Alginate Structure

Any brown algae can be used as a source of alginate. However, its actual chemical structure differs from one genus to another, and among different tissues in the algae. Different factors have an effect on Alginate composition, quantity and sequential structure such as species, season, tissue age and environmental conditions (Jothisaraswathi et al., 2006; Rioux et al ., 2007).

Different brown algae species produce alginates with compositional differences in proportion of polyguluronic acid structure. These differences are related to the physico-chemical properties of alginate, which depend on the distribution of M and G units along the polysaccharidic chain and overall M/G ratio (Nyvall et al., 2003; Rinaudo et al ., 2008).

Alginates rich

Different factors controls the quantity and quality of the alginates extracted from brown algae. The used raw material for alginate extraction should be a good for obtaining a high yield of alginate. A high quality alginate forms strong gels and gives thick aqueous solutions.

Alginate is present in the cell wall of brown algae forming different salts of alginic acid as sodium, calcium and magnesium salts having different properties. For making the extraction of alginate salts more easily, the first step by acidification. The alginate salts are converted to alginic acid by treatment with dilute HCl. The acidification step will remove contaminant glycans, like laminaran and fucan (Hernández-Carmona et al., 1998). Then, the insoluble alginic acid is transformed into soluble sodium alginate by alkaline extraction, with NaOH solution. Calcium and magnesium salts would be insoluble so the extraction is done by by solid-liquid separation. The algal residue is separated by filtration (Hernández-Carmona et al., 1999; Vauchel et al.,

After a series of purifications, the alginate is dried powdered. The color of extracted alginate will depend on the used algal raw material as well as the age of the algae .However, the pigmentation of alginate can be controlled by bleaching (Mchugh et al., 2001).

1.1.2. Bacterial alginate

Several bacteria can produce alginate such as Pseudomonas and Azotobacter species (Rehm, 2002). Monomer blocks structure was found to be similar in alginate extracted by marine algae and produced from Azotobacter vinelandii, while the alginate synthesized by Pseudomonas is different in that it doesn't have G-blocks (Skjak et al., 1986). The different biological functions of the alginates due to these differences in alginate structure (Donati and Paoletti, 2009).

The alginate from algae is different from alginate produced by bacteria. The main difference is mannuronate residues acetylation in bacterial alginate in positions 2 and / or O-3 (Windhues and Borchard,