Gelation of triple helical (1→ 3)-β- D -glucan: The scleroglucan case

Abstract

The topic of this thesis has been gelation of the triple helical (1→3)- β glucan, scleroglucan.

Two basically different methods of scleroglucan gelation were studied. Gels were made by altering the primary structure of scleroglucan, which may also, effect the tertiary structure (scleraldehyde gels) or by perturbing the tertiary structure alone (renaturation gels). Both systems were previously mentioned in the literature, but not studied in detail. Annealing of the renaturation gels resulted in a third category of gels (annealing gels), which were not previously described.

For the renaturation gels, a suitable procedure for making homogeneous gels was developed. Scleroglucan gels were prepared by neutralisation of aqueous alkaline solution of scleroglucan by in situ release of acid.

The gelation process for the scleraldehyde gels and the renaturation gels were further studied with respect to gelation kinetics, critical polysaccharide concentration and the concentration effect above this. Gels were incubated in aqueous solutions. The dependence of mechanical properties on pH, temperature, ionic strength and time of incubation was studied.

A model for fitting the stress-strain relation for large-deformation measurements was developed. The model is based on a continuous transition between two regions of stress-strain relations. At low values of strain the stress-strain relation is linear. At a material dependent value of strain a continuous transition to an exponential relation of stress-strain is proposed.

The model, using two material parameters, the elastic modulus and the transition strain, was adequately fitted to large-deformation data from uniaxial compression measurements for both scleraldehyde and annealing gels.