The level of sulfate substitution of polysaccharide regulates thermal-induced egg white protein gel properties: The characterization of gel structure and intermolecular forces.

Sulfated polysaccharides exhibit great potential for regulating protein-protein interactions. In the present study, three sulfated microcrystalline cellulose (MCS) with different degrees of sulfate substitution (DS_S: 0.33, 0.51, 0.61) were synthesized and the effects of DS_S on the regulation of egg white protein (EWP) aggregation and gelation properties were investigated. The results found that the improvement of protein mechanical properties by MCS is closely related to the level of sulfate substitution. The higher the DS_S, the more ordered protein aggregates and compact gel network formed during heating as compared to that of pure EWP. Lower DS_S (0.33) shows little effect on the mechanical properties of EWP. Furthermore, all the MCSs could significantly destroy the tertiary structure of protein molecules during heating, while for the secondary structure, MCS with higher DS_S (0.51 and 0.61) could effectively control the decreasing tendency of α-helix and increasing tendency of β-sheet. Hydrophobic interactions were recognized as the major intermolecular force in the compact mixed gels (EWP/MCS2 and EWP/MCS3 gels, DS_S was 0.51 and 0.61, respectively). These findings provide a vital understanding of the gelling mechanism of the protein-polysaccharide system and the application of sulfated polysaccharides in protein-based food products.