Enhancing lutein productivity of an indigenous microalga Scenedesmus obliquus FSP-3 using light-related strategies

Strategies for producing high value small molecules in microalgae

Eukaryotic microalgae are a diverse group of organisms that can be used for the sustainable production of a wide range of high value compounds, including lipids, flavours and dyes, bioplastics, and cosmetics. Optimising total biomass production often does not lead to optimal product yield and more sophisticated biphasic growth strategies are needed, introducing specific stresses to induce product synthesis. Genetic tools have been used to increase yields of natural products or to introduce new pathways to algae, and wider deployment of these tools offers promising routes for commercial production of high value compounds utilising minimal inputs.

Evolving perspectives on lutein production from microalgae - A focus on productivity and heterotrophic culture

Increased consumer awareness for healthier and more sustainable products has driven the search for naturally sourced compounds as substitutes for chemically synthesized counterparts. Research on pigments of natural origin, such as carotenoids, particularly lutein, has been increasing for over three decades. Lutein is recognized for its antioxidant and photoprotective activity. Its ability to cross the blood-brain barrier allows it to act at the eye and brain level and has been linked to benefits for vision, cognitive function and other conditions. While marigold flower is positioned as the only crop from which lutein is extracted from and commercialized, microalgae are proposed as an alternative with several advantages over this terrestrial crop. The main barrier to scaling up lutein production from microalgae to the commercial level is the low productivity compared to the high costs. This review explores strategies to enhance lutein production in microalgae by emphasizing the overall productivity over lutein content alone. Evaluation of how culture parameters, such as light quality, nitrogen sufficiency, temperature and even stress factors, affect lutein content and biomass development in batch phototrophic cultures was performed. Overall, the total lutein production remains low under this metabolic regime due to the low biomass productivity of photosynthetic batch cultures. For this reason, we describe findings on microalgal cultures grown under different metabolic regimes and culture protocols (fed-batch, pulse-feed, semi-batch, semi-continuous, continuous). After a careful literature examination, two-step heterotrophic or mixotrophic cultivation strategies are suggested to surpass the lutein productivity achieved in single-step photosynthetic cultures. Furthermore, this review highlights the urgent need to develop technical feasibility studies at a pilot scale for these cultivation strategies, which will strengthen the necessary techno-economic analyses to drive their commercial production.

Light Intensity Enhances the Lutein Production in Chromochloris zofingiensis Mutant LUT-4

Chromochloris zofingiensis, a unicellular green alga, is a potential source of natural carotenoids. In this study, the mutant LUT-4 was acquired from the chemical mutagenesis pool of C. zofingiensis strain. The biomass yield and lutein content of LUT-4 reached 9.23 g·L-1, and 0.209% of dry weight (DW) on Day 3, which was 49.4%, and 33% higher than that of wild-type (WT), respectively. The biomass yields of LUT-4 under 100, 300, and 500 µmol/m2/s reached 8.4 g·L-1, 7.75 g·L-1, and 6.6 g·L-1, which was 10.4%, 21%, and 29.6% lower compared with the control, respectively. Under mixotrophic conditions, the lutein yields were significantly higher than that obtained in the control. The light intensity of 300 µmol/m2/s was optimal for lutein biosynthesis and the content of lutein reached 0.294% of DW on Day 3, which was 40.7% more than that of the control. When LUT-4 was grown under 300 µmol/m2/s, a significant increase in expression of genes implicated in lutein biosynthesis, including phytoene synthase (PSY), phytoene desaturase (PDS), and lycopene epsilon cyclase (LCYe) was observed. The changes in biochemical composition, Ace-CoA, pyruvate, isopentenyl pyrophosphate (IPP), and geranylgeranyl diphosphate (GGPP) contents during lutein biosynthesis were caused by utilization of organic carbon. It was thereby concluded that 300 µmol/m2/s was the optimal culture light intensity for the mutant LUT-4 to synthesize lutein. The results would be helpful for the large-scale production of lutein.

Impact of green and blue-green light on the growth, pigment concentration, and fatty acid unsaturation in the microalga Monoraphidium braunii

The spectral composition of light is an important factor for the metabolism of photosynthetic organisms. Several blue light-regulated metabolic processes have already been identified in the industrially relevant microalga Monoraphidium braunii. However, little is known about the spectral impact on this species' growth, fatty acid (FA), and pigment composition. In this study, M. braunii was cultivated under different light spectra (white light: 400-700 nm, blue light: 400-550 nm, green light: 450-600 nm, and red light: 580-700 nm) at 25°C for 96 h. The growth was monitored daily. Additionally, the FA composition, and pigment concentration was analyzed after 96 h. The highest biomass production was observed upon white light and red light irradiation. However, green light also led to comparably high biomass production, fueling the scientific debate about the contribution of weakly absorbed light wavelengths to microalgal biomass production. All light spectra (white, blue, and green) that comprised blue-green light (450-550 nm) led to a higher degree of FA unsaturation and a greater concentration of all identified pigments than red light. These results further contribute to the growing understanding that blue-green light is an essential trigger for maximized pigment concentration and FA unsaturation in green microalgae.

A robust multinutrient kinetic model for enhanced lutein and biomass yields in mixotrophic microalgae cultivation: A step towards successful large-scale productions

Mixotrophic cultivation holds great promise to significantly enhance the productivities of biomass and valuable metabolites from microalgae. In this study, a new kinetic model is developed, explicitly describing the effect of the most influential environmental factors on both biomass growth and the production of the high-value product lutein. This extensive study of multinutrient kinetics for Tetradesmus obliquus in a mixotrophic regime covers various nutritional conditions. Crucial nutrients governing the model include nitrate, phosphate, and glucose. Using seven state variables and 13 unknown parameters, the model's accuracy was ensured through a well-designed two-factor, four-level experimental setup, providing ample data for reliable calibration and validation. Results accurately predict dynamic concentration profiles for all validation experiments, revealing broad applicability. Optimizing nitrogen availability led to significant increases in biomass (up to fourfold) and lutein production (up to 12-fold), with observed maximum biomass concentration of 6.80 g L-1 and lutein reaching 25.58 mg L-1. Noticeably, the model exhibits a maximum specific growth rate of 4.03 day-1, surpassing reported values for photoautotrophic and heterotrophic conditions, suggesting synergistic effects. Valuable guidance is provided for applying the method to various microalgal species and results are large-scale production-ready. Future work will exploit these results to develop real-time photobioreactor operation strategies.

Nanoplastics inhibit carbon fixation in algae: The effect of aging

Despite the considerable efforts devoted to the toxicological assessment of nanoplastics, the effect of UV-irradiation induced aging, a realistic environmental process, on the toxicity of nanoplastics toward microalgae and its underlying mechanisms remain largely unknown. Herein, this study comparatively investigated the toxicities of polystyrene nanoplastics (nano-PS) and the UV-aged nano-PS on the eukaryotic alga Chlorella vulgaris, focusing on evaluating their inhibitory effects on carbon fixation. Exposure to environmentally relevant concentrations (0.1-10 mg/L) of nano-PS caused severe damage to chloroplast, inhibited the photosynthetic efficiency and electron transport, and suppressed the activities of carbon fixation related enzymes. Multi-omics results revealed that nano-PS interfered with energy supply by disrupting light reactions and TCA cycle and hindered the Calvin cycle, thereby inhibiting the photosynthetic carbon fixation of algae. The above alterations partially recovered after a recovery period. The aged nano-PS were less toxic than the pristine ones as evidenced by the mitigated inhibitory effect on algal growth and carbon fixation. The aging process introduced oxygen-containing functional groups on the surface of nano-PS, increased the hydrophilicity of nano-PS, limited their attachment on algal cells, and thus reduced the toxicity. The findings of this work highlight the potential threat of nanoplastics to the global carbon cycle.

Effect of light stress on lutein production with associated phosphorus removal from a secondary effluent by the autoflocculating microalgae consortium BR-UANL-01

Microalgae have become promising microorganisms for generating high-value commercial products and removing pollutants in aquatic systems. This research evaluated the impact of sunlight intensity on intracellular pigment generation and phosphorus removal from secondary effluents by autoflocculating microalgae consortium BR-UANL-01 in photobioreactor culture. Microalgae were grown in a secondary effluent from a wastewater treatment plant, using a combination of low and high light conditions (photon irradiance; 44 μmol m-2 s-1 and ≈ 1270 μmol m-2 s-1, respectively) and 16:8 h light:dark and 24:0 h light:dark (subdivided into 18:6 LED:sunlight) photoperiods. The autoflocculant rate by consortium BR-UANL-01 was not affected by light intensity and achieved 98% in both treatments. Microalgae produced significantly more lutein, (2.91 mg g-1) under low light conditions. Phosphate removal by microalgae resulted above 85% from the secondary effluent, due to the fact that phosphorus is directly associated with metabolic and replication processes and the highest antioxidant activity was obtained in ABTS•+ assay by the biomass under low light condition (51.71% μmol ET g-1). In conclusion, the results showed that the autoflocculating microalgae consortium BR-UANL-01 is capable of synthesizing intracellular lutein, which presents antioxidant activity, using secondary effluents as a growth medium, without losing its autoflocculating activity and assimilating phosphorus.

Microalgal lutein: Advancements in production, extraction, market potential, and applications

Lutein, a bioactive xanthophyll, has recently attracted significant attention for numerous health benefits, e.g., protection of eye health, macular degeneration, and acute and chronic syndromes etc. Microalgae have emerged as the best platform for high-value lutein production with high productivity, lutein content, and scale-up potential. Algal lutein possesses numerous bioactivities, hence widely used in pharmaceuticals, nutraceuticals, aquaculture, cosmetics, etc. This review highlights advances in upstream lutein production enhancement and feasible downstream extraction and cell disruption techniques for a large-scale lutein biorefinery. Besides bioprocess-related advances, possible solutions for existing production challenges in microalgae-based lutein biorefinery, market potential, and emerging commercial scopes of lutein and its potential health applications are also discussed. The key enzymes involved in the lutein biosynthesizing Methyl-Erythritol-phosphate (MEP) pathway have been briefly described. This review provides a comprehensive updates on lutein research advancements covering scalable upstream and downstream production strategies and potential applications for researchers and industrialists.

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

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

Microalgae as tools for bio-circular-green economy: Zero-waste approaches for sustainable production and biorefineries of microalgal biomass

Microalgae are promising organisms that are rapidly gaining much attention due to their numerous advantages and applications, especially in biorefineries for various bioenergy and biochemicals. This review focuses on the microalgae contributions to Bio-Circular-Green (BCG) economy, in which zero-waste approaches for sustainable production and biorefineries of microalgal biomass are introduced and their possible integration is discussed. Firstly, overviews of wastewater upcycling and greenhouse gas capture by microalgae are given. Then, a variety of valuable products from microalgal biomass, e.g., pigments, vitamins, proteins/peptides, carbohydrates, lipids, polyunsaturated fatty acids, and exopolysaccharides, are summarized to emphasize their biorefinery potential. Techno-economic and environmental analyses have been used to evaluate sustainability of microalgal biomass production systems. Finally, key issues, future perspectives, and challenges for zero-waste microalgal biorefineries, e.g., cost-effective techniques and innovative integrations with other viable processes, are discussed. These strategies not only make microalgae-based industries commercially feasible and sustainable but also reduce environmental impacts.

Lutein production from microalgae: A review

Lutein production from microalgae is a sustainable and economical strategy to offer the increasing global demands, but is still challenged with low lutein content at the high-cell density for commercial production. This review summarizes the suitable conditions for cell growth and lutein accumulation, and presents recent cultivation strategies to further improve lutein productivity. Light and nitrogen play critical roles in lutein biosynthesis that lead to the efficient multi-stage cultivation by increasing lutein content at the later stage. In addition, metabolic and genetic designs for carbon regulation and lutein biosynthesis are discussed at the molecule level. The in-situ lutein accumulation in fermenters by regulating carbon metabolism is considered as a cost-effective direction. Then, downstream processes are summarized for the efficient lutein recovery. Finally, challenges of current lutein production from microalgae are discussed. Meanwhile, potential solutions are proposed to improve lutein content and drive down costs of microalgal biomass.

Microalgae-Derived Pigments for the Food Industry

In the food industry, manufacturers and customers have paid more attention to natural pigments instead of the synthetic counterparts for their excellent coloring ability and healthy properties. Microalgae are proven as one of the major photosynthesizers of naturally derived commercial pigments, gaining higher value in the global food pigment market. Microalgae-derived pigments, especially chlorophylls, carotenoids and phycobiliproteins, have unique colors and molecular structures, respectively, and show different physiological activities and health effects in the human body. This review provides recent updates on characteristics, application fields, stability in production and extraction processes of chlorophylls, carotenoids and phycobiliproteins to standardize and analyze their commercial production from microalgae. Potential food commodities for the pigment as eco-friendly colorants, nutraceuticals, and antioxidants are summarized for the target products. Then, recent cultivation strategies, metabolic and genomic designs are presented for high pigment productivity. Technical bottlenecks of downstream processing are discussed for improved stability and bioaccessibility during production. The production strategies of microalgal pigments have been exploited to varying degrees, with some already being applied at scale while others remain at the laboratory level. Finally, some factors affecting their global market value and future prospects are proposed. The microalgae-derived pigments have great potential in the food industry due to their high nutritional value and competitive production cost.

Lutein isolated from Scenedesmus obliquus microalga boosts immunity against cyclophosphamide-induced brain injury in rats

Lutein is a naturally potent antioxidant carotenoid synthesized in green microalgae with a potent ability to prevent different human chronic conditions. To date, there are no reports of the immune-stimulating effect of pure lutein isolated from Scenedesmus obliquus. Thus, we isolated the natural lutein from S. obliquus and evaluated its effectiveness as an immunostimulant against cyclophosphamide-induced brain injury. We purified all-E-(3R, 3'R, 6'R)-Lutein from S. obliquus using prep-HPLC and characterized it by ¹H- and ¹³C-NMR spectroscopy. We assigned rats randomly to four experimental groups: the Control group got a vehicle for lutein dimethyl sulfoxide for ten successive days. The Cyclophosphamide group received a single i.p injection of Cyclophosphamide (200 mg/kg). Lutein groups received 50 and 100 (mg/kg) of lutein one time per day for ten successive days after the cyclophosphamide dose. Lutein administration reduced brain contents of Macrophage inflammatory protein2 (MIP2), cytokine-induced- neutrophil chemoattractant (CINC), and Matrix metalloproteinase 1 (MMP1). Besides, it lowered the contents of interleukin 1 beta (IL-1β) and interleukin 18 (IL-18), associated with low content of NLR pyrin domain protein 3 (NLRP3) and consequently caspase-1 compared to the cyclophosphamide group. In the histomorphometric analysis, lutein groups (50 and 100 mg/Kg) showed mild histopathological alterations as they significantly reduced nuclear pyknosis numbers by 65% and 69% respectively, compared to the cyclophosphamide group. This is the first study that showed the immunomodulatory roles of lutein against cyclophosphamide-induced brain injury via decreasing neuroinflammation, chemokines recruitment, and neuron degeneration with the modulation of immune markers. Hence, lutein can be an effective immunomodulator against inflammation-related immune disorders.

Combined effect of nitrogen and phosphorus on growth and biochemical composition of Tetradesmus obliquus (Turpin) M.J. Wynne

Microalgae have many biotechnological applications in various industries including food and feed, fertilizer, biofuel, cosmetics, pharmaceutics, and wastewater treatment. Since hey produce secondary metabolites under stress conditions such as pigments, carotenoids, hydrocarbons, and vitamins, investigating the effects of stress factors on growth parameters and biochemical composition of microalgal biomass is needed in producing bioproducts. In this paper, the combined effects of nitrogen and phosphorus on growth and the protein/amino acid and Lipid-FAMEs profiles of microalgae Tetradesmus obliquus (MAKUMACC-037) were investigated. Nitrogen and phosphorus deficiency reduced the algal growth. Biochemical composition was changed in a nitrogen and phosphorus dependent manner. High concentration of protein and lipid were associated with increased nitrogen and phosphorus concentration However, the FAMEs profiles were changed depending on only the nitrogen concentration.

Microalgae: Bioactive Composition, Health Benefits, Safety and Prospects as Potential High-Value Ingredients for the Functional Food Industry

Global population is estimated to reach about 9.22 billion by 2075. The increasing knowledge on the relationship between food biochemistry and positive health gives an indication of the urgency to exploit food resources that are not only sustainable but also impact human health beyond basic nutrition. A typical example of such novel food is microalgae, an aquatic microorganism with a plethora of diverse bioactive compounds including phenolics, carotenoids, vitamin B₁₂ and peptides. Microalgal bioactive compounds have been shown to possess positive health effects such as antihypertensive, anti-obesity, antioxidative, anticancer and cardiovascular protection. Although, the utilization of microalgal biomass by the functional food industry has faced lots of challenges because of species diversity and variations in biomass and cultivation factors. Other documented challenges were ascribed to changes in functional structures during extraction and purification due to inefficient bio-processing techniques, inconclusive literature information on the bioavailability and safety of the microalgal bioactive compounds and the fishy odor and taste when applied in food formulations. In spite of these challenges, great opportunities exist to exploit their utilization for the development of functional foods. Microalgae are a renewable resource and have fast growth rate. Therefore, detailed research is needed to bridge these challenges to pave way for large-scale commercialization of microalgal-based healthy foods. The focus of this review is to discuss the potential of microalgae as natural ingredients for functional food development, factors limiting their acceptance and utilization in the food industry as well as their safety concerns with respect to human consumption.

Microalgal Biomass as Feedstock for Bacterial Production of PHA: Advances and Future Prospects

The search for biodegradable plastics has become the focus in combating the global plastic pollution crisis. Polyhydroxyalkanoates (PHAs) are renewable substitutes to petroleum-based plastics with the ability to completely mineralize in soil, compost, and marine environments. The preferred choice of PHA synthesis is from bacteria or archaea. However, microbial production of PHAs faces a major drawback due to high production costs attributed to the high price of organic substrates as compared to synthetic plastics. As such, microalgal biomass presents a low-cost solution as feedstock for PHA synthesis. Photoautotrophic microalgae are ubiquitous in our ecosystem and thrive from utilizing easily accessible light, carbon dioxide and inorganic nutrients. Biomass production from microalgae offers advantages that include high yields, effective carbon dioxide capture, efficient treatment of effluents and the usage of infertile land. Nevertheless, the success of large-scale PHA synthesis using microalgal biomass faces constraints that encompass the entire flow of the microalgal biomass production, i.e., from molecular aspects of the microalgae to cultivation conditions to harvesting and drying microalgal biomass along with the conversion of the biomass into PHA. This review discusses approaches such as optimization of growth conditions, improvement of the microalgal biomass manufacturing technologies as well as the genetic engineering of both microalgae and PHA-producing bacteria with the purpose of refining PHA production from microalgal biomass.

Blue-green light is required for a maximized fatty acid unsaturation and pigment concentration in the microalga Acutodesmus obliquus

Blue-green light is known to maximize the degree of fatty acid (FA) unsaturation in microalgae. However, knowledge on the particular waveband responsible for this stimulation of FA desaturation and its impact on the pigment composition in microalgae remains limited. In this study, Acutodesmus obliquus was cultivated for 96 h at 15°C with different light spectra (380-700 nm, 470-700 nm, 520-700 nm, 600-700 nm, and dark controls). Growth was monitored daily, and qualitative characterization of the microalgal FA composition was achieved via gas chromatography coupled with electron impact ionization mass spectrometry (GC-EI/MS). Additionally, a quantitative analysis of microalgal pigments was performed using high-performance liquid chromatography with diode array detection (HPLC-DAD). Spectra that included wavelengths between 470 and 520 nm led to a significantly higher percentage of the polyunsaturated fatty acids (PUFA) 18:3 and 16:4, compared to all other light conditions. However, no significant differences between the red light cultivations and the heterotrophic dark controls were observed for the FA 18:3 and 16:4. These results indicate, that exclusively the blue-green light waveband between 470 and 520 nm is responsible for a maximized FA unsaturation in A. obliquus. Furthermore, the growth and production of pigments were impaired if blue-green light (380-520 nm) was absent in the light spectrum. This knowledge can contribute to achieving a suitable microalgal pigment and FA composition for industrial purposes and must be considered in spectrally selective microalgae cultivation systems.

Influence of Irradiance and Wavelength on the Antioxidant Activity and Carotenoids Accumulation in Muriellopsis sp. Isolated from the Antofagasta Coastal Desert

Microalgae are a valuable natural resource for a variety of biocompounds such as carotenoids. The use of different light spectra and irradiance has been considered as a promising option to improve the production of these compounds. The objective of this study was to evaluate the influence of different wavelengths (white, red, and blue) and irradiances (80 and 350 µmol photons/m2/s) on the photosynthetic state, total carotenoids and lutein productivity (HPLC), lipids (Nile red method) and antioxidant activity (DPPH) of the microalgae Muriellopsis sp. (MCH-35). This microalga, which is a potential source of lutein, was isolated from the coastal desert of Antofagasta, Chile, and adapted to grow in seawater. The results indicate that the culture exposed to high-intensity red light showed the highest biomass yield (2.5 g/L) and lutein productivity (>2.0 mg L−1day−1). However, blue light was found to have a stimulating effect on the synthesis of lutein and other carotenoids (>0.8% dry wt). Furthermore, a direct relationship between lipid accumulation and high light intensity was evidenced. Finally, the highest antioxidant activity was observed with high-intensity white light, these values have no direct relationship with lutein productivity. Therefore, the findings of this study could be utilized to obtain biocompounds of interest by altering certain culture conditions during the large-scale cultivation of MCH-35.

Light Stress after Heterotrophic Cultivation Enhances Lutein and Biofuel Production from a Novel Algal Strain Scenedesmus obliquus ABC-009

Scenedesmus obliquus ABC-009 is a microalgal strain that accumulates large amounts of lutein, particularly when subjected to growth-limiting conditions. Here, the performance of this strain was evaluated for the simultaneous production of lutein and biofuels under three different modes of cultivation - photoautotrophic mode using BG-11 medium with air or 2% CO₂ and heterotrophic mode using YM medium. While it was found that the highest fatty acid methyl ester (FAME) level and lutein content per biomass (%) were achieved in BG-11 medium with CO₂ and air, respectively, heterotrophic cultivation resulted in much higher biomass productivity. While the cell concentrations of the cultures grown under BG-11 and CO₂ were largely similar to those grown in YM medium, the disparity in the biomass yield was largely attributed to the larger cell volume in heterotrophically cultivated cells. Post-cultivation light treatment was found to further enhance the biomass productivity in all three cases and lutein content in heterotrophic conditions. Consequently, the maximum biomass (757.14 ± 20.20 mg/l/d), FAME (92.78 ± 0.08 mg/l/d), and lutein (1.006 ± 0.23 mg/l/d) productivities were obtained under heterotrophic cultivation. Next, large-scale lutein production using microalgae was demonstrated using a 1-ton open raceway pond cultivation system and a low-cost fertilizer (Eco-Sol). The overall biomass yields were similar in both media, while slightly higher lutein content was obtained using the fertilizer owing to the higher nitrogen content.

A novel flat-panel photobioreactor for simultaneous production of lutein and carbon sequestration by Chlorella sorokiniana TH01

Carbon dioxide is the major cause of global warming. However, it is a carbon source for phototrophic production of chemicals from microalgae. In this work, a novel flat-panel photobioreactor (FPP) was used for maximization of biomass and lutein production and CO₂ fixation by a lutein-rich C. sorokiniana TH01. CO₂ concentration, light intensity and aeration rate were optimized as 5%, 150 µmol/m²/s and 1 L/min, respectively. The highest biomass productivity, lutein productivity and CO₂ fixation efficiency were measured for indoor single and sequential FPPs were 284 - 469 mg/L/d, 2.57 - 4.57 mg/L/d, and 63 - 100%, respectively. In a climatic condition of 25.5 - 33 °C and 86 - 600 µmol/m²/s, C. sorokiniana TH01 achieved lutein productivity and CO₂ fixation efficiency of 2.1 - 3.03 mg/L/d and 56 - 81%, respectively, while the comparable biomass productivity of 284 - 419 mg/L/d was maintained. This pioneered FPP system was efficiently demonstrated for production of algal lutein from CO₂.

Aeroterrestrial and Extremophilic Microalgae as Promising Sources for Lipids and Lipid Nanoparticles in Dermal Cosmetics

Microscopic prokaryotic and eukaryotic algae (microalgae), which can be effectively grown in mass cultures, are gaining increasing interest in cosmetics. Up to now, the main attention was on aquatic algae, while species from aeroterrestrial and extreme environments remained underestimated. In these habitats, algae accumulate high amounts of some chemical substances or develop specific compounds, which cause them to thrive in inimical conditions. Among such biologically active molecules is a large family of lipids, which are significant constituents in living organisms and valuable ingredients in cosmetic formulations. Therefore, natural sources of lipids are increasingly in demand in the modern cosmetic industry and its innovative technologies. Among novelties in skin care products is the use of lipid nanoparticles as carriers of dermatologically active ingredients, which enhance their penetration and release in the skin strata. This review is an attempt to comprehensively cover the available literature on the high-value lipids from microalgae, which inhabit aeroterrestrial and extreme habitats (AEM). Data on different compounds of 87 species, subspecies and varieties from 53 genera (represented by more than 141 strains) from five phyla are provided and, despite some gaps in the current knowledge, demonstrate the promising potential of AEM as sources of valuable lipids for novel skin care products.

Biocomposites Using Whole or Valuable Component-Extracted Microalgae Blended with Polymers: A Review

Global demand for plastics has increased steadily alongside industrial development. Despite their versatility and convenience, environmental pollution caused by plastics are a major issue. With a reduction in the market size of plastics being seemingly impossible, bioplastics may become key to tackle this issue. Among a wide range of sources of bioplastics, microalgae have come into the limelight. While abundant and valuable components in microalgae have the potential to replace preexisting plastics, complex processes and low cost performances have prevented them from entering the market. In this study, we examined techniques for biocomposites in which polymers are blended with microalgae. We focused on microalgae-based biocomposite blending processed from the perspective of functionality and cost performance.

Sustainable Bioactive Packaging Based on Thermoplastic Starch and Microalgae

This study combines the use of corn starch and Tetradesmus obliquus microalgae for the production of antioxidant starch films as flexible packaging material. Starch was plasticized with glycerol and blended with 1 w% polyallylamine chosen as an agent to modify the film physical properties. The addition of polyallylamine improved film water stability and water vapor transmission rate as well as mechanical stiffness and tenacity. The dried Tetradesmus obliquus microalgae, which showed an EC₅₀ value of 2.8 mg/mg DPPH (2.2-Diphenyl-1-picrylhydrazyl radical), was then used as antioxidant filler. The addition of microalgae provided the films with good antioxidant activity, which increased with microalgae content increasing. To our knowledge, this is the first study reporting the development of sustainable bioactive packaging films composed of almost 100% starch, and follows the European union's goals on plastics strategy concerning the promotion of bio-based, compostable plastics and the setting up of approaches to prevent food waste with a simple plastic packaging.

Acclimation and Characterization of Marine Cyanobacterial Strains Euryhalinema and Desertifilum for C-Phycocyanin Production

This study involves evaluation of two native cyanobacterial strains Euryhalinema and Desertifilum isolated from a mangrove pond in Haikou (China) for their possible phycocyanin (C-PC) production. Maximal growth rate with highest chlorophyll and C-PC accumulation were observed at 28°C and 60 μmol photons m^-2 s^-1 photon flux density for Euryhalinema sp., while for Desertifilum sp. at 32°C and 80 μmol photons m^-2 s^-1. Nitrogen and iron concentration trails revealed that double strength concentration of sodium nitrate and ferric ammonium citrate in original BG11 media increased growth rate and accumulation of C-PC for both strains. Three different C-PC extraction methods were tested. The combined extraction protocol of freeze-thaw and ultrasonication markedly increased the C-PC extraction efficiency and attained the food grade purity (A ₆₂₀/A ₂₈₀ ratio >0.7), whereas a higher C-PC yield was found with Na-phosphate buffer. Furthermore, the clarified crude extract was used to purify C-PC by fractional ammonium sulfate [(NH₄)₂SO₄] precipitation, Sephadex G-25 gel filtration chromatography, and DEAE-sephadex ion exchange chromatography and attained analytical grade purity (A ₆₂₀/A ₂₈₀ ratio >3.9). Taken together, both strains showed their potential to be domesticated for valuable phycocyanin production.

Lutein and β-carotene biosynthesis in Scenedesmus sp. SVMIICT1 through differential light intensities

The study evaluated the biosynthesis of lutein and β-carotene by Scenedesmus sp. SVMIICT1 under five different light intensities (50, 250, 500, 750 and 1000 µE/m²/s). Liquid chromatography/mass spectrometry (LC/MS) was used to determine relative quantities of lutein and β-carotene. Relatively, high lutein content of 1.43 ± 0.04 and 0.70 ± 0.02 mg/g was found with 50 and 500 µE/m²/s conditions respectively. β-Carotene content was quantified as 0.15 ± 0.01, 0.1 ± 0.01 and 0.12 ± 0.02 mg/g with 50, 250 and 500 µE/m²/s conditions respectively. The light intensities altered photosystem II and photosystem I. At 50 µE intensity, high chlorophyll content and high photosystem II quantum efficiency (F_V/F_M) was observed. Low F_V/F_M ratio of around 0.3 was detected in high light intensities (750 µE and 1000 µE) due to photoinhibition. Lipid fraction increased with increasing light intensity and the fatty acid profiles were similar in all five conditions.

Microalgae Xanthophylls: From Biosynthesis Pathway and Production Techniques to Encapsulation Development

In the last 20 years, xanthophylls from microalgae have gained increased scientific and industrial interests. This review highlights the essential issues that concern this class of high value compounds. Firstly, their chemical diversity as the producer microorganisms was detailed. Then, the use of conventional and innovative extraction techniques was discussed. Upgraded knowledge on the biosynthetic pathway of the main xanthophylls produced by photosynthetic microorganisms was reviewed in depth, providing new insightful ideas, clarifying the function of these active biomolecules. In addition, the recent advances in encapsulation techniques of astaxanthin and fucoxanthin, such as spray and freeze drying, gelation, emulsification and coacervation were updated. Providing information about these topics and their applications and advances could be a help to students and young researchers who are interested in chemical and metabolic engineering, chemistry and natural products communities to approach the complex thematic of xanthophylls.

Influence of Light Conditions on Microalgae Growth and Content of Lipids, Carotenoids, and Fatty Acid Composition

Microalgae are a valuable natural resource for a variety of value-added products. The growth of microalgae is determined by the impact of many factors, but, from the point of view of the implementation of autotrophic growth, light is of primary importance. This work presents an overview of the influence of light conditions on the growth of microalgae, the content of lipids, carotenoids, and the composition of fatty acids in their biomass, taking into account parameters such as the intensity, duration of lighting, and use of rays of different spectral composition. The optimal light intensity for the growth of microalgae lies in the following range: 26-400 µmol photons m-2 s-1. An increase in light intensity leads to an activation of lipid synthesis. For maximum lipid productivity, various microalgae species and strains need lighting of different intensities: from 60 to 700 µmol photons m-2 s-1. Strong light preferentially increases the triacylglyceride content. The intensity of lighting has a regulating effect on the synthesis of fatty acids, carotenoids, including β-carotene, lutein and astaxanthin. In intense lighting conditions, saturated fatty acids usually accumulate, as well as monounsaturated ones, and the number of polyunsaturated fatty acids decreases. Red as well as blue LED lighting improves the biomass productivity of microalgae of various taxonomic groups. Changing the duration of the photoperiod, the use of pulsed light can stimulate microalgae growth, the production of lipids, and carotenoids. The simultaneous use of light and other stresses contributes to a stronger effect on the productivity of algae.

Biochemical and Immunological implications of Lutein and Zeaxanthin

Throughout history, nature has been acknowledged for being a primordial source of various bioactive molecules in which human macular carotenoids are gaining significant attention. Among 750 natural carotenoids, lutein, zeaxanthin and their oxidative metabolites are selectively accumulated in the macular region of living beings. Due to their vast applications in food, feed, pharmaceutical and nutraceuticals industries, the global market of lutein and zeaxanthin is continuously expanding but chemical synthesis, extraction and purification of these compounds from their natural repertoire e.g., plants, is somewhat costly and technically challenging. In this regard microbial as well as microalgal carotenoids are considered as an attractive alternative to aforementioned challenges. Through the techniques of genetic engineering and gene-editing tools like CRISPR/Cas9, the overproduction of lutein and zeaxanthin in microorganisms can be achieved but the commercial scale applications of such procedures needs to be done. Moreover, these carotenoids are highly unstable and susceptible to thermal and oxidative degradation. Therefore, esterification of these xanthophylls and microencapsulation with appropriate wall materials can increase their shelf-life and enhance their application in food industry. With their potent antioxidant activities, these carotenoids are emerging as molecules of vital importance in chronic degenerative, malignancies and antiviral diseases. Therefore, more research needs to be done to further expand the applications of lutein and zeaxanthin.

Microalgae for high-value products: A way towards green nutraceutical and pharmaceutical compounds

Microalgae is a renewable bioresource with the potential to replace the conventional fossil-based industrial production of organic chemicals and pharmaceuticals. Moreover, the microalgal biomass contains carotenoids, vitamins, and other biomolecules that are widely used as food supplements. However, the microalgal biomass production, their composition variations, energy-intensive harvesting methods, optimized bio-refinery routes, and lack of techno-economic analysis are the major bottleneck for the life-sized commercialization of this nascent bio-industry. This review discusses the microalgae-derived key bioactive compounds and their applications in different sectors for human health. Furthermore, this review proposes advanced strategies to enhance the productivity of bioactive compounds and highlight the key challenges associated with a safety issue for use of microalgae biomass. It also provides a detailed global scenario and market demand of microalgal bioproducts. In conclusion, this review will provide the concept of microalgal biorefinery to produce bioactive compounds at industrial scale platform for their application in the nutraceutical and pharmaceutical sector considering their current and future market trends.

Response to Static Magnetic Field-Induced Stress in Scenedesmus obliquus and Nannochloropsis gaditana

Magnetic fields in biological systems is a promising research field; however, their application for microalgae has not been fully exploited. This work aims to measure the enzymatic activity and non-enzymatic activity of two microalgae species in terms of superoxide dismutase (SOD), catalase (CAT), and carotenoids, respectively, in response to static magnetic fields-induced stress. Two magnet configurations (north and south) and two exposure modes (continuous and pulse) were applied. Two microalgae species were considered, the Scenedesmus obliquus and Nannochloropsis gaditana. The SOD activity increased by up to 60% in S. obliquus under continuous exposure. This trend was also found for CAT in the continuous mode. Conversely, under the pulse mode, its response was hampered as the SOD and CAT were reduced. For N. gaditana, SOD increased by up to 62% with the south configuration under continuous exposure. In terms of CAT, there was a higher activity of up to 19%. Under the pulsed exposure, SOD activity was up to 115%. The CAT in this microalga was increased by up to 29%. For N. gaditana, a significant increase of over 40% in violaxanthin production was obtained compared to the control, when the microalgae were exposed to SMF as a pulse. Depending on the exposure mode and species, this methodology can be used to produce oxidative stress and obtain an inhibitory or enhanced response in addition to the significant increase in the production of antioxidant pigments.

Lutein production with Chlorella sorokiniana MB-1-M12 using novel two-stage cultivation strategies - metabolic analysis and process improvement

Microalgae-derived carotenoids have increasingly been considered as feasible green alternatives for synthetic antioxidants. In this study, the lutein high-yielding strain (Chlorella sorokiniana MB-1; henceforth MB-1) and its mutant derivative (C. sorokiniana MB-1-M12; henceforth M12) were evaluated for their growth, biomass production, and lutein accumulation in three different cultivation modes - photoautotrophy, mixotrophy, and heterotrophy. M12 could grow effectively under heterotrophic conditions, but the lutein content was lower, indicating the necessity of photo-induction for lutein accumulation. Metabolic analysis of MB-1 and M12 in autotrophic growth in the presence of carbon dioxide indicated that carbon assimilation and channeling of the fixed metabolites towards carotenoid accumulation was elevated in M12 compared to MB-1. Novel two-stage alternative cultivation strategies (Autotrophic/Heterotrophic and Mixotrophic/Heterotrophic cultures) were applied for enhancing lutein production in M12. Maximum lutein quantity (6.17 mg/g) and production (33.64 mg/L) were obtained with the TSHM strategy that is considered the best two-stage operation.

Engineering microalgae: transition from empirical design to programmable cells

Domesticated microalgae hold great promise for the sustainable provision of various bioresources for human domestic and industrial consumption. Efforts to exploit their potential are far from being fully realized due to limitations in the know-how of microalgal engineering. The associated technologies are not as well developed as those for heterotrophic microbes, cyanobacteria, and plants. However, recent studies on microalgal metabolic engineering, genome editing, and synthetic biology have immensely helped to enhance transformation efficiencies and are bringing new insights into this field. Therefore, this article, summarizes recent developments in microalgal biotechnology and examines the prospects for generating specialty and commodity products through the processes of metabolic engineering and synthetic biology. After a brief examination of empirical engineering methods and vector design, this article focuses on quantitative transformation cassette design, elaborates on target editing methods and emerging digital design of algal cellular metabolism to arrive at high yields of valuable products. These advances have enabled a transition of manners in microalgal engineering from single-gene and enzyme-based metabolic engineering to systems-level precision engineering, from cells created with genetically modified (GM) tags to that without GM tags, and ultimately from proof of concept to tangible industrial applications. Finally, future trends are proposed in microalgal engineering, aiming to establish individualized transformation systems in newly identified species for strain-specific specialty and commodity products, while developing sophisticated universal toolkits in model algal species.

Current perspectives on integrated approaches to enhance lipid accumulation in microalgae

In recent years, research initiatives on renewable bioenergy or biofuels have been gaining momentum, not only due to fast depletion of finite reserves of fossil fuels but also because of the associated concerns for the environment and future energy security. In the last few decades, interest is growing concerning microalgae as the third-generation biofuel feedstock. The CO₂ fixation ability and conversion of it into value-added compounds, devoid of challenging food and feed crops, make these photosynthetic microorganisms an optimistic producer of biofuel from an environmental point of view. Microalgal-derived fuels are currently being considered as clean, renewable, and promising sustainable biofuel. Therefore, most research targets to obtain strains with the highest lipid productivity and a high growth rate at the lowest cultivation costs. Different methods and strategies to attain higher biomass and lipid accumulation in microalgae have been extensively reported in the previous research, but there are fewer inclusive reports that summarize the conventional methods with the modern techniques for lipid enhancement and biodiesel production from microalgae. Therefore, the current review focuses on the latest techniques and advances in different cultivation conditions, the effect of different abiotic and heavy metal stress, and the role of nanoparticles (NPs) in the stimulation of lipid accumulation in microalgae. Techniques such as genetic engineering, where particular genes associated with lipid metabolism, are modified to boost lipid synthesis within the microalgae, the contribution of "Omics" in metabolic pathway studies. Further, the contribution of CRISPR/Cas9 system technique to the production of microalgae biofuel is also briefly described.

Challenges and Potential in Increasing Lutein Content in Microalgae

Research on enhancing lutein content in microalgae has made significant progress in recent years. However, strategies are needed to address the possible limitations of microalgae as practical lutein producers. The capacity of lutein sequestration may determine the upper limit of cellular lutein content. The preliminary estimation presented in this work suggests that the lutein sequestration capacity of the light-harvesting complex (LHC) of microalgae is most likely below 2% on the basis of dry cell weight (DCW). Due to its nature as a structural pigment, higher lutein content might interfere with the LHC in fulfilling photosynthetic functions. Storing lutein in a lipophilic environment is a mechanism for achieving high lutein content but several critical barriers must be overcome such as lutein degradation and access to lipid droplet to be stored through esterification. Understanding the mechanisms underlying lipid droplet biogenesis in chloroplasts, as well as carotenoid trafficking through chloroplast membranes and carotenoid esterification, may provide insight for new approaches to achieve high lutein contents in algae. In the meantime, building the machinery for esterification and sequestration of lutein and other hydroxyl-carotenoids in model microorganisms, such as yeast, with synthetic biology technology provides a promising option.

Microalgae as sustainable food and feed sources for animals and humans - Biotechnological and environmental aspects

Offering a potential solution for global food security and mitigating environmental issues caused by the expansion of land-based food production, the carbon-hunger and nutrient-rich microalgae emerged as a sustainable food source for both humans and animals. Other than as an alternative source for protein, microalgae offer its most valuable nutrients, omega-3 and 6 long-chain polyunsaturated fatty acids where the content can compete with that of marine fish with lower chemicals contamination and higher purity. Furthermore, the colorful pigments of microalgae can act as antioxidants together with many other health-improving properties as well as a natural colorant. In addition, the supplementation of algae as animal feed provides plentiful benefits, such as improved growth and body weight, reduced feed intake, enhanced immune response and durability towards illness, antibacterial and antiviral action as well as enrichment of livestock products with bioactive compounds. The significant breakthrough in algal biotechnology has made algae a powerful "cell factory" for food production and lead to the rapid growth of the algal bioeconomy in the food and feed industry. The first overview of this review was to present the general of microalgae and its potential capability. Subsequently, the nutritional compositions of microalgae were discussed together with its applications in human foods and animal feeds, followed by the exploration of their economic feasibility and sustainability as well as market trends. Lastly, both challenges and future perspectives were also discussed.

Marine Microalgae for Potential Lutein Production

Lutein is particularly known to help maintain normal visual function by absorbing and attenuating the blue light that strikes the retina in our eyes. The effect of overexposure to blue light on our eyes due to the excessive use of electronic devices is becoming an issue of modern society due to insufficient dietary lutein consumption through our normal diet. There has, therefore, been an increasing demand for lutein-containing dietary supplements and also in the food industry for lutein supplementation in bakery products, infant formulas, dairy products, carbonated drinks, energy drinks, and juice concentrates. Although synthetic carotenoid dominates the market, there is a need for environmentally sustainable carotenoids including lutein production pathways to match increasing consumer demand for natural alternatives. Currently, marigold flowers are the predominant natural source of lutein. Microalgae can be a competitive sustainable alternative, which have higher growth rates and do not require arable land and/or a growth season. Currently, there is no commercial production of lutein from microalgae, even though astaxanthin and β-carotene are commercially produced from specific microalgal strains. This review discusses the potential microalgae strains for commercial lutein production, appropriate cultivation strategies, and the challenges associated with realising a commercial market share.

Effects of Nitrogen Availability on the Antioxidant Activity and Carotenoid Content of the Microalgae Nephroselmis sp

Nephroselmis sp. was previously identified as a species of interest for its antioxidant properties owing to its high carotenoid content. In addition, nitrogen availability can impact biomass and specific metabolites' production of microalgae. To optimize parameters of antioxidant production, Nephroselmis sp. was cultivated in batch and continuous culture conditions in stirred closed photobioreactors under different nitrogen conditions (N-repletion, N-limitation, and N-starvation). The aim was to determine the influence of nitrogen availability on the peroxyl radical scavenging activity (oxygen radical absorbance capacity (ORAC) assay) and carotenoid content of Nephroselmis sp. Pigment analysis revealed a specific and unusual photosynthetic system with siphonaxanthin-type light harvesting complexes found in primitive green algae, but also high lutein content and xanthophyll cycle pigments (i.e., violaxanthin, antheraxanthin, and zeaxanthin), as observed in most advanced chlorophytes. The results indicated that N-replete conditions enhance carotenoid biosynthesis, which would correspond to a higher antioxidant capacity measured in Nephroselmis sp. Indeed, peroxyl radical scavenging activity and total carotenoids were higher under N-replete conditions and decreased sharply under N-limitation or starvation conditions. Considering individual carotenoids, siphonaxanthin, neoxanthin, xanthophyll cycle pigments, and lycopene followed the same trend as total carotenoids, while β-carotene and lutein stayed stable regardless of the nitrogen availability. Carotenoid productivities were also higher under N-replete treatment. The peroxyl radical scavenging activity measured with ORAC assay (63.6 to 154.9 µmol TE g-1 DW) and the lutein content (5.22 to 7.97 mg g-1 DW) were within the upper ranges of values reported previously for other microalgae. Furthermore, contents of siphonaxanthin ere 6 to 20% higher than in previous identified sources (siphonous green algae). These results highlight the potential of Nephroselmis sp. as a source of natural antioxidant and as a pigment of interest.