Macromolecular behavior, structural characteristics and rheological properties of alkali-neutralization curdlan at different concentrations

Curdlan is insoluble in water at ambient temperatures due to its rigid triple helix structure, which greatly limits its applications in the food industry. Alkali-neutralization (AN) treatment is a promising strategy for curdlan dissolution. In this study, the changes in macromolecular behaviors, microstructures, structural characteristics and rheological properties of curdlan before and after AN treatment at different alkali and acid concentrations (0.1-1.0 M) were analyzed and evaluated. Results showed that the AN-treated curdlans in aqueous solutions underwent conformation transitions from ordered triple helices to loose triple helices and then random coils with increased water solubility and reduced intrinsic viscosity, molecular weight, and rheological property. These findings were attributed to the breakdown of intra-/inter-molecular hydrogen bonds. Compared with untreated commercial curdlan, AN treatment significantly affected the microstructure, crystallinity, and thermal property of the AN-treated curdlans but hardly changed their (1 -> 3)-beta-D-glucopyranosidic linkages. Therefore, this study would provide a theoretical basis for gaining insight into the AN treatment for curdlan and further give a feasible and effective way for improving solubility of water-insoluble curdlan to expand its potential applications in food industry and biomedicine.