Agar

Agar is a polysaccharide found in the cell walls of some red algae and is unusual in containing sulfated galactose monomers. Certain marine algae of the class Rhodophyceae, called Red Sea weeds are the source of this polysaccharide. Some of the chief algal sources are Gelidium cartilagineum, Gracilaria conferroides and Pteroclaia capillcea. The structure and composition of the agar extract of Gelidium amansii showed that it is composed of two major fractions - agarose, a neutral polymer and agaropectin, a charged, sulfated galactan (Galactose, 3-6-anhydrogalactose). The ratios of these two polymers vary widely and the percentage of agarose in agar-bearing seaweeds ranges from 50% to 90%.  The composition of agar is discussed herewith along with the structure as shown in the figure.