Ingvild Johanne Haug

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

Abstract Gelatin from cold water fish species and κ-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.

Cross-Linking and Depolymerisation of γ-Irradiated Fish Gelatin and Porcine Gelatin Studied by SEC-MALLS and SDS-PAGE: A Comparative Study

γ-Irradiation of gelatin and collagen hydrogels can be used for sterilization and mechanical stabilization, providing biomaterials suitable for both tissue engineering and drug-delivery systems. Controversial results have been reported regarding the extent of irradiation-induced cross-linking and degradation, which depend on both protein concentration and irradiation dose. In this work the relative contributions of these processes were studied for irradiation doses between 0 and 1.0 kGy and concentrations between 0.3% and 5% using size-exclusion chromatography (SEC) with multi-angle laser light scattering (MALLS) and viscosity detection, as well as SDS-PAGE. It was demonstrated that chain degradation and cross-linking occur simultaneously in fish gelatin (FG), porcine gelatin (PG) and porcine collagen (PC), by the gradual appearance of protein fragments (10–80) × 103 concomitant with the formation of structures of high molecular weight. FG and PG behaved rather similarly, despite the fact they were irradiated and analyzed above and below their denaturation temperatures, respectively, suggesting little or no influence of molecular ordering under the conditions used. PC showed an increasing amount of degradation products following heat treatment prior to SEC-MALLS, suggesting that chain cleavage may occur within ordered collagen structures without complete release of the protein fragments.