**2. Chemical components of edible seaweeds**

### **2.1 Polysaccharides**

Polysaccharides are the main components of green, brown and red seaweed. Algae cell walls contain numerous polysaccharides such as, alginates, alginic acid, carrageenans, agar, laminarans, fucoidans, ulvans and derivatives with storage and structural functions (Perez et al., 2016; [42, 43]). As it is shown in **Figure 4** [44], agar polysaccharides have complex molecular structure with alternating composition of 3-linked-d-galacropyranose (G unit) and 4-linked-3,6-anhydrol-galactopyranose (LA unit) [45]. Substitution of hydroxyl group by ester sulfate, methyl groups and pyruvic acid at various positions have direct impact on physical and rheological properties of polysaccharides [44, 46–50].

Polysaccharides have noticeable effects in immunomodulatory and anti-cancer as one of the most important macromolecules. These effects are driving force for wide research in biochemical and medical areas. As it was mentioned above, polysaccharides are abundant in cell walls and their composition is under the influence of season, age, species and geographical location. Their main goal in plants are food reservoir, however they can provide strength, and flexibility encountering wave actions and also balancing the ionic equilibrium inside the cell. Other structural benefits of polysaccharides, such as regularity of the hydroxyl group, can increase the ion interactions our of cell walls and interchain hydrogen bonding and causing gelation.

Depending on seaweeds, different polysaccharides can be produced by alginates, fucoidans, and laminarans. Laminarans, fucoidans as water soluble and high molecular mass alginic acids as alkali soluble polysaccharides are main products of brown seaweeds [51]. Main components of brown algae wall are cellulose microfibrils merged in amorphous polysaccharide while they relate to each other via proteins. There are two kinds of acid polysaccharides in extracellular structure of brown algae, sulfated fucans and alginic acid (Perez et al., 2016).

**197**

*2.1.1 Fucans*

**Figure 5.**

**Figure 4.**

*2.1.2 Fucoidans*

molecule [54].

*Major Natural Vegetation in Coastal and Marine Wetlands: Edible Seaweeds*

*Chemical structure of agar polysaccharides with the different types of monomers [44].*

Fucans as one of the acid polysaccharides present in extracellular structure of brown algae (**Figure 5**) are categorized into three major groups: fucoidans, xylofu-

Fucoidan is a branched sulfate ester polysaccharide with branching. The major branches in this polysaccharide are l-fucose-4 sulfate or sulfate ester at C3. Fucoidan has molecular weight ranging from 100 kDa [52] to 1600 kDa [53]. Main components of Fucoidan are fucose, uronic acids, galactose, xylose and sulfated fucose. Fucoidan structure contains sulfated fucans backbone, which is made of different sugars, fucose, or uronic acid. The backbone also has different degrees of branching. This structure is highly dependent on the algae's species. Due to the complex structure, especially due to branching, it is very difficult to study the whole

As a known fact, fucoidan has solubility in water and acid solution [53] and acid hydrolysis can result various amounts of d-xylose, d-galactose, and uronic acid. Algal fucoidans as very common sulfated polysaccharide present in all brown algae are mainly found in Fucales and Laminariales, also present in Chordariales,

coglycuronans and glycorunogalactofucans [51].

*(a) Structure of fucoidan [51] and (b) structure of laminaran [51].*

*DOI: http://dx.doi.org/10.5772/intechopen.88303*

*Major Natural Vegetation in Coastal and Marine Wetlands: Edible Seaweeds DOI: http://dx.doi.org/10.5772/intechopen.88303*

**Figure 4.** *Chemical structure of agar polysaccharides with the different types of monomers [44].*

### **Figure 5.**

*Plant Communities and Their Environment*

lung cancer cell line which is known A549 cell line [41].

**2. Chemical components of edible seaweeds**

and rheological properties of polysaccharides [44, 46–50].

and glutathione [40].

diabetic activity.

**2.1 Polysaccharides**

Seaweeds are known to contain strong natural anti-oxidants, since algae contain a lot of secondary metabolites such as tocopherol, carotenoids, polyphenols, flavonoids, tannins, lignans, and mycosporine-like amino acids (MAA), vitamin C,

The studies have shown that seaweeds possess anticancer agents and there are hopes they can be effective in treatment of tumors and leukemia [34]. As the efforts have continued, scientists successfully isolated chemical compounds from brown seaweed with anticancer and antitumor activities [38, 39]. It has been reported that fucoidan from *U. pinnatifida* shows very good anti-cancer activity against human

Some studies in last decades show that fucoxanthin and fucoxanthinol from *U. pinnatifida* shows also anti-obesity activity. As obesity is known a serious health issue and has cost significant economic problem, that edible seaweeds possess anti-obesity activity, is very notable because; it is well known that obesity cost to some chronic diseases, such as liver steatosis, cardiovascular disease, osteoarthritis, type 2 diabetes, and some types of cancer. Alongside having antiobesity activity, some reports show that fucoxanthin and fucoxanthinol from *U. pinnatifida* possesses anti-diabetic activity [41]. Therefore, it can be considered that anti-obesitity activity and anti-diabetic activity are related each other. It is expected that if seaweeds have anti-obesity activity, they can able to show anti-

Polysaccharides are the main components of green, brown and red seaweed. Algae cell walls contain numerous polysaccharides such as, alginates, alginic acid, carrageenans, agar, laminarans, fucoidans, ulvans and derivatives with storage and structural functions (Perez et al., 2016; [42, 43]). As it is shown in **Figure 4** [44], agar polysaccharides have complex molecular structure with alternating composition of 3-linked-d-galacropyranose (G unit) and 4-linked-3,6-anhydrol-galactopyranose (LA unit) [45]. Substitution of hydroxyl group by ester sulfate, methyl groups and pyruvic acid at various positions have direct impact on physical

Polysaccharides have noticeable effects in immunomodulatory and anti-cancer as one of the most important macromolecules. These effects are driving force for wide research in biochemical and medical areas. As it was mentioned above, polysaccharides are abundant in cell walls and their composition is under the influence of season, age, species and geographical location. Their main goal in plants are food reservoir, however they can provide strength, and flexibility encountering wave actions and also balancing the ionic equilibrium inside the cell. Other structural benefits of polysaccharides, such as regularity of the hydroxyl group, can increase the ion interactions our of cell walls and interchain hydrogen bonding and causing

Depending on seaweeds, different polysaccharides can be produced by alginates, fucoidans, and laminarans. Laminarans, fucoidans as water soluble and high molecular mass alginic acids as alkali soluble polysaccharides are main products of brown seaweeds [51]. Main components of brown algae wall are cellulose microfibrils merged in amorphous polysaccharide while they relate to each other via proteins. There are two kinds of acid polysaccharides in extracellular structure of

brown algae, sulfated fucans and alginic acid (Perez et al., 2016).

**196**

gelation.

*(a) Structure of fucoidan [51] and (b) structure of laminaran [51].*

## *2.1.1 Fucans*

Fucans as one of the acid polysaccharides present in extracellular structure of brown algae (**Figure 5**) are categorized into three major groups: fucoidans, xylofucoglycuronans and glycorunogalactofucans [51].

### *2.1.2 Fucoidans*

Fucoidan is a branched sulfate ester polysaccharide with branching. The major branches in this polysaccharide are l-fucose-4 sulfate or sulfate ester at C3. Fucoidan has molecular weight ranging from 100 kDa [52] to 1600 kDa [53]. Main components of Fucoidan are fucose, uronic acids, galactose, xylose and sulfated fucose. Fucoidan structure contains sulfated fucans backbone, which is made of different sugars, fucose, or uronic acid. The backbone also has different degrees of branching. This structure is highly dependent on the algae's species. Due to the complex structure, especially due to branching, it is very difficult to study the whole molecule [54].

As a known fact, fucoidan has solubility in water and acid solution [53] and acid hydrolysis can result various amounts of d-xylose, d-galactose, and uronic acid. Algal fucoidans as very common sulfated polysaccharide present in all brown algae are mainly found in Fucales and Laminariales, also present in Chordariales,

Dictyotales, Dictyosiphonales, Ectocarpales, and Scytosiphonales. Although algal is present in brown algae but it seems to be absent in green algae, red algae, as well as in freshwater algae and terrestrial plants [55].

Study the structural composition of polysaccharides showed that xylofucoglycuronans or ascophyllans have polyuronide backbone, fundamentally poly-b-(1,4) d-mannuronic acid branched with 3-O-d-xylosyl-l-fucose-4-sulfate or sometimes uronic acid. While, glycuronogalactofucans are composed of linear chains of (1,4)-d-galactose branched at C5 with l-fuco-syl-3-sulfateoroccasionallyuronicacid [56]. This backbone consists of (1 → 3)-linked α-l-fucopyranose residues (type 1, **Figure 6A**) or alternating (1 → 3)-linked α-l-fucopyranose, (1 → 4)-linked α-l-fucopyranose residues (type 2, **Figure 6B**), and fucose and sulfate branching (**Figure 6C**) [54].

## *2.1.3 Carrageenans*

Carrageenan as linear sulfated polysaccharides are extracted from edible red seaweeds. Carrageenan name is from *Chondrus crispus* species of seaweed known as Carrageen Moss or Irish Moss in England, and Carraigin in Ireland [57]. This large and highly flexible polysaccharide contain 15–40% of ester-sulfate as the main component of sulfated polygalactan with average molecular weight of 100 kDa. The structural composition shows alternate units of anhydrogalactose (3,6-AG) and d-galactose. These units are joint by α-1,3 and β-1,4-glycosidic linkage. There are different classes of carrageenan such as λ, κ, ι, ε, μ. All these classes have sulfate groups in range of 22–35%. The number and position of the ester sulfate is the key for the primary differences in different types of carragenans. It must be mentioned that these nomenclatures have no reflect on the chemical structures. Kappa and Iota type have ester sulfate content around 25–30% and 3,6-AG content of about 25–30%. While, Lambda type has higher ester sulfate content of about 32–39% and no content of 3,6-AG (**Figure 7**) [57, 58].

### *2.1.4 Alginic acids*

Alginic acid or algin is a linear polysaccharide with 1,4-linked, b-d-mannuronic and a-l-guluronic acid (**Figure 8**) as building blocks which are arranged in nonregular and different sequences fashion [59]. Alginic acid is derived from brown seaweed in form of sodium and calcium alginate with main application in food and pharmaceutical industries. Structural functionalities make them able to bind with

**199**

**Figure 7.**

anti-oxidant [55, 60, 61].

*Chemical structure of carrageenans [57].*

*Major Natural Vegetation in Coastal and Marine Wetlands: Edible Seaweeds*

metal ions and obtained very viscous solutions when hydrated. This water absorption property makes alginate suitable for different applications specially in biological studies with potential application as anti-coagulant, anti-tumor, anti-viral and

*DOI: http://dx.doi.org/10.5772/intechopen.88303*

**Figure 6.** *Structure of fucoidans [54].*

*Major Natural Vegetation in Coastal and Marine Wetlands: Edible Seaweeds DOI: http://dx.doi.org/10.5772/intechopen.88303*

*Plant Communities and Their Environment*

(**Figure 6C**) [54].

*2.1.3 Carrageenans*

*2.1.4 Alginic acids*

in freshwater algae and terrestrial plants [55].

no content of 3,6-AG (**Figure 7**) [57, 58].

Dictyotales, Dictyosiphonales, Ectocarpales, and Scytosiphonales. Although algal is present in brown algae but it seems to be absent in green algae, red algae, as well as

Study the structural composition of polysaccharides showed that xylofucoglycuronans or ascophyllans have polyuronide backbone, fundamentally poly-b-(1,4) d-mannuronic acid branched with 3-O-d-xylosyl-l-fucose-4-sulfate or sometimes uronic acid. While, glycuronogalactofucans are composed of linear chains of (1,4)-d-galactose branched at C5 with l-fuco-syl-3-sulfateoroccasionallyuronicacid [56]. This backbone consists of (1 → 3)-linked α-l-fucopyranose residues (type 1, **Figure 6A**) or alternating (1 → 3)-linked α-l-fucopyranose, (1 → 4)-linked α-l-fucopyranose residues (type 2, **Figure 6B**), and fucose and sulfate branching

Carrageenan as linear sulfated polysaccharides are extracted from edible red seaweeds. Carrageenan name is from *Chondrus crispus* species of seaweed known as Carrageen Moss or Irish Moss in England, and Carraigin in Ireland [57]. This large and highly flexible polysaccharide contain 15–40% of ester-sulfate as the main component of sulfated polygalactan with average molecular weight of 100 kDa. The structural composition shows alternate units of anhydrogalactose (3,6-AG) and d-galactose. These units are joint by α-1,3 and β-1,4-glycosidic linkage. There are different classes of carrageenan such as λ, κ, ι, ε, μ. All these classes have sulfate groups in range of 22–35%. The number and position of the ester sulfate is the key for the primary differences in different types of carragenans. It must be mentioned that these nomenclatures have no reflect on the chemical structures. Kappa and Iota type have ester sulfate content around 25–30% and 3,6-AG content of about 25–30%. While, Lambda type has higher ester sulfate content of about 32–39% and

Alginic acid or algin is a linear polysaccharide with 1,4-linked, b-d-mannuronic and a-l-guluronic acid (**Figure 8**) as building blocks which are arranged in nonregular and different sequences fashion [59]. Alginic acid is derived from brown seaweed in form of sodium and calcium alginate with main application in food and pharmaceutical industries. Structural functionalities make them able to bind with

**198**

**Figure 6.**

*Structure of fucoidans [54].*

metal ions and obtained very viscous solutions when hydrated. This water absorption property makes alginate suitable for different applications specially in biological studies with potential application as anti-coagulant, anti-tumor, anti-viral and anti-oxidant [55, 60, 61].

### **Figure 8.**

*(a) b-d-mannuronic acid in alginic acid and (b) a-l-guluronic acid in alginic acid (a and b adapted from [51, 62]).*

## *2.1.5 Laminarans*

Laminarans, the nutritional reserve of all brown algae, was first detected in Laminaria species. The molecular weight of the laminaran is about 5000 Da depending on the degree of polymerization. The main sugar, structure and composition of the laminaria species is the laminar, which varies according to the algae species. Laminaran is a polysaccharide, which is soluable in water and consisting 20–25 glucose units including of (1,3)-b-d-glucan including of (1,3)-b-d-glucan, b (1,6) branched (**Figure 8b**). There are two kinds of laminar chain, called M or G, which are different at the reduction ends. While the M chains ends with a mannitol residue, the G chains end with a glucose residue. Most of the laminates, which are impervious to hydrolysis in the upper gastrointestinal tract (GIT) and which are considered to be dietary fiber, are stabilized by cross-chain hydrogen bonds [63]. The activity of structure of laminarans, which are affected by environmental factors such as water temperature, nutrient salt, salinity, waves, sea flow and plunge depth, vary. Besides the role of laminar as a prebiotic and dietary fiber, it is also interesting to have anti-microbial and anti-cancer activities [63].

### **2.2 Alkaloids**

Alkaloids are organic compounds, which contains nitrogen atom in their structures. Various structures of amines, cyclic nitrogen and halogenated containing organic compounds exist in the plants and natural materials. Cyclic nitrogen containing alkaloids are only be found in marine organisms and marine algae and are classifies in three main categories [64].

## *2.2.1 Phenylethylamine alkaloids (PEA)*

β/2-phenylethylamine, phenethylamine also known as PEA is made of benzene ring with different ethylamine side chains (**Figure 9a**). These important alkaloids are precursors for making natural and synthetic compounds. Many pharmaceutical precursors can be achieved from substituted PEAs present in plant and animals, such as, simple phenylamine (tyramine, hordenine) and catecholamine (dopamine) [64].

Some type of brown algae, *Gracilaria bursa-pastoris*, *Halymenia floresii*, *Phyllophora crispa*, *Polysiphonia morrowii* and *Polysiphonia tripinnata*, have PEA in their structures [65].

### *2.2.2 Indole and halogenated indole alkaloids*

Morales-Ríos et al. recorded that the alkaloids produced by *Flustra foliacea*, possessing an unusual pyrroloindoline skeleton, are divided into simple indoles (1–6)

**201**

*2.2.3 Other alkaloids*

**Figure 10.**

*Major Natural Vegetation in Coastal and Marine Wetlands: Edible Seaweeds*

and a quinoline 7 (**Figure 10**), and those with a pyrrolo[2,3-b]indole framework (8–23), including hexahydro-1,2-oxazino[5,6-b]indole (24) (**Figure 11**). Main metabolites in marine seaweeds such bryozoan *Flustra foliacea* are brominated indoles. The structure of these seaweeds have number of brominated indoles with

*Structure of indoles (1–6) and quinoline (7) extracted from F. foliacea (adapted from [66]).*

*Structures of phenylethylamine derivatives: (a) PEA; (b) N-ACPEA; (c) TYR; (d) N-ACTYR; (e) HORD;* 

The marine cheilostome bryozoan *Flustra foliacea* contain an order of brominated pyrroloindolines and indoles, terpenes, and a kind of quinoline, having a variety of biological activities, including anti-microbial, anti-tumor and some

Main alkaloids achieved form algae are from family of 2-phenylethylamine and indole with different substitutions and functionalities. 2,7-naphthyridine derivatives are also alkaloids. Substitutions such as bromide and chloride are specifically seen in Chlorophyta (Perez et al., 2016; [67]). Regarding to the medical properties

prenyl or isoprenyl substituents at different positions [66].

biological activities, as secondary metabolites [66].

*DOI: http://dx.doi.org/10.5772/intechopen.88303*

**Figure 9.**

*(f) DOP (adapted from [65]).*

*Major Natural Vegetation in Coastal and Marine Wetlands: Edible Seaweeds DOI: http://dx.doi.org/10.5772/intechopen.88303*

**Figure 9.**

*Plant Communities and Their Environment*

Laminarans, the nutritional reserve of all brown algae, was first detected in Laminaria species. The molecular weight of the laminaran is about 5000 Da depending on the degree of polymerization. The main sugar, structure and composition of the laminaria species is the laminar, which varies according to the algae species. Laminaran is a polysaccharide, which is soluable in water and consisting 20–25 glucose units including of (1,3)-b-d-glucan including of (1,3)-b-d-glucan, b (1,6) branched (**Figure 8b**). There are two kinds of laminar chain, called M or G, which are different at the reduction ends. While the M chains ends with a mannitol residue, the G chains end with a glucose residue. Most of the laminates, which are impervious to hydrolysis in the upper gastrointestinal tract (GIT) and which are considered to be dietary fiber, are stabilized by cross-chain hydrogen bonds [63]. The activity of structure of laminarans, which are affected by environmental factors such as water temperature, nutrient salt, salinity, waves, sea flow and plunge depth, vary. Besides the role of laminar as a prebiotic and dietary fiber, it is also

*(a) b-d-mannuronic acid in alginic acid and (b) a-l-guluronic acid in alginic acid (a and b adapted from* 

interesting to have anti-microbial and anti-cancer activities [63].

are classifies in three main categories [64].

*2.2.2 Indole and halogenated indole alkaloids*

*2.2.1 Phenylethylamine alkaloids (PEA)*

Alkaloids are organic compounds, which contains nitrogen atom in their structures. Various structures of amines, cyclic nitrogen and halogenated containing organic compounds exist in the plants and natural materials. Cyclic nitrogen containing alkaloids are only be found in marine organisms and marine algae and

β/2-phenylethylamine, phenethylamine also known as PEA is made of benzene ring with different ethylamine side chains (**Figure 9a**). These important alkaloids are precursors for making natural and synthetic compounds. Many pharmaceutical precursors can be achieved from substituted PEAs present in plant and animals, such as, simple phenylamine (tyramine, hordenine) and catecholamine

Morales-Ríos et al. recorded that the alkaloids produced by *Flustra foliacea*, possessing an unusual pyrroloindoline skeleton, are divided into simple indoles (1–6)

Some type of brown algae, *Gracilaria bursa-pastoris*, *Halymenia floresii*, *Phyllophora crispa*, *Polysiphonia morrowii* and *Polysiphonia tripinnata*, have PEA in

*2.1.5 Laminarans*

**Figure 8.**

*[51, 62]).*

**2.2 Alkaloids**

(dopamine) [64].

their structures [65].

**200**

*Structures of phenylethylamine derivatives: (a) PEA; (b) N-ACPEA; (c) TYR; (d) N-ACTYR; (e) HORD; (f) DOP (adapted from [65]).*

### **Figure 10.**

*Structure of indoles (1–6) and quinoline (7) extracted from F. foliacea (adapted from [66]).*

and a quinoline 7 (**Figure 10**), and those with a pyrrolo[2,3-b]indole framework (8–23), including hexahydro-1,2-oxazino[5,6-b]indole (24) (**Figure 11**). Main metabolites in marine seaweeds such bryozoan *Flustra foliacea* are brominated indoles. The structure of these seaweeds have number of brominated indoles with prenyl or isoprenyl substituents at different positions [66].

The marine cheilostome bryozoan *Flustra foliacea* contain an order of brominated pyrroloindolines and indoles, terpenes, and a kind of quinoline, having a variety of biological activities, including anti-microbial, anti-tumor and some biological activities, as secondary metabolites [66].

### *2.2.3 Other alkaloids*

Main alkaloids achieved form algae are from family of 2-phenylethylamine and indole with different substitutions and functionalities. 2,7-naphthyridine derivatives are also alkaloids. Substitutions such as bromide and chloride are specifically seen in Chlorophyta (Perez et al., 2016; [67]). Regarding to the medical properties

**Figure 11.**

*Indolines 8–24, including indolenine (13), isolated from F. foliacea (adapted from [66]).*

of marine alkaloids, further research and study successfully separated sufficient amount of pure organic derivatives for biological testing [66].

### **2.3 Terpenes**

Terpenes known as main algae metabolites, have chemical structure including five-carbon precursor. They are classified into, hemiterpenes, including five carbons (C5); monoterpenes, including ten carbons (C10); sesquiterpenes, including fifteen carbons (C15); diterpenes, including twenty carbons (C20); sesterterpenes, including twenty-five carbons (C25); triterpenes, including thirty carbons (C30) and polyterpenes, including above thirty carbons (>C30). It is known that some seaweeds contains terpenes. Chlorophyceae is one of them. It contains cyclic and linear sesqui-, di-, and triterpenes. The other one is Rhodophyceae and contains high structural diversity of halogenated secondary metabolites whose polyhalogenated monoterpenes show a variety of antibacterial properties (Perez et al., 2016; [68]).

## **3. Conclusion**

In recent decades, seaweed was thought as an abundant and renewable natural resource. Especially, edible seaweeds are rich in polysaccharides, unsaturated fatty acids, protein composition, vitamins, and minerals, as well as natural bioactive compounds such as alkaloids. Their main component, polysaccharides may vary

**203**

**Author details**

Ilknur Babahan1

University, Aydin, Turkey

Menderes University, Aydin, Turkey

provided the original work is properly cited.

\*, Birsen Kirim2

and Hamideh Mehr3

1 Department of Chemistry, Faculty of Arts and Sciences, Adnan Menderes

2 Department of Aquaculture Engineering, Faculty of Agriculture, Adnan

\*Address all correspondence to: ilknurbabahan@yahoo.com

3 Department of Polymer Engineering, University of Akron, Akron, Ohio, USA

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*Major Natural Vegetation in Coastal and Marine Wetlands: Edible Seaweeds*

depending on seaweeds and growth conditions. Because of their components, edible seaweeds possess various bioactivities such as anti-oxidant, anti-cancer, anti-

*DOI: http://dx.doi.org/10.5772/intechopen.88303*

The authors declare no conflict of interest.

obesity, and anti-diabetes activity.

**Conflict of interest**

depending on seaweeds and growth conditions. Because of their components, edible seaweeds possess various bioactivities such as anti-oxidant, anti-cancer, antiobesity, and anti-diabetes activity.
