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Kappaphycus alvarezii (Doty) L. M. Liao, a red seaweed widely cultivated for carrageenan polysaccharide, is also a potential source of the valuable pigment phycoerythrin (PE). Therefore, this study aims to extract phycoerythrin from K. alvarezii , evaluate its antimicrobial, antioxidant, and anticancer activities, and identify its biomedical potential for future therapeutic applications. The protein content of phycoerythrin pigment extracted from K. alvarezii was found to be 69.84% and showed excellent antimicrobial activity against Klebsiella oxytoca and Proteus mirabilis , with a minimum inhibition zone of 11 mm. It showed significant in vitro antioxidant activity, as analyzed using total antioxidant, hydrogen peroxide scavenging, reducing power, DPPH, and ABTS assays. Further, the pigment exhibited potent cytotoxicity against a human lung cancer cell line, with an IC 50 value of 131.7 µg mL −1 . Furthermore, increasing concentration of phycoerythrin pigment decreased the cell proliferation and induced apoptosis, as confirmed by Annexin V/PI staining. Comprehensive characterization using FT-IR, HPLC, and GC-MS analysis revealed the nature of pigment and functional groups, highlighting its potential for biomedical applications. The molecular docking of K. alvarezii -derived compounds revealed significant binding affinities with 13 antibacterial target proteins. These results highlight the potential of K. alvarezii bioactive compounds as promising antibacterial agents. The phycoerythrin extract from K. alvarezii demonstrated potent antimicrobial, antioxidant, and anticancer properties, with significant cytotoxicity against lung cancer cells and confirmed apoptosis induction. Structural analysis revealed its bioactive composition, emphasizing its potential as a natural therapeutic agent. These findings support its potential application in the biomedical and pharmaceutical industries.

C-phycoerythrin (C-PE) is a phycobiliprotein that prevents oxidative stress and cell damage. The aim of this study was to evaluate whether C-PE also counteracts endoplasmic reticulum (ER) stress as a mechanism contributing to its nephroprotective activity. After C-PE was purified from Phormidium persicinum by using size exclusion chromatography, it was characterized by spectrometry and fluorometry. A mouse model of HgCl2-induced acute kidney injury (AKI) was used to assess the effect of C-PE treatment (at 25, 50, or 100 mg/kg of body weight) on oxidative stress, the redox environment, and renal damage. ER stress was examined with the same model and C-PE treatment at 100 mg/kg. C-PE diminished oxidative stress and cell damage in a dose-dependent manner by impeding the decrease in expression of nephrin and podocin normally caused by mercury intoxication. It reduced ER stress by preventing the activation of the inositol-requiring enzyme-1α (IRE1α) pathway and avoiding caspase-mediated cell death, while leaving the expression of protein kinase RNA-like ER kinase (PERK) and activating transcription factor 6α (ATF6α) pathways unmodified. Hence, C-PE exhibited a nephroprotective effect on HgCl2-induced AKI by reducing oxidative stress and ER stress.

Phycoerythrin (PE) is a pink/red-colored pigment found in rhodophytes, cryptophytes, and blue-green algae (cyanobacteria). The interest in PE is emerging from its role in delivering health benefits. Unfortunately, the current cyanobacterial-PE (C-PE) knowledge is still in the infant stage. It is essential to acquire a more comprehensive understanding of C-PE. This study aimed to review the C-PE structure, up and downstream processes of C-PE, application of C-PE, and strategies to enhance its stability and market value. In addition, this study also presented a strengths, weaknesses, opportunities, and threats (SWOT) analysis on C-PE. Cyanobacteria appeared to be the more promising PE producers compared to rhodophytes, cryptophytes, and macroalgae. Green/blue light is preferred to accumulate higher PE content in cyanobacteria. Currently, the prominent C-PE extraction method is repeated freezing–thawing. A combination of precipitation and chromatography approaches is proposed to obtain greater purity of C-PE. C-PE has been widely exploited in various fields, such as nutraceuticals, pharmaceuticals, therapeutics, cosmetics, biotechnology, food, and feed, owing to its bioactivities and fluorescent properties. This review provides insight into the state-of-art nature of C-PE and advances a step further in commercializing this prospective pigment.

Cyanobacterial phycobiliproteins, such as phycoerythrin (PE) and phycocyanin (PC), are colored potential bioactive proteins that have antioxidant and antimicrobial properties. In this study, we formulated a new food prototype based on PE and PC-fortified low-fat yogurt and cream cheese. Four distinct low-fat yogurt and cream cheese products were manufactured, including a control group (No PE and PC), samples produced with phycoerythrin (+ PE), samples produced with phycocyanin (+ PC), and samples produced with both phycoerythrin and phycocyanin (PC + PE). Afterwards statistically compared the physicochemical composition, colorimetric properties, antioxidant and antimicrobial activities, and sensory profile of the fortified foods at 4 °C and 8 °C for 28 and 42 days. Additionally, we confirmed that PE and PC are not toxic to Caenorhabditis elegans at concentrations up to 1 mg/mL. The results showed that the MIC of PE and PC against E. coli was significantly higher than against S. aureus (3.12 ± 0.05 µg/mL vs. 1.56 ± 0.01 µg/mL, respectively; p  ≤ 0.05). Additionally, the maximum diameter of the inhibition zone of PE and PC against S. aureus was significantly higher than against E. coli (6.6 ± 0.011 mm vs. 11.66 ± 0.02 mm, respectively; p  ≤ 0.05). Results of color parameters showed that the control group had significantly higher L* values than the samples enriched with PE and PC. Moreover PE and PC significantly increased the a* and b* values respectively. The amount of ΔE in the control yogurts and cream cheese was higher than in the samples with PE and PC. Overall, the results showed that adding PE and PC had a significant effect on all measured factors ( p  < 0.01). Cream cheeses and low-fat yogurts enriched with either PE or PE + PC had the greatest antioxidant activity and the lowest number of psychrophilic bacteria and mold, and yeast counts at the end of the test period. Therefore, low-fat yogurt and cream cheese containing cyanobacterial PE and PC can be considered an innovative dairy product for the food industry. This study marks the initial effort to employ PE and PC derived from Nostoc sp. and Spirulina sp. as antioxidant and antimicrobial agents in the food industry.

We examined the inhibitory activity of angiotensin I converting enzyme (ACE) in protein hydrolysates from dulse, Palmaria palmata. The proteins extracted from dulse were mainly composed of phycoerythrin (PE) followed by phycocyanin (PC) and allophycocyanin (APC). The dulse proteins showed slight ACE inhibitory activity, whereas the inhibitory activity was extremely enhanced by thermolysin hydrolysis. The ACE inhibitory activity of hydrolysates was hardly affected by additional pepsin, trypsin and chymotrypsin treatments. Nine ACE inhibitory peptides (YRD, AGGEY, VYRT, VDHY, IKGHY, LKNPG, LDY, LRY, FEQDWAS) were isolated from the hydrolysates by reversed-phase high-performance liquid chromatography (HPLC), and it was demonstrated that the synthetic peptide LRY (IC50: 0.044 μmol) has remarkably high ACE inhibitory activity. Then, we investigated the structural properties of dulse phycobiliproteins to discuss the origin of dulse ACE inhibitory peptides. Each dulse phycobiliprotein possesses α-subunit (Mw: 17,477–17,638) and β-subunit (Mw: 17,455–18,407). The sequences of YRD, AGGEY, VYRT, VDHY, LKNPG and LDY were detected in the primary structure of PE α-subunit, and the LDY also exists in the APC α- and β-subunits. In addition, the LRY sequence was found in the β-subunits of PE, PC and APC. From these results, it was suggested that the dulse ACE inhibitory peptides were derived from phycobiliproteins, especially PE. To make sure the deduction, we carried out additional experiment by using recombinant PE. We expressed the recombinant α- and β-subunits of PE (rPEα and rPEβ, respectively), and then prepared their peptides by thermolysin hydrolysis. As a result, these peptides showed high ACE inhibitory activities (rPEα: 94.4%; rPEβ: 87.0%). Therefore, we concluded that the original proteins of dulse ACE inhibitory peptides were phycobiliproteins.

Several studies have described that cyanobacteria use blue light less efficiently for photosynthesis than most eukaryotic phototrophs, but comprehensive studies of this phenomenon are lacking. Here, we study the effect of blue (450 nm), orange (625 nm), and red (660 nm) light on growth of the model cyanobacterium Synechocystis sp. PCC 6803, the green alga Chlorella sorokiniana and other cyanobacteria containing phycocyanin or phycoerythrin. Our results demonstrate that specific growth rates of the cyanobacteria were similar in orange and red light, but much lower in blue light. Conversely, specific growth rates of the green alga C. sorokiniana were similar in blue and red light, but lower in orange light. Oxygen production rates of Synechocystis sp. PCC 6803 were five-fold lower in blue than in orange and red light at low light intensities but approached the same saturation level in all three colors at high light intensities. Measurements of 77 K fluorescence emission demonstrated a lower ratio of photosystem I to photosystem II (PSI:PSII ratio) and relatively more phycobilisomes associated with PSII (state 1) in blue light than in orange and red light. These results support the hypothesis that blue light, which is not absorbed by phycobilisomes, creates an imbalance between the two photosystems of cyanobacteria with an energy excess at PSI and a deficiency at the PSII-side of the photosynthetic electron transfer chain. Our results help to explain why phycobilisome-containing cyanobacteria use blue light less efficiently than species with chlorophyll-based light-harvesting antennae such as Prochlorococcus, green algae and terrestrial plants.

In vitro antioxidant virtue and life-prolonging effect of phycoerythrin (PE; a pigment protein isolated from Phormidium sp. A09DM) have been revealed in our previous reports (Sonani et al. in Age 36:9717, 2014a ; Sonani et al. in Process Biochem 49:1757–1766, 2014b ). It has been hypothesized that the PE expands life span of Caenorhabditis elegans (bears large resemblance with human aging pathways) due to its antioxidant virtue. This hypothesis is tested in present study by checking the effect of PE on intracellular reactive oxygen species (ROS) generation and associated physiological deformities using mouse and human skin fibroblasts, C. elegans , and Drosophila melanogaster Oregon R + and by divulging PE’s structural attributes responsible for its antioxidant asset. PE treatment displayed noteworthy decrease of 67, 48, and 77 % in ROS level in mouse fibroblast ( 3T3-L1 ), human fibroblast, and C. elegans N2 , respectively, arisen under chemical-induced oxidative stress. PE treatment delayed the development of paraquat-induced Alzheimer phenotype by 14.5 % in C. elegans CL4176 . Furthermore, PE improved the locomotion of D. melanogaster Oregon R + under oxidative stress with simultaneous up-regulation in super-oxide dismutase and catalase activities. The existence of 52 Glu + Asp + His + Thr residues (having metal ion sequestration capacity), 5 phycoerythrobilin chromophores (potential electron exchangers) in PE’s primary structure, and significant hydrophobic patches on the surface of its α- and β-subunits are supposed to collectively contribute in the antioxidant virtues of PE. Altogether, results support the hypothesis that it is the PE’s antioxidant asset, which is responsible for its life-prolonging effect and thus could be exploited in the therapeutics of ROS-associated abnormalities including aging and neurodegeneration in eukaryotes.

The marine unicellular red alga Rhodosorus marinus is a promising source of the valuable phycobiliprotein phycoerythrin and essential omega-3 polyunsaturated fatty acids (PUFAs), yet the environmental triggers for their optimal co-production remain to be fully elucidated. This study was conducted to investigate the effects of thermal and photic stress in terms of maximizing the yield of these high-value bioactive compounds. R. marinus was cultivated under a range of temperatures (18–24 °C) and light intensities (100–335 µmol photons m−2 s−1) to assess its physiological and biochemical responses, particularly focusing on lipid accumulation. This study investigates the effects of thermal (18–24 °C) and photic (100–335 µmol photons m−2 s−1) stress on the concurrent production of the valuable phycobiliprotein, phycoerythrin (PE), and essential omega-3 polyunsaturated fatty acids (PUFAs) in the marine red microalga Rhodosorus marinus. Fatty acid profiles were quantified using gas chromatography (GC), while pigment content was assessed via spectrophotometry. Statistical analyses, including one-way ANOVA and Tukey’s post hoc test, were employed to determine the significance of environmental effects. Our results demonstrate that a mild hypothermic condition of 18 °C significantly enhanced the production of eicosapentaenoic acid (EPA) compared to higher temperatures. Conversely, cell density was maximized at 22 °C. Under the 18 °C thermal regime, lower light intensities (100–185 µmol photons m−2 s−1) promoted a superior synthesis of both bioactive lipids and pigments. In conclusion, the strategic application of mild hypothermia combined with moderate light intensity is an effective approach to substantially boost the metabolic yield of high-value compounds in R. marinus, highlighting its potential as a sustainable source for nutraceutical and pharmaceutical applications.

R-phycoerythrin is a fluorescent red protein-pigment complex present in red algae. It belongs to the light-harvesting phycobiliprotein family with phycocyanin and allophycocyanin, which together make up the phycobilisome. The protein is most commonly used for its fluorescence properties in biochemistry. To determine the highest R-phycoerythrin yielding red algal species, a reliable quantification method is required. Calculating R-phycoerythrin yield from the crude extract’s absorption values has been the quickest and most widely used technique but at the same time, often misleading approach when impurities are present. Small phycoerythrin, which is often present in red algal suspensions, alters the absorption curve and leads to erroneous results. In the given study, we utilized an HPLC-SEC method with fluorescence and photo-diode array detectors, which is capable of separating the phycobiliproteins from interfering compounds. Also, the technique can detect and quantitate R-phycoerythrin yields reliably. A total of nine red algal species from Estonian and Japanese waters were tested, and small phycoerythrin was detected from most of the samples. For two of the tested species, the spectrophotometric quantification methods overestimated the yields by more than 200%.

Nowadays, there is a growing interest in finding new coloring molecules of natural origin that can increase and diversify the offer of natural food dyes already present in the market. In the present work, a B-phycoerythrin extract from the microalgae Porphyridium cruentum was tested as a food colorant in milk-based products. Using spectroscopy and colorimetry, the extract was characterized and gave evidence of good properties and good stability in the pH range between 4.0 and 9.0. Coloring studies were conducted to demonstrate that samples carrying the pink extract could be used for simulating the pink color of marketed milk-based products. The staining factors, representing the amount of pink protein to be added to reproduce the color of strawberry commercial products, ranged between 1.6 mg/L and 49.5 mg/L, being sufficiently low in all samples. Additionally, color stability during a short period of cold storage was studied: it demonstrated that the three tested types of dairy products remained stable throughout the 11-day analysis period with no significant changes. These results prove the potential of the B-phycoerythrin extract as a natural colorant and alternative ingredient to synthetic coloring molecules.