The influence of the six constituent xanthan repeating units on the order–disorder transition of xanthan

• Influence of the repeating units on the transitional behavior of xanthan was studied.
• Acetylation of the outer mannose stabilizes the ordered xanthan conformation.
• Acetylation of the inner mannose does not stabilize the ordered conformation.
• Pyruvylated RUs are regularly distributed over the entire xanthan molecule.
• Acetylated RUs are irregularly distributed in specific xanthan segments.

Xanthans occurring in different levels of disordered conformation were enzymatically hydrolyzed to their six pentamer repeating units (RUs). The RUs present in the enzyme digests were analyzed using LC–MS. As only disordered xanthan segments are degraded by cellulases, the influence of the six different RUs on the transitional behavior of xanthan could be studied. The results indicate that especially xanthan segments rich in RUs that are acetylated on the outer mannose unit stabilize the xanthan conformation. Acetylation of the inner mannose did not show to have a clear stabilizing effect on the xanthan conformation. As the enzymatic release of pyruvylated RUs gradually increased with increasing levels of disordered xanthan segments, it is concluded that the distribution of these RUs is random. On the contrary, single and double acetylated RUs are distributed over specific xanthan segments as these RUs were instantly hydrolyzed.