Structural modification of egg white proteins enhances electrostatic complexation with sodium alginate and hydrogel particle formation: mechanistic insights and functional applications

Many bioactive compounds, such as fish oil, are prone to oxidation, which limits their incorporation into functional foods. Egg white proteins (EWP) have notable antioxidant properties, making them promising candidates for stabilizing such compounds, but their compact globular structure limits flexibility and reduces their ability to form stable hydrogel particles with polysaccharides. Based on this, the purpose of this study was to explore the structural modification of EWP via pH-shifting and heat treatment to enhance their electrostatic complexation with sodium alginate (NaAlg) and subsequent hydrogel particle formation. We compared different modification treatments and found that treatment at pH 13 and 50 °C produced the optimal effect, effectively exposing tryptophan and tyrosine residues and increasing the structural flexibility of EWP while maintaining its ionization properties. These conformational changes promoted strong electrostatic interactions with NaAlg, resulting in uniformly distributed hydrogel particles. Confocal microscopy confirmed the encapsulation of fish oil emulsion within the hydrogel particles, and the formed particles exhibited improved oxidative stability and dispersion compared to simple dispersions. These enhancements were attributed to both the physical encapsulation within the hydrogel matrix and the intrinsic antioxidant properties of EWP. This work demonstrates how increasing protein flexibility can facilitate polysaccharide complexation and hydrogel formation, providing mechanistic insights and guiding potential applications for compact globular proteins in functional food systems.