Exploring the versatile applications of Spirulina: A comprehensive research review

Spirulina's role extends to environmental management, particularly in wastewater treatment. A study by Olguín (2003) [36] demonstrated its effectiveness in reducing nitrogen, phosphorus, and heavy metals in wastewater, thus improving water quality. Recognized as a "food of the future," Spirulina is celebrated for its minimal resource requirements and adaptability to diverse environments, contributing to food security. However, it faces challenges related to production costs, quality control, and regulatory requirements (Belay, 2013) [10] . Its high nutritional density also makes it suitable for space missions, as organizations like NASA have explored its use in closed-loop life support systems for long-term space travel.

Nutritional and Dietary Applications of Spirulina

Spirulina's protein content, ranging from 55% to 70% by dry weight, ranks among the highest of any natural food source, comparable to animal proteins like eggs, dairy, and meat. Its amino acid composition meets the World Health Organization's recommendations for protein needs, supporting its use as a high-quality protein supplement. Studies indicate a net protein utilization (NPU) of approximately 60% to 70% (Wang et al., 2021; Belay, 2002) [47,48,9] , highlighting its efficiency for athletes, bodybuilders, and individuals recovering from illness. Elderly individuals can benefit significantly from Spirulina's nutrient density, as it offers an easily digestible source of protein that meets daily requirements despite dietary limitations. Additionally, Spirulina has been explored as a solution for protein-energy malnutrition, particularly in lowincome regions. Nuhu (2023) [35] emphasized its potential to combat malnutrition due to its nutrient density and high bioavailability.

Malnutrition Treatment

Spirulina's efficacy in treating malnutrition has been evaluated in various humanitarian projects. A study in Bangladesh by Misbahuddin et al. (2022) [33] showed that children receiving Spirulina supplementation exhibited better weight gain, increased mid-upper arm circumference, and higher haemoglobin levels, demonstrating its effectiveness in addressing moderate malnutrition. Spirulina also provides substantial amounts of vitamin B12, making it valuable for vegetarian and vegan diets. A systematic review by Ahuja et al. (2021) [2,3] confirmed its role in nutrition programs targeting vulnerable groups.

Weight Management

Spirulina aids in weight management due to its nutrient density and high protein content. A randomized controlled trial by Kim et al. (2023) [23] reported improvements in lipid profiles and reductions in body mass index (BMI) among overweight adults supplemented with Spirulina. Its low glycemic index also stabilizes blood glucose levels, beneficial for individuals with type 2 diabetes (Patel et al., 2022) [38,39] .

Pharmaceutical and Therapeutic Applications of Spirulina

Spirulina is recognized for its rich composition of bioactive compounds, offering antioxidant, anti-inflammatory, cardiovascular, immune-boosting, and antidiabetic properties.

Key components like phycocyanin, polysaccharides, and essential fatty acids make it a promising candidate in complementary and alternative medicine.

Antioxidant and Anti-Inflammatory Properties

Phycocyanin, the blue pigment unique to spirulina, serves as a potent antioxidant, scavenging free radicals and protecting against oxidative damage. Recent studies have shown that its antioxidant capabilities rival those of vitamins C and E. Spirulina also inhibits pro-inflammatory mediators like cyclooxygenase-2 (COX-2), benefiting conditions such as rheumatoid arthritis. Other compounds, including betacarotene and vitamin E, enhance its anti-inflammatory effects, aiding tissue repair.

Cardiovascular Benefits

Spirulina improves lipid metabolism, reducing total cholesterol, low-density lipoprotein (LDL), and triglycerides while increasing high-density lipoprotein (HDL) cholesterol.

A study by Patel et al. (2022) [38,39] demonstrated significant improvements in these parameters, which are crucial for reducing coronary artery disease risk. Gamma-linolenic acid (GLA) in spirulina further supports cardiovascular health by enhancing blood circulation and reducing inflammation.

Immune System Modulation

Spirulina enhances or suppresses immune activity, making it useful for immune-compromised individuals. Its polysaccharides stimulate cytokine production and enhance natural killer (NK) cell activity, aiding in the fight against infections and supporting those with autoimmune disorders.

Anticancer Potential

Research indicates that spirulina can inhibit cancer cell proliferation and induce apoptosis. A study by Lee et al.

(2023) [23,28] suggests that it may enhance conventional cancer treatments by mitigating side effects and improving patient outcomes.

Antidiabetic Effects

Spirulina regulates blood sugar levels, improves insulin sensitivity, and enhances glucose uptake. Shanmugam et al.

(2023) [44] confirmed that spirulina supplementation significantly lowers fasting blood glucose levels, supporting better metabolic health and potentially reducing the need for conventional antidiabetic medications.

Cosmetic and Skin Care Applications of Spirulina

Spirulina is recognized for its rich composition of bioactive compounds, offering antioxidant, anti-inflammatory, cardiovascular, immune-boosting, and antidiabetic properties.

Key components like phycocyanin, polysaccharides, and essential fatty acids make it a promising candidate in complementary and alternative medicine.

Antioxidant and Anti-Inflammatory Properties

Phycocyanin, the blue pigment unique to spirulina, serves as a potent antioxidant, scavenging free radicals and protecting against oxidative damage. Recent studies have shown that its antioxidant capabilities rival those of vitamins C and E. Spirulina also inhibits pro-inflammatory mediators like cyclooxygenase-2 (COX-2), benefiting conditions such as rheumatoid arthritis. Other compounds, including beta-carotene and vitamin E, enhance its anti-inflammatory effects, aiding tissue repair.

Cardiovascular Benefits

Spirulina improves lipid metabolism, reducing total cholesterol, low-density lipoprotein (LDL), and triglycerides while increasing high-density lipoprotein (HDL) cholesterol. A study by Patel et al. (2022) [38,39] demonstrated significant improvements in these parameters, which are crucial for reducing coronary artery disease risk. Gamma-linolenic acid (GLA) in spirulina further supports cardiovascular health by enhancing blood circulation and reducing inflammation.

Immune System Modulation

Spirulina enhances or suppresses immune activity, making it useful for immune-compromised individuals. Its polysaccharides stimulate cytokine production and enhance natural killer (NK) cell activity, aiding in the fight against infections and supporting those with autoimmune disorders.

Anticancer Potential

Research indicates that spirulina can inhibit cancer cell proliferation and induce apoptosis. A study by Lee et al.

(2023) [23,28] suggests that it may enhance conventional cancer treatments by mitigating side effects and improving patient outcomes.

Antidiabetic Effects

Spirulina regulates blood sugar levels, improves insulin sensitivity, and enhances glucose uptake. Shanmugam et al. (2023) [44] confirmed that spirulina supplementation significantly lowers fasting blood glucose levels, supporting better metabolic health and potentially reducing the need for conventional antidiabetic medications.

Agricultural and Environmental Applications of Spirulina

Spirulina's nutrient content and eco-friendly attributes make it valuable for sustainable agricultural and environmental applications. Its roles in animal nutrition, soil health, wastewater management, and climate change mitigation are especially noteworthy.

Animal Feed Supplement

Spirulina is an effective supplement in aquaculture and livestock feed, providing 50-70% protein, essential amino acids, vitamins, and bioactive compounds that enhance growth and immunity. Early studies (Habib et al., 2008) [20] highlighted Spirulina's benefits in fish, with recent research confirming improved growth and feed efficiency in tilapia and carp. Spirulina also enhances livestock health and reduces antibiotic use; a 2024 study in Journal of Animal Science and Biotechnology found it increased muscle protein and egg yolk pigmentation in poultry. Other research (Evans et al., 2005) [15] has shown similar benefits, reinforcing its potential in sustainable animal feed.

Biofertilizer

Spirulina's nutrient richness, particularly in nitrogen, phosphorus, and potassium, makes it an effective biofertilizer. A 2024 study in Sustainability demonstrated that Spirulina applications boost soil organic matter and microbial activity, enhancing plant growth and nutrient uptake. Studies support its role in sustainable farming by reducing reliance on chemical fertilizers, promoting beneficial microbes, and improving nutrient cycling. Bashan et al. (2004) [5,6] also noted Spirulina's ability to enhance soil fertility, aligning with modern eco-friendly practices.

Wastewater Treatment

Spirulina's capacity to remove nitrogen, phosphorus, and metals makes it valuable for wastewater treatment. Research in Environmental Science and Pollution Research (2024) showed Spirulina's efficacy in reducing nitrogen and phosphorus levels by over 70%, supporting Olguín's (2003) [36] findings on microalgae's role in bioremediation. Additionally, Spirulina's ability to absorb metals like lead and cadmium has been noted since Volesky (1990) [51] , with recent studies (Markou et al., 2023) [31] suggesting it can be reused as biofertilizer or animal feed, creating a circular economy (Table 2).

Soil Erosion Control and Carbon Sequestration

Spirulina biomass aids in soil cohesion and erosion prevention. Journal of Applied Phycology (2023) [12] reported that Spirulina-treated soils showed increased microbial activity and organic matter, supporting findings by Metting (1996) [32] on microalgae's role in soil stabilization. Furthermore, Spirulina's CO₂ absorption contributes to carbon sequestration. Large-scale cultivation for atmospheric CO₂ reduction was suggested by Richmond (1986) [40] and further validated by Sánchez et al. (2023) [43] , emphasizing its potential in climate mitigation.

Space Nutrition and Future Applications

Spirulina is increasingly recognized for its role in space nutrition due to its dense nutrients, easy cultivation, and low space requirements. This edible microalga holds promise for long-term space missions, providing essential nutrients while contributing to life support through oxygen production and carbon dioxide recycling (Gitelson et al., 2017; Yadav et al., 2023) [18,50] .

Nutritional Benefits for Space Missions

Spirulina's high protein content (55-70%), vitamins, minerals, and essential fatty acids make it ideal for space missions, where nutrient-dense, compact food sources are essential. It helps maintain muscle mass and bone density, both critical in microgravity environments. Its antioxidants, such as phycocyanin and β-carotene, counter oxidative stress from space radiation, enhancing cellular protection and recovery for astronauts (Chen et al., 2023) [13] .

Oxygen Production and Carbon Dioxide Recycling

In closed-loop life support systems, Spirulina absorbs CO₂ and releases oxygen via photosynthesis, contributing to a breathable atmosphere. NASA and ESA have integrated Spirulina into bio-regenerative systems to recycle air, water, and food, which reduces dependency on resupply missions (Bubenheim et al., 2019) [11] .

Cultivation in Space

Spirulina's low resource needs make it well-suited for space cultivation. It can grow in controlled environments, such as photobioreactors, which optimize growth factors and nutrient flow even in microgravity (Kliss et al., 2022) [27] . This efficient system minimizes resource use, aligning with sustainable practices for extended missions (Yadav et al., 2023) [50] .

Addressing Space-Induced Health Challenges

Long-term missions expose astronauts to muscle atrophy, immune suppression, and radiation. Spirulina's immuneboosting polysaccharides and anti-inflammatory compounds like phycocyanin help mitigate these risks. Its calcium, magnesium, and iron content supports bone health and red blood cell production (Gusev et al., 2020) [19] .

Future Prospects for Space Exploration

As missions reach Mars and beyond, Spirulina could evolve from a supplement to a primary food staple in closed-loop ecosystems. Research into palatable Spirulina-based foods aims to improve astronaut diets, with innovations like spacefriendly recipes increasing its acceptability (Bubenheim et al., 2019) [11] .

Potential Applications on Earth

Advances in space-driven Spirulina cultivation benefit Earth, particularly in addressing food insecurity and resource scarcity. Closed-loop farming techniques developed for space can support urban and vertical farming, enhancing sustainable agriculture to meet global food needs (Kliss et al., 2022; Gitelson et al., 2017) [27,18] .

Challenges and Limitations

Despite the numerous benefits associated with Spirulina, its large-scale cultivation and widespread utilization face several challenges that must be addressed to facilitate its mainstream adoption across various industries. These challenges span economic, regulatory, safety, and environmental aspects, all of which can impact the feasibility and acceptance of Spirulina products.

High Production Costs

One of the significant limitations of Spirulina cultivation is the high cost associated with large-scale production. Spirulina requires specific conditions for optimal growth, including precise light, temperature, pH levels, and nutrient availability, which can be challenging to maintain consistently. Naturally, Spirulina grows in alkaline water bodies, which may not be readily available for large-scale farming. Controlled-environment cultivation techniques, such as photobioreactors or artificial ponds, are often necessary to achieve consistent production. However, these methods incur substantial expenses due to the infrastructure, energy consumption, and nutrient inputs required (Richmond & Hu, 2013) [10] . The economic feasibility of Spirulina production is particularly problematic in regions where resources such as water and energy are scarce or expensive. Furthermore, maintaining optimal cultivation conditions can be laborintensive and technically demanding. To reduce production costs, ongoing research is exploring innovative methods, including the use of low-cost substrates, enhancing light utilization efficiency, and integrating Spirulina farming with wastewater treatment (García & Bashan, 2016) [16] . These approaches aim to make Spirulina cultivation more economically viable.

Quality Control

Quality control is crucial for Spirulina products, particularly those intended for human consumption. Spirulina harvested from natural water bodies can be contaminated with heavy metals, pesticides, and harmful algal toxins such as microcystins, posing health risks and compromising product safety (Gershwin & Belay, 2007) [17] . Implementing stringent quality control measures is essential for commercial production, including routine monitoring of growth conditions, raw materials, and final products. Closed photobioreactors offer an advantage over open-pond systems by reducing the risk of contamination. Another challenge lies in the variability of Spirulina's nutrient composition, which can differ based on growth conditions and harvesting methods. This variability can make it difficult to standardize Spirulina-based nutritional supplements or pharmaceuticals, posing challenges for regulatory approval and consumer trust (Becker, 2013) [7,8] . Third-party certifications and compliance with food safety standards can help build consumer confidence in Spirulina products.

Regulatory Hurdles

The regulatory landscape for Spirulina-based products is complex, especially for pharmaceutical and therapeutic applications. While Spirulina is widely accepted as a dietary supplement, gaining regulatory approval for its use in pharmaceutical products or as a therapeutic agent involves extensive clinical trials and scientific evidence to support therapeutic claims. Regulatory agencies such as the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) require rigorous documentation and compliance with safety standards, which can be timeconsuming and costly (Spolaore et al., 2006) [46] . In some regions, regulations restrict the use of certain algal extracts in food and supplements due to concerns about safety and contaminants. Companies must navigate these regulations by adhering to quality assurance practices, food safety laws, and comprehensive documentation.

Environmental and Sustainability Concerns

Although Spirulina is generally considered a sustainable source of nutrition, large-scale cultivation can still pose environmental challenges. The use of fertilizers or synthetic growth media to promote Spirulina growth can contribute to nutrient pollution if waste management practices are inadequate (García & Bashan, 2016) [16] . Additionally, the energy required for controlled-environment cultivation, such as artificial lighting and temperature regulation, can increase the carbon footprint of Spirulina production, particularly in regions where renewable energy sources are limited (Richmond & Hu, 2013) [10] . To enhance sustainability, it is crucial to balance the environmental benefits of Spirulina cultivation with potential ecological impacts. Approaches such as recycling nutrients from wastewater, integrating Spirulina farming with renewable energy sources, and developing more efficient cultivation systems can help reduce water and nutrient inputs, making the production process more ecofriendly.

Market Limitations and Consumer Perception

While Spirulina is often marketed as a superfood, its adoption may be restricted by factors such as taste, texture, and cost. Spirulina's natural flavor, often described as earthy or slightly bitter, may not appeal to all consumers, limiting its use in mainstream food products. The relatively high cost of Spirulina supplements compared to other protein sources, such as soy or whey, may also limit its market reach, especially in regions with lower purchasing power. Efforts to educate consumers about the unique benefits of Spirulina and the development of cost-effective formulations could help broaden its appeal. Innovations in food processing and product development aimed at improving palatability without compromising nutritional benefits are necessary for expanding its consumer base.

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