Assessment of the Use of Coconut Water as a Cultivation Medium for Limnospira (Arthrospira) platensis (Gomont): Effects on Productivity and Phycocyanin Concentration

Abstract

Due to the scarcity of sustainable inputs for photosynthetic microorganisms’ biotechnology, the search for natural substrates such as coconut water has gained prominence. This by-product is a substrate rich in macro- and micronutrients, as well as endogenous phytohormones that support microbial growth. In this context, this study aimed to use it as an alternative cultivation medium for Limnospira platensis (Gomont), formerly known as Arthrospira platensis, a high-value cyanobacterium. We evaluated growth parameters, phycocyanin concentration, purity, and biomass yield cultivated in coconut water and in SAG_1x medium, a modified Zarrouk medium. Over 35 days of cultivation, both media efficiently supported cyanobacterial growth. In coconut water, the specific growth rate was 0.305 d⁻¹, the maximum growth rate was 0.629 d⁻¹, and the productivity was 0.256 g L⁻¹ d⁻¹. In SAG_1x medium, the values obtained were 0.240 d⁻¹, 0.676 d⁻¹, and 0.218 g L⁻¹ d⁻¹, respectively. Phycocyanin obtained from cultivation in SAG_1x medium presented food-grade purity (OD620/OD280 ratio > 0.7), while in coconut water, it was 0.6. The pigment concentration and yield in SAG_1x (19.1 mg/L and 34.3%, respectively) also slightly exceeded those obtained with coconut water (14.3 mg/L and 25.5%, respectively). Despite this, the data reinforce the potential of coconut water as a viable and economically competitive alternative to conventional media for L. platensis production.

1. Introduction

Cyanobacteria, also known as blue–green algae, are a group of prokaryotic, photosynthetic, and unicellular microorganisms that, due to their easy adaptation to environments with adverse conditions, can be found in almost all habitats on Earth, including those with low nutrient availability [1,2]. In recent years, these microorganisms have gained prominence as a rich source of bioactive compounds, with them being considered one of the most promising groups for the production of such molecules [3,4].

Among the species of greatest economic relevance, Limnospira platensis (Gomont), formerly known as Arthrospira platensis [5], stands out, a filamentous cyanobacterium widely recognized for its use as a nutritional supplement and food additive, due to its high protein content (70% on dry weight basis) [6], polysaccharides, carbohydrates, lipids, and enzymes. Furthermore, it is an excellent source of phycobiliproteins, a protein-pigment complex that captures light in cyanobacteria [7]. There are three main classes of phycobiliproteins that differ in protein structure, consisting of C-phycocyanin (C-PC), allophycocyanin, and phycoerythrin. C-phycocyanin represents the main group of phycobiliproteins [8] and has wide applicability in the pharmaceutical industry as an antioxidant, anti-inflammatory, immunomodulatory, and antitumor agent [9,10,11,12]. Additionally, it has also been used as a color additive in the food and cosmetics industries [13,14]. This is an important topic, as the U.S. Department of Health and Human Services (HHS) and the Food and Drug Administration (FDA) have recently indicated a significant shift toward the restriction and gradual phase-out of synthetic dyes, especially those derived from petroleum, due to growing evidence of health risks [15,16].

In view of this, the phycocyanin market size is expected to increase by 33.8% by 2030 [17], which implies that production will likely rise in the coming years. This results in greater interest in research on new processing methods. However, for these applications to become viable at an industrial scale, it is essential to optimize the cultivation conditions of biomass rich in C-PC [18]. Biomass growth and pigment synthesis are influenced by light, temperature, pH, and agitation. Nevertheless, nutrient availability is one of the main promising strategies to alter and control cyanobacterial growth and pigment production [19,20]. During cultivation, essential nutrients consist of nitrogen sources and carbon sources, either organic or inorganic, which represent one of the most economically impactful factors in production and other micronutrients necessary for cell development [21,22], as well as other micronutrients necessary for cell development, such as iron, magnesium, zinc, and others [23,24].

Consequently, the replacement of basic carbon sources in the medium by other organic components as an alternative strategy for cultivation medium formulation has shown promise, aiming at cost reduction, which represents approximately 35% of the total cost of algal biomass production, and greater availability of nutrient sources [25,26]. Previously, the use of chicken or goat manure [27,28] and sugarcane molasses [29] has been reported. The use of these alternative cultivation media increased nutrient use efficiency and Limnospira productivity, indicating that other natural products may also have potential for this purpose.

In this context, coconut water, a liquid present in the endosperm of Cocos nucifera L. seeds, stands out as a promising option, as it is a free by-product and a nutrient-rich substrate for microbial cultivation [30], consisting mainly of water (95.5%), as well as 4% sugars, 0.1% fat, 0.02% calcium, 0.01% phosphorus, 0.5% iron, and considerable amounts of carbohydrates, proteins, amino acids, minerals, vitamins, and endogenous phytohormones essential for the growth and maintenance of cyanobacteria such as L. platensis [31]. The use of coconut water as an alternative cultivation method for the growth of L. platensis is an approach that offers several benefits, potentially improving quality and productivity compared to traditional cultivation methods [30,32]. For example, coconut water has been successfully employed as a growth medium for Meyer lemon, as well as for various microbes and fungi, and has provided a straightforward and cost-effective strategy for large-scale growth, making it suitable for commercial-scale operations [31,33,34].

Furthermore, the global coconut water market has been consistently growing, particularly in Asia and the Pacific, especially in Indonesia, the Philippines, India, Sri Lanka, and Brazil, which together account for the majority of global coconut production. In these countries, there is a well-established infrastructure for collection, transportation, and processing, ensuring sufficient supply to meet the needs of both the food industry and potential biotechnological applications [35,36,37]. The operational costs associated with this production, which are already considerably low, can be further reduced by utilizing residual or industrial by-product coconut water. This subproduct, typically considered a low-value waste, can be obtained at virtually no cost, thereby significantly decreasing expenditures on inputs [38,39]. The cost of the standard Zarrouk medium for the production of L. platensis is approximately USD 0.08 per liter, representing up to 35% of the total biomass cost, whereas alternative media or residual substrates have been shown to reduce this cost by about fivefold (USD 0.016 per liter) [40]. This context contributes to strengthening the local economy and promotes production sustainability, offering new perspectives for the implementation of more sustainable and adaptable production.

Thus, in view of its abundance, low cost and suitable chemical composition, coconut water was tested in this study as an alternative growth medium for L. platensis, a nutritionally demanding and high-value cyanobacterial species, with the aim of evaluating its impact on growth rates and on the production and purity of C-PC in comparison with a standard cultivation medium, thereby contributing to its feasibility as a potential microbial growth medium.

2. Materials and Methods

2.1. Inoculum Preparation, Culture Media and Experimental Design

The cultivation of L. platensis (UTEX 1926) was carried out using two distinct growth media: Spirulina 1x modified medium (SAG_1x) [41], considered a modified variation of the SAG medium (Sammlung von Algenkulturen Göttingen), developed by University of Texas Algae Culture Collection (UTEX) and closely resembling Zarrouk’s medium, and coconut water (Cocos nucifera L.), corresponding to the liquid endosperm extracted from fresh fruits approximately two months old. For the formulation of the coconut water-based medium, the liquid was previously filtered through a 0.22 µm sterilizing membrane and then supplemented with the same metal (P-IV) and micronutrient (Chu) solution used in the SAG_1x medium. The pH was adjusted to 9.0 by adding sodium carbonate (Na₂CO₃) [42]. The composition of the growth media, including the reagents used for their preparation, is described in

Table 1. Composition of SAG_1x medium and presence of corresponding components in coconut water. Concentrations are expressed in g L⁻¹. The presence of components in coconut water is indicated qualitatively and quantitatively, based on values reported in the literature [43,44,45].

Chemicals/Compounds	Concentration in SAG1x Medium (g L−1)	Concentration Naturally Present in Coconut Water (g L−1)	Supplemented in Coconut Water? (g L−1)
NaHCO3	27.22	n.d.	No
Na2CO3	8.06	n.d.	Yes (for pH adjustment)
K2HPO4	1	0.027–0.033	No
NaNO3	5	0.0002–0.0010 (traces)	No
K2SO4	2	0.02–0.062	No
NaCl	2	0.40–1.20	No
MgSO4·7H2O	0.4	0.10–0.12	No
CaCl2·2H2O	0.08	0.074–0.185	No
Vitamin B12	2 mL	n.d.	No
P-IV Metal Solution	12 mL	-	-
Composition of Metal Solution
Na2EDTA·2H2O	0.75	n.d.	Yes—0.75
FeCl3·6H2O	0.097	0.0001–0.0005 (traces)	Yes—0.097
MnCl2·4H2O	0.041	0.00002–0.0001 (traces)	Yes—0.041
ZnCl2	0.005	0.00001–0.00006 (traces)	Yes—0.005
CoCl2·6H2O	0.002	<0.000001 (traces)	Yes—0.002
Na2MoO4·2H2O	0.004	<0.000001 (traces)	Yes—0.004
Chu Micronutrient Solution	2 mL	-	-
Composition of Micronutrient Solution
CuSO4·5H2O	0.02	0.00002–0.00005 (traces)	Yes—0.02
ZnSO4·7H2O	0.044	0.00001–0.00006 (traces)	Yes—0.044
CoCl2·6H2O	0.02	<0.000001 (traces)	Yes—0.02
MnCl2·4H2O	0.012	0.00002–0.0001 (traces)	Yes—0.012
Na2MoO4·2H2O	0.012	n.d.	Yes—0.012
H3BO3	0.62	0.005–0.009	Yes—0.062
Na2EDTA·2H2O	0.05	n.d.	Yes—0.05

The values in the column “Concentration naturally present in coconut water (g L⁻¹)” are aggregated ranges obtained from the indicated references. “n.d.” = not detected. “traces” = present in trace amounts.

.

The inoculum was prepared by cultivating the cyanobacterium in SAG_1x medium until reaching the exponential growth phase. At this stage, the wet biomass was harvested and washed by centrifugation three times with distilled water, a procedure that served as a transition step to completely remove the previous medium before the transfer to coconut water and to SAG_1X medium. The cell concentration was adjusted to 50 mg L⁻¹ based on spectrophotometric measurements at 560 nm using a previously established growth curve. This inoculum was then used to initiate the cultivation in 16 independent 250 mL Erlenmeyer flasks, each filled with 150 mL of culture (eight containing SAG_1x medium and eight containing coconut water, of two fresh fruits), maintained under continuous agitation on an orbital shaker at 120 rpm and continuous illumination, at a temperature of 28 ± 2 °C and a light intensity of 45 ± 5 μmol photons m⁻² s⁻¹.

During the cultivation days (35 d), until the death phase, 1 mL aliquots were withdrawn daily from all eight flasks containing SAG_1x and coconut water. The cell concentration was determined by measuring OD 560 nm in a spectrophotometer. Each aliquot was measured in triplicate (analytical replicates), and the mean of the three readings was considered as the value for that flask on each day. Before withdrawing the aliquots, the cultures were homogenized by gentle agitation, and both the positions of the flasks and the sampling order were randomized to minimize possible biases. To determine the other growth parameters and phycocyanin production, the wet biomass was collected at the stationary phase of the cultures (15 days for both media) and concentrated by centrifugation (5 min at 2000 rpm). The concentrated wet biomass was then used to determine the growth parameters and phycocyanin content by standardized analytical methods, without prior drying or additional extraction steps.

2.2. Growth Parameters

The growth of the culture was determined daily based on the OD at 560 nm, and the specific growth rate was calculated using the equation:

$$\mu ={\displaystyle \frac{\ln \left({OD}_{\mathrm{x}}\right)-\mathrm{l}\mathrm{n}\left({OD}_0\right)}{t_{\mathrm{x}}-t_0}}$$

where μ is the specific growth rate, OD_x is the maximum optical density, OD₀ is the initial optical density at t₀ (time zero), and t_x is the cultivation time at the maximum OD_x.

The maximum growth rate (μ_max) was calculated as:

$${\mu }_{\max }={\displaystyle \frac{1}{\Delta t}}\mathrm{l}\mathrm{n}\left({\displaystyle \frac{X_j}{X_{j-1}}}\right)$$

where X_j e X_j−1 are the cell concentrations at the end and the beginning of each time interval (Δt = 1 day).

Finally, the average cell productivity (P_x) was calculated by dividing the variation in cell concentration (X_max − X_i) by the cultivation time (T_c), according to the equation:

$$P_{\mathrm{x}}={\displaystyle \frac{X_{\mathrm{m}\mathrm{a}\mathrm{x}}-X_i}{T_c}}$$

where X_max is the maximum cell concentration and X_i is the initial cell concentration at the cultivation time (T_c).

2.3. Pigment Analysis

To determine the phycocyanin concentration, the absorbance of the collected wet biomass was measured using a spectrophotometer at 280, 615, and 652 nm. The quantification was calculated according to the equations of Bennett and Bogorad [46]:

$$\mathrm{C}\mathrm{F}={\displaystyle \frac{{OD}_{615}-0.474\times {OD}_{652}}{5.34}}$$

where CF is the phycocyanin concentration, and OD₆₁₅ and OD₆₅₂ refer to the optical density readings at 615 and 652 nm, respectively.

The phycocyanin purity ratio was determined according to Antelo et al. [47], using the equation:

$$\mathrm{P}\mathrm{E}={\displaystyle \frac{{OD}_{615}}{{OD}_{280}}}$$

where PE corresponds to the purity of the extract, and OD₆₁₅ and OD₂₈₀ refer to the optical density readings at 615 and 280 nm, respectively.

The cultivation yield was determined following the methodology described by Silveira et al. [48], according to the equation:

$$\mathrm{R}\left(\%\right)=\mathrm{P}\mathrm{C}\times \mathrm{V}{\displaystyle \frac{\mathrm{P}\mathrm{C}\times \mathrm{V}}{\mathrm{D}\mathrm{B}}}$$

where PC is the phycocyanin concentration, V is the solvent volume (mL), and DB is the biomass (dry weight in g).

2.4. Statistical Analysis

The data were checked for normality using the Shapiro-Wilk test. Based on these results, Pearson or Spearman correlation tests were performed to determine the relationship between cultivation time and biomass growth in both media. In addition, to verify the significance between the two media regarding pigment production, a one-way analysis of variance (ANOVA) with Tukey’s post-hoc test was applied. Finally, to determine differences in growth parameters between SAG_1x medium and coconut water, the non-parametric Mann-Whitney test was used. The data related to pigment production and growth parameters were obtained from measurements performed on three independent flasks, randomly selected at the stationary phase of growth. All analyses were carried out using GraphPad Prism 8.0.1, and the results were expressed as mean ± standard deviation. A p-value ≤ 0.05 was considered statistically significant.

3. Results and Discussion

Due to the high cost of chemical culture media, which can account for up to 35% of the total cost of L. platensis biomass production, there is a growing interest in the search for more economical alternatives [49,50,51]. Coconut water stands out as a promising alternative to conventional culture media, as it is a natural matrix rich in sugars, amino acids, vitamins, and minerals essential for microbial growth. Its availability in many tropical regions where coconut cultivation is common makes it a potentially attractive resource for cyanobacterial biomass production under specific geographic and economic conditions. In addition, coconut water has a relatively low cost when compared to other media. A conceptual cost analysis indicates that the use of coconut water reduces the number of chemical reagents required in other media, laboratory steps, preparation time, and energy demand [43,52]. For example, the price of NaHCO₃, the reagent most commonly used in standard media, can reach approximately USD 49.15 per kg, whereas the average price of coconut water ranges from USD 0.17–0.34 [53].

In this study, coconut water appears to provide a slightly more favorable environment for the growth of L. platensis, as it showed a trend toward higher biomass production compared to the SAG_1x medium, although the difference was not statistically significant (p = 0.8549) (Figure 1). Growth curve analysis showed that both media supported exponential growth until the tenth day of cultivation. However, coconut water sustained higher cell concentrations during the stationary phase. After this phase, a declining trend was observed in both media. Nevertheless, a weak but significant positive correlation (r = 0.3790; p = 0.0271) was observed in the culture with SAG_1x, suggesting a moderately consistent increase in biomass over time. In contrast, in the culture with coconut water, the positive correlation was not significant (r = 0.2590; p = 0.1391), indicating greater variability in the growth response in this medium, with faster growth and a shorter stability phase.

The replacement of a standard culture medium with cheaper and more accessible organic sources for the production of Limnospira has previously been implemented as a strategy to reduce cultivation costs. In the study by Thathsatani et al. [54], the carbon source (NaHCO₃) of Zarrouk’s medium was replaced with mungbean flour in different proportions (25%, 50%, 75%, and 100%). On the first day of inoculation, no significant differences in growth were observed among the treatments. However, by the end of the seventh day of incubation, cultures with 75% and 100% replacement showed a significant reduction in growth, resulting in cyanobacteria death by the 13th day. Similarly, the replacement of the micronutrient solution of Kosaric medium with banana leaf ash extract, as well as the use of papaya peel extract diluted in water and enriched with different concentrations of urea, NaCl, and NaHCO₃, also compromised the cell growth of L. platensis [55,56].

The addition of coconut water to the culture medium has also been analyzed in other studies; however, only low concentrations (3, 5, and 10%) were well tolerated by L. platensis cells [57,58]. In the study by Khasena et al. [57], the cultures entered the decline phase on the 8th day, shortly after reaching peak cell density on the 7th day. In contrast, in the present study, the decline phase was observed only from the 20th day onward, demonstrating greater stability of cell growth over time. This difference in the observed growth of the strain used and the initial concentration of the inoculum and nutrients employed in both media [59,60,61,62]. There is also reason to believe that experimental differences may have contributed to the different responses observed among the studies: factors such as the pH of the coconut water, which was adjusted by supplementation with sodium carbonate (Na₂CO₃), increasing carbon availability, as well as temperature and light intensity, which vary considerably among culture protocols, may have influenced the results obtained, since these are conditions to which the strain used in our experiment was already highly adapted [63,64].

Additionally, quantitative growth parameters were compared between SAG_1x medium and coconut water. The comparative analysis of these parameters also revealed significant differences in the performance of the cultures (p < 0.05) (

Table 2. Comparative growth parameters of L. platensis cultured in SAG_1x medium and coconut water supplemented with trace metals and micronutrients.

Growth Parameter	SAG1x Medium	Coconut Water	p-Value
Specific growth rate (μ)	0.240 ± 0.024 d−1	0.305 ± 0.023 d−1	0.0043 *
Maximum growth rate (μmax)	0.676 ± 0.0034 d−1	0.629 ± 0.0019 d−1	0.0022 *
Productivity (Px)	0.218 ± 0.0019 g L−1·d−1	0.256 ± 0.0019 g L−1·d−1	0.0022 *

Values are expressed as the mean ± standard deviation (SD). Asterisks indicate significant differences compared to the negative control (ANOVA, p ≤ 0.05).

). The specific growth rate (μ), calculated between days 2 and 10, corresponding to the exponential phase, indicated faster growth in the coconut water medium (0.305 d⁻¹) compared to SAG_1x medium (0.240 d⁻¹). This difference was statistically significant (p = 0.0043), suggesting that coconut water provides a more favorable environment for the initial development of L. platensis biomass. In addition, the μ_max obtained over intervals of consecutive days, was significantly higher in SAG_1x medium (0.676 d⁻¹) than in coconut water (0.629 d⁻¹) (p = 0.0022), which may indicate rapid growth peaks in both media, although at different stages of cultivation. The average cell productivity in both cultures also showed similar results. In coconut water, L. platensis exhibited a P_x of 0.256 g L⁻¹·d⁻¹, while in SAG_1x medium, the P_x was 0.218 g L⁻¹·d⁻¹ (p = 0.0022).

The results obtained in this study demonstrate higher productivity compared to media described in the literature using chemical products and other alternative media. For example, in unmodified Zarrouk medium, the cell productivity was 0.235 g L⁻¹ d⁻¹ [65]. When the medium was supplemented with sugarcane molasses, a by-product of the sugar-alcohol industry with a high sugar content (>50%), the daily cell productivity was lower (0.130 g L⁻¹ d⁻¹), with a μ_max of 0.147 d⁻¹ [66]. In turn, the replacement of Zarrouk medium components with commercial fertilizers (such as ammonium nitrate (NH₄NO₃), urea (CO·(NH₂)₂), and single super phosphate fertilizer SSP (Ca·(H₂PO₄)₂·H₂O)) resulted in a productivity of 0.028 mg L⁻¹ d⁻¹ and a μ_max of 0.233 div d⁻¹ [67]. Similarly, the use of anaerobically digested dairy manure wastewater, a culture medium highly rich in organic compounds, achieved a P_x of 0.080 g L⁻¹ d⁻¹ [68].

These results indicate that the presence of organic compounds in the medium promotes mixotrophic growth of the cultures, which could confer advantages for the growth of L. platensis [69,70]. However, this may also favor an imbalance in autotrophic or heterotrophic metabolism, and when this occurs, the limiting factor for the unfavorable metabolic process (light in the case of photosynthesis or organic carbon for heterotrophic growth) can inhibit growth [71]. The findings of Michael et al. [65] clearly illustrate this metabolic balance, since the macronutrients (N, P, K) in Zarrouk medium were replaced by the commercial fertilizer NPK 10-20-20 (10% ammonia (NH₃), 20% phosphorus pentoxide (P₂O₅), and 20% potassium oxide (K₂O)), combined with the addition of sodium bicarbonate (NaHCO₃), sodium chloride (NaCl), and a trace element solution to meet the nutritional requirements of L. platensis. Under these conditions, the cell productivity was 0.254 g L⁻¹ day⁻¹, a result similar to that obtained with coconut water used in the present study (0.256 g L⁻¹ day⁻¹).

These data demonstrate that, although some alternative sources show economic viability, there is considerable variability in cellular growth efficiency, making it necessary to evaluate the nutritional composition and physicochemical conditions of the culture medium [72]. In this context, the enhanced growth observed in the formulation with SAG_1x medium and coconut water can be attributed to the more balanced nutritional composition of these substrates. SAG_1x medium contains organic and inorganic sources that enhance nutrient availability and facilitate uptake by the biomass [41]. Coconut water, besides containing essential macro- and micronutrients also present in SAG_1x medium, stands out due to the presence of growth-regulating substances such as cytokinins (5.8 mg L⁻¹), auxins (0.07 mg L⁻¹), and small amounts of gibberellins, which together promote a biochemically favorable environment for cellular multiplication and the development of L. platensis [30,73]. This reinforces the potential of the proposed formulation as a viable and economically competitive alternative compared to conventional media or those composed of agro-industrial residues, which could result in imbalances in growth conditions.

Finally, the concentration of pigments present in the media was evaluated (Figure 2). When L. platensis grew in SAG_1x medium, it exhibited a higher cellular concentration of phycocyanin (19.1 mg/mL) (p < 0.0001), a higher purity index (0.7) (p = 0.0088), and an extraction yield of 34.3% (p < 0.0001). In contrast, cultivation in coconut water resulted in a phycocyanin concentration of 14.3 mg/mL, with a purity of 0.6 and a yield of 25.8%. These results indicate that, although coconut water sustained biomass growth, SAG_1x medium was slightly more efficient in promoting phycocyanin synthesis and recovery.

To date, no published study has quantified the phycocyanin content in microalgae or cyanobacteria specifically cultivated in coconut water. However, previous research has explored other alternative culture media, such as Zarrouk medium supplemented with leachate. After extraction by ultrasonication with sodium dihydrogen phosphate buffer (NaH₂PO₄) and sodium chloride (NaCl), followed by three freeze-thaw cycles, the extract of Limnospira maxima (formerly Spirulina maxima) presented a phycocyanin concentration of 6.19 mg L⁻¹ [74]. Higher concentrations were obtained from Spirulina sp. cultivated in Zarrouk medium supplemented with liquid molasses, where phycocyanin was extracted by two-step precipitation with ammonium sulfate ((NH₄)₂SO₄) (32.1 mg/g). However, the purity levels of phycocyanin were 0.5 for the extract obtained under photoautotrophic cultivation (unmodified Zarrouk medium) and 0.6 for mixotrophic cultivation (supplemented Zarrouk medium) [75].

The purity of phycocyanin obtained from biomass cultivated in SAG_1x medium is considered food-grade (OD₆₂₀/OD₂₈₀ ratio ≥ 0.7), meeting the minimum criteria for application in products intended for human consumption [76]. Although coconut water exhibited slightly lower purity (0.6), the data indicate its potential as an alternative medium, especially considering its accessibility and natural origin [31]. In addition, extraction and purification techniques should be employed, since the yield of this pigment is directly related to these additional steps [7,77]. Therefore, the results indicate that both SAG_1x medium and coconut water are promising for the production of L. platensis and coproduction of phycocyanin, highlighting coconut water as a viable, naturally derived, and cost-effective alternative.

4. Conclusions

The results of this study demonstrate that a more accessible and naturally renewable source, such as coconut water, can be used as a substitute substrate for the production of L. platensis. In this work, coconut water efficiently supported the growth of L. platensis, maintaining higher cell concentrations when compared to SAG_1x medium, a standard medium with synthetic sources used for cyanobacteria cultivation. Furthermore, similar values were observed for specific growth rate, maximum growth rate, and cellular productivity, indicating that both media have the potential to sustain cyanobacteria growth.

Finally, phycocyanin production was analyzed, and the biomasses cultivated in both media were able to produce significant concentrations of the pigment, with purity indexes higher than those reported in other alternative media described in the literature. Therefore, this study indicates that coconut water is a competitive alternative medium to synthetic media, such as SAG_1x (a modified zarrouk medium), which is frequently used as a reference and contains many of the nutrients present in other Limnospira cultivation media, as it produces comparable results in terms of productivity and pigment production, while also offering the advantage of significantly reduced production costs.

Moreover, future studies should explore the integration of bioreactors to optimize cultivation conditions in real time, ensuring efficient and scalable production. Additionally, it is also important to apply Coconut water characterization and biomass extraction techniques to improve pigment recovery and overall process efficiency, as well as performing a complete economic analysis that includes logistics, storage, and labor, with the goal of enabling the use of coconut water as a sustainable and functional cultivation medium for the growth of L. platensis and other high-value photosynthetic microorganisms.