Ultrasonic treatment affects the macromolecular, conformational, structural and rheological properties of curdlan in different solvents

Curdlan is a microbial extracellular polysaccharide composed of β-(1 → 3)-glycosidic linkages, which exhibits poor water solubility at room temperature due to its formation of crystalline regions through intra- and inter-molecular hydrogen bonding interactions. The chain conformations of curdlan can be modified by different solvents. Thus, this study examined the effects of ultrasonication on the macromolecular, structural, and rheological characteristics of curdlan in three different solvents (0.1 M NaOH, DMSO, and 0.1 M alkali-neutralization (AN)). The results showed that the water solubility of curdlan treated with ultrasonic for 60 min in DMSO, NaOH and AN condition cexhibited 16.26 ± 0.46 %, 13.62 ± 0.23 %, and 15.37 ± 0.61 %, respectively, while their molecular weight values were 10.53 kDa, 19.27 kDa and 17.25 kDa, respectively. This phenomenon indicated that curdlan preferentially dissolved and was susceptible to ultrasonic degradation in DMSO than that in other two solvents, thus enhancing its water solubility. After ultrasonic treatment, the conformation of curdlan in DMSO transformed from flexible chain to irregular helices due to the breaking of both inter- and intra-molecular hydrogen bonds, while there was no significant change in three-helix conformation of curdlan in the other two solvents, implying that curdlan with a flexible chain is more susceptible to degrade by ultrasonic than in rigid rod. Additionally, ultrasonic treatment resulted in decreased rheological properties of curdlan. Overall, this study will offer a theoretical foundation for the ultrasonic modification of curdlan in different solvents, broadening its potential applications in the food industry and biomedicine.