Molecular interactions in, and rheological properties of, a mixed biopolymer system undergoing order/disorder transitions

Gelatin from cold water fish species and kappa-carrageenan are both thermo-setting biopolymers of a poly-electrolytic character. By adjusting parameters such as pH and ionic strength, these polymers can, in the disordered state, associatively interact through electrostatic interactions. In the present study, the changes taking place at the molecular level are sought and linked to the rheological properties in a mixed system of these two biopolymers under conditions initially favouring associative phase separation (pH below IEP of the gelatin and low ionic strength). More specifically, these changes were followed as function of temperature with special emphasis on changes taking place close to the order/disorder temperature regimes of the two polymers. The present study concludes that a variety of complex structural arrangements can be obtained, and that dynamic processes in the form of structural re-arrangements are present when the single components are forced to undergo order/disorder transitions. (C) 2003 Elsevier Science Ltd. All rights reserved.