gum xanthan Xanthan gum is a polysaccharide produced by the bacteria Xanthomonas campestris. It is composed of pentasaccharide repeat units, comprising two glucose units, two mannose units, and one glucuronic acid unit. Its main chain consists of beta-D-glucose units linked at the 1 and 4 positions. Trisaccharide side chains contain a D-glucuronic acid unit between two D-mannose units linked at the O-3 position of every other glucose residue in the main chain. Approximately one-half of the terminal D-mannose contains a pyruvic acid residue linked via keto group to the 4 and 6 positions, with an unknown distribution. D-Mannose unit linked to the main chain contains an acetyl group at position O-6.