Innovations in Limnospira platensis Fermentation: From Process Enhancements to Biotechnological Applications

Abstract

The cyanobacterium Limnospira platensis, vulgarly Spirulina, has gained significant attention due to its high protein content, rich bioactive compounds, and health benefits, making it a valuable resource in biotechnology, nutraceuticals, food supplements, biopharmaceuticals, and cosmetics. Recent advancements in fermentation technology have considerably improved the efficiency, scalability, and cost-effectiveness of L. platensis production while addressing environmental sustainability and enhancing product quality. Based on well-recognized databases (Google Scholar, PubMed, Scopus, Web of Science), this review explores the latest developments in L. platensis fermentation, emphasizing strain improvement, bioprocess engineering, and optimization of fermentation parameters. It also examines key factors such as bioreactor design, downstream processing, and innovative monitoring technologies aimed at maximizing biomass yield and bioactive compound production. Additionally, emerging applications of fermented L. platensis in various industries and future perspectives, including large-scale production, regulatory barriers, and biosafety considerations, are discussed. These insights provide a comprehensive outlook on the future of L. platensis fermentation in biotechnological applications.

1. Introduction

Limnospira platensis (L. platensis, formerly Arthrospira platensis, and commonly known as Spirulina), a filamentous cyanobacterium, has gained global recognition for its remarkable nutritional profile and biotechnological potential [1]. It is a rich source of essential amino acids (leucine and methionine), vitamins (vitamin E and some vitamins of B complex), minerals (calcium, magnesium, potassium, and sodium), and bioactive compounds (antioxidant pigments), including phycocyanin, γ-linolenic acid (GLA), and polysaccharides [2,3]. L. platensis is also important for astaxanthin production as it has a high value of β-carotene, zeaxanthin, canthaxanthin, and astaxanthin preconditions [4,5]. Several studies considered that astaxanthin has 100–500 times higher antioxidant properties compared to α-tocopherol [6]. Due to these attributes, L. platensis is frequently referred to as a “superfood” and has become commercially significant, particularly in regions with favorable climates for its production, such as Asia and Africa [7].

Economically, L. platensis has value in biotechnology, driven by its relatively low production costs compared to other microalgae and sustainable cultivation practices. It thrives in alkaline water and efficiently fixes carbon dioxide, contributing to carbon sequestration and advancing green technologies [8]. The global L. platensis market was valued at over USD 350 million in 2020, with projections suggesting a compound annual growth rate of 10.5% from 2021 to 2028 [9]. This growth is attributed to the rising demand for natural food supplements, bioactive compounds, and environmentally sustainable production methods [7].

Due to its rich composition, L. platensis has found widespread applications across various industries. In the nutraceutical sector, it is primarily used as a dietary supplement, available in powder or tablet form, and valued for its high protein and antioxidant content [10]. The pharmaceutical industry has focused on L. platensis’ bioactive compounds, such as phycocyanin and polysaccharides, which have been explored for their anti-inflammatory, antiviral, and immunomodulatory properties [11]. Additionally, L. platensis is increasingly used in cosmetics due to its antioxidant properties, which protect the skin from oxidative stress and promote overall skin health [12].

L. platensis is also raising interest in the functional food and beverage sectors, where it is used to enhance the nutritional value of products such as yogurt, health drinks, and energy bars [13]. Its digestibility and high levels of bioactive compounds make it an ideal supplement for human and animal nutrition [7]. Furthermore, L. platensis’ potential in developing new biopharmaceuticals and nutraceuticals continues to drive its commercial relevance [14]. The health-promoting effects and disease-reducing benefits of consuming fermented L. platensis have shone attention on its potential [15].

Fermentation is a critical technique for enhancing the bioactivity, scalability, and economic viability of L. platensis production [16]. Microbial fermentation, particularly with lactic acid bacteria (LAB), can significantly enhance the nutritional profile of L. platensis. Fermentation can increase the production of bioactive compounds such as γ-aminobutyric acid (GABA), L-glutamic acid, and other essential nutrients [13]. Fermentation can also benefit the breaking down of the cell wall of L. platensis, facilitating the release of beneficial compounds like phycocyanin and peptides [12]. This process improves nutrient bioavailability, enhances flavor, and reduces undesirable odors, making L. platensis more suitable for food applications [14,16].

At an industrial scale, fermentation allows for more efficient biomass production. Optimized bioreactor designs and process controls enable scalable production of L. platensis with consistent quality and high yields [10]. Moreover, the integration of L. platensis into biorefinery processes, such as the simultaneous production of bioethanol and peptides, underscores the versatility of fermentation in unlocking the biotechnological potential of this cyanobacterium [11].

This review aims to provide a comprehensive evaluation of the advances in L. platensis fermentation, with a focus on process optimization, biotechnological applications, and future perspectives. A systematic search was conducted in the databases Google Scholar (Google LLC, Mountain View, CA, USA), PubMed (NCBI, Bethesda, MD, USA), Scopus (Elsevier B.V., Amsterdam, The Netherlands), and Web of Science (Clarivate Analytics, Philadelphia, PA, USA). Search terms included “L. platensis fermentation”, “bioprocess engineering”, “strain improvement”, and “bioactive compound production”. Peer-reviewed studies were prioritized, with a focus on recent research. This review synthesizes current findings on the optimization of L. platensis fermentation processes, including enhancements in bioactive compound production, strain improvement, and scale-up technologies. Additionally, it explores the emerging industrial applications of fermented L. platensis in nutraceuticals, pharmaceuticals, and functional foods.

2. Strain Improvement

2.1. Genetic and Metabolic Engineering Approaches

Recent advances in genetic and metabolic engineering have revolutionized the optimization of L. platensis strains for industrial applications, particularly in enhancing bioactive compound production [17]. Various genetic tools, including random mutagenesis, metabolic engineering, and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR), have been used to target specific metabolic pathways, enhancing the biosynthesis of high-value compounds like phycocyanin, astaxanthin, and GLA [18,19,20].

One highly effective approach involves Atmospheric and Room Temperature Plasma (ARTP) mutagenesis, which has been demonstrated to yield mutants with enhanced astaxanthin production, a valuable antioxidant. ARTP treatment of L. platensis resulted in a nearly 200% increase in astaxanthin production by enhancing the metabolic pathways associated with carotenoid biosynthesis, confirming the tool’s power in improving strain performance [21]. Additionally, studies have shown that metabolic engineering, such as the overexpression of key enzymes, can increase the production of bioactive compounds by redirecting the metabolic pathway. For example, targeting the fatty acid synthesis pathway through genetic modification has increased the biosynthesis of GLA, a crucial fatty acid used in cosmetics and nutraceuticals [22].

Moreover, metabolic engineering efforts also focus on manipulating the pigment biosynthesis pathways to enhance the production of compounds like phycocyanin. By altering the genes responsible for nutrient uptake and light capture, engineered L. platensis strains have demonstrated increased pigment yields, making them more efficient for commercial applications [23]. Further, recombinant DNA techniques have been developed to transform L. platensis into a viable platform for expressing therapeutic proteins. This innovation offers a scalable and cost-effective method for producing pharmaceuticals using L. platensis, marking a significant breakthrough in its application as a biomanufacturing platform [24].

Genetic engineering also offers the potential to modify regulatory pathways that control carbon fixation, which is essential for improving the growth rate and biomass accumulation in L. platensis. Techniques such as genome-scale metabolic modeling have been used to predict metabolic changes that can lead to higher carbon utilization and enhanced glycogen production, which are crucial for increasing overall biomass yield [25].

2.2. Mutagenesis and Selection of Robust Strains

Mutagenesis is a well-established technique for developing high-performance L. platensis strains, particularly those that are more resistant to environmental stressors. Traditional mutagenesis methods, such as γ-ray irradiation, have been used to generate mutants with improved growth rates and carbon fixation capabilities. One study demonstrated that L. platensis strains exposed to γ-rays exhibited a 500% increase in biomass yield when cultivated under high CO₂ concentrations (after domestication under up to 15 vol.% CO₂). This remarkable improvement was attributed to modifications in the cell wall, which enhanced carbon dioxide absorption [26].

In addition to γ-ray irradiation, ARTP mutagenesis has emerged as a potent tool for creating mutant libraries with diverse phenotypes. This technique allows for the generation of strains optimized for various industrial purposes, such as increasing carbohydrate content and growth rate. For instance, L. platensis mutants created through ARTP showed a 78% increase in carbohydrate content, with some strains also demonstrating a 10.5% improvement in growth rate. These traits, combined with the stability of the mutants across multiple generations, make ARTP an invaluable tool for developing robust L. platensis strains suitable for large-scale fermentation processes [27].

Combining random mutagenesis with metabolic engineering has also been explored as an effective strategy for improving strain performance. A study by Deshpande et al. [22] on cyanobacteria demonstrated that this combination outperformed either technique used alone. By combining these approaches, researchers were able to create mutants with enhanced tryptophan production, which could serve as a model for similar efforts to increase L. platensis’ output of other valuable compounds.

The selection of robust strains is critical for ensuring stability in industrial fermentation processes, where consistency in production is vital. Fluorescence-Activated Cell Sorting (FACS) has been used to screen millions of mutant cells to identify those with desirable traits, such as improved biomass yield or higher bioactive compound production [28]. This technique offers an ultra-high-throughput approach for selecting mutants, allowing for the rapid development of strains with superior industrial properties.

Together, these mutagenesis and selection strategies, combined with genetic and metabolic engineering approaches, provide a powerful toolkit for enhancing L. platensis production.

3. Fermentation Techniques for L. platensis

3.1. Submerged vs. Solid-State Fermentation

Fermentation techniques are essential for optimizing the yield and enhancing the bioactive compound production of L. platensis. The two main methods employed are Submerged fermentation (SMF) and Solid-State Fermentation (SSF). Each has distinct advantages depending on the desired outcome and the nature of the end product.

Submerged fermentation involves cultivating L. platensis in a liquid medium, allowing precise control over variables such as pH, nutrient concentration, temperature, and aeration. SMF offers several advantages, particularly when aiming for large-scale biomass production, where uniform mixing and nutrient supply can be controlled for consistency. This method is favored in industrial settings where the primary goal is to maximize biomass yield and ensure a controlled environment that minimizes contamination risks. SMF has been widely used in both food and pharmaceutical industries due to its scalability and ease of process control [29].

On the other hand, SSF involves the cultivation of L. platensis on solid substrates with minimal free water. SSF has demonstrated superior results in enhancing bioavailability and producing higher concentrations of bioactive compounds such as GABA and L-glutamic acid. For example, Tolpeznikaite et al. [13] found that SSF using LAB significantly increased GABA concentration, a critical compound with health benefits like stress reduction. SSF also shows enhanced antimicrobial properties against opportunistic pathogens such as Staphylococcus aureus. However, a notable drawback of SSF is the potential formation of biogenic amines by LAB, which must be carefully managed due to their possible harmful effects. The formation of biogenic amines is based on one-step decarboxylation reactions of their respective amino acids; they can also be formed through the agmatinase pathway, which directly converts agmatine to urea and putrescine, or by the agmatine deiminase pathway, common in LAB [30].

Studies comparing SMF and SSF have revealed that while SSF may produce higher concentrations of specific bioactive compounds, such as L-glutamic acid (L-Glu), gamma-aminobutyric acid (GABA), and biogenic amines (BA), SMF offers more reliable control over the fermentation process, making it better suited for mass production [13,31]. For example, SMF allows for greater control over environmental parameters such as oxygen and nutrient distribution, which is crucial for maintaining consistent biomass quality and avoiding microbial contamination [13]. Conversely, SSF’s lower water requirement makes it a more environmentally friendly option, particularly for regions with limited water resources. This method is preferred in applications where a high concentration of bioactive compounds like phycocyanin is necessary.

The choice between SMF and SSF often depends on the specific goals of the fermentation process. SSF may be more suitable for producing high-value compounds such as antioxidant (phenolic compounds) and antimicrobial (oxytetracycline, penicillin, rifamycin-B, and tetracycline) agents, while SMF is ideal for processes where scalability and uniformity are essential [32].

It is important to note that while SSF with lactic acid bacteria involves microbial interactions, it is distinct from the mixed fermentation approach described in Section 3.2. In SSF, the focus is on the fermentation technique, which employs a solid substrate and minimal water, enhancing the bioavailability of certain bioactive compounds. In contrast, mixed fermentation explicitly refers to the simultaneous use of different microbial species to achieve synergistic metabolic effects. Thus, SSF with lactic acid bacteria is categorized based on its operational setup, whereas mixed fermentation focuses on intentional microbial co-cultivation to enhance product properties.

3.2. Mixed Fermentation Processes

Mixed fermentation, which involves the use of multiple microorganisms, has been studied as a way of enhancing the nutritional profile and flavor of L. platensis-based products. A typical example is the co-fermentation of L. platensis with Lactiplantibacillus plantarum and Bacillus subtilis. Mixed fermentation enhances the breakdown of complex molecules like proteins into simpler compounds, improving bioavailability and nutritional value, as it allows one-third of L. platensis proteins to be hydrolyzed, with 16% polypeptide yield and improving to 1.5-fold the ratio of essential amino acids to total free amino acids compared to the unfermented L. platensis, which was the maximum nutritional value [14]. For instance, a study by Bao et al. [14] found that the co-fermentation of L. platensis with these two bacteria not only improved protein hydrolysis but also significantly reduced off-flavors, which are often a barrier to consumer acceptance. Approximately one-third of the proteins were hydrolyzed during fermentation, increasing the content of essential amino acids.

Mixed fermentation also improves the flavor profile of L. platensis by producing compounds like acetoin and other odorants that contribute to a creamier and more palatable aroma. This is particularly beneficial for incorporating L. platensis into functional foods and nutraceuticals, where taste and consumer acceptance are critical factors for market success. The dual microbial approach enhances both nutritional value and flavor by combining the proteolytic activity of Bacillus subtilis, which breaks down proteins into peptides, with the lactic acid fermentation properties of Lactiplantibacillus plantarum, which increases the shelf life and safety of the final product.

Additionally, mixed fermentation processes have been shown to increase the bioavailability of essential nutrients, including peptides and proteins. This improvement makes L. platensis more versatile as an ingredient in various food products, including protein supplements, health drinks, and other nutraceuticals. The combination of L. plantarum and B. subtilis allows for both enhanced nutrient absorption and microbial safety, making it a valuable technique for enhancing the overall quality of L. platensis-based products [14].

Overall, mixed fermentation with multiple microorganisms represents a promising approach for improving the functional and sensory properties of L. platensis. The synergistic effects of combining different microbial activities can lead to higher nutritional value, better flavor, and improved product stability, expanding L. platensis’ potential applications in the food industry.

In the context of L. platensis fermentation, selecting the appropriate fermentation method is crucial for optimizing both yield and bioactive compound production.

Table 1. Comparison of L. platensis fermentation methods.

Fermentation Method	Advantages	Disadvantages	Key Applications	References
Submerged fermentation (SMF)	Precise control over environmental parameters (oxygen, pH, nutrient distribution, and temperature) Possibility of scale-up and mass production	Higher water and energy consumption	Widely used in food and pharmaceutical industries	[29]
Solid-State Fermentation (SSF)	Higher concentration of bioactive compounds (phycocyanin, antioxidants) Lower water requirement (environmentally friendly)	Formation of biogenic amines	Production of bioactive compounds, antioxidants, and peptides	[13,33]
Mixed Fermentation	Use of multiple microorganisms enhances the nutritional profile and flavor of L. platensis-based products, enhances the breakdown of complex molecules, and enhances bioavailability	Complex microbial interactions	Functional foods, nutraceuticals	[14]

provides a detailed comparison of these fermentation methods, including their advantages, disadvantages, and key applications.

4. Bioprocess Engineering and Optimization

4.1. Bioreactor Design and Scaling Up

Optimizing bioreactor design is essential for high-density cultivation of L. platensis, especially for large-scale production. Recent innovations in bioreactor design have focused on improving light penetration, gas exchange, and nutrient supply to enhance biomass production [34,35,36]. One such innovation is the development of flat-plate and tubular photobioreactors, which maximize light exposure and improve photosynthetic efficiency. Tayebati et al. [10] demonstrated that a flat-plate photobioreactor with optimized aeration and light conditions led to a significant increase in biomass production of L. platensis. This system also benefited from the use of glucose and sodium sulphite in the nutrient medium, which enhanced biomass yield under high-density conditions [10]. These photobioreactors are ideal for large-scale operations due to their ability to prevent photoinhibition, enhance carbon dioxide absorption, and maintain stable oxygen levels.

Airlift bioreactors represent another notable advancement for L. platensis cultivation, particularly in terms of minimizing mechanical stress on the cells [37]. The gentle mixing provided by airlift bioreactors preserves cell integrity during long-term cultivation. Studies have shown that airlift bioreactors achieve higher biomass productivity compared to conventional stirred-tank reactors. Zhu et al. [38] highlighted the efficiency of airlift bioreactors in sustaining high cell densities while ensuring adequate nutrient distribution, making them suitable for industrial-scale operations.

Additionally, Fibonacci-type tubular photobioreactors have been developed to optimize light distribution and improve biomass yield [39]. This novel design efficiently maintains optimal temperature, pH, and dissolved oxygen levels, ensuring high light utilization even under outdoor conditions. These photobioreactors have shown promise in maintaining stable L. platensis growth, both indoors and outdoors, with a photosynthetic efficiency of over 8%, thus supporting large-scale production under high irradiance conditions [39].

Scaling up bioreactor systems requires maintaining consistent productivity while transitioning from laboratory to industrial scales. The successful scale-up of a pilot-plant photobioreactor for continuous L. platensis cultivation demonstrated the importance of managing physical parameters such as light distribution, gas exchange, and nutrient mixing. Vernerey et al. [40] successfully scaled up a photobioreactor tenfold by optimizing these interactions, leading to improved biomass yield in large-scale systems.

4.2. Key Fermentation Parameters

The success of L. platensis fermentation depends on precise control of critical parameters such as pH, temperature, stirring, nutrient supply, and aeration. Studies have shown that maintaining an optimal pH of 8.5 to 9.5 and a temperature of around 30 °C is critical for maximizing biomass yield and bioactive compound production, as described in Ogbonda et al. [41]. This study observed that these optimal conditions had higher values of biomass (4.9 mg/mL) and total crude protein (48.2 g/100 g). Moraes et al. [7] demonstrated that deviations from these optimal conditions can result in reduced growth and productivity, emphasizing the importance of maintaining stable environmental conditions during fermentation.

Stirring intensity and aeration rates are also crucial for efficient nutrient distribution and carbon dioxide supply. Insufficient stirring can lead to nutrient depletion and localized hypoxia, while excessive aeration can cause shear stress on cells, resulting in reduced viability. A study by Cui et al. [42] found that increasing the aeration rate from 100 L/h to 800 L/h significantly improved biomass yield, highlighting the need for balanced aeration to optimize nutrient uptake and oxygen transfer.

Temperature, light intensity, and nutrient supply are also critical factors. In a study of outdoor cultivation, Zhu et al. [38] found that regulating temperature and light exposure in floating horizontal photobioreactors increased biomass production by optimizing carbon utilization efficiency. This highlights the importance of maintaining controlled environmental conditions for large-scale L. platensis cultivation [38].

4.3. Monitoring Technologies

Innovative monitoring technologies have become crucial in optimizing L. platensis fermentation processes, allowing for real-time adjustments to key parameters such as pH, dissolved oxygen levels, light intensity, and nutrient concentrations. Advanced sensor technologies, coupled with artificial neural networks (ANNs), have been integrated into bioreactors to automate environmental control. These systems predict changes in culture conditions and make real-time adjustments to maintain optimal growth. Hu et al. [43] demonstrated that closed-loop control systems equipped with ANN-based controllers improved biomass yield and enhanced phycocyanin production by optimizing light and nutrient supply.

These monitoring technologies provide high-precision control over critical parameters, ensuring that L. platensis cultures remain within optimal conditions throughout the fermentation process. The use of real-time monitoring and automated systems minimizes the risk of process disruptions, allowing for continuous, high-efficiency cultivation at industrial scales.

5. Downstream Processing

5.1. Separation and Purification of Bioactive Compounds

Efficient extraction and purification of bioactive compounds, such as phycocyanin and proteins, are essential for the industrial applications of L. platensis. Among the most promising techniques for this purpose is ultrasound-assisted extraction (UAE), which applies high-frequency sound waves to disrupt L. platensis cell membranes, significantly enhancing the release of heat-sensitive compounds like phycocyanin. UAE not only improves extraction yields but also preserves the bioactivity of these compounds, making them particularly suitable for industrial applications. Rodrigues É et al. [29] demonstrated that UAE improved the yield of phycocyanin compared to traditional methods, highlighting its efficiency in both time and energy use.

Vernès et al. [12] further optimized the UAE process by combining it with an aqueous two-phase extraction system, which led to higher purity levels of phycocyanin. This combined approach also reduces processing times and makes large-scale production more feasible due to its energy efficiency and scalability. The authors showed that this method increased the purity of phycocyanin from 0.42 to 1.31 in a single extraction step [12].

Additionally, microwave-assisted extraction (MAE) has been explored as an alternative to UAE. Studies suggest that MAE can produce higher concentrations of phycocyanin with greater purity than UAE, making it a competitive option for extracting this valuable pigment on an industrial scale [33]. The combination of both UAE and MAE applied sequentially has been suggested to further optimize the yield and quality of bioactive compounds from L. platensis biomass.

Finally, pressurized liquid extraction (PLE) is gaining attention as a green and efficient method for extracting bioactive compounds from L. platensis. Zhou et al. [44] demonstrated that PLE significantly increased antioxidant capacity and protein yield under optimized conditions, making it a valuable technique for industrial applications.

5.2. Process Integration for Bioethanol and Biopeptide Production

A biorefinery approach offers the potential to maximize the value of L. platensis biomass by producing multiple high-value products simultaneously. In this approach, L. platensis biomass can be processed not only for the extraction of bioactive compounds but also for the production of bioethanol and peptides. Luiza Astolfi et al. [11] demonstrated that an integrated saccharification and fermentation process efficiently converts L. platensis biomass into bioethanol while the remaining protein fraction is broken down into bioactive peptides with high antioxidant activity.

In this process, enzymes are used to hydrolyze polysaccharides in L. platensis, releasing sugars that are fermented by yeast to produce ethanol. Simultaneously, the protein fraction undergoes enzymatic hydrolysis, generating bioactive peptides. These peptides have been shown to possess antioxidant and antihypertensive properties, offering significant potential for use in nutraceuticals and functional foods [45].

This biorefinery concept allows for the sustainable processing of L. platensis biomass, enabling the production of bioethanol as a renewable energy source while generating peptides for the food and pharmaceutical industries. The integration of these processes enhances the economic viability of L. platensis production, making it an attractive option for industries aiming to reduce waste and improve sustainability. Moreover, the versatility of L. platensis as a feedstock for multiple valuable products further supports its potential in biotechnological applications [45].

6. Applications of Fermented L. platensis

6.1. Functional Food Ingredients

Fermented L. platensis has garnered significant attention as a functional food ingredient due to its rich content of bioactive compounds, including antioxidants, peptides, and essential amino acids, and its beneficial effects on health. The fermentation process enhances the bioavailability of these nutrients and increases their concentration. For instance, fermentation with Lactiplantibacillus plantarum has been shown to increase the levels of GABA and L-glutamic acid, which are beneficial for health and neuroprotective functions. A study found that after 36 h of fermentation, total phenolic content and antioxidant activity (measured by FRAP (Fluorescence Recovery After Photobleaching) and DPPH (2,2-Diphenyl-1-picrylhydrazyl) assays) were significantly enhanced, making fermented L. platensis a potent source of bioactive compounds for nutraceutical applications [46].

Fermentation has also been shown to improve L. platensis’ protein digestibility and increase the release of bioactive peptides. These peptides, which are known for their antioxidant and antimicrobial properties, can be incorporated into various functional food products such as beverages, snacks, and supplements. For instance, a study highlighted that L. platensis fermented in combination with probiotics significantly improved its amino acid content and antioxidant properties, making it suitable for inclusion in health drinks and fermented snacks [47].

The functional food industry has embraced fermented L. platensis as an ingredient in lactose-free beverages, particularly for its ability to enhance antioxidant content and improve gut health through its probiotic action. A study that fermented L. platensis with LAB in a soybean drink showed a substantial increase in phenolic compounds and in vitro antioxidant activity, and the digestibility of the product was also improved [48]. This underscores the potential of fermented L. platensis as a versatile functional ingredient that enhances the nutritional and sensory qualities of food products.

6.2. Pharmaceutical and Cosmetic Applications

In the pharmaceutical industry, L. platensis’ bioactive compounds have been increasingly recognized for their therapeutic potential. Fermented L. platensis releases bioactive peptides and antioxidants that demonstrate immunomodulatory and anti-inflammatory properties, making it a promising candidate for biopharmaceutical applications. The fermentation process enhances the availability of these peptides, which have been shown to modulate immune responses and reduce oxidative stress. For example, peptides derived from fermented L. platensis have been found to stimulate the proliferation of immune cells, such as lymphocytes, and modulate cytokine production, which is critical for maintaining immune homeostasis [49].

Moreover, L. platensis’ antioxidant properties make it an attractive ingredient for cosmeceutical applications. Antioxidants help combat oxidative stress, which contributes to skin aging, making L. platensis-based products ideal for anti-aging formulations. A study by Lafarga et al. [50] reported that bioactive peptides from fermented L. platensis exhibited strong antioxidant activity and could be used in cosmetics to protect skin cells from oxidative damage. The antimicrobial properties of these peptides further enhance their value in cosmetic products, protecting against skin pathogens such as Staphylococcus aureus [50].

6.3. Sustainability Aspects

L. platensis is increasingly recognized for its environmental benefits, particularly in its potential for sustainable production and carbon sequestration. As a microalga, L. platensis efficiently captures carbon dioxide and converts it into biomass through photosynthesis. This process not only reduces greenhouse gas emissions but also produces high-nutrient biomass that can be used for food and bioactive compound production. Studies have shown that L. platensis can fix significant amounts of carbon dioxide, contributing to carbon sequestration efforts and making it a key player in the development of green technologies [2].

In addition to carbon capture, L. platensis can be integrated into refineries to produce biofuels, such as bioethanol, alongside other valuable by-products. The biorefinery approach maximizes the economic and environmental efficiency of L. platensis cultivation by producing multiple high-value products from a single biomass stream. For example, a study demonstrated that L. platensis biomass could be used to produce both bioethanol and peptides with high antioxidant activity, offering a sustainable solution to biofuel production while also generating valuable nutraceutical compounds [11].

Furthermore, L. platensis is being explored for its role in wastewater treatment. Its ability to absorb nutrients and contaminants from wastewater makes it a sustainable option for treating agricultural runoff and industrial effluents. This dual function of wastewater treatment and biomass production enhances the environmental sustainability of L. platensis cultivation and supports its role as a versatile and eco-friendly biotechnological resource [51].

Table 2. Major areas of applications of fermented L. platensis and related key benefits.

Application Area	Key Benefits	References
Functional Food Ingredients	Enhances bioavailability of bioactive compounds: antioxidants, peptides, and essential amino acids. L. platensis + L. plantarum enhance GABA and L-glutamic acid: beneficial for health and neuroprotective functions. Enhances protein digestibility and increases bioactive peptides with antioxidative and antimicrobial properties and is used in functional foods. Ingredient in lactose-free beverages: enhances antioxidative function and improves gut health through probiotic action	[45,46,47,48,52]
Pharmaceutical and Cosmetic	The fermentation process releases bioactive peptides and antioxidants and improves availability. Stimulates proliferation of immune cells and modulates cytokine production: immunomodulatory and anti-inflammatory functions. Biopharmaceutical applications Antioxidative bioactive compounds combat oxidative stress and contribute to skin aging: ideal for anti-aging products. Antimicrobial properties: protection against skin pathogens such as S. aureus	[49,50,53,54]
Sustainability	Environmental benefits: sustainable production and carbon sequestration. L. platensis efficiently captures carbon dioxide and converts it into biomass: decreases greenhouse gas emissions + enhances high-nutrient biomass. Biorefineries: bioethanol production Wastewater treatment	[2,11,51]

outlines the primary applications of fermented L. platensis, categorized into three sectors: functional food ingredients, pharmaceuticals and cosmetics, and sustainability.

7. Future Perspectives and Challenges

7.1. Large-Scale Production Challenges

Scaling up L. platensis production presents several technical and economic challenges, particularly those related to bioreactor design and process control. Large-scale systems, such as open ponds and photobioreactors, require precise control over environmental conditions, including light, nutrient supply, pH, and temperature. One of the main challenges is ensuring uniform light distribution, as insufficient light penetration can limit the growth of L. platensis in high-density cultures. Advanced bioreactor designs, such as tubular and flat-plate photobioreactors, offer better control of these parameters, but the transition from lab-scale to industrial-scale systems often leads to unforeseen issues like contamination, fouling, and increased energy costs [40]. Additionally, maintaining the necessary aeration and agitation in large bioreactors can significantly increase operational costs, posing economic barriers to scalability [40].

Outdoor cultivation systems, such as those used in South Africa, face additional challenges related to environmental variability, such as temperature fluctuations and contamination from external sources. Even though outdoor systems have the potential to reduce operational costs by utilizing natural sunlight, they often experience inconsistent production rates due to varying weather conditions [55]. This inconsistency creates a need for hybrid systems that combine the benefits of both controlled indoor environments and cost-effective outdoor cultivation [55].

7.2. Regulatory and Biosafety Considerations

As the commercial use of L. platensis expands, regulatory frameworks must adapt to accommodate new technologies, especially when dealing with genetically modified (GM) strains. The use of GM L. platensis presents biosafety concerns, particularly related to the potential for horizontal gene transfer and environmental impact if these strains are accidentally released into natural ecosystems. Current regulatory frameworks in regions such as the European Union are stringent, requiring rigorous testing and approval processes before GM organisms can be used commercially. In contrast, regulatory approaches in other parts of the world may be more lenient, which could lead to discrepancies in the global market for L. platensis-based products [24]. Therefore, developing a comprehensive international regulatory standard is essential for ensuring the safe use of GM L. platensis while fostering innovation in the field [24].

7.3. Potential Research Directions

Several promising areas for future research could address existing knowledge gaps and enhance the scalability and efficiency of L. platensis production. One key area is the development of more robust strains through genetic and metabolic engineering. Advances in CRISPR and other genome-editing technologies could allow for the creation of L. platensis strains with improved resistance to environmental stressors, faster growth rates, and enhanced production of valuable bioactive compounds such as phycocyanin and bioactive peptides [50]. Additionally, further research into optimizing fermentation processes, including mixed fermentation techniques and the integration of biorefinery models, could improve the overall economic viability of L. platensis production [50].

Research should also focus on improving the sustainability of L. platensis cultivation. Integrating L. platensis production with wastewater treatment or carbon capture technologies offers significant environmental benefits while also reducing production costs. Further investigations into the use of alternative, low-cost nutrient sources, such as agricultural by-products or wastewater, could make large-scale production more sustainable and affordable [51].

8. Conclusions

The fermentation of L. platensis has emerged as a fundamental technique in enhancing the bioavailability and functionality of its bioactive compounds, such as antioxidants, peptides, and phycocyanin. Advances in strain improvement, including genetic and metabolic engineering, have paved the way for optimized L. platensis strains with higher yields and improved production of valuable bioactive compounds. The comparison between SMF and SSF methods has shown that each offers distinct advantages, with SSF providing superior bioactive compound extraction in certain contexts. Furthermore, innovations in bioreactor design, such as tubular and flat-plate photobioreactors, have enhanced the scalability of L. platensis production, while the integration of sustainable approaches, such as biorefinery models, has maximized the economic and environmental benefits.

Applications of fermented L. platensis have expanded beyond nutraceuticals into pharmaceuticals and cosmetics, driven by its rich profile of bioactive compounds. The potential for L. platensis to play a role in carbon sequestration and green technologies further underscores its versatility as a biotechnological resource. Nevertheless, challenges remain, particularly in scaling up production, addressing regulatory and biosafety concerns, and optimizing fermentation parameters for consistent, high-quality yields.

Looking ahead, the potential for large-scale L. platensis production and its commercialization in biotechnology is immense. Continued research into strain engineering, bioprocess optimization, and fermentation techniques will be crucial in overcoming the existing challenges of scaling up. Furthermore, integrating L. platensis cultivation into sustainable production systems, such as wastewater treatment and carbon capture technologies, could dramatically enhance its role in addressing global environmental and food security challenges. As advancements in genetic engineering and bioprocess technologies progress, L. platensis is well-positioned to become a cornerstone of future biotechnological applications in food, pharmaceuticals, cosmetics, and environmental management.