Melting behaviour of a triple helical polysaccharide schizophyllan in aqueous solution

Two sonicated samples of schizophyllan in aqueous solution at temperatures from 20 to 160°C were investigated by viscometry. The temperature dependence of the viscosity coefficient η showed that schizophyllan in water undergoes an irreversible thermal transition at about 135°C. The values of $\text{(ln η}{}_{\mathrm{r}}\text{)}\text{c}$ (ηr is the relative viscosity and c is the polymer concentration (w/v)) at 25°C determined after preheating aqueous schizophyllan indicated that the major conformations of schizophyllan in water at 120 and 150°C are triple helix and single random coil, respectively. Thus, it was concluded that the change in η at about 135°C with an increase in temperature is due to the melting of triple helices to single chains. Schizophyllan denatured to single chains at about 150°C did not restore the intact triple helix, but formed aggregates, when the solution was cooled to 25°C. It was also found that the aggregates form a gel when c is higher than a certain value.