1. Introduction
Seaweed extracts are a desirable substitute to traditional therapies due to several factors. One of these advantages is their degradability into less harmful substances for the environment [
1]. The interest in seaweed has been growing in the past few years due to the wide range of biological actions, including anticancer, anti-inflammatory, antioxidant, anti-obesity [
2,
3,
4] .
The seaweeds can be divided into three phyla and the principal characteristic responsible to that division are the different pigments that they possess (
Table 1). Chlorophyll (Chl), carotenoids and phycobiliproteins (PBPs) are the three main categories of pigments [
5,
6,
7,
8,
9].
Calliblepharis jubata is a benthic seaweed, which belongs to phylum Rhodophyta, class Florideophyceae, genus
Calliblepharis Kützing, species
Calliblepharis jubata (Goodenough & Woodward) Kützing [
11].
C. jubata is a brownish red seaweed with a thallus made up of holdfast with branches that grows into an upright frond and then spreads out into a dichotomous or unevenly split blade. The frond´s shape might vary although it frequently has a cylindrical or hardly compressed stipe. It has blades that are 30 cm long, 6 mm wide, and have slender branching. The branches have a lengthy, tendril-like appearance. The blade surface and branch edges produce long branchlets, or proliferations [
11].
As a gametangial,
C. jubata have both male and female reproductive organs. Around April, the female reproductive structures (cystocarps), which have a diameter of 1-2 mm, start to emerge as noticeable globose formations on the branchlets. Tetrasporangia, which are known to occur in April, June, and July, are the sexual reproductive structures. Although they occasionally appear sparsely on the blades, they are found on the chanceless. The tetrasporangia grow in the cortex with zonately organized tetraspores [
11].
The studies on this seaweed have focused mostly on its polysaccharide composition.
C. jubata has hybrid iota or iota-kappa carrageenan with extremely low content of kappa-carrageenan [
12].
F. vesiculosus belongs to the phylum Ochrophyta, class Phaeophyceae, genus
Fucus Linnaeus, species
Fucus vesiculosus Linnaeus [
11]. This seaweed is normally approximately 40 cm long (although fronds can grow longer) and have a color range of olive green to olive brown to reddish brown to almost black. It uses a tiny disc-shaped holdfast to attach to rocky superficies. There are some studies reporting some activities and, or some application of this seaweed.
F. vesiculosus can be used in agriculture as a fertilizer, in bioremediation as a biosorbent of heavy metals because of his high capacity to capture environmental pollution [
12]. Despite of having good quantities of proteins, minerals, and fatty acids it’s not advisable to ingest this seaweed due to the capacity to absorb heavy metals. In pharmacology, this seaweed has reports in helping with problems related to obesity and cellulite, it has anti-cancer potential, helps reducing blood pressure pathologies [
13,
14].
Natural pigments exist in a wide range of hues and have been widely used throughout history in daily life. A few examples worth mentioning are food production, textile and paper industries, water science and tecnhology, as well as agricultural research and practise. Pigments exhibit advantageous biological activities such as antioxidants, antidiabetic, antiangiogenic, anti-inflammatory and anticancer. These qualities make them suitable for use in these various industrial contexts [
2,
3,
4] As a result, they have a great chance of meeting current market needs, which increasingly focus on the health and biotechnology sectors in search of natural substances and products with established positive impacts on human health [
15,
16].
Seaweeds inhabit aqueous habitats with a rich diversity of microorganisms. Seaweeds consequently acquired some antibacterial qualities. They can be viewed as suitable alternatives to the resistance to traditional antimicrobial. In several publications, seaweeds have been suggested as potential sources of compounds with antimicrobial proprieties. However, knowledge about the antimicrobial activities of certain components of such pigments remain scarce, although seaweeds produce a wide range of pigments. Studies about these pigments have mostly focused on their antioxidant potential [
6,
17,
18,
19,
20]. A few studies highlight the antibacterial properties of carotenoids particularly the action of fucoxanthin against Gram-positive and Gram-negative bacteria [
6,
21,
22,
23]. It has also been shown that lutein has antiviral properties against the hepatitis B virus (HBV) [
24,
25].
Antifungal resistance has been identified as a significant public health problem in the twenty-first century by the World Health Organization (WHO). This resistance mechanism may be due to clinical factors such as insufficient dosage, inaccurate diagnosis, inappropriate or irresponsible treatment, microbiological factors like genetic alterations or both aspects [
26].
Opportunistic fungal infections have significantly increased in recent years [
27,
28]. Although fungi do not generate pandemics or epidemics, the frequency of severe systemic fungal infections has dramatically increased, mostly due to the sharp rise in the number of immunosuppressed patients [
29,
30]. The dermatophytes infections have considerably grown, even in immunocompetent hosts [
29]. Natural compounds with antifungal activities have also received considerable attention during the past few decades, namely from terrestrial plants and seaweeds [
29,
31]. Due to the increasing number of fungal infections, the emerging resistance to the traditional antifungals, the limited number of antifungals available, and because superficial mycosis and onychomycoses require long periods of topical and systemic treatment that are associated to adverse effects, contraindications, and sometimes interaction with other drugs, it is essential to screen for novel antifungal compounds. The objective of the present work was to isolate and characterize
C. jubata and F. vesiculosus pigments and extracts, and to evaluate the pigments’ antifungal effect against fungi agents of skin infections. Also was secondary, to observe if a crude and enriched extract can be key to a better welfare future.
3. Discussion
With the continuous rise of fungal infections and the increase in fungal resistance to traditional antifungals, there is a need to find new treatment alternatives. Seaweeds are potential sources of novel therapeutic agents since they produce a wide range of secondary metabolites that, when compared to the ones produce by terrestrial plants, have an extraordinary molecular structure and pharmacological effects, including anticancer, antibacterial, antifungal, antiviral, anti-inflammatory, among others [
53,
54,
55].
During the extraction protocols, it was observed that the extraction of pigments from seaweeds depends on several variables including the solvent type, extraction duration, and samples state (whether fresh, dried, frozen, or milled) in accordance with previous reports [
56,
57]. The entire extraction process was thought up to obtain the most efficient method of extracting pigments. Due to the distance from the beach to the laboratory, it wasn´t possible to use the fresh seaweed, so the fresh biomass was stored in the freezer until further used. After thawing, the seaweeds were washed, as described in the methods, and dried in an air forced oven at 40
oC. The temperature of drying is important because high temperatures can compromise the process of extraction influencing the concentration of pigments extracted. Despite of some studies reporting the use of fresh seaweed, in this study it was used dried milled seaweed because of the bigger accessibility of the solvents to all the structures of the seaweed [
57]. If fresh seaweed was used the solvent would not reach all the seaweeds cellular structures and the extraction wouldn’t be as efficient.
As previously mentioned, the efficiency of pigment extraction depends on several factors and one of them is the solvent. It is important to test the behavior of the solvent used for the extraction in the different seaweeds because their efficiency can vary with the pigments that are pretended. For example, most of the carotenoids are fat-soluble, so to monetize the extraction it must be used fat solvents like, acetone, alcohols, esters, and hexanes [
58]. In this work two solvents were used, ethanol 96% and acetone 99%. The aim was to see which one of them was more efficient in the pigment extraction. At the naked eye, both seem to extract the pigment from biomass until the exhaustion but in the column chromatography the acetone extracts showed to be better separated through the column. The number of fractions is also higher than the ones obtained with in the ethanol. With this analysis it was conclude that the best solvent to extract pigment was acetone. This is in agreement with the literature, in which other studies conclude that acetone is the best solvent to extract pigments in general [
56,
58,
59,
60]. Another detail observed through the weeks of assays was that despite of being solubilized in water, the pigments extracted with acetone remain more stable than those who were extracted with ethanol. After several days, the ethanol extracts start to show some deposit in the bottom of the falcon. The explanation for this observation wasn´t found in literature, so more studies must be done to understand this finding.
In the course of this work, it was possible to perceive that the process of identification and characterization of pigments is complex, and it is not possible to use only a simple technique to accomplish it. To obtain a characterization more consistent three techniques were used to the identification of the pigments, UV-visible spectrophotometry, FTIR and TLC. Due to the lack of information about the characterization of seaweeds pigments, these techniques complement themselves and gave a result more trustworthy.
The PBPs have several applications in biotechnology, biomedicine, pharmacology, dye, cosmetics, and food colorants [
61]. In the pharmacology, it has shown a strong antioxidant effect against reactive oxygen species (ROS). Some
in vitro studies showed the PBPs anti-inflammatory, anti-viral and anti-tumor activities [
62]. The extract S was identified as a phycobiliprotein and was the one with the highest bioactivity This extract showed antifungal activity against all the dermatophytes tested. There are already some reports of the antifungal and antimicrobial activities of the PBPs. Righini et al. [
47] described the antifungal activity of PBPs against spore germination and mycelial growth of the phytopathogen fungi
Botrytis cinerea. This class of pigment also showed antibacterial activity against
Staphylococcus aureus,
Streptococcus pyogenes,
Escherichia coli and others [
63,
64]. Crude ethanol extract from
C. jubata harbors more than one pigment, so, it can be considered an enriched extract. This presented antifungal and fungicidal activity against
T. mentagrophytes,
T. rubrum and
M. canis at 3450 μg/mL. Consistently, the fraction isolated from this crude extract also exhibited antifungal and fungicidal activity against the three dermatophytes tested at a lower concentration (2783.25 μg/mL). Nevertheless, the bioactivity of the extracts R and S decrease during the 3-week period of assays, demonstrating that during this period of time the pigments are not stable. Further studies are needed to unravel how to maintain the stability of the pigments preventing degradation. The chlorophylls are the most widely distributed pigments in every seaweed, and they are highly sensitive to heat, light, oxygen, and enzymes leading to their easy degradation and color alteration [
65,
66]. The color change of the chlorophyll can occur due to replacement of the magnesium atom in chlorophyll´s structure to hydrogen ions, causes the structure of chlorophyll to shift to pheophytin becoming olive brown color [
65,
67]. The mainly reasons for the carotenoid’s degradation could be oxidation and isomerization, which reduce the redness and yellowness of the extracts. Normally, carotenoids oxidize in the presence of oxygen, however other factors such light, heat, metal ions, and enzymes can also speed up the process [
65,
68]. Despite of the lack of information about the PBPs in the generality there are starting to appear their application as food colorants and for that is necessary to understand the stability of this pigments [
69,
70]. Studies have been showing that PBPs are stable under basic pH, and in this case, they remain stable from 0 to 50 °C. The color of the PBPs remains stable during 20 days after the extraction. So, from this information and from the results observed during the work the PBPs are the most stable pigments present in seaweeds [
71].
The tendency of using natural sources of pigments has been growing due to environmental safety, conservation, and awareness. The natural pigments obtained from native flora and fauna are a desirable source for human usage because they are non-toxic, biodegradable, and non-carcinogenic [
72,
73]. Due to this characteristic and the properties of the pigments these are being studied to integrate certain products/materials.
Often the colours of food are what catch the attention of consumers. Pigments have been studied for application in food industry because they are non-synthetic, safe food additives and because of their health properties [
10]. Due to the antimicrobial properties shown by the pigments and because of the antifungal results presented above the pigments can be added to food products to increase their shelf life [
21,
54].
The textile industry is another sector where the use of the natural pigments has been growing most specifically in medical textiles. The hospital environment contains a huge amount of the microorganism and a great amount of textile materials (like uniforms, sheets, towels and so on) that accumulate microbes [
7,
23,
24,
25]. The emergence of studies on the antimicrobial properties of pigments makes their application in the textile industry more appealing, thus motivating the decrease in the use of heavy metals in this industry [
7,
72,
74].
Due to the properties of the pigments, they can be integrated in the formulation of cosmetic products with various purpose being one of the them antimicrobial products, like antimicrobial creams [
15,
21,
23,
25,
72,
74]. The antifungal activity observed in our study indicates that the pigments extracted, characterize and selected might be used in topical applications to cure dermatophytosis.
Author Contributions
Conceptualization, L.G., J.C., C.F., T.G. and L.P..; methodology, L.G., J.C., C.F. and T.G..; validation, C.F., T.G. and L.P.; investigation, L.G., J.C. and C.F.; resources, T.G. and L.P.; writing—original draft preparation, L.G. and J.C..; writing—review and editing, C.F., T.G. and L.P.; supervision, T.G. and L.P. All authors have read and agreed to the published version of the manuscript.