Polyphenol modulation of alkali-induced egg white gel: Transmembrane behavior and mechanism

Polyphenols have demonstrated significant potential in enhancing the mechanical properties of the protein gels; however, their specific effects and mechanisms in preserved egg white gel (EWG) remain insufficiently understood. This study systematically investigates the impact of polyphenols on alkali-induced EWG by employing the eggshell membrane (ESM) selective permeation method. Four representative polyphenols-black tea polyphenols (BTP), green tea polyphenols (GTP), apple peel polyphenols (APP), and pomegranate seed polyphenols (PSP)-were selected to analyze their alkali oxidation and transmembrane behavior following regulatory effects on EWG properties. Key findings revealed that alkali-oxidized polyphenols underwent structural modifications, forming quinone compounds with significantly increased particle sizes (P < 0.05). Among them, BTP exhibited the most pronounced changes, achieving a quinone content of 174.0 ± 1.8 μg mL^-1. The improvement in gel mechanical properties was attributed to two primary mechanisms: (i) covalent bonding (CN, CS) between polyphenol-derived quinones and egg white proteins (EWPs), and (ii) promotion of β-sheet formation and disulfide bond cross-linking. Notably, the gel-strengthening effects exhibited concentration dependence, with optimal performance observed at polyphenol concentrations of 0.04-0.2 %. Comparative analysis indicated that transmembrane BTP and GTP at 0.10-0.20 % exhibited the most significant enhancement in EWG quality. This study provides a theoretical foundation for the rational application of polyphenols as natural gel enhancers in preserved egg manufacturing.