Agar is a polysaccharide complex extracted by bleaching and hot water treatment of agarocytes from the red alga Rhodophyceae, and usually consisting of the genera Gelidium, Acanthopeltis, Ceramium,Pterocladia and Gracilaria. The algae are typically found in the Pacific and Indian Oceans and in the Sea of Japan. It is primarily composed of two different units: Agarose and Agaropectin; Agarose is a neutral gelling component which is composed of a linear polymer of alternating D-galactose and 3,6-anhydrogalactose units. Agaropectin is a non-gelling component which consists of D-1,3-glycosidically linked D-galactose units, some of which are sulfated at the 6th position.
Agar is typically used in (According to the Merck Index): Substitute for gelatin, isinglass, etc. in making emulsions including photographic, gels in cosmetics, and as thickening agent in foods especially confectionaries and dairy products; in meat canning; in production of medicinal encapsulations and ointments; as dental impression mold base; as corrosion inhibitor; sizing for silks and paper; in the dyeing and printing of fabrics and textiles; in adhesives. In nutrient media for bacterial cultures.