The biological rationale begins with reactive oxygen species, or ROS. These molecules, including superoxide anion, hydroxyl radical, and singlet oxygen, are unavoidable byproducts of oxidative metabolism, generated inside cells by electron leakage in mitochondria and outside them by ultraviolet radiation and pollution. At low levels, ROS act as legitimate signaling molecules in many cellular processes. But when their production outpaces the body’s antioxidant defenses, oxidative stress ensues, damaging DNA, proteins, and lipids, and driving cells toward apoptosis. The skin, as the body’s largest organ and its first line of contact with the environment, is particularly exposed. ROS accumulation triggered by ultraviolet light is considered a central event in photoaging, marked by collagen degradation, rupture of elastic fibers, and heightened activity of matrix metalloproteinases, the enzymes that dismantle the skin’s structural scaffolding.

Conventional skincare addresses oxidative stress with synthetic antioxidants and physical treatments, but these often irritate the skin, provoke photosensitivity, and deliver only temporary benefits. Natural antioxidants are generally less likely to cause irritation or allergy, and they align with the fast-growing consumer movement toward so-called clean beauty. What makes microalgae and cyanobacteria especially compelling is their evolutionary history. These are the oldest photosynthetic microorganisms on Earth, and populations living in hot springs, salt lakes, deserts, and high-irradiance intertidal zones have endured intense ultraviolet exposure, desiccation, and oxidative pressure for millions of years. Their response was to build elaborate chemical defenses, synthesizing structurally distinct antioxidants that terrestrial plants rarely produce, while also growing quickly and cultivable at scale on non-arable land.

The standout molecule is astaxanthin, a ketocarotenoid whose long chain of thirteen conjugated double bonds, capped by oxygenated ionone rings, gives it extraordinary capacity to quench singlet oxygen, outperforming other carotenoids as well as vitamins C and E. The green microalga Haematococcus pluvialis is the industrial workhorse, accumulating astaxanthin to five to eight percent of its dry cell weight, with annual production reaching tens of tons. In laboratory studies, concentrations of five to ten micromolar astaxanthin efficiently quenched UVA-induced ROS clusters in human dermal fibroblasts and lowered levels of malondialdehyde, a marker of lipid peroxidation. Mechanistically, astaxanthin also activates the cell’s own defenses: it promotes the release of the transcription factor Nrf2 from its cytoplasmic inhibitor Keap1, allowing Nrf2 to enter the nucleus and switch on genes for antioxidant enzymes such as glutathione S-transferases, glutathione peroxidase, superoxide dismutase, and NQO1.

Fucoxanthin, a polyunsaturated carotenoid with a reactive allenic bond and an epoxy group, delivers broad-spectrum radical scavenging and, in human keratinocytes, boosts glutathione through the same Nrf2 pathway. The diatom Phaeodactylum tricornutum and the haptophyte Tisochrysis lutea, which can reach nearly eighty milligrams of fucoxanthin per gram under optimized culture, are leading production candidates, and microalgae contain roughly ten to one hundred times more of the pigment than macroalgae. Beta-carotene, famously over-accumulated by the halotolerant green alga Dunaliella salina at up to fifteen percent of dry weight, quenches singlet oxygen through energy transfer and, in its 9-cis isomer form found uniquely in algae, exhibits strong antioxidant power. Lutein, currently harvested commercially only from marigold petals, could shift to algal sources that promise two to five times the per-hectare yield with eighty percent less water consumption and growth cycles as short as one to two weeks.

Beyond pigments, the review highlights polysaccharides, phycocyanin, polyphenols, mycosporine-like amino acids, and scytonemin as complementary actives. Sulfated exopolysaccharides from the red microalga Porphyridium cruentum and cyanobacterial EPS from Arthrospira and Nostoc scavenge radicals, chelate iron and copper ions that would otherwise fuel Fenton chemistry, and even form physical barriers against membrane lipid peroxidation. Phycocyanin, the brilliant blue pigment that makes up ten to twenty percent of Spirulina’s dry weight, directly eliminates ROS and reactive nitrogen species while enhancing intracellular antioxidant enzymes. Mycosporine-like amino acids, or MAAs, are especially elegant: these water-soluble molecules under four hundred daltons absorb UV-A and UV-B radiation with superb photostability, dissipating the energy harmlessly as heat rather than generating ROS, and compounds such as palythine and porphyra-334 rival ascorbic acid in radical-scavenging assays. Scytonemin, a lipophilic dimeric pigment produced in the extracellular sheaths of more than three hundred cyanobacterial species, absorbs across the UV-A, UV-B, and UV-C ranges.

What elevates these compounds above simple radical sponges is the breadth of their secondary effects on skin biology. Phycocyanin suppresses cyclooxygenase-2 and downstream prostaglandin E2, easing inflammation; fucoxanthin damps inflammatory cytokines through NF-kappaB signaling. On the anti-aging front, Spirulina polysaccharide complexes restore mitochondrial function in aged fibroblasts and spur collagen regeneration, while porphyra-334 increases procollagen, type I collagen, and elastin expression in UVA-irradiated skin fibroblasts. Several molecules inhibit the matrix metalloproteinases that degrade collagen and elastin: mycosporine-2-glycine from the halotolerant cyanobacterium Aphanothece halophytica matches the collagenase inhibitor aminoguanidine, C-phycocyanin reduces MMP-1 and MMP-9 in UVB-treated keratinocytes, and polysaccharides from Nostochopsis lobatus outperform the natural hyaluronidase inhibitor disodium cromoglycate. Microalgal polyphenols and phenolic acids also inhibit tyrosinase, the rate-limiting enzyme in melanin synthesis, offering safer alternatives to unstable or irritating whitening agents such as hydroquinone and kojic acid.

Commercial traction is already visible. Estee Lauder markets skincare lines featuring Chlorella extract for hydration and oil-water balance, while L’Oreal holds patents on marine polysaccharides for moisturizing and hair care. Astaxanthin appears in brightening serums and eye creams, and clinical trials suggest that oral doses of three to six milligrams per day reduce UV-induced wrinkles and enhance collagen synthesis. In the sunscreen space, Mibelle AG Biotechnology’s Helioguard 365, a porphyra-334 and shinorine complex from the red alga Porphyra umbilicalis, increased skin firmness by ten percent and reduced wrinkle depth by twelve percent over four weeks of application. Spirulina-derived extracts are found in anti-wrinkle and even antifungal formulations, and engineered microalgae-nanodrug delivery systems and live algal hydrogels are being explored for tissue repair, exploiting their capacity to produce oxygen through photosynthesis at wound sites.

Significant obstacles remain before these compounds reach their full potential. Extraction from tough algal cell walls is inefficient and often relies on polluting organic solvents, prompting interest in greener methods such as supercritical water extraction, ultrasound-assisted extraction, and enzyme-assisted processing. Stability is another vulnerability: carotenoids and phycobiliproteins degrade under light, heat, oxygen, and pH shifts, shortening shelf life, while hydrophilic and macromolecular ingredients struggle to cross the stratum corneum. Nanocarriers, including liposomes, nanoemulsions, and solid lipid nanoparticles, are emerging as solutions that shield actives and improve skin penetration, and the authors point to artificial intelligence-designed responsive delivery systems as a future frontier. Perhaps most critically, rigorous clinical evidence on biosafety, irritation, sensitization, and long-term effects remains thin for many novel species. The review calls for large-scale, multicenter, randomized, double-blind, placebo-controlled trials across diverse skin types and age groups, combined with omics-based mechanistic studies, to convert a promising laboratory story into the backbone of next-generation dermatological treatments and functional cosmeceuticals.

Subject of Research: Natural antioxidants from microalgae and cyanobacteria and their applications in skincare

Article Title: Natural antioxidants derived from microalgae and cyanobacteria and their applications in skincare

Article References: Natural antioxidants derived from microalgae and cyanobacteria and their applications in skincare. (n.d.). https://doi.org/10.1186/s44315-025-00050-w

Image Credits: AI Generated

DOI: 10.1186/s44315-025-00050-w

Keywords: microalgae, cyanobacteria, antioxidants, skincare, astaxanthin, phycocyanin, mycosporine-like amino acids, carotenoids, photoaging, Nrf2 pathway, sunscreen, cosmetics

Spirulina, the dried biomass of Limnospira platensis and its congener L. maxima, is cultivated worldwide at industrial scale, exceeding 12,000 tons per year, and holds GRAS status from both the U.S. Food and Drug Administration and the European Food Safety Authority. Its market value rests on an exceptional nutritional profile, including protein content reaching up to 70 percent of dry weight, essential amino acids, vitamins B12 and E, bioactive lipids such as gamma-linolenic acid, and a suite of photosynthetic pigments. Among these, C-phycocyanin is the most valuable, prized as a natural colorant and functional ingredient across the food, cosmetic, and pharmaceutical sectors for its antioxidant, immunomodulatory, and anti-inflammatory properties. But extracting this pigment leaves behind a mountainside of residual material whose fate has remained largely unexamined, despite European policies that strongly encourage waste valorization and circular economy approaches in agriculture.

Researchers at Tor Vergata University of Rome, working with biomass supplied by the Italian producer Algaria Srl, set out to determine whether the residue left after phycocyanin extraction, which they call POST biomass, could serve as an effective biofertilizer. They compared it with untreated biomass collected before extraction, termed PRE biomass, and with a commercial NPK fertilizer, using chicory (Cichorium intybus) as the test plant. Chicory is a leafy vegetable of high nutritional and cultural importance in the Mediterranean diet, making it an ideal candidate for a fertilizer destined for sustainable horticulture. The team grew the cyanobacterium in a 300 square meter open raceway pond under natural sunlight, collected both biomass fractions, centrifuged and freeze-dried them, and then characterized their chemical composition.

The compositional analysis delivered the first encouraging surprise. Although phycocyanin extraction removed some of the protein, the POST biomass still contained 50.2 percent protein by dry weight, alongside 6.8 percent total nitrogen and 0.78 percent phosphorus, only moderately lower than the intact PRE biomass. In other words, the industrial extraction process strips out the blue pigment but leaves behind a nutrient-dense matrix. This matters because cyanobacterial biomass is known to carry phytohormones including auxins, cytokinins, gibberellins, and abscisic acid, plus amino acids, carbohydrates, and exopolymeric substances with documented biostimulant effects on plants.

Germination experiments revealed a nuanced early response. Seeds treated with POST biomass suspensions showed a transient delay in radicle emergence during the first days, an effect that strengthened with increasing concentration. Yet by day six, final germination had caught up with, or exceeded, the water control, with the 5 milligrams per milliliter treatment reaching a germination percentage of 96.6 percent against the control’s 91.6 percent. The researchers interpret this pattern of initial slowdown followed by equal or improved final germination as a priming-like response, in which bioactive compounds activate metabolic pathways associated with germination without harming the seed. By contrast, PRE biomass proved more inhibitory, significantly reducing germination at intermediate and high concentrations, suggesting the extraction process actually improves the bioavailability profile of the residual material.

The growth results were even more striking. Under controlled laboratory conditions, POST biomass increased shoot fresh weight in a dose-dependent fashion, with values of 0.76 grams at 7.5 milligrams per milliliter and 1.06 grams at 10 milligrams per milliliter, far exceeding the commercial fertilizer’s 0.39 grams. Leaf fresh weight followed the same trend, peaking at 0.94 grams versus 0.31 grams for the fertilizer control. Under greenhouse conditions, where temperature ranged from 19.7 to 32.5 degrees Celsius and humidity fluctuated naturally, the effects grew stronger rather than weaker. The highest POST treatment pushed shoot fresh weight to 4.0 grams, nearly triple the 1.47 grams achieved by the commercial product, and roots benefited significantly as well. The robustness of the response under variable environmental conditions is critical evidence that the effect can survive the messiness of real-world agriculture.

Photosynthetic pigment measurements helped explain where the extra biomass came from. POST-treated plants accumulated significantly more chlorophyll a and chlorophyll b than either control, reaching 981.9 micrograms per gram fresh weight of chlorophyll a in the laboratory and 578.3 micrograms per gram in the greenhouse, compared with 641.9 and 320.9 micrograms per gram respectively for fertilizer-treated plants. Carotenoid levels rose in parallel. The coordinated increase in chlorophyll b is particularly telling, since this pigment anchors the light-harvesting antenna complexes of photosystem II; its accumulation implies an expanded photosynthetic apparatus and greater capacity to capture light, which plausibly drove the observed gains in plant mass. PRE biomass produced weaker and less consistent pigment responses, with chlorophyll b often lagging behind the control and the chlorophyll a to chlorophyll b ratio rising, a signature of limited antenna development.

Just as important was what the researchers did not find. Phenolic compounds and flavonoids are classic markers of oxidative and environmental stress in plants, so their accumulation would have signaled that the biofertilizer was stressing the crop rather than helping it. In POST-treated greenhouse plants, total phenolic and flavonoid contents remained essentially unchanged relative to controls at most concentrations, confirming that the growth promotion was achieved without triggering adverse physiological responses. The residue acts as a genuine biostimulant, not a low-grade stressor masquerading as one. This biochemical evidence complements the growth and pigment data in portraying the leftover biomass as a safe and multifunctional agricultural input.

The study builds on the group’s earlier demonstration that spirulina processing waste can fertilize lettuce in aquaponic systems, and together the two works suggest the activity of L. platensis leftovers holds across different crops, substrates, and cultivation environments. The broader implications touch the economics of the entire spirulina sector. Commercial cyanobacterial biostimulants remain scarce largely because production costs exceed those of conventional fertilizers, and nearly half of all research on cyanobacteria in agriculture between 2006 and 2020 focused on L. platensis without translating into widespread products. By folding agricultural reuse into the existing phycocyanin biorefinery chain, producers could convert a disposal liability into a second revenue stream while reducing the environmental footprint of both the pigment industry and the farms that adopt the residue. The researchers conclude that integrating this upcycling step into spirulina biorefineries could substantially improve the economic and environmental sustainability of cyanobacterial production, turning process waste into functional bio-based products for sustainable agriculture. Remaining questions include optimizing dosing for different species and soils and validating performance at field scale, but the central message of this work is clear: the blue gold of the spirulina industry may be hiding a green treasure in what it throws away.

Subject of Research: Upcycling of industrial Limnospira platensis residual biomass as a biofertilizer for chicory cultivation

Article Title: From waste to resource: agricultural potential of Limnospira platensis (spirulina) leftovers in chicory cultivation

Article References: Savio, S., Di Cave, A., Ortenzi, F., Rugnini, L., Scuderi, F., Migliore, G., Canini, A., Braglia, R., & Congestri, R. (2026). From waste to resource: agricultural potential of Limnospira platensis (spirulina) leftovers in chicory cultivation. Plant Biosystems, 160(5), Article 265. https://doi.org/10.1007/s44473-026-00249-8

Image Credits: AI Generated

DOI: 10.1007/s44473-026-00249-8

Keywords: spirulina, Limnospira platensis, biofertilizer, phycocyanin, chicory, circular economy, biostimulant, plant biotechnology, cyanobacteria, sustainable agriculture, seed priming, industrial leftovers

The choice of organism is central to the strategy. Galdieria sulphuraria, a unicellular red alga of the class Cyanidiophyceae, thrives in conditions that would kill nearly all competing microbes: acidic environments with pH values between 1 and 5 and temperatures up to 56 degrees Celsius. In this study, the alga was grown at pH 1.8 and 45 degrees Celsius in complete darkness, drawing energy from organic substrates rather than photosynthesis. This heterotrophic mode of growth offers clear advantages for industrial waste valorization. Because the extreme culture conditions suppress bacterial and fungal contaminants, the process can run under non-sterile conditions, dramatically reducing costs compared with conventional fermentation. At the same time, the organism tolerates the complex and variable chemistry of real industrial residues, a persistent stumbling block for cleaner cultivation systems.

The raw materials came from a German shrimp processing facility and included wastewater, sludge, and minced shrimp heads and shells. Compositional analysis by near-infrared spectroscopy revealed that shrimp residues were remarkably protein dense, containing 57 percent protein and 11 percent lipids by weight, while the sludge contained 28 to 32 percent protein, roughly 13 percent carbohydrates, and 2 to 8 percent fat. The wastewater, with only 0.85 percent solids and negligible free amino nitrogen and phosphate, served not as a nutrient source but as a dilution medium. To unlock the nutrients locked inside the solid residues, the team tested a series of hydrolysis strategies: enzymatic treatment with the acidic protease Protease S-02, enzymatic treatment with Glucoamylase AN, a combination of both enzymes, and a chemical pretreatment with 1 percent sulfuric acid at 90 degrees Celsius followed by enzymatic digestion.

The hydrolysis results carried an important and somewhat sobering message. Free amino nitrogen recovered from sludge hydrolysates remained low, at only 1 to 2 milligrams per gram of sludge, regardless of the treatment applied. Shrimp residues performed far better, yielding 10 to 15 times more free amino nitrogen when digested with protease, the enzyme cocktail, or acid-assisted enzymatic hydrolysis over 48 hours. Strikingly, control experiments without any enzymes showed that a large share of the recoverable nutrients, around 15 milligrams of free amino nitrogen per gram of shrimp residue and 100 to 150 milligrams of phosphate per gram of both residues, could be released simply by solubilizing and mixing the materials. The yields were also notably below the 50 to 90 percent recovery figures often reported for proteolytic hydrolysis of fish and meat processing wastes, a discrepancy the authors attribute to limited protein accessibility, suboptimal mixing and solids concentrations, or a mismatch between the chosen protease and its substrate.

With hydrolysates in hand, the researchers turned to cultivation trials. In shaken flask cultures held for seven days in the dark, Galdieria sulphuraria grew exponentially in sludge hydrolysate concentrations of 25 to 50 percent by volume, reaching a maximum growth rate of 1.36 per day at the 50 percent level supplemented with 2.5 grams per liter of glucose. This rate matches values previously reported for heterotrophic growth of the species. However, the windows of tolerance were narrow. At 75 percent sludge hydrolysate, growth was inhibited, and shrimp hydrolysate supported growth only at concentrations of 25 percent or less. The culprit appears to be organic acids: experiments showed that acetate concentrations of 0.3 grams per liter and above blocked growth, while lower levels were metabolized. The mechanism is well understood in acidophilic microbiology. Below the pKa of acetic acid, the molecule becomes protonated, diffuses across the cell membrane, and releases its proton inside the cell, acidifying the cytoplasm and disrupting metabolism.

To push biomass concentrations higher, the team moved to fed-batch cultivation in a 5-liter bioreactor. Cultures were started with a mixture of 15 percent sludge hydrolysate and 10 percent shrimp hydrolysate plus 10 grams per liter of glucose, and on days three and four were fed an additional 300 to 400 milliliters of a richer solution containing 70 percent sludge hydrolysate, 30 percent shrimp hydrolysate, and 22.5 grams per liter of glucose, delivered by peristaltic pump. The initial batch phase produced consistent growth rates of 1.19 to 1.25 per day, corresponding to doubling times between 13.3 and 14.0 hours, and biomass reached 6 to 8 grams per liter. In the best-performing run, continued growth after feeding pushed the biomass concentration to nearly 10 grams per liter, with the produced cells containing 47 to 62 percent protein and 7 to 8.6 percent lipids.

The pigment phycocyanin, a natural blue colorant with established markets in food and nutraceutical industries, accumulated to as much as 8 milligrams per gram of dry biomass during the initial exponential growth phase, falling to around 4 milligrams per gram in stationary phase in one culture. Yet another culture produced only 1 to 2 milligrams per gram despite similar nutrient conditions. This variability pointed the researchers toward a deeper question: whether growth depends not just on how much nitrogen is available, but on which nitrogen compounds are present. Because the nitrogen species in residue hydrolysates are difficult to identify, the team ran a systematic screening, supplying the alga with 50 millimolar solutions of individual amino acids and comparing growth against ammonium sulfate, the standard nitrogen source.

The screen revealed pronounced substrate specificity. Ammonium sulfate supported a growth rate of 0.95 per day, and only two amino acids came close: alanine at 0.87 per day and proline at 0.80 per day, marking them as highly suitable nitrogen donors. Glutamic acid, aspartic acid, leucine, arginine, glycine, and methionine supported measurable but weaker growth between 0.59 and 0.73 per day, while tryptophan, lysine, phenylalanine, isoleucine, threonine, serine, histidine, and valine performed poorly, with rates between 0.16 and 0.48 per day. Lysine and cysteine permitted no or only weak, delayed growth. The practical implication is significant: residues must be selected not only for their total nitrogen content but for the amino acid composition of that nitrogen, since the alga cannot universally exploit amino acids. The low phycocyanin yield in one fed-batch culture may reflect exactly this gap, where free amino nitrogen was abundant but the right amino acids were missing.

Taken together, the study maps both the promise and the constraints of a decentralized, circular bioeconomy in which aquaculture farms recycle their own residues into protein-rich algal feed or pigment feedstocks. The authors identify three dominant control points: the limited and variable release of nitrogen from residues, growth inhibition at high hydrolysate concentrations driven by organic acids such as acetate, and carbon limitation caused by glucose depletion even under fed-batch operation. Because much of the phosphate and some free amino nitrogen are released by mixing alone, pretreatment must be tailored to each substrate and enzyme combination to remain cost-effective. If those parameters can be mastered, the extreme lifestyle of Galdieria sulphuraria, its tolerance of heat, acidity, and contamination, could transform the waste streams of the world’s fastest growing food sector into a reliable source of protein and natural colorants, closing a nutrient loop that has until now leaked into rivers and coastal waters.

Beyond protein and phycocyanin, the biomass produced in such a process carries additional commercial value. Galdieria sulphuraria is known to accumulate highly branched glycogen, a form of storage carbohydrate of interest for nutritional applications, and its protein fraction is reported to offer a favorable amino acid profile suitable for animal feed and human nutrition. Because the alga was cultivated heterotrophically in the dark, productivity is not constrained by light availability or photobioreactor geometry, allowing the high cell densities typical of stirred-tank fermentation to be approached.

The fed-batch strategy used here also illustrates a broader principle of residue-based bioprocessing. Rather than exposing the culture to a single hydrolysate at full strength, the researchers diluted inhibitory components during start-up and then supplied nutrients progressively, keeping the alga in exponential growth while limiting the accumulation of organic acids. This kind of staged feeding mirrors established practice in industrial fermentation, where substrate toxicity is managed through controlled dosing rather than batch addition.

Decentralization is another notable aspect of the concept. Since the residues originate at shrimp processing facilities and aquaculture farms, a compact cultivation unit operating at acidic pH and elevated temperature could, in principle, run on-site without sterilization equipment, converting waste into feed or pigment precursors where it is generated. The remaining challenges are largely quantitative: stabilizing hydrolysate composition across batches, matching nitrogen quality to the alga’s substrate specificity, and balancing carbon dosing against acetate inhibition. Addressing these control points will determine whether laboratory yields of roughly ten grams per liter of protein-rich biomass can be translated into an economically viable, closed-loop component of the aquaculture industry.

Subject of Research: Heterotrophic cultivation of Galdieria sulphuraria on aquaculture residue hydrolysates for protein- and phycocyanin-rich biomass production.

Article Title: Valorization of Aquaculture Residues by Heterotrophic Cultivation of the Extremophilic Microalga Galdieria Sulphuraria for Protein- and Phycocyanin-Rich Biomass Production

Article References: Kleps, C., Händel, N., Schönfelder, S., Baum, L., Ogurek, M., & Pleissner, D. (2026). Valorization of Aquaculture Residues by Heterotrophic Cultivation of the Extremophilic Microalga Galdieria Sulphuraria for Protein- and Phycocyanin-Rich Biomass Production. Waste and Biomass Valorization. https://doi.org/10.1007/s12649-026-03778-7

Image Credits: AI Generated

DOI: 10.1007/s12649-026-03778-7

Keywords: Galdieria sulphuraria, aquaculture residues, phycocyanin, microalgae, waste valorization, circular bioeconomy, hydrolysis, heterotrophic cultivation, shrimp waste, protein-rich biomass, bioprocess engineering, Valorization