The fungus Gliocephalotrichum simplex as a source of abundant, extracellular melanin for biotechnological applications

Biosorption of halophilic fungal melanized membrane - PUR/melanin polymer for heavy metal detoxification with electrospinning technology

Eradication of heavy metal pollution has become the prime priority over the conservation of water resources in the upcoming era. Herein, the study involved the halophilic fungal melanin from Curvularia lunata showed a promising biosorbent for the removal of toxic heavy metals which shows eco-friendly, cost-effective, high stability, and adsorbent efficiency. Polyurethane blended with fungal melanin polymers, makes polymeric nanofibrous membranes through electrospinning techniques. BET isotherms revealed the raw fungal melanin holds a surface area of 3.54 m2/g exhibiting type IV isotherms. BJH results in a total pore volume of 5.79 cc/g with a pore diameter of 6.54 ± 1 nm for pores smaller than 4544.8 Å. Exhibits Eumelanin properties were characterized by FE - SEM and FTIR functional elements. ICPMS confirmed the metal adsorption proficiency on both raw and melanized membranes before and after treatments. Over 17 heavy metals, Ni2+ were adsorbed with 100% efficiency by raw melanin alone with 42.48 µg/L of Ni2+ concentration in the water sample, whereas, Cu2+, Zn2+, Co2+, Cr2+, Pb2+, Mn2+, Al3+, Mo6+, Sb3+, Ba2+, Fe2+, and Mg2+ stands next with 99%. In this study, gentle/simple application of raw fungal melanin (without PUR tailored) can detoxify the maximum concentration of heavy metals present in the water bodies which are further used for irrigation and even drinking purposes. This mycoremediation approach can be easily adapted to industrial production than other high-performance membrane materials with minimal process modification, making it a promising strategy for improving the adsorption properties used in various applications after still furthermore investigation.

Efficient production and characterization of melanin from Thermothelomyces hinnuleus SP1, isolated from the coal mines of Chhattisgarh, India

In the present study, fungi were isolated and screened from barren land in south-eastern Coalfields limited (SECL) in Chhattisgarh, India. Out of 14 isolated fungi, only three fungal isolates exhibited pigmentation in screening studies. The isolated fungal strain SP1 exhibited the highest pigmentation, which was further utilized for in vivo production, purification, and characterization of melanin pigment. The physical and chemical properties of the fungal pigment showed insolubility in organic solvents and water, solubility in alkali, precipitation in acid, and decolorization with oxidizing agents. The physiochemical characterization and analytical studies of the extracted pigment using ultraviolet-visible spectroscopy and Fourier transform infrared (FTIR) confirmed it as a melanin pigment. The melanin-producing fungus SP1 was identified as Thermothelomyces hinnuleus based on 18S-rRNA sequence analysis. Furthermore, to enhance melanin production, a response surface methodology (RSM) was employed, specifically utilizing the central composite design (CCD). This approach focused on selecting efficient growth as well as progressive yield parameters such as optimal temperature (34.4°C), pH (5.0), and trace element concentration (56.24 mg). By implementing the suggested optimal conditions, the production rate of melanin increased by 62%, resulting in a yield of 28.3 mg/100 mL, which is comparatively higher than the actual yield (17.48 ± 2.19 mg/100 mL). Thus, T. hinnuleus SP1 holds great promise as a newly isolated fungal strain that could be used for the industrial production of melanin.

The Enigmatic World of Fungal Melanin: A Comprehensive Review

Synthetic dyes are generally not safe for human health or the environment, leading to the continuous search and growing demand for natural pigments that are considered safer, biodegrade more easily, and are environmentally beneficial. Among micro-organisms, fungi represent an emerging source of pigments due to their many benefits; therefore, they are readily viable on an industrial scale. Among all the bioactive pigments produced by fungi, melanin is an enigmatic, multifunctional pigment that has been studied for more than 150 years. This dark pigment, which is produced via the oxidative polymerization of phenolic compounds, has been investigated for its potential to protect life from all kingdoms, including fungi, from biotic and abiotic stresses. Over time, the research on fungal melanin has attracted a significant amount of scientific interest due to melanin's distinct biological activities and multifarious functionality, which is well-documented in the literature and could possibly be utilized. This review surveys the literature and summarizes the current discourse, presenting an up-to-date account of the research performed on fungal melanin that encompasses its types, the factors influencing its bioactivity, the optimization of fermentation conditions to enhance its sustainable production, its biosynthetic pathways, and its extraction, as well as biochemical characterization techniques and the potential uses of melanin in a wide range of applications in various industries. A massive scope of work remains to circumvent the obstacles to obtaining melanin from fungi and exploring its future prospects in a diverse range of applications.

A comparative study using response surface methodology and artificial neural network towards optimized production of melanin by Aureobasidium pullulans AKW

The effect of three independent variables (i.e., tyrosine, sucrose, and incubation time) on melanin production by Aureobasidium pullulans AKW was unraveled by two distinctive approaches: response surface methodology (i.e. Box Behnken design (BBD)) and artificial neural network (ANN) in this study for the first time ever using a simple medium. Regarding BBD, sucrose and incubation intervals did impose a significant influence on the output (melanin levels), however, tyrosine did not. The validation process exhibited a high consistency of BBD and ANN paradigms with the experimental melanin production. Concerning ANN, the predicted values of melanin were highly comparable to the experimental values, with minor errors competing with BBD. Highly comparable experimental values of melanin were achieved upon using BBD (9.295 ± 0.556 g/L) and ANN (10.192 ± 0.782 g/L). ANN accurately predicted melanin production and showed more improvement in melanin production by about 9.7% higher than BBD. The purified melanin structure was verified by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction pattern (XRD), and thermogravimetric analysis (TGA). The results verified the hierarchical architecture of the particles as small compasses by SEM analysis, inter-layer spacing in the XRD analysis, maximal atomic % for carbon, and oxygen atoms in the EDX analysis, and the great thermal stability in the TGA analysis of the purified melanin. Interestingly, the current novel endophytic strain was tyrosine-independent, and the uniquely applied ANN paradigm was more efficient in modeling the melanin production with appreciate amount on a simple medium in a relatively short time (168 h), suggesting additional optimization studies for further maximization of melanin production.

Characterization of a novel polyextremotolerant fungus, Exophiala viscosa, with insights into its melanin regulation and ecological niche

Black yeasts are polyextremotolerant fungi that contain high amounts of melanin in their cell wall and maintain a primar yeast form. These fungi grow in xeric, nutrient depletes environments which implies that they require highly flexible metabolisms and have been suggested to contain the ability to form lichen-like mutualisms with nearby algae and bacteria. However, the exact ecological niche and interactions between these fungi and their surrounding community are not well understood. We have isolated 2 novel black yeasts from the genus Exophiala that were recovered from dryland biological soil crusts. Despite notable differences in colony and cellular morphology, both fungi appear to be members of the same species, which has been named Exophiala viscosa (i.e. E. viscosa JF 03-3 Goopy and E. viscosa JF 03-4F Slimy). A combination of whole genome sequencing, phenotypic experiments, and melanin regulation experiments have been performed on these isolates to fully characterize these fungi and help decipher their fundamental niche within the biological soil crust consortium. Our results reveal that E. viscosa is capable of utilizing a wide variety of carbon and nitrogen sources potentially derived from symbiotic microbes, can withstand many forms of abiotic stresses, and excretes melanin which can potentially provide ultraviolet resistance to the biological soil crust community. Besides the identification of a novel species within the genus Exophiala, our study also provides new insight into the regulation of melanin production in polyextremotolerant fungi.

Penicillium citrinum NP4 mediated production, extraction, physicochemical characterization of the melanin, and its anticancer, apoptotic, photoprotection properties

The biopolymer melanin is reported for many biological processes to secure biological entities over unfavorable environmental factors. The present study aimed to isolate soil fungi and screen for melanin production. The potent fungus was identified as Penicillium citrinum NP4 based on morphological and molecular characterization with accession number OP070954. Using standardized tyrosine broth conditions melanin was produced by NP4 and extracted by acidification. Extracted melanin exhibited maximum UV-Visible absorption at 223 nm; FTIR peaks validate the occurrence of CO, CN, CH, and CC functional groups present in the indole/pyrrole structure. TLC analysis exhibited a prominent single band with a Retardation factor (Rf) of 0.68, Resonance peaks at 6.621, 7.061, and 7.185 ppm exhibited aromatic hydrogen in the indole/pyrole system in ¹H NMR. The EDX peaks confirm the presence of carbon, oxygen, sulfur, and nitrogen elements which are the key factors in melanin structure, and TGA reports the thermal stability of the melanin. An In silico molecular docking approach on lung cancer causing proteins EGFR (3g5z), KRAS (6vc8), and TP53 (8 dc4) were conducted to determine the active binding sites of the melanin, and proteins exhibited binding affinity of -8.0 for 3g5z, -9.8 for 6vc8, and - 10.1 kcal/mol for TP53 protein with melanin. Anticancer activity of the melanin showed significant inhibition of A549 cells in dose-dependent mode with significant IC₅₀ of 65.49 μg/mL; apoptotic examination reveals that melanin showed 46.14 % apoptosis for melanin and 46.36 % apoptosis for standard drug (cisplatin). Melanin exhibited good photoprotection capacity at 1 μg/mL. In conclusion, the extracted melanin exhibited significant results on many biological applications and it can be used in the pharmaceutical field to avoid chemical-based drugs.

Fungi as a source of eumelanin: current understanding and prospects

Melanins represent a diverse collection of pigments with a variety of structures and functions. One class of melanin, eumelanin, is recognizable to most as the source of the dark black color found in cephalopod ink. Sepia officinalis is the most well-known and sought-after source of non-synthetic eumelanin, but its harvest is limited by the availability of cuttlefish, and its extraction from an animal source brings rise to ethical concerns. In recent years, these limitations have become more pressing as more applications for eumelanin are developed-particularly in medicine and electronics. This surge in interest in the applications of eumelanin has also fueled a rise in the interest of alternative, bio-catalyzed production methods. Many culinarily-utilized fungi are ideal candidates in this production scheme, as examples exist which have been shown to produce eumelanin, their growth at large scales is well understood, and they can be cultivated on recaptured waste streams. However, much of the current research on the fungal production of eumelanin focuses on pathogenic fungi and eumelanin's role in virulence. In this paper, we will review the potential for culinary fungi to produce eumelanin and provide suggestions for new research areas that would be most impactful in the search for improved fungal eumelanin producers.

Targeting Nrf2-Mediated Oxidative Stress Response in Traumatic Brain Injury: Therapeutic Perspectives of Phytochemicals

Traumatic brain injury (TBI), known as mechanical damage to the brain, impairs the normal function of the brain seriously. Its clinical symptoms manifest as behavioral impairment, cognitive decline, communication difficulties, etc. The pathophysiological mechanisms of TBI are complex and involve inflammatory response, oxidative stress, mitochondrial dysfunction, blood-brain barrier (BBB) disruption, and so on. Among them, oxidative stress, one of the important mechanisms, occurs at the beginning and accompanies the whole process of TBI. Most importantly, excessive oxidative stress causes BBB disruption and brings injury to lipids, proteins, and DNA, leading to the generation of lipid peroxidation, damage of nuclear and mitochondrial DNA, neuronal apoptosis, and neuroinflammatory response. Transcription factor NF-E2 related factor 2 (Nrf2), a basic leucine zipper protein, plays an important role in the regulation of antioxidant proteins, such as oxygenase-1(HO-1), NAD(P)H Quinone Dehydrogenase 1 (NQO1), and glutathione peroxidase (GPx), to protect against oxidative stress, neuroinflammation, and neuronal apoptosis. Recently, emerging evidence indicated the knockout (KO) of Nrf2 aggravates the pathology of TBI, while the treatment of Nrf2 activators inhibits neuronal apoptosis and neuroinflammatory responses via reducing oxidative damage. Phytochemicals from fruits, vegetables, grains, and other medical herbs have been demonstrated to activate the Nrf2 signaling pathway and exert neuroprotective effects in TBI. In this review, we emphasized the contributive role of oxidative stress in the pathology of TBI and the protective mechanism of the Nrf2-mediated oxidative stress response for the treatment of TBI. In addition, we summarized the research advances of phytochemicals, including polyphenols, terpenoids, natural pigments, and otherwise, in the activation of Nrf2 signaling and their potential therapies for TBI. Although there is still limited clinical application evidence for these natural Nrf2 activators, we believe that the combinational use of phytochemicals such as Nrf2 activators with gene and stem cell therapy will be a promising therapeutic strategy for TBI in the future.

Bioprocess of Microbial Melanin Production and Isolation

Melanin is one of the most abundant pigments found in the biosphere. Owing to its high biocompatibility and diverse biological activities, it has been widely applied as a functional biomaterial in the cosmetic, pharmaceutical, biopolymer, and environmental fields. In this study, the production of melanin was comprehensively reviewed concerning bioconversion and isolation processes. First, several melanogenic microbes, including fungi and bacteria, were summarized. Melanin production was classified by host and melanin type and was analyzed by titers in g/L in addition to reaction conditions, including pH and temperature. The production was further interpreted using a space-time yields chart, which showed two distinct classifications in productivity, and reaction conditions were analyzed using a pH-temperature-titer chart. Next, the extraction process was summarized by crude and pure melanin preparation procedures, and the extraction yields were highlighted. Finally, the recent applications of melanin were briefly summarized, and prospects for further application and development in industrial applications were suggested.

Microbial melanin: Recent advances in biosynthesis, extraction, characterization, and applications

Melanin is a common name for a group of biopolymers with the dominance of potential applications in medical sciences, cosmeceutical, bioremediation, and bioelectronic applications. The broad distribution of these pigments suggests their role to combat abiotic and biotic stresses in diverse life forms. Biosynthesis of melanin in fungi and bacteria occurs by oxidative polymerization of phenolic compounds predominantly by two pathways, 1,8-dihydroxynaphthalene [DHN] or 3,4-dihydroxyphenylalanine [DOPA], resulting in different kinds of melanin, i.e., eumelanin, pheomelanin, allomelanin, pyomelanin, and neuromelanin. The enzymes responsible for melanin synthesis belong mainly to tyrosinase, laccase, and polyketide synthase families. Studies have shown that manipulating culture parameters, combined with recombinant technology, can increase melanin yield for large-scale production. Despite significant efforts, its low solubility has limited the development of extraction procedures, and heterogeneous structural complexity has impaired structural elucidation, restricting effective exploitation of their biotechnological potential. Innumerable studies have been performed on melanin pigments from different taxa of life in order to advance the knowledge about melanin pigments for their efficient utilization in diverse applications. These studies prompted an urgent need for a comprehensive review on melanin pigments isolated from microorganisms, so that such review encompassing biosynthesis, bioproduction, characterization, and potential applications would help researchers from diverse background to understand the importance of microbial melanins and to utilize the information from the review for planning studies on melanin. With this aim in mind, the present report compares conventional and modern ideas for environment-friendly extraction procedures for melanin. Furthermore, the characteristic parameters to differentiate between eumelanin and pheomelanin are also mentioned, followed by their biotechnological applications forming the basis of industrial utilization. There lies a massive scope of work to circumvent the bottlenecks in their isolation and structural elucidation methodologies.

Microbial production of melanin and its various applications

Melanins are natural biopolymers that are known to contribute to different biological processes and to protect organisms from adverse environmental conditions. During the past decade, melanins have attracted increasing attention for their use in organic semiconductors and bioelectronics, drug delivery, photoprotection and environmental bioremediation. Although considerable advances in these fields have been achieved, real-world applications of melanins are still scarce, probably due to the limited and expensive source of natural melanin. Nevertheless, recent biotechnological advances have allowed for relatively large-scale production of microbial melanins, which could replace current commercial melanin. In this review, we first describe different melanin sources and highlight the advantages and disadvantages of each production method. Our focus is on the microbial synthesis of melanins, including the methodology and mechanism of melanin formation. Applications of microbial melanins are also discussed, and an outlook on how to push the field forward is discussed.

Production and characterization of melanin pigments derived from Amorphotheca resinae

As melanin has emerged as functional pigment with cosmetic, health and food applications, the demand for the pigments is expected to increase. However, the conventional sources (e.g. mushroom, hair, and wool) of melanin production entail pigments inside the substrates which requires the costly extraction procedures, leading to inappropriate scalable production. In this study, we screened 102 of fungal isolates for their ability to produce melanin in the supernatant and selected the only Amorphotheca resinae as a promising candidate. In the peptone yeast extract glucose broth, A. resinae produced the melanin rapidly during the autolysis phase of growth, reaching up 4.5 g/L within 14 days. Structural characterization of the purified melanin from A. resinae was carried out by using elemental analysis, electron paramagnetic resonance, ¹³C solid-state nuclear magnetic resonance spectroscopy, and pyrolysis-gas chromatography-mass spectrometry in comparison with the standard melanins. The results indicate that the structural properties of A. resinae melanin is similar to the eumelanin which has a wide range of industrial uses. For example, the purified melanin from A. resinae has the potent antioxidant activities as a result of free radical scavenging assays. Consequently, A. resinae KUC3009 can be a promising candidate for scalable production of industrially applicable melanin.

Production of Melanins With Recombinant Microorganisms

The melanins constitute a diverse group of natural products found in most organisms, having functions related to protection against chemical and physical stresses. These products originate from the enzyme-catalyzed oxidation of phenolic and indolic substrates that polymerize to yield melanins, which include eumelanin, pheomelanin, pyomelanin, and the allomelanins. The enzymes involved in melanin formation belong mainly to the tyrosinase and laccase protein families. The melanins are polymeric materials having applications in the pharmaceutical, cosmetic, optical, and electronic industries. The biotechnological production of these polymers is an attractive alternative to obtaining them by extraction from plant or animal material, where they are present at low concentrations. Several species of microorganisms have been identified as having a natural melanogenic capacity. The development and optimization of culture conditions with these organisms has resulted in processes for generating melanins. These processes are based on the conversion of melanin precursors present in the culture medium to the corresponding polymers. With the application of genetic engineering techniques, it has become possible to overexpress genes encoding enzymes involved in melanin formation, mostly tyrosinases, leading to an improvement in the productivity of melanogenic organisms, as well as allowing the generation of novel recombinant microbial strains that can produce diverse types of melanins. Furthermore, the metabolic engineering of microbial hosts by modifying pathways related to the supply of melanogenic precursors has resulted in strains with the capacity of performing the total synthesis of melanins from simple carbon sources in the scale of grams. In this review, the latest advances toward the generation of recombinant melanin production strains and production processes are summarized and discussed.

Characterization of natural melanin from Auricularia auricula and its hepatoprotective effect on acute alcohol liver injury in mice

This study characterized the natural melanin from Auricularia auricula and investigated its hepatoprotective effect on mice with acute alcoholic liver injury. The characterization of the melanin was analyzed based on elemental analysis, gel permeation chromatography (GPC), UV-visible spectroscopy (UV-visible), infrared spectrum (IR) and nuclear magnetic resonance spectra (NMR). To determine the liver protective effect of Auricularia auricula melanin, mice were administered with the melanin once daily for 3 weeks before ethanol induced liver injury. Biochemical parameters of liver function, histopathological sections, mRNA and protein expression of antioxidant enzyme were compared between mice with or without the melanin administered. Results showed that A. auricula melanin was a eumelanin and the average molecular weight was 48.99 kDa. The melanin can protect the mice from ethanol-induced liver injury by extending the duration of the righting reflex, and shortening the duration of the recovery. The liver index, serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), γ-glutamyl transpeptidase (γ-GT) and liver malondialdehyde (MDA) levels in mice treated with the melanin were significantly decreased. At the same time, the levels of liver alcohol dehydrogenase (ADH), and antioxidase such as catalase (CAT), and superoxide dismutase (SOD) were increased. Its protective effect may be related to the activation of nuclear factor E2-related factor 2 (Nrf2) and its downstream antioxidant enzymes such as glutamate cysteine ligase catalytic (GCLC), glutamate cysteine ligase modifier (GCLM), and NADP(H) quinine oxidoreductase 1 (NQO-1). These results suggested that A. auricula melanin may be an effective strategy to alleviate alcohol-induced liver damage.

Scalable Biosynthesis of Melanin by the Basidiomycete Armillaria cepistipes

Natural melanin features many interesting properties, including the ability to shield electromagnetic radiation, the ability to act as scavenger for radical and reactive oxygen species and the capacity to chelate different metal ions. For these reasons, melanin is becoming increasingly relevant for the development of functional materials with potential applications in cosmetics, drug delivery, and water purification. However, the extraction and purification of melanin from conventional sources (e.g., sepia ink, hair, and wool) is inefficient and not easily scalable, hence diverting its technological applications. Some fungal species, especially wood-decay basidiomycetes, can be regarded as promising sources of melanin. In the present study, we screened different fungi in regard to their melanin-biosynthesis abilities using l-tyrosine as a precursor, and we found that an Armillaria cepistipes strain (Empa 655) produced the highest yield of melanin (27.98 g L^-1). Physicochemical characterization of the obtained fungal melanin revealed a typical eumelanin structure. The method for the biosynthesis of fungal melanin we propose is efficient, scalable, and sustainable and has the potential to provide support for further technological exploitation.

Study on the Preparation and Chemical Structure Characterization of Melanin from Boletus griseus

In this study, melanin (BgM) was obtained from Boletus griseus. The chemical composition and structure of BgM were characterized by UV-visible absorption spectrum, Fourier transform infrared spectrum, elemental analysis, nuclear magnetic resonance, pyrolysis gas chromatography mass spectrometry, and ultra-performance liquid chromatography–high resolution mass spectrometry. The percentage contents of C, H, N, S and O elements were 56.38%, 5.86%, 6.17%, 2.44%, and 28.04%, and the S/N and C/N ratios were 0.17 and 10.66, respectively. The UV-vis spectrum of BgM showed a maximum absorption peak at 214 nm. Characteristic absorption peaks were observed at 3426, 1600 and 1105 cm⁻¹, and BgM contained phenolic hydroxyl, amidogen, carbonyl, methylene, and methyl groups. Moreover, BgM is an eumelanin, and its main skeleton has both a benzene ring and an indole, and the branched chain mainly consists of alkanes, alcohols, and fatty acids. BgM was hydrolyzed by H₂O₂ and four compounds were tentatively analyzed from the UPLC-MS/MS profile. The chemical structure of BgM was characterized as 5,6-dihydroxyindole eumelanin, and the condensed molecular formula is [C₂₈(OR₁)₄(OR₂)₃H₁₁O₆N₄]_n.

Functions of fungal melanin beyond virulence

Melanins are ancient biological pigments found in all kingdoms of life. In fungi, their role in microbial pathogenesis is well established; however, these complex biomolecules also confer upon fungal microorganisms the faculty to tolerate extreme environments such as the Earth's poles, the International Space Station and places contaminated by toxic metals and ionizing radiation. A remarkable property of melanin is its capacity to interact with a wide range of electromagnetic radiation frequencies, functioning as a protecting and energy harvesting pigment. Other roles of fungal melanin include scavenging of free radical, thermo-tolerance, metal ion sequestration, cell development, and mechanical-chemical cellular strength. In this review, we explore the various functions ascribed to this biological pigment in fungi and its remarkable physicochemical properties.

Production of melanin pigment from Pseudomonas stutzeri isolated from red seaweed Hypnea musciformis

Hypnea musciformis red seaweed is popularly known to produce carrageenan was collected from the Gulf of Mannar, India. Strain HMGM-7 [MTCC 11712] was isolated from the surface of this seaweed, which was capable of producing an extracellular black-coloured polymeric pigment. Based on phenotypic characterization and 16S rDNA sequencing, the strain HMGM-7 was identified as Pseudomonas stutzeri. Biophysical characterization by UV-visible, FT-IR, EPR and XRD spectroscopic studies confirmed the pigment as melanin. Further chemical characterization showed that it was acid-resistant, alkali-soluble and alkali-insoluble in most of the organic solvents and distilled water. To our knowledge, this is a first report on a marine Pseudomonas stutzeri strain producing significant amounts of melanin of about 6·7 g l(-1) without L-tyrosine supplementation in the sea-water production medium.

SIGNIFICANCE AND IMPACT OF THE STUDY

This investigation reports a marine Pseudomonas stutzeri strain HMGM-7 [MTCC 11712] that produces significant quantities of melanin (6·7 g l(-1) ) in sea-water medium without the supplementation of L-tyrosine. The confirmation of the produced melanin was carried out by various chemical and physical characterization studies. The isolated melanin may find potential application for use in cosmetic and/or pharmaceutical industries.

Preparation of water-soluble melanin from squid ink using ultrasound-assisted degradation and its anti-oxidant activity

Water-soluble squid melanin fractions were firstly prepared using ultrasound-assistant degradation method under alkaline condition, which is optimized by response surface methodology. The processing melanin fractions were divided into different molecular weight (Mw) fractions by membrane separation (below 10 kDa, among 10-50 kDa and over 50 kDa). The AFM image and particle-size analysis showed monomer units of the melanin were destroyed, and huge polymers were degraded into smaller soluble particles after ultrasound. While, UV, IR and solid (13)C NMR spectra indicated that the basic structure of melanin fraction was still retained after ultrasound process. Further analysis showed soluble melanin fractions obtained in 0.5 and 1 M NaOH, with Mw above 10 kDa exhibited much higher in vitro antioxidant potency. The IC50 of these fractions (IC50 among 19-80 μg) on scavenging O 2 ∙¯ is more efficient than carnosine (IC50 = 355 μg/ml.), a commercialized antioxidant. They (IC50 mong 115-180 μg/ml) are as efficient as carnosine (IC50 = 110 μg/ml) on scavenging ∙OH. Our research has reported a novel method for preparation of water-soluble melanin fractions from squid ink, which could be a promising free radical scavenger from nature resource.