Characterisation of some enzymic hydrolysis products of xanthan

Samples of xanthan gum have been hydrolysed with cellulase preparations to produce a number of fragments, which include one, two, and three of the five-sugar repeat units. Enzyme-resistant polymeric material still remains after 72 h digestion. Modified xanthan samples, e.g. acetate-free (AF) pyruvate-free (PF) and acetate-free/pyruvate-free (AF/PF) are hydrolysed more rapidly than the native polymer. Substantial enzymic hydrolysis occurs only at 50°C in the absence of external salt, confirming earlier observations that the xanthan needs to be largely in the disordered conformation. In all cases, the pyruvate and acetate levels in the enzyme-resistant polymeric remainders are higher than those in the oligomeric products. The cellulase preparation AP3 contains endo-1 → 4-β-d-glucanase, and exo-β-d-glucosidase activities. The endo-enzyme(s) act rapidly but to a limited extent on the xanthan backbone, and the exo-enzyme(s) act on the resulting polymeric products to release oligosaccharides of d.p. up to 15, plus glucose.