Research

Microalgae as sustainable mineral sources

May 11, 2026

118

Mineral deficiencies remain a critical global health challenge, affecting over 5 billion people worldwide who fail to consume adequate amounts of at least one essential micronutrient. Iron deficiency alone causes anaemia in approximately one in four people globally, while calcium, zinc, and magnesium deficiencies contribute to numerous chronic conditions, from cardiovascular disease to impaired immune function. Conventional dietary sources, whether animal-based or plant-derived, present sustainability concerns or limitations in bioavailability due to absorption inhibitors. Against this backdrop, microalgae have emerged as promising alternative nutrient sources, offering dense mineral profiles alongside proteins, lipids, and bioactive compounds.

A recent study published in Current Research in Food Science by Gao et al. (2026) provides the first comprehensive, species-wide comparison of both mineral bioaccessibility and iron bioavailability across nine commercially produced microalgae species. This research addresses a critical knowledge gap: while microalgae are recognised as mineral-rich, their nutritional value depends not merely on content but on the extent to which these minerals can be released during digestion (bioaccessibility) and subsequently absorbed by intestinal cells (bioavailability). The findings demonstrate that microalgae represent highly promising sustainable food sources, though with substantial inter-species variation requiring careful selection for specific nutritional applications.

Table of Contents

Methodology and experimental design

The research team evaluated nine microalgae samples representing taxonomically diverse species widely used in commercial food and feed applications:

three variants of Chlorella vulgaris (green, yellow, and white);
Arthrospira platensis (Spirulina);
Tetraselmis chuii;
Nannochloropsis oceanica;
Dunaliella salina;
Haematococcus pluvialis, in both its unlysed and lysed forms.

The comprehensive analytical approach combined:

mineral profiling using inductively coupled plasma mass spectrometry (ICP-MS);
standardised in vitro digestion following the INFOGEST 2.0 protocol;
cellular absorption assessment using differentiated human intestinal epithelial (Caco-2) cells.

The INFOGEST 2.0 protocol simulated the three sequential phases of human gastrointestinal digestion: oral, gastric, and intestinal phases, conducted under physiological conditions at 37°C (Brodkorb et al., 2019). Approximately 125 mg of each microalgae sample was subjected to simulated salivary fluid, followed by gastric digestion at pH 3.0 with pepsin for two hours, and finally intestinal digestion at pH 7.0 with pancreatin and bile extract for an additional two hours. Post-digestion samples were centrifuged to separate the bioaccessible fraction (supernatant containing solubilised nutrients) from undigested residues.

For iron bioavailability assessment, the Caco-2 cell model was employed — a well-established system that mimics the human intestinal epithelium. Cells were cultured for 12 days to achieve differentiation, then exposed to iron-deficient conditions before measurement. Using the fluorescent probe Calcein-AM, whose signal is quenched upon iron absorption, the research team quantified cellular iron uptake kinetically over 90 minutes. Ferrous sulphate (FeSO₄) served as the positive control, representing a highly soluble reference iron source.

Mineral content: substantial inter-species variation

The total mineral content analysis revealed striking differences among the nine microalgae species. Iron content ranged from 72.1 mg/kg in C. vulgaris yellow to an exceptional 3,120.9 mg/kg in T. chuii — a more than 40-fold variation. To contextualise these values, even the lowest iron concentration exceeded that of beef (25.6 mg/kg fresh weight), while T. chuii contained approximately 22 times more iron than soybean seeds (143.0 mg/kg). Arthrospira platensis, Haematococcus pluvialis (lysed), and Dunaliella salina presented intermediate but still substantial iron levels ranging from 382.8 to 709.2 mg/kg.

Calcium concentrations displayed similarly wide variation, from 516.9 mg/kg in H. pluvialis (unlysed) to 24,146.3 mg/kg in T. chuii. Notably, A. platensis and D. salina also exhibited high calcium content (12,920.8 and 10,359.6 mg/kg, respectively), substantially exceeding conventional plant sources such as tofu (275 mg/kg) and approaching or surpassing soybean seeds (1,742–2,688 mg/kg). For zinc, green C. vulgaris demonstrated the highest concentration (282.1 mg/kg) — over three times that of milk powder (86.2 mg/kg) — while Haematococcus species showed the lowest values (12.1–12.7 mg/kg). Magnesium content ranged from 379.2 mg/kg in H. pluvialis (lysed) to an impressive 15,245.9 mg/kg in D. salina.

Beyond these primary minerals, the study quantified copper (1.3–3.3 mg/kg), manganese (13.6–112.3 mg/kg), phosphorus (942.6–13,917.9 mg/kg), and potassium (9,042.1–61,235.9 mg/kg) across species. The comprehensive mineral profiles underscore microalgae as dense micronutrient sources, though content alone provides incomplete nutritional assessment without bioaccessibility and bioavailability data.

Bioaccessibility: the critical disconnect between content and availability

The bioaccessibility results revealed a fundamental finding: high mineral content does not guarantee high nutritional availability. Iron bioaccessibility varied from merely 0.5% in T. chuii — despite its highest total iron content — to 83.4% in green C. vulgaris, which contained one of the lowest total iron concentrations. This dramatic disconnect demonstrates that structural and biochemical characteristics fundamentally influence nutrient release during digestion. Arthrospira platensis and the lysed H. pluvialis showed moderate-to-high iron bioaccessibility (45.8% and 55.8%, respectively), while Nannochloropsis oceanica and D. salina exhibited low values (5.1% and 7.7%).

Comparing these findings to conventional foods highlights microalgae’s potential: the 83.4% iron bioaccessibility of green C. vulgaris substantially exceeds values reported for thermally treated lamb meat (4–19%), beef (~29%), and even plant sources such as soybean and quinoa (~39–41%) (see also Gao et al., 2025). Calcium bioaccessibility ranged from negative values in lysed H. pluvialis (−3.2%, likely due to calcium-phosphate precipitation) to 82.3% in D. salina, with C. vulgaris green (72.5%) and A. platensis (70.2%) also showing favourable release. These values compare very favourably to beef, chicken, and pork (8–30%) and dairy-fortified matrices (20–36%).

Zinc bioaccessibility was detectable only in A. platensis and the three Chlorella vulgaris variants, ranging from 51.9% to 62.2% — lower than quinoa (92%) and soybean (87%) but comparable to lentils (67%) and tuna (66%). Other minerals showed high bioaccessibility: magnesium ranged from 68.0% to 92.2% across species (exceeding cooked lamb at 41–54%), while potassium consistently exceeded 91% in nearly all species (versus 64–76% in lamb meat). Copper, manganese, and phosphorus exhibited species-dependent patterns, with green C. vulgaris consistently demonstrating high bioaccessibility across multiple minerals.

The researchers propose several mechanistic explanations for inter-species variation:

cell wall architecture — including thickness, rigidity, and polymer composition — likely influences the extent of intracellular mineral release during enzymatic and physicochemical digestion. Species with thick, multi-layered walls such as Chlorella and Nannochloropsis may exhibit reduced bioaccessibility unless subjected to pre-treatment;
additionally, mineral-binding compounds including polyphenols and phytic acid can form insoluble complexes, limiting solubilisation (Kumar et al., 2010);
finally, different intracellular mineral speciation — such as polyphosphate granules or varying oxidation states — may strongly influence dissolution under gastrointestinal pH conditions.

Bioavailability assessment: cellular iron uptake reveals functional value

The Caco-2 cellular absorption assays provided critical functional evidence complementing the bioaccessibility measurements. Under acidic conditions (pH 5.5), which mimic the upper small intestine environment, four microalgae species exhibited measurable iron uptake: A. platensis, H. pluvialis unlysed, T. chuii, and D. salina. Remarkably, A. platensis (94.8% relative bioavailability at 30 minutes, LOWESS-smoothed) and H. pluvialis unlysed (87.3%) showed no statistically significant difference compared to the FeSO₄ reference (p > 0.05), indicating comparable absorption efficiency to this highly soluble inorganic iron source.

Tetraselmis chuii (64.2%) and D. salina (59.1%) demonstrated moderately high relative bioavailability, significantly exceeding conventional food sources. For context, fish and beef exhibit substantially lower iron bioavailability compared to FeSO₄ even with 1 mmol/L ascorbic acid enhancement, while soybean seed ferritin shows markedly reduced absorption (Glahn et al., 1998). Intriguingly, the remaining five species — C. vulgaris (all three variants), N. oceanica, and lysed H. pluvialis — showed no measurable iron uptake despite varying bioaccessibility levels. This finding underscores that bioaccessibility and bioavailability represent distinct, complementary measures of nutritional value.

The absence of iron absorption in certain species, despite released iron in the digesta, likely reflects multiple factors. The chemical form and redox state of iron critically influences intestinal uptake: ferrous iron (Fe²⁺) is directly transported by divalent metal transporter 1 (DMT1), while ferric iron (Fe³⁺) exhibits poor solubility and readily precipitates at near-neutral pH (Zhu et al., 2006). The study detected no ascorbic acid in digested samples, suggesting limited endogenous reducing capacity to maintain iron in the absorbable ferrous form — ascorbic acid both reduces Fe³⁺ to Fe²⁺ and stabilises iron through complexation (Lynch & Cook, 1980). Additionally, inhibitory compounds including polyphenols and phytic acid may chelate iron, forming insoluble complexes that reduce cellular uptake (He et al., 2008).

At neutral pH (7.0), no measurable iron uptake occurred in any species, demonstrating the critical role of pH in iron absorption through the proton-coupled DMT1 mechanism. This finding aligns with previous research showing decreased iron uptake at elevated pH between 5.8 and 7.2 (Zhu et al., 2006). The results emphasise that intestinal absorption depends on maintaining appropriate pH conditions and iron chemistry, not merely on releasing minerals from the food matrix.

Carbon and nitrogen: macronutrient bioaccessibility

Beyond minerals, the study quantified total carbon (C) and nitrogen (N) content as indicators of carbohydrate/lipid and protein availability, respectively:

most microalgae exhibited carbon content exceeding 450 mg/g, except D. salina (150.3 mg/g) and T. chuii (278.7 mg/g);
nitrogen content, reflecting protein levels, was highest in A. platensis (76.4 mg/g), C. vulgaris white (70.2 mg/g), and C. vulgaris green (66.4 mg/g), while D. salina showed the lowest value (8.5 mg/g). These nitrogen concentrations align with literature values and confirm the recognised protein-rich nature of spirulina and chlorella species.

Carbon bioaccessibility ranged from 12.4% in unlysed H. pluvialis to 78.1% in A. platensis, with the lysed H. pluvialis (69.3%) and white C. vulgaris (64.2%) also showing high values. For nitrogen, bioaccessibility was generally elevated, reaching 93.8% in lysed H. pluvialis and exceeding 84% in white C. vulgaris and A. platensis. The lowest nitrogen bioaccessibility occurred in D. salina (63.1%). Translating these percentages into absolute bioaccessible content, A. platensis, H. pluvialis lysed, and C. vulgaris white emerged as superior sources, providing 336–364 mg/g bioaccessible carbon and 59–65 mg/g bioaccessible nitrogen — substantially higher than other species tested.

These findings suggest that cell disruption (as in the lysed Haematococcus sample) and inherent cellular characteristics influence either mineral release and organic nutrient bioaccessibility. The variations observed reinforce that microalgae species selection should consider the full nutritional profile and processing history when designing functional food applications.

Practical implications and future directions

The comprehensive dataset demonstrates that microalgae represent highly promising sustainable mineral sources for addressing global micronutrient deficiencies, but species selection must be informed by specific nutritional targets:

for populations at risk of iron deficiency anaemia, A. platensis and unlysed H. pluvialis emerge as optimal choices, offering bioavailability comparable to inorganic iron supplements whilst providing additional macronutrients and bioactive compounds;
for individuals with lactose intolerance or following plant-based diets requiring non-dairy calcium sources, D. salina, green C. vulgaris, and A. platensis offer highly bioaccessible calcium exceeding conventional plant sources;
Chlorella vulgaris green stands out for zinc supplementation, providing exceptional bioaccessibility (62.1%) coupled with high absolute bioaccessible content (175.1 mg/kg) — substantially exceeding conventional foods;
for magnesium, D. salina and T. chuii offer outstanding bioaccessible content (14,059.8 and 7,191.9 mg/kg, respectively), far surpassing animal-derived sources;
the study’s finding that potassium consistently exhibits >91% bioaccessibility across species highlights microalgae as superior sources of this often-deficient electrolyte compared to meat products.

The researchers identify several strategies to enhance mineral bioavailability in microalgae-based food products:

cell-disruption techniques including high-pressure homogenisation (HPH) or pulsed electric field (PEF) treatment can increase permeability and nutrient release;
optimising cultivation conditions — such as heterotrophic growth or modulated light/nutrient stress — may alter cellular composition and mineral speciation;
implementing washing procedures during harvest could reduce overestimation of surface-bound minerals from biosorption rather than intracellular accumulation;
food formulation strategies including ascorbic acid fortification, enzymatic reduction of phytates and polyphenols, and maintenance of mildly acidic conditions could substantially improve iron absorption from microalgae sources.

The regulatory gap: reality vs. labelling

The findings by Gao et al. (2026) expose a significant loophole in the Nutrition and Health Claims Regulation (EC) No 1924/06:

while Article 5.1.c stipulates that a claim should only be made ‘where applicable’ if the nutrient is in a form ‘available to be used by the body’, current enforcement often defaults to simple quantitative analysis;
in practice, a product can be labeled ‘High in Iron’ based solely on its raw mineral content, even if — as seen in the case of Tetraselmis chuii — the iron is biologically ‘locked’ within a rigid cell wall and largely unabsorbable.

This research underscores the need for a regulatory shift toward bioavailability-based labeling, ensuring that health claims reflect the actual physiological benefit to the consumer rather than mere chemical presence.

Conclusions and research significance

This study provides the first integrated assessment combining mineral content analysis, standardised in vitro digestion, and cellular bioavailability measurement across commercially relevant microalgae species. The key finding — that high mineral content does not guarantee nutritional value — fundamentally challenges simplistic compositional assessments and emphasises the necessity of evaluating both bioaccessibility and bioavailability for accurate nutritional characterisation. The substantial inter-species variation observed suggests that microalgae production can be strategically optimised for specific mineral fortification applications rather than treated as a homogeneous category.

The exceptional performance of certain species — particularly A. platensis for iron bioavailability, D. salina for calcium and magnesium bioaccessibility, and green C. vulgaris for zinc — positions microalgae as viable alternatives to conventional dietary mineral sources. Compared to animal-derived foods, microalgae offer superior sustainability profiles with lower environmental impact, while addressing bioavailability limitations often associated with plant-based sources due to anti-nutritional factors. The findings support the hypothesis that microalgae can serve as sustainable nutritional resources offering highly bioaccessible minerals and bioavailable iron for human nutrition.

Future research priorities include in vivo validation studies to confirm cellular model predictions in human feeding trials, investigation of processing impacts on mineral availability, and exploration of microalgae-based food formulations that maximise bioavailability through synergistic ingredient combinations. Additionally, metabolomic and proteomic analyses could elucidate the molecular mechanisms underlying inter-species differences in mineral bioaccessibility, informing targeted cultivation and processing strategies. As global food systems face mounting sustainability pressures whilst micronutrient deficiencies persist, microalgae represent an innovative solution warranting continued scientific investigation and commercial development.

Dario Dongo

References

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