How does dextran sulfate promote the egg white protein to form transparent hydrogel?the gelation mechanism and molecular force changes

Most globular protein solutions will form turbid gels when heated and exhibit unsatisfactory mechanical strength. Our previous study found that highly charged dextran sulfate (DS) has the potential to induce egg white protein (EWP) to form transparent hydrogel with excellent gelation properties. However, the mechanism is not clear. Therefore, the effect of DS on the gelation characteristics of EWP was investigated, including rheological properties, microstructures, water distributions, molecule conformation, and intermolecular forces. Results showed that DS addition significantly prevented the formation of large insoluble aggregates of EWP during heating, which is the prerequisite for forming a transparent gel. The EWP/DS hydrogel possesses remarkably higher gel strength and water holding capacity compared to EWP. The microstructure analysis showed that EWP/DS has a highly ordered fibrous mesh structure after heat treatment. Fourier transform infrared spectroscopy (FT-IR) revealed that DS addition promotes the denaturation of EWP (decrease in α-helices and increase in β-sheets). In addition, hydrophobic interactions are confirmed to be the major intermolecular force in EWP/DS, rather than disulfide bonds in EWP and EWP/dextran gels. Overall, combining the data from turbidity, FT-IR, and microstructure analysis, we found that the EWP/DS complex formation effectively suppresses the further disordered aggregation process of denatured protein by electrostatic repulsion. This work will be beneficial to understand the mechanism of DS on the gelation of EWP after thermal treatment, which will expand the application of sulfated polysaccharides on food structure design.