Agaropectin is a sulfated galactan mixture which composes agar by 30% composition.

It is made up of alternating units of D-galactose and L-galactose heavily modified with acidic side-groups which are usually sulfate, glucuronate, and pyruvate.

[2][3][4] Pyruvic acid is possibly attached in an acetal form to the D-galactose residues of the agarobiose skeleton.

The sulfate content of the agar depends on the source of the raw material from which it is derived.

[5] Agaropectin has no commercial value and is discarded during the commercial processing of agar, and food grade agar is mainly composed of agarose with a molecular weight of about 120 kDa.