Impact of the extrusion process on xanthan gum behaviour.

Processing xanthan gum by extrusion and subsequent drying produces a biopolymer showing particulate, rather than molecular behaviour in aqueous solution. This form of xanthan disperses very readily to give a viscosity that is strongly dependent on salt concentration. On heating above the temperature of the order-disorder transition as determined by calorimetry, there is a viscosity transition that is indicative of the irreversible loss of the particulate structure. It is suggested that the extrusion process melts and aligns xanthan macromolecules. On cooling reordering will occur but in the highly concentrated environment in the extruder ( approximately 45% water w/w), inter-molecular association between neighbouring macromolecules cannot proceed to completion due to kinetic trapping. As a consequence a network structure is created maintained by associations involving ordered regions. A xanthan solution can be prepared from this particulate material by dispersing and subsequent heating far more readily than can be achieved with non-processed xanthan.