**Abstract**

Algae are recognized as the main producer of commercial alginate. Alginate produced using algae is located in the walls and intracellular regions of their cells. Its properties vary depending on the species, growing and harvesting seasons, and extraction methods. Alginate has attracted the attention of several industries, thanks to its unique properties such as its biodegradability, biocompatibility, renewability and lack of toxicity features. For example, it is considered a good encapsulation agent due to the transparent nature of the alginate matrices. Also, this biopolymer is recognized as a functional food in the food industry. It can be tolerated easily in human body and has the ability to reduce the risk of chronic diseases. Besides, it is used as an abrasive agent, antioxidant, and thickening and stabilizing agents in cosmetic and pharmaceutic industries. Generally, it is used in emulsion systems and wound dressing patches. Furthermore, this polysaccharide has the potential to be used in green nanotechnologies as a drug delivery vehicle via cell microencapsulation. Moreover, it is suitable to adopt as a coagulant due to its wide range of flocculation dose and high shear stability. In this chapter, the mentioned usage areas of algal alginate are explained in more detail.

**Keywords:** algae, algal alginate, immobilization, food, cosmetic, pharmaceutic, green nanotechnology, wastewater treatment

## **1. Introduction**

Algae are photosynthetic eukaryotic organisms that are found in many environments such as sea, freshwater, and land and they are significantly important for oxygen production all around the world. Most of them are microscopic organisms, and their cell size can vary from 1 μm up to 10 m. There are around 72,500 algal species that produce different metabolites and products such as carbohydrates, proteins, vitamins, and many other secondary metabolites that have different benefits to humans and other organisms [1]. Since algae are exposed to stress in their nature, such as high UV radiation, salinity, desiccation and so on, their metabolites can have high antioxidant and anti-inflammatory activity, which make them valuable. They support almost all life forms in the biosphere, being a food source with high protein content (~20%) [2].

Alginate is an unbranched polymer which consists of two different residues; α-L-guluronic acid (G block) and β-d-mannuronic acid (M block) that are linearly

**Figure 1.**

*(a) Chemical structure of G and M blocks; (b) Most used algae strains in alginate production [3–10].*

linked together by 1–4 linkages to form the polymer as shown in **Figure 1a** [11, 12]. It is the most abundant biopolymer in the world and one of the primary carbohydrates in brown seaweeds [*Laminaria* sp., *Macrocystis* sp., *Lessonia* sp., etc. (**Figure 1b**)], reaching up to 40% of the dry weight depending on species [11–13]. A major source of alginate is the cell walls of brown seaweeds and their intracellular spaces [12]. Alginates are used commercially as thickening agents by the food and pharmaceutical industries as binders, gelling agents, and wound absorbents [11, 13]. Alginate and their derivatives and other forms such as zinc alginate, copper alginate, sodium calcium alginate, propylene glycol alginate, alginic acid, ester of alginic acid, and calcium, ammonium, and potassium salts are used in different industries in mostly textile industry with 50%, food industry follows it with 30%, and medical, cosmetic, and pharmaceutical industry with 20% of the annual production of 38,500 t alginate worldwide [12, 14].

The present book chapter focusses on alginate biosynthesis in algae and its extraction, immobilization of algae in alginate, and utilization of alginate in food and cosmetics sectors, pharmaceutical and biomedical applications, green nanotechnologies, and wastewater treatment as a coagulant.
