Gelation behaviors of schizophyllan-sorbitol aqueous solutions

On addition of D-sorbitol, schizophyllan (SPG) aqueous solution forms a thermoreversible gel upon cooling. The gelation process is characterized by rheology, differential scanning calorimetry (DSC), and optical rotation measurement (ORD). It is found that the Winter-Chambon criterion works well in determining the critical gelation point of the present system, although the criterion has been scarcely applicable to systems that show weak-gel properties even before gelation. Moreover, ORD and DSC results indicate that a disordered to ordered conformational change accompanies the gelation process, which is attributed to the transition from SPG triple helix II to I. The gelation temperature of SPG-sorbitol aqueous solution is almost independent of SPG concentration in the examined concentration range and is slightly decreased by lowering SPG molecular weight, while greatly influenced by sorbitol content. The gelation is considered to be induced by the transition from SPG triple helix II to I, which leads to a three-dimensional network constituted by the extremely entangled and stiff SPG triple helices I. Furthermore, it is proved that neither junction zone nor aggregation of SPG triple helices is involved in the SPG-sorbitol gels. The SPG-sorbitol gel is structurally like a solution that is unable to flow within a timescale of usual observation.