An analysis of the structure of alginate (alginic acid) and the investigation of its extraction process and stability

Alginic acid is a non-ionic polysaccharide, also called algin or alginate. Alginic acid has the formula n (C۶H۸O۶) and is a polysaccharide compound that is widely distributed in the cell walls of brown algae. Alginic acid is a hydrophilic compound and forms a viscous gum when hydrated. With metals such as sodium and calcium, its salts are known as alginate. Algenic acid is the acidic and insoluble form of algin, which is a white to yellowish fibrous powder obtained from the brown seaweed species Macrocystis pyrifera-like. Soluble derivatives of algin include sodium, potassium and ammonium alginate and propylene glycol alginate. This compound is used as an ingredient in tablets and antacids. Alginate is an attractive marine resource-based biopolymer, which has been widely used in pharmaceutical, food and textile industries. This paper reviewed the latest development of the conventional and alternative processes for alginate extraction from brown seaweed. To improve extraction yield and product quality, various studies have been carried out to optimize the operation condition. Based on literature survey, the most commonly used protocol is soaking milled seaweed in ۲% (w/v) formaldehyde, overnight, solid loading ratio of ۱:۱۰–۲۰ (dry weight biomass to solution), then collecting the solid for acid pre-treatment with HCl ۰.۲–۲% (w/v), ۴۰–۶۰ °C, ۱:۱۰–۳۰ ratio for ۲–۴ h. Next, the solid residue from the acid pre-treatment is extracted using Na۲CO۳ at ۲–۴% (w/v), ۴۰–۶۰ °C, ۲–۳ h, ۱:۱۰–۳۰ ratio. Then the liquid portion is precipitated by ethanol (۹۵%+) with a ratio of ۱:۱ (v/v). Finally, the solid output is dried in oven at ۵۰–۶۰ °C. Novel extraction methods using ultrasound, microwave, enzymes and extrusion improved the extraction yield and alginate properties, but the financial benefits have not been fully justified yet. To improve the sustainable production of alginate, it is required to promote seaweed cultivation, reduce water footprint, decrease organic solvent usage and co-produce alginate with other value-added products.

کلیدواژه ها:

sodium alginate ، brown seaweed ، Phaeophyceae ، green processing ، alginic acid