Agar is a polysaccharide complex obtained through bleaching and hot water extraction of agarocytes from the red alga Rhodophyceae, found in the Pacific and Indian Oceans and in the Sea of Japan. The genera Gelidium, Acanthopeltis, Ceramium, Pterocladia and Gracilaria predominate in agar production. Agar is composed of about 70% agarose and 30% agaropectin.
Agar is used in microbiology and bacteriology to make solid culture media for microorganisms; as an antistaling agent in bakery products, confectionery, meats and poultry; as a gelling agent is cosmetics, desserts and beverages; as a corrosion inhibitor; in sizing for paper and silks; in adhesives; in the dyeing and printing of textiles and fabrics; and as a protective colloid in ice cream, pet foods, health foods, laxatives, pharmaceuticals, dental impressions, lab reagents and photographic emulsions.
Agar is strongly hydrophilic and can slowly absorb about 20 times its weight of cold water, swelling in the process.1 Sigma tests the solubility of agar powder in water at 1 mg/ml with boiling, and obtains a clear, colorless solution. Agar is not soluble in alcohol.