal and supraoptimal temperatures negatively impact growth and photosynthetic performance with a subsequent effect on lipid accumulation. It is generally recognised that lower temperatures trigger an increase in fatty acid desaturation while higher temperatures trigger the opposite reaction. The effect of temperature on lipid classes has been less studied in microalgae and in certain cases, the effect of light cannot be completely excluded. In this research, the effect of temperature on growth, photosynthesis, and lipid class accumulation in Nannochloropsis oceanica was studied at a fixed light gradient with a constant incident light intensity (670 μmol m^-2 s^-1). A turbidostat approach was used to achieve temperature acclimated cultures of Nannochloropsis oceanica. Optimal growth was found at 25-29°C, while growth was completely arrested at temperatures higher than 31°C and lower than 9°C. Acclimation to low temperatures triggered a decrease in absorption cross section and photosynthesis rates with a tipping point at 17°C. Reduced light absorption was correlated with a decrease in content of the plastid lipids monogalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol. The increase of diacylglyceryltrimethylhomo-serine content at lower temperatures indicated a relevant role of this lipid class in temperature tolerance. Triacylglycerol content increased at 17°C and decreased at 9°C emphasising a metabolic switch in stress response. Total and polar eicosapentaenoic acid content remained constant at 3.5 and 2.4% w/w, despite the fluctuating lipid contents. Results show an extensive mobilisation of eicosapentaenoic acid between polar lipids classes at 9°C to ensure cell survival under critical conditions.

Killing two birds with one stone: chemical and biological upcycling of polyethylene terephthalate plastics into food

Most polyethylene terephthalate (PET) plastic waste is landfilled or pollutes the environment. Additionally, global food production must increase to support the growing population. This article explores the feasibility of using microorganisms in an industrial system that upcycles PET into edible microbial protein powder to solve both problems simultaneously. Many microorganisms can utilize plastics as feedstock, and the resultant microbial biomass contains fats, nutrients, and proteins similar to those found in human diets. While microbial degradation of PET is promising, biological PET depolymerization is too slow to resolve the global plastic crisis and projected food shortages. Evidence reviewed here suggests that by coupling chemical depolymerization and biological degradation of PET, and using cooperative microbial communities, microbes can efficiently convert PET waste into food.

Developing algae as a sustainable food source

Current agricultural and food production practices are facing extreme stress, posed by climate change and an ever-increasing human population. The pressure to feed nearly 8 billion people while maintaining a minimal impact on the environment has prompted a movement toward new, more sustainable food sources. For thousands of years, both the macro (seaweed and kelp) and micro (unicellular) forms of algae have been cultivated as a food source. Algae have evolved to be highly efficient at resource utilization and have proven to be a viable source of nutritious biomass that could address many of the current food production issues. Particularly for microalgae, studies of their large-scale growth and cultivation come from the biofuel industry; however, this knowledge can be reasonably translated into the production of algae-based food products. The ability of algae to sequester CO₂ lends to its sustainability by helping to reduce the carbon footprint of its production. Additionally, algae can be produced on non-arable land using non-potable water (including brackish or seawater), which allows them to complement rather than compete with traditional agriculture. Algae inherently have the desired qualities of a sustainable food source because they produce highly digestible proteins, lipids, and carbohydrates, and are rich in essential fatty acids, vitamins, and minerals. Although algae have yet to be fully domesticated as food sources, a variety of cultivation and breeding tools exist that can be built upon to allow for the increased productivity and enhanced nutritional and organoleptic qualities that will be required to bring algae to mainstream utilization. Here we will focus on microalgae and cyanobacteria to highlight the current advancements that will expand the variety of algae-based nutritional sources, as well as outline various challenges between current biomass production and large-scale economic algae production for the food market.

Potential of Spirulina platensis as a feed supplement for poultry to enhance growth performance and immune modulation

Increase in drug resistance as well as ineffective immunization efforts against various pathogens (viruses, bacteria and fungi) pose a significant threat to the poultry industry. Spirulina is one of the most widely used natural ingredients which is becoming popular as a nutritional supplement in humans, animals, poultry and aquaculture. It contains protein, vitamins, minerals, fatty acids, pigments, and essential amino acids. Moreover, it also has considerable quantities of unique natural antioxidants including polyphenols, carotenoids, and phycocyanin. Dietary supplementation of Spirulina can beneficially affect gut microbial population, serum biochemical parameters, and growth performance of chicken. Additionally, it contains polyphenolic contents having antibacterial effects. Spirulina extracts might inhibit bacterial motility, invasion, biofilm formation, and quorum sensing in addition to acting directly on the bacterium by weakening and making the bacterial cell walls more porous, subsequently resulting in cytoplasmic content leakage. Additionally, Spirulina has shown antiviral activities against certain common human or animal viruses and this capability can be considered to exhibit potential benefits against avian viruses also. Spirulan, a calcium-rich internal polysaccharide of Spirulina, is potentially responsible for its antiviral effect through inhibiting the entry of several viruses into the host cells, boosting the production of nitric oxide in macrophages, and stimulating the generation of cytokines. Comparatively a greater emphasis has been given to the immune modulatory effects of Spirulina as a feed additive in chicken which might boost disease resistance and improve survival and growth rates, particularly under stress conditions. This manuscript reviews biological activities and immune-stimulating properties of Spirulina and its potential use as a dietary supplement in poultry to enhance growth, gut health and disease resistance.

Role of microalgae in achieving sustainable development goals and circular economy

In 2015, the United Nations General Assembly (UNGA) set out 17 Sustainable Development Goals (SDGs) to be achieved by 2030. These goals highlight key objectives that must be addressed. Each target focuses on a unique perspective crucial to meeting these goals. Social, political, and economic issues are addressed to comprehensively review the main issues combating climate change and creating sustainable and environmentally friendly industries, jobs, and communities. Several mechanisms that involve judicious use of biological entities are among instruments that are being explored to achieve the targets of SDGs. Microalgae have an increasing interest in various sectors, including; renewable energy, food, environmental management, water purification, and the production of chemicals such as biofertilizers, cosmetics, and healthcare products. The significance of microalgae also arises from their tendency to consume CO2, which is the main greenhouse gas and the major contributor to the climate change. This work discusses the roles of microalgae in achieving the various SDGs. Moreover, this work elaborates on the contribution of microalgae to the circular economy. It was found that the microalgae contribute to all the 17th SDGs, where they directly contribute to 9th of the SDGs and indirectly contribute to the rest. The major contribution of the Microalgae is clear in SDG-6 "Clean water and sanitation", SDG-7 "Affordable and clean energy", and SDG-13 "Climate action". Furthermore, it was found that Microalgae have a significant contribution to the circular economy.

Simultaneous photoautotrophic production of DHA and EPA by Tisochrysis lutea and Microchloropsis salina in co-culture

Marine microalgae have received much attention as a sustainable source of the two health beneficial omega-3-fatty acids docosahexaenoic acid (DHA, C22:6) and eicosapentaenoic acid (EPA, C20:5). However, photoautotrophic monocultures of microalgae can only produce either DHA or EPA enriched biomass. An alternative may be the photoautotrophic co-cultivation of Tisochrysis lutea as DHA-producer with Microchloropsis salina for simultaneous EPA production to obtain EPA- and DHA-rich microalgae biomass in a nutritionally balanced ratio. Photoautotrophic co-cultivation processes of T. lutea and M. salina were studied, applying scalable and fully controlled lab-scale gas-lift flat-plate photobioreactors with LED illumination for dynamic climate simulation of a repeated sunny summer day in Australia [day-night cycles of incident light (PAR) and temperature]. Monocultures of both marine microalgae were used as reference batch processes. Differences in the autofluorescence of both microalgae enabled the individual measurement, of cell distributions in co-culture, by flow cytometry. The co-cultivation of T. lutea and M. salina in artificial sea water with an inoculation ratio of 1:3 resulted in a balanced biomass production of both microalgae simultaneously with a DHA:EPA ratio of almost 1:1 (26 mgDHA gCDW-1, and 23 mgEPA gCDW-1, respectively) at harvest after depletion of the initially added fertilizer. Surprisingly, more microalgae biomass was produced within 8 days in co-cultivation with an increase in the cell dry weight (CDW) concentration by 31%, compared to the monocultures with the same amount of light and fertilizer. What is more, DHA-content of the microalgae biomass was enhanced by 33% in the co-culture, whereas EPA-content remained unchanged compared to the monocultures.

Industry chain and challenges of microalgal food industry-a review

Currently, the whole world is facing hunger due to the increase in the global population and the rising level of food consumption. Unfortunately, the impact of environmental, climate, and political issues on agriculture has resulted in limited global food resources. Thus, it is important to develop new food sources that are environmentally friendly and not subject to climate or space limitations. Microalgae represent a potential source of nutrients and bioactive components for a wide range of high-value products. Advances in cultivation and genetic engineering techniques provide prospective approaches to widen their application for food. However, there are currently problems in the microalgae food industry in terms of assessing nutritional value, selecting processes for microalgae culture, obtaining suitable commercial strains of microalgae, etc. Additionally, the limitations of real data of market opportunities for microalgae make it difficult to assess their actual potential and to develop a better industrial chain. This review addresses the current status of the microalgae food industry, the process of commercializing microalgae food and breeding methods. Current research progress in addressing the limitations of microalgae industrialization and future prospects for developing microalgae food products are discussed.

Life cycle assessment of microalgal biorefinery: A state-of-the-art review

Microalgal biorefineries represent an opportunity to economically and environmentally justify the production of bioproducts. The generation of bioproducts within a biorefinery system must quantitatively demonstrate its viability in displacing traditional fossil-based refineries. To this end, several works have conducted life cycle analyses on microalgal biorefineries and have shown technological bottlenecks due to energy-intensive processes. This state-of-the-art review covers different studies that examined microalgal biorefineries through life cycle assessments and has identified strategic technologies for the sustainable production of microalgal biofuels through biorefineries. Different metrics were introduced to supplement life cycle assessment studies for the sustainable production of microalgal biofuel. Challenges in the comparison of various life cycle assessment studies were identified, and the future design choices for microalgal biorefineries were established.

Growth of Spirulina Maxima in an Optimized Concentric Internal Tube Photobioreactor

BACKGROUND

Microalgae have the potential to generate high-value products. The design of photobioreactors (PBRs), in which microalgae are cultured, is crucial because alterations in their configuration and operational conditions can affect the biomass production and productivity.

OBJECTIVE

The objective of this study was to optimize the diameter of the internal tube of an airlift PBR and to characterize the growth of Spirulina maxima in an optimized design.

MATERIAL AND METHODS

S. maxima was cultured in a mineral medium without an organic carbon source. The PBR consisted of an acrylic cylinder with an operational volume of 7 L. Daily determinations of biomass (by filtration), chlorophyll, N-NO₃ and P-PO₄ (spectrophotometrically) were carried out.

RESULTS

The use of a concentric tube with a diameter of 3 inches led to an increased biomass concentration of 1.14 ± 0.136 g.L_-1, allowing a global biomass productivity of 153 mg.L_-1.d_-1. The culture reached a volumetric consumption velocity of 27.34 ± 1.596 and 2.29 ± 0.353 mg.L_-1.d_-1 for N and P, respectively.

CONCLUSIONS

It was concluded that operational conditions must be specifically selected for each cultivated strain and that this configuration of airlift PBR can produce Spirulina biomass under laboratory conditions with a high biomass productivity.

Progress towards a targeted biorefinery of Chromochloris zofingiensis: a review

Biorefinery approaches offer the potential to improve the economics of the microalgae industry by producing multiple products from a single source of biomass. Chromochloris zofingiensis shows great promise for biorefinery due to high biomass productivity and a diverse range of products including secondary carotenoids, predominantly astaxanthin; lipids such as TAGs; carbohydrates including starch; and proteins and essential amino acids. Whilst this species has been demonstrated to accumulate multiple products, the development of an integrated downstream process to obtain these is lacking. The objective of this review paper is to assess the research that has taken place and to identify the steps that must be taken to establish a biorefinery approach for C. zofingiensis. In particular, the reasons why C. zofingiensis is a promising species to target for biorefinery are discussed in terms of cellular structure, potential products, and means to accumulate desirable components via the alteration of culture conditions. Future advances and the challenges that lie ahead for successful biorefinery of this species are also reviewed along with potential solutions to address them.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13399-022-02955-7.

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.

Design of melanogenesis regulatory peptides derived from phycocyanin of the microalgae Spirulina platensis

Pigmentation issues are common conditions associated with excessive or insufficient production of melanin. Recently peptides are investigated to discover novel melanogenesis regulators as low molecular weight compounds to regulate skin pigmentation. In this study, an internal library of peptides obtained through in silico enzymatic digestion of phycocyanin from microalgae S. platensis was tested to apprehend their anti-melanogenic effects. Seven peptides were investigated for their inhibitory potential against mushroom and B16-F10 murine tyrosinase enzymes. According to the results, P5 (SPSWY) and P7 (AADQRGKDKCARDIGY) were effective in lowering the activity of mushroom and B16-F10 tyrosinases. P5 was the most potent (IC₅₀ value, 12.1 µM) in mushroom which was followed by P2 (MAACLR, 86.9 µM). Although the peptides were particularly powerful in inhibiting monophenolase activity, only moderate inhibition was observed for diphenolase activity in mushroom tyrosinase assay. Apart from tyrosinase inhibition, P2 and P3 (RCLNGRL) were efficient DPPH radical scavengers at low concentrations (IC₅₀ < 200 µM). In the mammalian assay system, P5 and P7 were noticeably effective to decrease tyrosinase enzyme activity with IC₅₀ values of 48.9 and 34.2 µM, respectively. However, although P4 (RYVTYAVF) was a potent mushroom tyrosinase inhibitor, it increased melanin synthesis up to 3-fold in B16-F10 cells. The results indicate that C-terminal tyrosine residue is important for tyrosinase inhibition. This study shows, for the first time, that microalgae proteins can be regarded as sources for melanogenesis regulation.

Production, Processing, and Protection of Microalgal n-3 PUFA-Rich Oil

Microalgae have been increasingly considered as a sustainable “biofactory” with huge potentials to fill up the current and future shortages of food and nutrition. They have become an economically and technologically viable solution to produce a great diversity of high-value bioactive compounds, including n-3 polyunsaturated fatty acids (PUFA). The n-3 PUFA, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), possess an array of biological activities and positively affect a number of diseases, including cardiovascular and neurodegenerative disorders. As such, the global market of n-3 PUFA has been increasing at a fast pace in the past two decades. Nowadays, the supply of n-3 PUFA is facing serious challenges as a result of global warming and maximal/over marine fisheries catches. Although increasing rapidly in recent years, aquaculture as an alternative source of n-3 PUFA appears insufficient to meet the fast increase in consumption and market demand. Therefore, the cultivation of microalgae stands out as a potential solution to meet the shortages of the n-3 PUFA market and provides unique fatty acids for the special groups of the population. This review focuses on the biosynthesis pathways and recombinant engineering approaches that can be used to enhance the production of n-3 PUFA, the impact of environmental conditions in heterotrophic cultivation on n-3 PUFA production, and the technologies that have been applied in the food industry to extract and purify oil in microalgae and protect n-3 PUFA from oxidation.

An overview of microalgae biomass as a sustainable aquaculture feed ingredient: food security and circular economy

Sustainable management of natural resources is critical to food security. The shrimp feed and fishery sector is expanding rapidly, necessitating the development of alternative sustainable components. Several factors necessitate the exploration of a new source of environmentally friendly and nutrient-rich fish feed ingredients. Microalgal biomass has the potential to support the growth of fish and shrimp aquaculture for global food security in the bio-economy. Algal biorefineries must valorize the whole crop to develop a viable microalgae-based economy. Microalgae have the potential to replace fish meal and fish oil in aquaculture and ensure sustainability standards. Microalgae biomasses provide essential amino acids, valuable triglycerides such as lipids, vitamins, and pigments, making them suitable as nutritional supplements in livestock feed formulations. Fish and microalgae have similar nutritional profiles, and digestibility is a critical aspect of the aquafeed formulation. A highly digestible feed reduces production costs, feed waste, and the risk of eutrophication. Due to low input costs, low carbon footprint, wastewater treatment benefits, and carbon credits from industrial CO₂ conversion, microalgae-based fish and shrimp feeds have the potential to provide significant economic benefits. However, several challenges must be addressed before microalgal biomass and bioproducts may be used as fish feeds, including heavy metal bioaccumulation, poor algal biomass digestion, and antinutrient effects. Knowledge of biochemical composition is limited and diverse, and information on nutritional value is scattered or contradictory. This review article presents alternative approaches that could be used in aquaculture to make microalgal biomass a viable alternative to fish meal.

Maximizing nutrient recycling from digestate for production of protein-rich microalgae for animal feed application

The integration of phototrophic microalgal production and anaerobic digestion can recycle excess nutrients across European surplus hotspots to produce protein-rich biomass for nutritional applications. However, the challenging physico-chemical properties of raw digestate constrain microalgal growth and limit digestate valorization potential. This study focused on the pre-treatment of food waste-based digestate using paper-filtration to improve its properties for cultivating Desmodesmus sp. and Chlorella vulgaris. The microalgal growth performance in paper-filtered digestate (PFD, 10 μm-pore size) was then compared to growth in membrane-filtered digestate (MFD, 0.2 μm-pore size). A microplate-based screening coupled with Cytation device assessment of PFD and MFD samples after dilution and with/without phosphorus supplementation showed that PFD was the best substrate. Moreover, phosphorus supplementation resulted in improved growth at higher digestate concentrations (5-10% v/v PFD), indicating the importance of using a balanced growth medium to increase the volumetric usage of digestate. Results were validated in a 3-L bioreactor at 10% PFD with phosphorus supplementation, reaching a biomass concentration of 2.4 g L^-1 with a protein and carbohydrate content of 67% and 13% w/w respectively. This trial indicates that paper-filtration is a promising pre-treatment technique to maximize digestate recycling and deliver a sustainable animal feed-grade protein alternative.

Perspectives of fluorescence spectroscopy for online monitoring in microalgae industry

Microalgae industrial production is viewed as a solution for alternative production of nutraceuticals, cosmetics, biofertilizers, and biopolymers. Throughout the years, several technological advances have been implemented, increasing the competitiveness of microalgae industry. However, online monitoring and real-time process control of a microalgae production factory still require further development. In this mini-review, non-destructive tools for online monitoring of cellular agriculture applications are described. Still, the focus is on the use of fluorescence spectroscopy to monitor several parameters (cell concentration, pigments, and lipids) in the microalgae industry. The development presented makes it the most promising solution for monitoring up-and downstream processes, different biological parameters simultaneously, and different microalgae species. The improvements needed for industrial application of this technology are also discussed.

Growth parameter estimation and model simulation for three industrially relevant microalgae: Picochlorum, Nannochloropsis, and Neochloris

Multiple models have been developed in the field to simulate growth and product accumulation of microalgal cultures. These models heavily depend on the accurate estimation of growth parameters. In this paper growth parameters are presented for three industrially relevant microalgae species: Nannochloropsis sp., Neochloris oleoabundans, and Picochlorum sp. (BPE23). Dedicated growth experiments were done in photobioreactors to determine the maximal biomass yield on light and maintenance rate, while oxygen evolution experiments were performed to estimate the maximal specific growth rate. Picochlorum sp. exhibited the highest specific growth rate of 4.98 ± 0.24 day⁻¹ and the lowest specific maintenance rate of 0.079 day⁻¹, whereas N. oleoabundans showed the highest biomass yield on light of 1.78 g_x·mol_ph⁻¹. The measured growth parameters were used in a simple kinetic growth model for verification. When simulating growth under light conditions as found at Bonaire (12 °N, 68° W), Picochlorum sp. displayed the highest areal biomass productivity of 32.2 g.m⁻²·day⁻¹ and photosynthetic efficiency of 2.8%. The presented growth parameters show to be accurate compared to experimental data and can be used for model calibration by scientists and industrial communities in the field.

Microalgae as a Potential Source of Bioactive Food Compounds

Microalgae are unicellular, photosynthethic organisms that can grow on diverse aquatic habitatss like ponds, lakes, rivers, oceans, waste water and humid soils. Recently, microalgae are gaining importance as renewable sources of biologically active food compounds such as polysaccharides, proteins, essential fatty acids, biopigments such as chlorophylls, carotenoids, astaxanthin, as well as vitamins and minerals.The bioactive food compounds of microalgae enable them to be part of multitude of applications in numerous industrial products for healthy life and ecosystem. This review article summarizes the applications of biologically active food compounds derived from microalgae as nutraceuticals, healthy dietary supplements, pharmaceuticals and cosmetics. Further, this review article highlights the importance of research focus on the identification and extraction of bioactive food compounds from the huge numbers of microlage that exist in nature for sustainable global food security and economy.

Genetic engineering of microalgae for enhanced lipid production

Microalgae have the potential to become microbial cell factories for lipid production. Their ability to convert sunlight and CO₂ into valuable lipid compounds has attracted interest from cosmetic, biofuel, food and feed industries. In order to make microalgae-derived products cost-effective and commercially competitive, enhanced growth rates and lipid productivities are needed, which require optimization of cultivation systems and strain improvement. Advances in genetic tool development and omics technologies have increased our understanding of lipid metabolism, which has opened up possibilities for targeted metabolic engineering. In this review we provide a comprehensive overview on the developments made to genetically engineer microalgal strains over the last 30 years. We focus on the strategies that lead to an increased lipid content and altered fatty acid profile. These include the genetic engineering of the fatty acid synthesis pathway, Kennedy pathway, polyunsaturated fatty acid and triacylglycerol metabolisms and fatty acid catabolism. Moreover, genetic engineering of specific transcription factors, NADPH generation and central carbon metabolism, which lead to increase of lipid accumulation are also reviewed.

Research advancement and commercialization of microalgae edible oil: a review

The global food crisis has led to a great deal of attention being given to microalgal oil as a sustainable natural food source. This article provides an overview of the progress and future directions in promoting the commercialization of microalgal edible oils, including microalgal triglyceride accumulation, suitable edible oil culture strategies for high nutritional value, metabolic engineering, production, and downstream technologies. The integration of the production process, biosafety, and the economic sustainability of microalgal oil production are analyzed for their critical roles in the commercialization of microalgal edible oil to provide a theoretical and scientific basis for the comprehensive development and utilization of microalgal edible oil. © 2021 Society of Chemical Industry.

Outdoor cultivation of a novel isolate of the microalgae Scenedesmus sp. and the evaluation of its potential as a novel protein crop

A Danish strain of the green microalgae Scenedesmus sp. was isolated, identified and characterized with respect to productivity under outdoor cultivation conditions at northern latitudes. The algae were cultivated outdoors in Denmark in closed tubular photobioreactors using only sunlight, simple inorganic nutrients and under ambient temperatures. The biomass composition was evaluated in terms of protein content and quality. The average volumetric and areal biomass productivity obtained for the Scenedesmus sp. isolate during outdoor cultivation was 0.083 g dry matter L^-1 and 6.40 g dm m^-2  day^-1 , respectively. Thus, productivities are comparable to data reported in the literature under similar conditions. A strain-specific nitrogen to protein conversion factor of 5.5 was determined for the Scenedesmus sp. strain enabling more accurate protein estimations from simple nitrogen determination methods like Kjeldahl analysis in the future. The protein content was determined to be 52.4% of dried biomass for this Scenedesmus strain. The sum of essential amino acids was 42% which is high compared to other microalgae. The results are compared and discussed in comparison to other microalgae and soybean as a common plant protein source.

Microalgal Lipid Extracts Have Potential to Modulate the Inflammatory Response: A Critical Review

Noncommunicable diseases (NCD) and age-associated diseases (AAD) are some of the gravest health concerns worldwide, accounting for up to 70% of total deaths globally. NCD and AAD, such as diabetes, obesity, cardiovascular disease, and cancer, are associated with low-grade chronic inflammation and poor dietary habits. Modulation of the inflammatory status through dietary components is a very appellative approach to fight these diseases and is supported by increasing evidence of natural and dietary components with strong anti-inflammatory activities. The consumption of bioactive lipids has a positive impact on preventing chronic inflammation and consequently NCD and AAD. Thus, new sources of bioactive lipids have been sought out. Microalgae are rich sources of bioactive lipids such as omega-6 and -3 polyunsaturated fatty acids (PUFA) and polar lipids with associated anti-inflammatory activity. PUFAs are enzymatically and non-enzymatically catalyzed to oxylipins and have a significant role in anti and pro-resolving inflammatory responses. Therefore, a large and rapidly growing body of research has been conducted in vivo and in vitro, investigating the potential anti-inflammatory activities of microalgae lipids. This review sought to summarize and critically analyze recent evidence of the anti-inflammatory potential of microalgae lipids and their possible use to prevent or mitigate chronic inflammation.

Fucoxanthin and docosahexaenoic acid production by cold-adapted Tisochrysis lutea

Tisochrysis lutea is an important microalgal species for fucoxanthin and docosahexaenoic acid (DHA) production with an optimum cultivation temperature of approximately 30 °C. The aim of the present work was to develop a winter strain with high productivity at 15 °C. The response of the original strain to a decrease in temperature from 30 °C to 15 °C was investigated in continuous turbidostat experiments. This was followed by adaptation for >180 days at 15 °C and 2 rounds of sorting for cells with high chlorophyll fluorescence (top 5%) using fluorescence-activated cell sorting (FACS). For the original strain the productivity of biomass, fucoxanthin, and DHA decreased by 92 %, 98 % and 85 % respectively when decreasing the temperature from 30 °C to 15 °C. In the sorted cold-adapted 'winter strain', biomass, fucoxanthin, and DHA productivities were similar to those at 30 °C. In addition, the fucoxanthin concentration increased from 1.11 to 4.24 mg g^-1 dry weight and the polar lipid fraction in total fatty acids increased from 21 % to 55 %. The winter strain showed a robust and stable phenotype after one year of cultivation, expanding the outdoor fucoxanthin and lipid production seasons for this species.

Emerging technologies for conversion of sustainable algal biomass into value-added products: A state-of-the-art review

Concerns regarding high energy demand and gradual depletion of fossil fuels have attracted the desire of seeking renewable and sustainable alternatives. Similar to but better than the first- and second-generation biomass, algae derived third-generation biorefinery aims to generate value-added products by microbial cell factories and has a great potential due to its abundant, carbohydrate-rich and lignin-lacking properties. However, it is crucial to establish an efficient process with higher competitiveness over the current petroleum industry to effectively utilize algal resources. In this review, we summarize the recent technological advances in maximizing the bioavailability of different algal resources. Following an overview of approaches to enhancing the hydrolytic efficiency, we review prominent opportunities involved in microbial conversion into various value-added products including alcohols, organic acids, biogas and other potential industrial products, and also provide key challenges and trends for future insights into developing biorefineries of marine biomass.

A critical review on different harvesting techniques for algal based biodiesel production

The fuels retrieved from renewable sources which are usually employed as both carbon and energy sources are termed as neutral based biofuels. The most promising feedstock from renewable sources with great potentiality in contributing to the inclining energy demand is microalgae. These microalgae can be harnessed readily in terms of obtaining qualitative biodiesel with greater energy consumption under limited operational cost. The process of harvesting or dewatering microalgae could be carried under single or sequential combinations of operations. The major drawback of harvesting such as huge operational cost could be lowered by increasing the level of automation than cost of investments. The present review concentrates and explores on the techno-economic analysis of the microalgal harvesting and dewatering processes on a large scale. Along with these advanced techniques enclosing the utilization of nanoparticles for harvesting has also been explored. And it also adds with the impacts of concerning facts on energy consumption, processing cost and recovery of resources during harvesting.

Valorization of microalgae biomass into bioproducts promoting circular bioeconomy: a holistic approach of bioremediation and biorefinery

The need for alternative source of fuel has demanded the cultivation of 3rd generation feedstock which includes microalgae, seaweed and cyanobacteria. These phototrophic organisms are unique in a sense that they utilise natural sources like sunlight, water and CO₂ for their growth and metabolism thereby producing diverse products that can be processed to produce biofuel, biochemical, nutraceuticals, feed, biofertilizer and other value added products. But due to low biomass productivity and high harvesting cost, microalgae-based production have not received much attention. Therefore, this review provides the state of the art of the microalgae based biorefinery approach to define an economical and sustainable process. The three major segments that need to be considered for economic microalgae biorefinery is low cost nutrient source, efficient harvesting methods and production of by-products with high market value. This review has outlined the use of various wastewater as nutrient source for simultaneous biomass production and bioremediation. Further, it has highlighted the common harvesting methods used for microalgae and also described various products from both raw biomass and delipidified microalgae residues in order to establish a sustainable, economical microalgae biorefinery with a touch of circular bioeconomy. This review has also discussed various challenges to be considered followed by a techno-economic analysis of the microalgae based biorefinery model.

Impact of dietary Chlorella vulgaris and carbohydrate-active enzymes incorporation on plasma metabolites and liver lipid composition of broilers

BACKGROUND

Chlorella vulgaris has been proposed as a sustainable green feedstock in poultry nutrition due to its ease of cultivation, minimal environmental impact and balanced nutritional composition. However, the majority of studies documents the use of C. vulgaris as a dietary supplement in broilers instead of a feed ingredient. To the best of our knowledge, no report has shown the effect of a high-level incorporation (>2 % in the diet) of C. vulgaris on plasma metabolites and hepatic lipid composition of broilers. One hundred and twenty Ross 308 male birds were housed in 40 wired-floor cages and randomly distributed by the following experimental diets at 22 days of age (n = 10) during 15 days: (1) a corn-soybean meal based diet (control); (2) based diet with 10% of C. vulgaris; (3) diet 2 supplemented with 0.005% Rovabio® Excel AP; and (4) diet 2 supplemented with 0.01% of a pre-selected four-CAZyme mixture.

RESULTS

The inclusion of C. vulgaris at 10% in the diet, regardless of the presence of exogenous CAZymes, changed plasma metabolites but did not compromise broilers growth. Plasma total lipids increased in broilers fed C. vulgaris combined with the two feed CAZymes (p < 0.001) compared with the control diet. Moreover, the supplementation with Rovabio® increased total cholesterol and LDL-cholesterol, while the addition of the four-CAZyme mixture increased triacylglycerols, VLDL-cholesterol and ALP activity. In opposition, HDL-cholesterol levels decreased in broilers fed microalga alone (p = 0.002). Regarding hepatic composition, the inclusion of C. vulgaris in broiler diets, individually or combined with exogenous CAZymes, had a minor effect on fatty acids but improved the n-6/n-3 ratio and total carotenoids.

CONCLUSIONS

In summary, the inclusion of a high level (10%) of C. vulgaris in broiler´s diet, regardless of the presence of exogenous CAZymes, improved hepatic antioxidant composition and did not impair broiler's performance. In addition, the feed supplementation with CAZymes increased broilers lipemia. Therefore, dietary C. vulgaris at this incorporation level seems to be safe for animal health and do not compromise performance traits, with no need of CAZymes supplementation.

Year-Round Cultivation of Tetraselmis sp. for Essential Lipid Production in a Semi-Open Raceway System

There is increasing demand for essential fatty acids (EFAs) from non-fish sources such as microalgae, which are considered a renewable and sustainable biomass. The open raceway system (ORS) is an affordable system for microalgae biomass cultivation for industrial applications. However, seasonal variations in weather can affect biomass productivity and the quality of microalgal biomass. The aim of this study was to determine the feasibility of year-round Tetraselmis sp. cultivation in a semi-ORS in Korea for biomass and bioactive lipid production. To maximize biomass productivity of Tetraselmis sp., f medium was selected because it resulted in a significantly higher biomass productivity (1.64 ± 0.03 g/L) and lower omega-6/omega-3 ratio (0.52/1) under laboratory conditions than f/2 medium (0.70/1). Then, we used climatic data-based building information modeling technology to construct a pilot plant of six semi-ORSs for controlling culture conditions, each with a culture volume of 40,000 L. Over 1 year, there were no significant variations in monthly biomass productivity, fatty acid composition, or the omega-6/omega-3 ratio; however, the lipid content correlated significantly with photosynthetic photon flux density. During year-round cultivation from November 2014 to October 2017, areal productivity was gradually increased by increasing medium salinity and injecting CO₂ gas into the culture medium. Productivity peaked at 44.01 g/m²/d in October 2017. Throughout the trials, there were no significant differences in average lipid content, which was 14.88 ± 1.26%, 14.73 ± 2.44%, 12.81 ± 2.82%, and 13.63 ± 3.42% in 2014, 2015, 2016, and 2017, respectively. Our results demonstrated that high biomass productivity and constant lipid content can be sustainably maintained under Korean climate conditions.

Magnetic fields exhibit a positive impact on lipid and biomass yield during phototrophic cultivation of Spirulina sp

This study aimed to investigate the effects of magnetic field (MF) application (1, 12 and 24 h day ^-1) to Spirulina sp. LEB 18 in different photosynthesis cycles (dark and/or light) during short (15 days) and long periods (50 days) of cultivation. MF application was performed via two sources: ferrite magnets and solenoids. At the end of cultivation, the biomass was characterized in terms of lipids, proteins, and carbohydrates. In the 15 day cultures, the highest maximum biomass concentrations (2.06 g L^-1 and 1.83 g L^-1) were observed when 30 mT was applied for 24 h day ^-1 or 12 h day ^-1 (on the light cycle), respectively. MF application throughout cultivation (24 h day ^-1) for more than 30 days is not recommended. In all conditions, there was an increase in the lipid concentration (from 14 to 45%). The protein profile suggested important changes in photosystems I and II due to MF application. Cell morphology was not altered by MF application. In conclusion, the effects on the metabolism of Spirulina sp. are directly related to the photosynthesis cycle and time period in which the MF was applied.

Sustained Photosynthesis and Oxygen Generation of Microalgae-Embedded Silk Fibroin Hydrogels

Microalgae immobilized in hydrogels offer advantages over those cultured in suspension culture in terms of carbon fixation and oxygen emission. However, alginate as a commonly used hydrogel for microalgal immobilization encounters problems with mechanical strength and stability. To address this limitation, silk fibroin (silk) hydrogels prepared by ultrasonication were utilized to host microalgae when mixed with the presonicated protein solution prior to its gelation. The gelation time, stability, and light transmission of these silk gels were evaluated, and a silk concentration of 4% w/v and a gel thickness of 1 mm provided mechanical strength and stability during algal culture in comparison to alginate hydrogels. Furthermore, silk hydrogels with algal cell densities of 7.6 × 10⁵ and 7.8 × 10⁷ cells/mL had better stability than those with a lower cell density (3.2 × 10³ cells/mL), likely due to cell confinement and impact on proliferation. The silk hydrogels with microalgae at a high density generated 6.13 mg/L of oxygen continuously for 7 days. An oxygen-generating device was fabricated by coating the surface of a dialysis tube with a thin layer of the microalgae-embedded silk hydrogel, where the microalgal cells were nourished with culture medium prefilled in the dialysis tube. When suspended in a sealed flask filled with CO₂ gas, the system continuously produced oxygen (151 mL) for at least 60 days, with an oxygen production efficiency 6 times that of microalgal suspension culture controls. This microalgae embedding and cultivation technique could have potential utility in air purification, tissue repair, and other applications due to the efficient and sustained generation of oxygen.