The influence of the primary and secondary xanthan structure on the enzymatic hydrolysis of the xanthan backbone

•Several xanthans were enzymatically hydrolyzed using cellulases.•The final degree of hydrolysis is solely controlled by the xanthan conformation.•Only disordered xanthan molecules are available for enzymatic hydrolysis.•At a given conformation, similar degradation levels are obtained for all xanthans.•Xanthans can be completely hydrolyzed to repeating units, independent on their primary structure. Differently modified xanthans, varying in degree of acetylation and/or pyruvylation were incubated with the experimental cellulase mixture C1-G1 from Myceliophthora thermophila C1. The ionic strength and/or temperature of the xanthan solutions were varied, to obtain different xanthan conformations. The exact conformation at the selected incubation conditions was determined by circular dichroism. The xanthan degradation was analyzed by size exclusion chromatography. It was shown that at a fixed xanthan conformation, the backbone degradation by cellulases is equal for each type of xanthan. Complete backbone degradation is only obtained at a fully disordered conformation, indicating that only the secondary xanthan structure influences the final degree of hydrolysis by cellulases. It is thereby shown that, independently on the degree of substitution, xanthan can be completely hydrolyzed to oligosaccharides. These oligosaccharides can be used to further investigate the primary structure of different xanthans and to correlate the molecular structure to the xanthan functionalities.