Chemical and microstructural characterization of three seaweed species from two locations of Veracruz, Mexico

Abstract

Seaweeds or marine macroalgae are sources of industrial important macro compounds. This work characterizes the chemical composition, morphology, cellular structure, morphometric parameters, protein distribution, density, and quantifies the chemical elements of three seaweed species. The morphological characterization performed by Digital Image Analysis (DIA) showed that the length/width ratio for UF (Ulva fasciata) (15.4/10.9 cm) was greater compared to SC (Sargassum cymosum) and GS (Grateloupia subpectinata) (8.9/7.6 cm and 87/5.3 cm). Using Schiff's and Coomassie blue reagents, identified carbohydrates and proteins in cells and protein bodies (PB). Cell morphology showed larger cells in the SC cortex (457.8 µm²) and smaller cells in the SC meristoderm (80.5 µm²). PB density (PB/area) and distribution (area occupied by the cell, %) were higher in the cortex of GS (10468 PB/mm², 20%) and lower in the meristoderm of SC (917 PB/mm², 7%). Chemical analysis showed as major compounds: carbohydrates (12-46%), ashes (13-42%), and proteins (6-17%). Meanwhile, the concentration of metals was below the toxicity level. These results contribute to the knowledge of the structure-function relationship of seaweeds metabolites which could be a source of compounds of interest for the industrial sector.

Keywords:
microscopy; histology; chemical composition; protein bodies; seaweeds

1 Introduction

Seaweeds are photosynthetic nonflowering plant-like organisms, divided into three major groups based on their dominant pigmentation: Chlorophyta or green algae, Rhodophyta, or red algae, and Ochrophyta that includes Phaeophyceae class or brown seaweed (Bonanno & Orlando-Bonaca, 2018). The macrostructure of seaweeds is like land plants, but the microstructure differs in the complexity of vascular tissues. Depending on the group, the morphological structure of algae consists of blades, e.g., Ulva genus (Ulvales: Ulvaceae), or thallus, e.g., Sargassum (Fucales: Sargassaceae) and Grateloupia (Halymeniales: Halymeniaceae). Such diversity is related to their chemical composition —determined by geographical and environmental conditions (Ak et al., 2021) — leading to the synthesis of compounds that participate in metabolic pathways: carbohydrates (ulvans, fucans, agarans, or carrageenans), enzymes (involved in photosynthesis; and synthesis of lipids, pigments, and amino acids) and minerals (P, K, Ca, S, Mn, Ni, Cu, Zn) (Harnedy & Fitz-Gerald, 2011; Wahlström et al., 2020).

Seaweed’s cell wall comprises carbohydrates and proteins, which provide flexibility, resistance, and protection against desiccation and other environmental adverse conditions (Harnedy & Fitz Gerald, 2011). Functional groups on cell walls surface —such as hydroxyl, carboxyl, sulfhydryl, and sulfate (negatively charged); and amino group (from polysaccharides, proteins, and lipids)— increase the ability of seaweed to uptake toxic metal ions, for example, heavy metal ions (Pb, Cd, Zn, Cu, Cr, and Ni) can bind to seaweed polysaccharides, and that provide them with a natural biosorption capacity (Barquilha et al., 2019; Bulgariu & Bulgariu, 2020), limiting their use for human or animal consumption.

Seaweed components (carbohydrates, protein, and metals) and morphology can be identified through different microscopy and histochemical techniques like optical microscopy (OM) and atomic absorption spectroscopy (AAS). Moreover, digital image analysis (DIA) may be a valuable tool for understanding the structure-functionality relationships based on microstructural features (Perea-Flores et al., 2011). This work aims to characterize three seaweed species through morphological parameters, cell structure identification, protein distribution and density and quantify the chemical elements to assess their toxicity potential.

2 Materials and methods

2.1 Biological material

Three samples of each seaweed species were collected in June 2018 in two locations. Grateloupia subpectinata (GS) was obtained from Tuxpan, Veracruz, Mexico (20°57'18” N, 97°23' 59” W); Sargassum cymosum (SC) and Ulva fasciata (UF), were collected from “El Pulpo” beach in Barra de Cazones, Veracruz, Mexico (20°44'10” N, 97°11' 38” W) and a record was made of the physicochemical parameters of the two zones (Table 1), pH of the water with potentiometer (Isolab), depth with Secchi disk, salinity by chemical test for chlorides (Hanna test kit, H13835), ambient and seawater temperature with thermometer scale 1 to 100 °C and dissolved oxygen determination (Hanna HI-9146 kit). Seaweed samples were rinsed with seawater and distilled water to eliminate salts and epiphytes adhered to the thallus after they were placed in amber-colored flasks with a solution of NaCl (35 ppm), 10% ethanol, and distilled water to avoid decomposition (Florez-Leiva et al., 2010). The seaweeds were identified using taxonomic keys (Dawes & Mathieson, 2008) according to a phycological specialist at the herbarium of ENCB- IPN Mexico. Two samples were fixed in 2% glutaraldehyde with sodium cacodylate (1:1 v/v) and refrigerated until microscopy analysis. For the proximal chemical analysis, 1 kg of samples was dried at room temperature and grounded to a fine powder and was determined by following the AOAC standard procedures (Association of Official Analytical Chemists, 2019), moisture by method 925.09, protein by method 954.01, fat by method 920.39 and total dietary fiber by method 985.29, total carbohydrates were estimated by diference

Table 1
Physicochemical parameters of the collection zone.

Physicochemical parameters	Collection zone
	Tuxpan beach	El Pulpo beach
pH	7.79 ± 0.20	8.80 ± 0.30
Depth (cm)	10.17 ± 0.02	19.30 ± 0.26
Salinity (g/kg)	19.63 ± 0.15	35.13 ± 0.02
Environmental temperature (°C)	24.06 ± 0.15	23.23 ± 0.58
Seawater temperature (°C)	23.60 ± 0.10	24.46 ± 0.58
Transparecy	90.00 ± 0.26	100 ± 0.001
Dissolved oxygen (mg/L)	7.13 ± 0.05	9.22 ± 0.07

• Results were expressed as the mean value ± standard error.

2.2 Morphological and micro-structural characterization of seaweeds

Morphological evaluations of the three seaweed species (UF, SC, GS) were determined by measuring the length and width of the thallus and other structures: blades of UF, leaves of SC, and cylindrical branches of GS. Each specimen was photographed (13 MP 1:2.2/39 ASPH resolution) and the length/width ratio of each structure was measured with Image J version 1.52a software (NIH-2019, Bethesda, MD, USA). To evaluate the microstructure, samples were cut with a histological scalpel in sections depending on the species. Images were obtained by Optical Microscopy (MO) and Digital Image Analyses (DIA) through Image J 1.52a software (NIH, Bethesda, MD, USA).

2.3 Optical microscopy (OM)

The OM technique reported by Vicente‐Flores et al. (2021) was used with some modifications. Firstly, four longitudinal sections and five cross-sections of seaweed species were acquired. Obtained the cuts from the apical blade section (UF), the apical leave section (SC), or the apical cylindrical branches section (GS). Additionally, were conducted a microstructural analysis (MAA) for the whole samples’ area. The tissues were washed, dehydrated, cleared, and placed in Paraplast® I and II, and 10 µm thick histological sections were obtained with a microtome (RM 2235, Leica, Germany). The cut was deparaffinized and stained with Schiff's reagent and Coomassie Blue Brilliant (Monte-Domecq et al., 2003) to observe the presence of carbohydrates and protein. Captured brightfield images of each structure with an optical microscope (Eclipse 50i, Nikon, Tokyo, Japan).

Microstructural characterization through Digital Image Analysis

In the case of SC, PB were analyzed in meristoderm cells (A and B) located in two areas of the leaves: meristoderm A (PB distant from medulla cells) and meristoderm B (PB close to medulla cells). Determined morphometric parameters of the cells in different areas due to the structural differences of the blade, leaves, and cylindrical branches. Blade cells were evaluated in UF, meristoderm, cortex, and medulla cells in SC and cortex cells in GS. PB was evaluated in blade cells for UF, in meristoderm cells for SC, and in cortex cells for GS. Images of morphometric parameters and PB were obtained at 600 X magnification, and SC medulla cells were captured at 400 X magnification. Binary images were employed to obtain area (A), perimeter (P), Feret diameter (FD), roundness (R), and aspect ratio (AR) (Perea-Flores et al., 2011), also assessed area, distribution (percentage occupied by the PB in a specific area of the blades, leaves, or cylindrical branches), and density (number cells or PB by mm²) for PB.

2.4 Quantification of toxic metals

The toxic metals evaluation by Atomic Absorption Spectrometry (AAS; Perkin Elmer Analyst 100, USA), using the direct flame aspiration technique, according to Tapia-Martínez et al. (2019) method.

2.5 Statistical analyses

Statistical analysis was performed using Analysis of variance (ANOVA), followed by Tukey's multiple comparison test (Tukey's HSD, honestly significant difference) with MINITAB®️17 software. All results are expressed as the mean value ± standard error.

3 Results and Discussion

3.1 Morphological and micro-structural description

Figure 1 describes the thallus structure of UF, SC, and GS. UF showed a brilliant green color, a blade (bla) like thallus, and a basal disk (di). The species’ dimensions were 15.3 cm in length and 10.9 cm in width (Figure 1a). SC had a dark brown color, a shrub-like thallus, and a basal disk (di) (Figure 1b). The collected species were 8.9 cm in length and 7.6 cm in width. These seaweeds presented stipes (st), one of their characteristic structures, and lateral branches alternated with elliptic, semi-rigid leaves (ph) with serrated borders and central midrib. GS had a reddish color with cylindrical, straight, and branched thalli, fixed through the basal disk (di) (Figure 1c). The species were 8.7 cm long and 5.3 cm wide; had cartilaginous, lax consistency; and bifurcated, opposite branching (1.1 cm long x 0.1 cm wide) and presented rounded and obtuse borders. Morphological structures revealed differences between the three species. The values obtained from the thalli of UF, SC, and GS showed significant differences (p ≤ 0.05) (Table 2).

Figure 1
Scheme of the morphology general (thallus) (a) U. fasciata (green); (b) S. cymosum (brown); and (c) G. subpectinata (red). di: basal fixation disk; bla: blade; base; ph: leaves; st: stipe; cb: cylindrical branches; MAA: microstructural analysis area.

Table 2
Measurements of representative structures and thalli of algae of UF, SC and GS.

Size measure (cm)	Blade of UF	Leaves of SC	Cylindrical branches of GS
Length	15.4 ± 0.3a	2.7 ± 0.1b	1.1 ± 0.1c
Width	0.9 ± 0.0 a	0.6 ± 0.0b	0.1 ± 0.0c
Global length thallus*	15.4 ± 0.3a	8.9 ± 0.4b	8.7 ± 0.4b
Global width thallus*	10.9 ± 0.2a	7.6 ± 0.4b	5.3 ± 0.2c

• The results were expressed as the mean value ± standard error (n = 20).
• ^*
  In the row, different letters indicate statistical differences (p<0.05) between the thalli of the three species studied. UF: U. fasciata; SC: S. cymosum; GS: G. subpectinata.

The largest thallus corresponded to UF, and the smallest to GS. However, Sargassum sp species can reach lengths of ≥200 cm (Guiry & Guiry, 2020). The morphological differences (Table 2) between the three seaweed species are associated with environmental conditions such as abiotic factors, high light intensity, temperature, and salinity (Lalegerie et al., 2020).

On the other hand, UF and SC grow in subtidal zones; hence, they are not exposed to low tide or extended periods of desiccation. GS grows in the intertidal zones, with alternating periods of emersion and immersion. The adverse environmental conditions (e.g., extended desiccation periods, solar radiation, osmotic changes, and nutrient limitation) induce adaptation and protection mechanisms in seaweeds that affect their growth (Kumar et al., 2014; Véliz et al., 2020).

Longitudinal and cross-section fields in different segments were observed to identify and describe the seaweeds microstructure (Figure 2). UF blade cells showed rectangular-square shapes in the transversal section (Figure 2b) and elongated or isodiametric forms in the longitudinal section (Figure 2d). Coomassie blue brilliant (CBB) staining method was used to visualize plastids (pl) in the seaweed cells. Within these organelles, pyrenoids were noticed; they form a dense structure inside chloroplasts of certain green seaweeds, which contain Ribulose biphosphate carboxylase, an enzyme that participates in photosynthesis (Meyer et al., 2020). Lastly, cell walls (cw) stained in magenta (Figure 2d) due to carbohydrate composition (Schiff reagent stain) were identified.

Figure 2
Scheme of the general microstructure of the U. fasciata blade, leaves and stipe of S. cymosum, and cylindrical branches of G. subpectinata. Transversal and longitudinal sections 10X (a, c, e, g, i, k, m, o) y 20X (b, d, f, h, j, l. n, p), cw: cell wall; pl: plastids; mer: meristoderm; cor: cortex; scor: subcortex; med: medulla; fm: filamentous medulla

SC leaves (ph) in the cross, and longitudinal sections are composed of three layers: meristoderm cells (mer) arranged on the periphery (as an epidermis), parenchyma (cortex cells) (cor), and compact-elongated medulla cells (med) (midrib) at the central zone (Figures 2e, 2g). The stipe (st) consists of several layers of cortex cells surrounded by a layer of meristoderm cells. The (cor) cells are separated by a large cell space, which allows the algae to float on the sea surface (Mateluna et al., 2020).

Cross and longitudinal sections (Figures 2m and 2o) obtained from GS cylindrical branches are composed of cortex cells (cor), star-shaped cells in the subcortex (scor), and filamentous medulla (fm) cells. Stained cell walls (cw) of UF seaweed (Figure 2d) correspond to sulfated polysaccharides, e.g., ulvans reported for Ulva sp (Stiger-Pouvreau et al., 2016). Figures 2f and 2h show longitudinal and cross-sections of SC (ph), where different structures (meri, cor, and med) are evidenced by cell wall staining. In this respect, Vijay et al. (2017) reported that cells carbohydrates of the Sargassum genus are constituted by fucoidan, laminaran, cellulose, and alginate,

Figures 2n and 2p display the carbohydrate composition of (cor) and (scor) cells obtained from GS. According to Sen et al. (1994), G. indica exhibits galactose units that form homoglycans. Complex carbohydrates in cell walls contribute to algae resistance and flexibility (Khora & Navya, 2020), regulate the ionic balance of the internal cells to prevent desiccation (O’Sullivan et al., 2010), and stimulate the synthesis of enzymes involved in metabolism. According to Lalegerie et al. (2020), carbohydrates are also associated with adaptation mechanisms.

Figure 2 shows blue-stained PB, resulting from the reaction between the triphenylmethane functional groups of the CBB colorant and the protein nitrogenated group. PB are synthesized from inorganic nitrogen compounds present in seawater (Yanagisawa, 2014). In UF, PB was mainly identified in blade cells’ chloroplasts (Figure 2b, 2d), related to catalytic proteins — located in thylakoid membranes or stored in vacuoles—that participate in photosynthesis (Trösch et al., 2018).

A cross-section image from SC (ph) shows the PB from meristoderm (Figure 2e). The (mer) segment closest to the medulla (mer B) exhibits higher PB accumulation (Figure 2f) in contrast to distant (mer A) (Figure 2f). GS transversal section of the cylindrical branch (Figure 2m) indicates a higher PB concentration at cortex and subcortex cells (Figure 2n, 2p).

PB are mainly located in the chloroplast, cell wall, and cytosol. Algae proteins act as a reserve for growth and have protection-defense activities (lectins) (Harnedy & Fitz Gerald, 2011). Conversely, López-Cristoffanini et al. (2015) reported catalytic proteins involved in energy metabolism, defense-antioxidants functions, environmental-genetic protection, and transportation, and it identified cytoskeleton-related proteins in red algae (92%) and other species (less than 2%).

3.2 Microstructural analysis of cells and protein bodies (PB)

The microstructural analysis revealed that the largest cells are located at SC (cor) (A: 457.8 µm²) (Figure 3e), whereas the smallest ones are at the meristoderm (80.5 µm²) (Figure 3e). SC (cor) cell area (457.8 µm²) was five times higher than GS area (399.3 µm²) (Figures 3e, 3l). UF blade cells (Figure 3b) comprise an area of 163.4 µm² (Table 3). SC (med) cells presented a greater perimeter (100.2 µm) than meristoderm cells (36.4 µm) (Table 3).

Figure 3
Transversal section (60X) of the blade, leaves, and cylindrical branches. Optical images (a, d, g, i, k) (stained with Schiff and Coomassie blue); segmented images of cells (b, e, h, l) and protein bodies (c, f, j, m). In UF (blade) there are blade cells, in SC (leaves), there are meristoderm (mer) and figure (d) refers to mer. Figure (i); refers mer; (B), cortex (cor), and medulla (med) cells, and GS, (branches) there are cortex cells (cor).

Table 3
Morphometric parameters of cells and protein bodies (PB) in transversal sections of the seaweed studied.

Cellular morphometric parameters *	UF	SC			GS
	Blade	Meristoderm	Cortex	Medulla	Cortex
A (µm2)	163.4 ± 7.8	80.5 ± 4.5	457.8 ± 36.7	399.3 ± 25.4	97.0 ± 6.3
P (µm)	52.6 ± 1.4	36.4 ± 1.0	89.2 ± 3.8	100.2 ± 3.4	37.7 ± 1.2
FD (µm)	18.2 ± 0.5	13.0 ± 0.4	31.7 ± 1.3	41.4 ± 1.5	13.6 ± 0.4
AR	1.4 ± 0.0	1.7 ± 0.0	1.8 ± 0.0	4.0 ± 0.1	1.7 ± 0.0
R	0.8 ± 0.0	0.6 ± 0.0	0.6 ± 0.0	0.3 ± 0.0	0.6 ± 0.0
Protein bodies (PB)*	Blade	Meristoderm A	Meristoderm B		Cortex
A (µm2)	93.5 ± 5.53	71.1 ± 37.0	45.5 ± 22.4		19.7 ± 0.6
Distribution (%)	32 ± 9.5	7 ± 2.0	14 ± 10.1		20 ± 4.0
Density (PB/mm2)	3 083 ± 769	917 ± 163	2 969 ± 2078		10 468 ±1805

• ^*
  Results were expressed as the mean value ± standard error (n=3); A: area; P: Perimeter; FD: Feret diameter; AR: Aspect ratio; R: Roundness. UF: U. fasciata; SC: S. cymosum; GS: G. subpectinata. In case of SC for Meristoderm A refers to distant al medulla cells and Meristoderm B refers to near at medulla cells.

GS (cor) cells showed a similar perimeter (37.7 µm) to SC (mer) cells, while UF (bla) cells had larger perimeters (52.6 µm) than GS (cor) cells and SC (mer) cells. Based on the morphometric parameters of aspect ratio (AR) and roundness (R), the cells of SC medulla are more elongated (AR:4.0, R:0.3) than those of the (mer) (AR:1.7, R:0.6) and the (cor) (AR:1.8, R:0.6). GS cells were similar in shape (AR:1.7, R:0.6). Rounder cells were found in UF (bla) (AR:1.4, R:0.8).

Image analyses revealed that PB in the UF (bla) cells had a larger area (93.5 µm²) than GS (cor) cells (19.7 µm²). According to these values, PB distribution was 32% inside UF (bla) cells, 20% in GS cortex cells, 14% in SC (mer) B, and 7% in SC (mer) A. Table 3 shows the PB density values of the three seaweed species, dependent on their size ranging from 19.7 µm² to 93.5 µm². Density values were 10468 PB/mm² for GS, 3083 PB/mm² for UF, 2969 PB/mm² for SC (mer) B, and 917 PB/mm² for SC (mer) A.

The image analysis allowed us to find differences in PB area, distribution, and density in the three seaweed species cells. Variations could be related to cell differentiation processes, regulated by enzymes such as nitrate-reductase (Yanagisawa, 2014) involved in the assimilation of inorganic nitrogen compounds by reducing nitrates to nitrites for protein synthesis. PB plays a fundamental role in seaweed metabolism. The quantification of the area, distribution, and density of those compounds in the cell contribute to understanding their potential function in different algae tissues (UF blade, SC leaves, and GS cylindrical branches).

3.3 Chemical proximal analyses

Table 4 shows the results from the proximate chemical analysis for the three studied seaweeds. Moisture content was lower than 13.7 g/100 g on a dry basis for all species. Moisture values below 10% are adequate to avoid microbial decomposition (Di Filippo-Herrera et al., 2018). Total carbohydrate content was variable. The carbohydrate content ranges between 12 in SC and 45 g/100 g in UF and SC. Nevertheless, previous research declared 35-49% values in different algae (Di-Filippo-Herrera et al., 2018; El-Sheekh et al., 2021; El Zokm et al., 2021). Regarding ash content, a higher concentration was found in SC (42 g/100 g), followed by GS (20.2 g/100 g) and UF (12.9 g/100 g). Ash content among seaweed species varies between 20-25 g/100 g (Di-Filippo-Herrera et al., 2018; Tapia-Martínez et al., 2019). Kumar et al. (2014) attributed these differences to growing area and harvesting season.

Table 4
Proximal chemical analysis and quantify metals of UF, SC, and GS.

Components	UF	SC	GS	Permissible limits**
Moisture	13.7 ± 0.2a	6.0 ± 0.2c	9.6 ± 0.1b	--
Total carbohydrates*	45.9 ± 1.4a	12.3 ± 1.1c	45.1 ± 0.5a	--
Dietary fiber*	28.2 ± 0.9b	35.1 ± 0.5 a	22.4 ± 0.2c	--
Proteins*	8.5 ± 0.0 b	5.9 ± 0.1c	16.9 ± 0.0a	--
Lipids*	4.5 ± 0.03ab	4.5 ± 0.1a	5.3 ± 0.5b
Ashes*	12.9 ± 1.5c	42.1 ± 0.0 a	20.2 ±0.1b
Metals 1				µg / g
Cu	0.27 ± 0.001a	0.90± 0.000b	1.48 ± 0.001c	<1000B
Cd	0.01 ± 0.001c	0.06 ± 0.001a	0.06± 0.001b	<0.5 A
Cr	0.42 ± 0.001a	0.20 ± 0.001c	0.21 ± 0.000b	< 100B
Ni	0.51 ± 0.001a	0.50 ± 0.001b	0.46 ± 0.000c	< 1B
Pb	0.17 ± 0.001c	0.75 ± 0.002a	0.65 ± 0.013b	<5A
Zn	0.32 ± 0.001c	0.96± 0.000a	0.76 ± 0.001b	<5000B
Hg	0.001 ± 0.000b	0.01 ± 0.000a	0.01 ± 0.000a	<0.1A

• ^*
  g/100 g dry base;
• ¹
  µg/g. Results were expressed as the mean value ± standard error (n=3); In the row, different letters indicate statistical differences (p<0.05) between the thalli of the three species studied.
• ^**
  Agence Française de Sécurité Sanitaire des Aliments (2009)^A; Agency for Toxic Substances and Disease Registry (2021)^B.

Protein content varied between 5. 9 and 16.9 g/100 g. The protein content of UF is within the stated values (4 to 15.9 g/100 g) for this species (Pirian et al., 2016; Ismail, 2017). SC presented a lower protein content than other Sargassum species, e.g., 9, 6.5, and 10.3 g/100 g for S. cymosum, S. horridum, S. liebmannii, respectively (Rubio et al., 2017; Di Filippo-Herrera et al., 2018; Tapia-Martínez et al., 2019). For GS, protein value was close to the G. turuturu species, 22.5 g/100 g (Rodrigues et al., 2015).

Regarding fiber content, UF had 28.2 g/100 g, consistent with Rasyid (2017) analysis. SC contained 35.1 g/100 g of fiber, in contrast to S. wightii that showed a higher ratio (53.52 g/100 g) (Praveen et al., 2019). GS fiber content was lower than G. turuturu (53.06 to 61.28 g/100 g) (Denis et al., 2010). Lipids represented less than 6% of the total weight of seaweeds. UF presented a concentration of 4.4 and SC, 4.5 g/100 g, showing a significant difference compared to GS (p <0.05). Studies reported that U. lactuca lipid content ranges from 0.56 to 0.85 g/100 g (Pirian et al., 2016). Brown seaweed species contain 1.45 to 2.20 g/100 g (Rodrigues et al., 2015). Seaweed lipids are a source of EPA (eicosapentaenoic acid), DHA (docosahexaenoic acid), and ARA (arachidonic acid), essential compounds for human health (Harwood, 2019).

Results obtained by AAS are presented in Table 4. The lowest values of metals considered toxic (Ak et al., 2021) were Hg 0.001-0.01 µg/g and Cd 0.01-0.06 µg/g. While the higher values for UF were Ni 0.51 µg/g; for SC, Zn 0.96 µg/g; and for GS, Cu 1.48 µg/g. Greater concentrations of toxic metals in edible brown algae have been reported: Cd 0.82 µg/g, Cr 0.04 µg/g, and Pb 0.02 µg/g; Hg 1.2-2.4 µg/g, and Pb 5 µg/g (Paz et al., 2019; Rubio et al., 2017). The concentration of toxic metals in the studied algae species was below the permissible levels for human consumption like Cd (0.01,0.06 and 0.06), Pb (0.17, 0.75, and 0.65), and Hg (< 0.001), for UF, SC, and GS respectively (Agence Française de Sécurité Sanitaire des Aliments, 2009; Agency for Toxic Substances and Disease Registry, 2021).

The high concentration of metals in some seaweed species is related to anthropogenic and industrial activities and environmental conditions that impact the biosorption capacity of algae (Chalkley et al., 2019; Paz et al., 2019). However, the metal content in seaweeds depends on the collection zone (Paz et al., 2019). Frequent consumption of seaweeds may benefit to human health, e.g., diabetes, cholesterol, heart disease, lipid lowering, cancer and others (Kumar & Sharma, 2021).

4 Conclusions

The chemical, morphological and microstructural characterization of three seaweeds species from the state of Veracruz, Mexico, allowed us to identify some major components of the blades, leaves, and cylindrical branches, such as proteins and carbohydrates. In addition, certain toxic elements were found at low concentration levels through quantitative chemical analyses. These results contribute to the knowledge of the structure-function relationship of the seaweed tissues, considered as a potential source of various metabolites that could be used in the food, pharmaceutical, and cosmetic industries.

Acknowledgements

This study was financially supported by the Instituto Politécnico Nacional, Mexico (SIP projects: 20200291, 20200299 and 20180489). Authors are grateful to CONACyT (Mexico) for the support provided through study grants, and to CIIEMAD-IPN for the technical assistance offered.

• Practical Application: Tissues seaweeds present interest macro compounds in food or biotechnology industry.

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Publication Dates

• Publication in this collection
  14 Mar 2022
• Date of issue
  2022

History

• Received
  10 June 2021
• Accepted
  21 Nov 2021