Comparative analysis of β-lactoglobulin complexes with different catechins: formation, structure, functionality, and emulsion stability

Complexes formed between polyphenols and proteins could be used as a good alternative to improve the phytochemical stability in food matrices. While interactions between tea catechins and milk proteins are prevalent in food systems, the effects of different structures of catechins on these interactions, and the resulting alterations in structural and functional properties of covalent complexes formed remain poorly understood. This study investigated the effect of different catechin structures on covalent interactions with β-lactoglobulin (β-Lg). (+)-Catechin (C), (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-gallocatechin gallate (GCG), and (-)-epigallocatechin gallate (EGCG) were covalently bound to β-Lg through the alkaline method. β-Lg-catechin complexes had lower fluorescence intensity, hydrophobicity, α-helix content, free amino groups, and sulfhydryl groups than native β-Lg. Binding to catechins (especially ECG, GCG, and EGCG) significantly enhanced β-Lg antioxidant activity, emulsification activity, and stability. Furthermore, β-Lg-catechin complexes substantially enhance emulsion freeze-thaw, thermal stability, storage stability, and oxidative stability. Galloylated catechins exhibited the greatest graft affinity towards β-Lg, and their complexes demonstrated far superior antioxidant activity and stability than non-galloylated catechins. In conclusion, customized β-Lg-catechin conjugates have considerable potential as carriers in food that can enhance emulsion phytochemical stability. • Six representative catechins were covalently bonded to β-lactoglobulin (β-Lg). • Gallate catechins showed more graft affinity to β-Lg. • β-Lg-catechins improved the stability of emulsions. • Gallate catechin complexes presented better antioxidant activity and stability.