**3. Plant polysaccharides**

Algae are found worldwide and the base of the food chain, serving as a source of nutrients for a variety of aquatic organisms. They are considered important photosynthetic organisms and represent an important source of biological compounds commonly used in industry. They can be classified into two large groups: macroalgae, which can be seen with the naked eye, and microalgae, which need a microscope to be observed [18].

The most abundant groups of macroalgae belong to green algae (Chlorophyta), which produce chlorophyll *a* and *b* as pigment; red algae (Rhodophyta), with phycoerythrin, and brown algae (Phaeophyceae), those that produce a xanthophyll pigment called fucoxanthin [19, 20].

Agarans and carrageenans are obtained from red algae, which is composed of a linear chain formed by β-D-galactose units linked 1 → 3 (A unit) to α-D/L-galactose linked in the positions 1 → 4 (unit B) arranged in the form of a repeating unit (AB). The α-D-galactose units in the disaccharide can be biologically converted into the anhydrous 3,6 derivatives by the elimination of sulfate groups at position 6. Carrageenans differ from agarans in that they have the B unit in the form of α-Dgalactose and are found in *Chondrus, Gigartina, Kappaphycus, Eucheuma, Meristotheca* and *Solieria* species (Rhodophyta). While the agarans, in the species *Gracilaria, Gelidium,* and *Pterocladiella* (Rhodophyta) [21].

Extracted from brown algae species (Phaeophyceae), the alginates are such as *Macrocystis*, *Ascophyllum, Laminaria, Ecklonia,* and *Sargassum*. This polysaccharide has a linear structure of mannuronic (M) and guluronic (G) acids, and the distribution of M and G blocks in the structure as well as the M/G ratio strongly influence its properties in solution [21].

#### **3.1 Alginic acid**

This acidic polysaccharide is a polyuronide consisting of β-D-mannuronic and α-L-guluronic acid units linked through (1 → 4) bonds. The proportion and distribution along the chain of the polymer varies according to the species [22].

The characterization, through chemical methods, such as partial acid hydrolysis, purification of the blocks and methylation of the carboxy-reduced polymer, as well as spectroscopic techniques, allowed us to determine that alginate from *Sargassum stenophyllum*, which has 21% yield, has a molar ratio between mannuronic (M) and guluronic (G) acid units of 1:1. These units are distributed throughout the polymer in the form of M blocks (5%) and G blocks (25%) with degrees of polymerization of 20 and 64, respectively, in addition to a high percentage of hybrid blocks (MG, 70%). *Alginate Extraction from Natural Resources Based on Legal Requirements: An Incentive… DOI: http://dx.doi.org/10.5772/intechopen.114217*

The determination of the chemical structure of alginates is of fundamental importance for its proper application in different sectors of industry since alginates rich in mannuronic acid have viscous properties and those rich in guluronic acid are more gelling [23].

Alginates with different molecular weights, viscosity and ratios of M and G units were obtained from *Sargassum vulgare*, which inhibited tumor cell growth *in vivo* [24, 25]. Alginate from the brown seaweed *Laminaria brasiliensis* was characterized structurally [26]. Although the M/G molar ratio is similar to that of *Sargassum stenophyllum*, the polymerization of the G blocks is lower (=20). The physicochemical properties presented by alginates depend both on the M/G ratio and on the percentage and size of the constituent blocks, which justifies a detailed study of the chain structure of alginates isolated from different species of brown algae for commercial use [24, 25].

## **4. Alginate sources**

Some compounds with therapeutic properties, produced by algae, are soluble polysaccharides, such as alginates and carrageenans, and sulfate polysaccharides, such as fucoidan, carotenoids, polyunsaturated fatty acids, vitamins, tocopherols and phycocyanin's [27–29], differing, between groups, in according to their physiology and photosynthetic pigments they produce [30]. Each group also has a different mineral content from the others, as well as protein and fiber content [31, 32].

Marine macroalgae, whose body is represented by a thallus, are aquatic plants without vascularization; most are benthic, that is, they live adhered to a substrate and are autotrophic [33, 34]. Brown algae, from Phaeophyceae, make up the most studied group and are commonly used in human food [35]. They can also be used as a complement to feed, in the cosmetic area, as sources of chemical products such as alginates [31, 32].

Because they are organisms exposed to environmental conditions of high luminosity and considerable concentrations of oxygen and carbon dioxide, algae have defense mechanisms against free radicals, thus forming an important source of natural antioxidants [36, 37]. Antioxidants are compounds that prevent the formation of reactive oxygen species that are accumulating between cells and causing oxidative stress. This, in turn, causes deregulation in cellular metabolism, reflecting at molecular, protein, and DNA levels [38].

Extracted both from species of brown algae, where it makes up the structure of the cell wall and intracellular spaces, promoting rigidity and, at the same time, flexibility, and extracellularly covering some bacterial species [39], due to its unique properties in the food, cosmetic, pharmaceutical, textile and of paper, alginate has become a product of commercial importance [40], as mentioned in **Table 1**. Among its pharmacological potential, the antioxidant characteristic of alginate has been relevant, due to its mechanisms and properties in helping serious illnesses [42], also conferring properties of texture to food, such as thickening, adhesion, emulsification, gelling or bulking [40].

Despite being applied in a wide range of areas, Brazil imports all of its demand for alginate [43]. In 2017, the country imported around US\$10.8 million worth of alginic acid from Chile, China, Norway, and Italy [44]. This dependence can be reduced through the national production of alginate from *Sargassum* spp., illustrated in **Figure 1**, which is abundant on the Brazilian coast, respecting the laws and regulations [45].


#### **Table 1.**

*Main applications of alginate.*

#### **Figure 1.** *Sargassum sp. (image from personal archive).*

Regarding algae of the Phaeophyceae class, according to the Reflora Virtual Herbarium—Plants of Brazil system, there are 49 genera cataloged as native to Brazil; among these, 102 species and 16 varieties [46]. The main species that produce alginate

## *Alginate Extraction from Natural Resources Based on Legal Requirements: An Incentive… DOI: http://dx.doi.org/10.5772/intechopen.114217*

of industrial interest are part of the genera *Laminaria* and *Sargassum*, as listed in **Table 2**, with their species and geographic distribution, among other aspects.

Alginate was characterized at the end of the nineteenth century and is currently obtained from brown algae, according to **Table 3**, from coastal regions [40]. It is a molecular polysaccharide that is high weight, composed of α-L-guluronic acid (G) and β-D-mannuronic acid (M) bonds, as shown in **Figure 2**, which interacts with ions metals by cation exchange mechanisms [48]. It can react with divalent ions forming a gel or with polyvalent ions forming crosslinks, as shown in **Figure 3**. The physical properties of the molecule depend on the proportion and size of the G blocks in the alginate chain [49].

Alginate is an acid that is insoluble in water at room temperature and soluble at elevated temperatures. Therefore, the sodium, calcium, and potassium salts present,



**Table 2.**

*Main native species of Brazil producing alginate.*

being soluble in water, are commonly used in the different areas of industry. Sodium alginate is the main one used in many applications, and it becomes insoluble through the addition of divalent cations, resulting in gels or films. These are not thermoreversible when high concentrations of calcium are used; however, when exposed to low concentrations, they can become thermo-reversible [39].

The alginate extraction process essentially comprises five steps, namely acidification, alkaline extraction, solid/liquid separation, precipitation, and drying. In the acidification step, the seaweed is immersed in a bath of sulfuric acid for several

*Alginate Extraction from Natural Resources Based on Legal Requirements: An Incentive… DOI: http://dx.doi.org/10.5772/intechopen.114217*


#### **Table 3.**

*Main species of alginate-producing brown algae, according to all the literature consulted for this work.*

#### **Figure 2.**

*Chemical structure of alginate. Source: Adapted from Fang et al. [47].*

$$\begin{aligned} \boxed{\mathbf{M}} \quad \mathbf{M} - \mathbf{M} - \mathbf{G} - \mathbf{G} - \mathbf{M} - \mathbf{G} - \mathbf{G} - \mathbf{M} - \mathbf{M} - \mathbf{G} - \mathbf{G} - \mathbf{M}} \xrightarrow[\epsilon \mathbf{M}]{} \mathbf{M} \end{aligned}$$

#### **Figure 3.**

*Polymeric chain representation from the G and M blocks of the alginate structure.*

hours to convert the insoluble alginate salts (Ca(Alg)2; Mg(Alg)2) present in the cell walls into alginic acid. The next stage is alkaline extraction, where the acidified seaweed is placed in a solution of sodium carbonate. The previously insoluble alginic acid is converted into soluble sodium alginate, which transfers to the aqueous phase. It takes several hours to achieve maximum extraction. Algae residues are separated from the sodium alginate solution using flotation/flocculation and filtration. Sulfuric acid or calcium chloride is then added to precipitate the alginates. The final product is pressed and dried through heating. Different alginate salts can be prepared by reacting alginic acid with the appropriate base [50, 51]. When alginate is added to an aqueous solution, it swells, increasing its viscosity. The solution's viscosity and the strength of the formed gel depend on temperature, pH, and the presence of metal cations [52].

Various alginate salts and their combinations influence different parameters. The matrices exhibited a greater ability to swell in neutral environments (pH 6.8) than in acidic conditions. pH changes from 6.8 to 1.2 affected polymer hydration and the

rheology of the alginate gel due to the interconversion of carboxylate anions (sodium alginate) to free carboxyl groups (alginic acid) with an increasing concentration of hydrogen ions [53, 54].

#### **4.1 Seaweed alginate** *vs.* **bacterial alginate**

Although the cell wall of brown algae has much in common with the cell wall of higher plants, alginic acid is found in all known *Phaeophyceae* species and is absent in other plant tissues. However, it is synthesized by bacteria such as *Pseudomonas* spp. and *Azotobacter vinelandii*, as a capsular polysaccharide and differs from alginic acid present in algae only by being more acetylated [39].

Brown algae containing alginate grows on rocky beaches or in areas of ocean with clear, rocky bottoms. They are found at high tide or centurion along the beach, at a depth of less than 38 m, the limit for sunlight penetration. Among all Phaeophyceae species, some are used as a commercial source of alginate, the giant seaweed *Macrocystis pyrifera*, which grows abundantly on the coasts of North and South America, being the main one [39].

The variability in the structures of the chain blocks, such as molecular weight, proportion, and relative distribution of the two monomers, M and G, along the molecule, and acetylation have an influence on the physicochemical properties of compost and the biological basis for this variability is therefore of scientific and practical importance. Alginates produced by bacteria and mannuronate residues from bacterial alginates are acetylated at the O-2 and/or O-3 positions. Therefore, alginates have significant differences for the industry and its applications. Like the species of *Laminaria, Ecklonia,* and *Aschophyllum nodosum*, they produce alginates with different proportions of polyguluronic acid, related to *M. pyrifera*, in their structure, thus resulting in different functionalities of this compound [39].

The production of alginic acid is concentrated in the cultivation of brown algae; however, the structure of the monomer residue blocks is similar in alginates produced by seaweed and synthesized by the bacteria *A. vinelandii*. According to Gorin and Spencer, the specific rotation of bacterial sodium alginate is very close to the rotation of sodium alginate derived from algae, thus suggesting that the glycosidic configurations are similar [55]. In contrast, all *Pseudomonas* alginates, although they have G monomers, do not have sequences of these monomers, that is, they do not have G blocks [56, 57].

#### **4.2 Alginate extraction**

There are several factors that influence the composition of an extract, and one of them is the extraction method [58]. The literature demonstrates several different methods and protocols that can be applied according to the objective of each research. **Table 4** lists two main methods of extracting bacterial alginate, from *Azotobacter vinelandii*, and from algae such *Sargassum cymosum*, as illustrated in **Figure 3**.

However, the methods have basic procedures, being the conversion of insoluble alginate into alginic acid [55]. This conversion occurs in the acid pre-treatment, a step carried out in the conventional extraction, commonly using hydrochloric acid, which also contributes to the increase in yield and removal of some contaminants such as fucoidans, laminarins, amino acids, and polyphenols. The addition of sodium carbonate to the solution, at a controlled time and temperature, will allow the precipitation of sodium alginate in its soluble form [61].


#### **Table 4.**

*Methods for extracting bacterial alginate from Azotobacter vinelandii and algae from Sargassum cymosum C. Agardh.*

The original brown color of alginate extracted from brown seaweed can cause rejection and dissatisfaction in the industrial market. Therefore, it is necessary to use bleaching agents, such as sodium hypochlorite. However, the use of hypochlorite and other chlorine salts has been a matter of concern, as these compounds are considered precursors in the formation of compounds that are harmful to health due to their high carcinogenic potential [62, 63].

The conventional approach to alginate production involves a multi-stage process. Essentially, fresh algae are washed, dried, and ground into powder. Subsequently, the algae biomass is soaked in water for rehydration, to which various chemicals are added to eliminate undesirable compounds in the algae. Next, an acid or alkaline pretreatment is applied to break down the plant's cell wall, followed by sodium carbonate extraction to obtain water-soluble alginate from the seaweed biomass matrix. There are three precipitation routes to recover alginate from solution, namely the sodium alginate route, the calcium alginate route and the alginic acid route, with the final product generally isolated in the form of sodium alginate. On the other hand, with a


#### **Table 5.**

*Greener extraction methods of alginate. Source: Adapted from Saji et al. [64].*

focus on sustainable development, more environmentally friendly ways of obtaining alginate have been explored. Several greener technologies have been developed and implemented in the field of biopolymer extraction. Some of these technologies, such as ultrasound-assisted extraction, microwave-assisted extraction, enzyme-assisted extraction, and extrusion-assisted extraction, can be employed in the extraction of alginate from brown seaweed, thereby increasing extraction efficiency, reducing energy consumption and minimizing waste generation, as mentioned in **Table 5** [64].

In general, as conventional processes have been investigated for more than a century, the technology is relatively mature, although innovations are still needed to further improve process efficiency. On the other hand, green extraction processes offer promising and environmentally friendly options, but their industrial applications have yet to be demonstrated on an industrial scale [64].

## **5. Innovation from genetic resources**

The concept of innovation, in general, includes the process from the creation of new ideas to their implementation and propagation. Innovation is also considered very important with regard to sustainability. In recent times, attention has focused on the use of bio-based natural compounds in different industrial sectors of application. Bio-based natural compounds, or those derived from plants, microorganisms, and animal resources, have several advantages (such as biocompatibility, availability, non-toxicity, and biodegradability) [65–67]. Due to their unique properties, such as biodegradable properties, biopolymers are gradually replacing synthetic ones. Among the biopolymers is alginate (NaC6H7O6), a group of polysaccharides that have been

#### *Alginate Extraction from Natural Resources Based on Legal Requirements: An Incentive… DOI: http://dx.doi.org/10.5772/intechopen.114217*

of great interest. Resulting from the depletion of renewable sources for obtaining resources, the adoption of sustainable practices also highlights the use of bioproducts for sustainable development. Alginate is widely used and has numerous usage features in biomedicals, food, agricultural, chemicals, cosmetics, pharmaceuticals, adsorbent, and water treatment industries, among many other industrial sectors [68, 69]. Innovation is needed with regard to the social and ecological benefits of the sustainable use of natural resources. Seaweeds, in turn, play an important role in maintaining ecological balance, as well as their potential for sustainable cultivation and biotechnology make them a very significant resource for innovative strategies related to technological development [70].

Considering the high potential of obtaining alginate from algae, added to the sustainable exploitation of natural resources in order to increase economic benefits, it is essential to seek ways to minimize environmental impacts. Moreover, it is possible to apply life cycle assessment (LCA) techniques to quantify the sustainability associated with technological development. The LCA methodology can measure the benefits associated with alginate production activities and obtain value-added products until their final destination. Thus, the LCA methodology, which is considered a "cradle-tograve" methodology, can assess the life cycle of a process or product from the extraction of raw materials to the end of its useful life. Moreover, to carry out innovative processes within legal requirements, it is necessary to analyze the environmental laws in force in the countries of origin of the species in question because both the activities of use of the species itself, as well as the activities of use of products derived from its metabolism, can be framed in environmental laws and have legal implications if there is no compliance with the requirements laid down in law [71].

Technological innovation can be used as a strategy with the purpose of achieving sustainable development, which has played a very important role in the economy in recent years. It is noteworthy that despite the positive impact of innovation on environmental issues, it is not in fact sufficient to offset the negative impacts previously caused. This fact may indicate the need to enable complementary measures to achieve sustainable development [72].
