Effect of free radical-induced aggregation on physicochemical and interface-related functionality of egg white protein

This study investigated the impact of free radical-induced aggregation by a redox pair (ascorbic acid + H2O2) on physicochemical characteristics, structure, and rheology as well as the emulsifying and foaming capacity of egg white protein (EWP). In general, this treatment led to oxidize the free -SH groups, a little change in secondary structure, increasing surface hydrophobic (H-0) and zeta-potential as well induce aggregation of egg white protein through disulfide cross-linking. The pH at which the oxidative aggregation reaction was performed had a significant effect on the functionality of the EWP. The EWP aggregated at pH 11 had a very high apparent viscosity, which justified by its greater H-0, higher aggregation yield and larger aggregates with high effective volume, as confirmed by SDS-PAGE and AFM. Furthermore, emulsions prepared by aggregated EWP samples, particularly the EWP aggregated at pH 11, showed higher stability against droplet flocculation and phase separation during storage for 30 days at various pH (4-7) and salt concentration (0-200 mM) as compared to emulsions made with native EWP, presumably due to create a more viscoelastic film with promoted steric hindrance on oil droplets. Moreover, a dramatically enhanced foam stability was obtained by the EWP aggregated at pH 11. This study suggested that radical induced aggregation has a potential to improve the interface-related properties of egg white protein.