**3. Extraction of alginate from algal material**

Commercial alginate is mainly obtained from the biomass of brown macroalgae, and the conventional extraction process consists of multiple steps integrated to maximize product yield. Generally, the protocol begins with a pretreatment stage in which harvested and dried biomass is exposed to an acidic solution in order to break the cell wall, solubilize the relevant components, and reduce the viscosity of alginate to a desired level [26]. The second step is the alkali extraction, which is the most critical part of whole process because it greatly affects the yield and specific features of extracted alginate. At this stage, acidified biomass is treated with a strong alkali solution mostly sodium carbonate or sodium hydroxide in order to recover the alginic acid as soluble sodium alginate. The residue is removed with centrifugation or filtration and then the obtained extract is precipitated with the use of calcium chloride, hydrochloric acid, or sulfuric acid so as to precipitate alginates

*Algal Alginate in Biotechnology: Biosynthesis and Applications DOI: http://dx.doi.org/10.5772/intechopen.101407*

**Figure 2.** *Classical alginate extraction procedure from macroalgae.*

in their acid or calcium salt form. Finally, the alginate product is dried, milled and ready for commercial use (**Figure 2**) [17, 39].

At the industrial level, the classical extraction method of alginate is widely used but it is highly complicated, time-consuming and requires high amount of solvents and chemicals. Therefore, novel approaches are suggested from several studies for the development of more suitable and effective extraction process (**Figure 3**). Sugiono et al. [40] performed an extrusion-assisted extraction procedure and optimized the key parameters (brown algae: solution ratio, feed rate and pH) for the alginate extraction from *Sargassum cristaefolium*. They reported that the extraction yield at optimum conditions reached the value of 34.96 ± 0.09%, and twin screw extruder was a promising method to extract alginate at the industrial scale. Youssouf et al. [41] proposed ultrasound-assisted extraction of alginate from *Sargassum muticum* to maximize extraction yield, minimize the use of chemicals, and shorten the process time. In another study, the deep eutectic solvent method combined with the subcritical water extraction technology were performed for the production of alginate from seaweed *Saccharina japonica*. The optimal conditions of different parameters were 150°C, 19.85 bar, 70% water content and 36.81 mL/g

**Figure 3.** *Flow diagram of different extraction techniques from literature [40–43].*

liquid/solid ratio giving an alginate yield of 28.1%. Also, the subcritical extraction method was defined as a clean, time-saving and effective process for the alginate extraction from seaweeds [42].

More recently, there has been a growing interest in the application of green technologies and biorefinery approach for the extraction of biological compounds. In this context, the development and optimization of biorefinery processes that integrate a sequential extraction steps in order to release multiple products of brown macroalgae is considered an effective, timesaving and green procedure. Several authors examined the extraction of a couple of components including alginate, fucoidan, laminarin, sugar, and so on with a biorefinery concept [33, 44, 45]. Yuan and Macquarrie [33] developed a step-by-step process to obtain a variety of products from *Ascophyllum nodosum* seaweed by the assistance of microwave technology. These products include fucoidan, alginates, sugars, and biochar (algae residue) and the obtained yields were 14.09, 18.24, 10.87, and 21.44% respectively. Kostas et al. [44] designed a bio-refinery procedure using *Laminaria digitata*, based on the extraction of the alginate and fucoidan, the subsequent production of bioethanol, and also the identification of bioactive compounds remaining in the residue. After the extraction of polysaccharides with the use of the conventional treatment method, the compositional structure of residue was analyzed and a high amount of glucose was determined, making this residue a potential feedstock for bioethanol production. This residue was exposed to acidic hydrothermal pretreatment and enzymatic saccharafication to release utilizable glucose and then it was fermented using *Saccharomyces cerevisiae* achieved an ethanol yield of 94.4%. Abraham et al. [45] developed and optimized a biorefinery process to extract polysaccharides of laminarin, fucoidan, and alginate from *Durvillaea potatorum*. The results established a novel biorefinery process for the extraction of multiple seaweed polysaccharides that could be used in specific industrial applications.

### **4. Immobilization of algae in alginate**

Microalgae are one of the most remarkable species utilized in biotechnology for numerous purposes. They are crucial for biofuel production [46], bioremediation, and biotransformation [47], fuel cells applications [48], and also for wastewater treatment [49]. For this matter, the adaptation of efficient immobilization methods for microalgal applications is crucial to develop novel manufacturing strategies (**Table 2**). Most of these industries require low-cost and easy immobilization methods, of which alginate is one of the most profound encapsulation agents can serve this demand [63]. Additionally, due to their transparent nature, alginate matrices do not interfere with the photosynthetic efficiency of algae [64]. Various microalgae (*Chlamydomonas reinhardtii*, *Chlorella sp.*, *Botryococcus braunii*, *Tetraselmis sp.*, *Nannochloropsis sp.* and *Scenedesmus sp*.) and cyanobacteria (*Anabaena sp., Nostoc*, *Spirulina*, *Oscillatoria sp.*, etc.) species have been explored in immobilized matrix systems as beads, biofilms, and various geometries [61, 64, 65].

Biohydrogen as a green alternative fuel is known to be produced by microalgae species under anaerobic conditions [66]. Although microalgae are important for biohydrogen production, large-scale operations are hindered due to the oxygen sensitivity of hydrogenase enzymes [67]. Successful immobilization of *Chlamydomonas reinhardtti* and several other cyanobacteria species are promising to increase the biohydrogen production capacity of immobilized microalgae as densely packed biohydrogen micro factories [61, 62].

Microalgae in wastewater systems can also be immobilized with alginate for the continuous removal of nitrogen and phosphorous to decrease organic loads of


**Table 2.**

*Microalgae immobilization methods.*

### *Algal Alginate in Biotechnology: Biosynthesis and Applications DOI: http://dx.doi.org/10.5772/intechopen.101407*

**75**

wastewater systems [53–55]. This approach is a clean and sustainable understanding for wastewater treatment, which inspired the utilization of microalgae for bioremediation purposes [68, 69] and removal of heavy metals [50] and other toxic molecules in the aquatic systems. There are also novel concepts to use immobilized microalgae networks as biosensors to check soil and water quality [58, 59].

Co-immobilization of different cell types can enhance the immobilized microalgae consortium. Microalgae growth-enhancing organisms can enhance the biomass accumulation in immobilized systems, which can increase the efficiency of immobilization for wastewater treatment, bioremediation, and biotransformation purposes [70, 71]. Symbiotic systems of algae-fungi in matrices can increase the efficacy of immobilization and decrease the toxic harms of heavy metals on algae [72].

Although alginate can provide a good environment for microalgae, there are several limitations concerning the stability of alginate gels. In aqueous systems, due to the diffusion of Ca+2 ions to aqueous environment, the alginate network can loosen, which subsequently damage the network. Thus, designer gels and/or blends with several other hydrogels can increase the durability and mechanical properties of alginate network [63, 73]. Another important aspect is although alginate does not affect cell proliferation, denser cultures may be needed, or due to dense culture diffusion limitation may increase cell death [62].

## **5. Algal alginate in food sector**

Recently, food consumers have begun to consider nutrition contents of foods and desire more natural foods instead of the synthetic ones. As a result of that, foods which contain alginate as a natural substance have become more popular [74]. Most importantly, the United State Food and Drug Administration (U.S. FDA) has classified the alginate as "generally regarded as safe" and European Food Safety Authority (EFSA) has recognized to use it in specific doses [75, 76]. In the food sector, alginate has many uses as food production, packaging, thickening and, stabilizing agents, thanks to its unique properties like biodegradability, biocompatibility, renewability, and lack of toxicity [17, 74, 75, 77–79]. It has been noticed that alginate is easily tolerated in human body [80]. For this reason, it has been harmlessly inserted in a wide range of food products. Those can be listed as tinned, baked and, frozen foods, meat, poultry, salad, seafood, pet food, cheese, fruit, beverage, jelly, dessert, jam, ice cream, sorbet, and mayonnaise [17, 76, 81–84]. Additionally, it is considered functional food that has ability to reduce the risk of chronic diseases and make them more controllable [17, 85]. Thus, it enhances the quality of life due to its anticancer and probiotic features [17]. In addition, it can be applied to dairy liquid products, beer, and drinks which are consumed by diabetic patients [17, 80]. Also, adding alginate in the foods decreases the transit time in the colon and this situation helps human body to prevent from colon cancer [86, 87]. Moreover, as a result of having the ability to reduce the feeling of hunger, this polymer can be consumed to cure obesity [17, 86]. Moreover, it induces gastrointestinal disorders and the risk of coronary heart diseases [15, 87, 88]. Alginate is used in food products in the range of 0.5–1.5% [87]. For example, Na-alginate can be used without any unhealthful side effects at the highest dose of 15.5 mg Na-alginate/kg (day)−1 [15]. Zn concentration should be carefully considered when Zn-alginate combination is used in food products. Because a high concentration of Zn2+ has negative effects on human body like nausea, diarrhea, and other diseases in the digestive system. So, its concentration must be in a suitable range. Zn-alginate can be added to purple corn to prevent the color in the drinks. Ca-alginate can be applied in yogurt, jams, and salads to control their smooth taste, in ice-cream to balance the crystal statement, and in

#### *Algal Alginate in Biotechnology: Biosynthesis and Applications DOI: http://dx.doi.org/10.5772/intechopen.101407*

noodles to increase the cohesion [78]. Propylene glycol-alginate can be included in salads and sauces [83]. Al3+ exhibit higher stable Al-alginate mixture than Ca2+ and Ba2+, thanks to its three-dimensional binding model. But it is possibly toxic and is not safe for using in food products. Unfortunately, Al-alginate uses in food industry are limited as packaging material of conserve meals [78].

The food package is used for covering the product for protection, preservation, containment, and conservation purposes. After the food product is produced, physical/mechanical damages, physicochemical, and biological changes can occur. As a result, the quality and safety of the food may be decreased. In order to avoid this, synthetic compounds have begun to be used as a packaging material. Thereafter, it has been noticed that synthetic package materials are liable for a huge amount of waste that is detrimental to marine and wildlife. Therefore, researchers have been focused on finding new natural compounds that can be a promising candidate as a food packaging material [76]. After many experiments, they have been established that alginate has the ability to decrease lipid oxidation, microbial contaminations, nutrition lost, and wizening. Thus, this polymer improves the foods shelf life and keeps them fresh [76, 78, 89]. Nowadays, alginate is used for packaging in a wide range of food products like potato strips, pineapple, sweet cherry, peach, melon, pork, and beef balls, roast beef, chicken meat, chicken nugget, chicken ball, hams, salmon, bream, perch, mozzarella cheese, coffee, powdered milk, resoluble tea, fresh cut foods like apple, carrot, and mango [15, 76].

Nowadays, 3D food printing is an efficient technology to produce high valuable food products. While printing the food, encapsulation of significant compounds (antioxidants, vitamins, probiotics, etc.) with alginate increases the strength of foods against the negative effects of light, heat, and oxygen at preparation and storage stages. The most important problem in this regard is the tendency of food products to deteriorate geometrically. At this point, the alginate improves the water dispersion and thus provides more stable products with good mechanical and thermal behavior [74].

Alginate can be utilized as a good thickening agent, thanks to its adhesion and cohesion features. Pure alginate shows a high viscosity ten times more when compared to commercial thickeners. Also, it has the ability to enhance food properties like its texture, organoleptic situation, and consumer acceptance. For example, it can improve yogurt's shape, creamy texture, adhesion feature and restrain the viscosity at the sterilization step. Also, this polymer can be added to the jelly to decrease the difficulty involved in swallowing [78].

In food applications, there are many molecular surfactants that are used as a stabilizer; they have negative effects on human health and environment. As a result of this, researchers have been focused to find new solid particles that can be used instead of molecular surfactants. Solid particles are divided into two groups as inorganic and naturally derived. Unfortunately, inorganic particles have a limited area of usage [77]. Because of that, a rapid increase in the tendency to use surfactant derived from natural sources was observed [77, 90]. In this case, alginate can be added to the beer for stabilizing the foam as a stabilizing agent [78, 83]. Additionally, alginate can be mixed with oil droplets for the preparation of emulsion gels, which are used in mayonnaise and similar foods [78].

Alginate has the ability to combine with two different cations to form a gel. Alginate contained products have significant elasticity that is controllable by changing the ratios of ions and alginate concentrations [78, 91]. Besides having this unique property, algal alginate may include some impurities like heavy metals, polyphenols, proteins and endotoxins because it is a natural compound [17, 79]. In the food industry, low levels these impurities can be acceptable, but in the cosmetic industry, they have to be removed [79].
