Abstract: β-lactoglobulin (β-LG), epigallocatechin gallate (EGCG) and glucose (Glc) were conjugated to obtain two covalent complexes by alkali method and the Maillard reaction with different addition sequences. The complexes were named as β-LG-EGCG-Glc con and β-LG-Glc-EGCG con, respectively. Compared with the non-covalent conjugates β-LGEGCG- Glc mix and β-LG-Glc-EGCG mix, the effects of different addition sequences on the structural and functional properties of ternary complexes were investigated. The results showed that the addition order had a greater effect on the covalent complexes than on the non-covalent complexes. The structure and function of β-LG-EGCG-Glc con and β-LGGlc- EGCG con were significantly different from each other, while there was little difference between β-LG-EGCG-Glc mix and β-LG-Glc-EGCG mix. SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and UV absorption spectroscopy results displayed that the order of addition had a great influence on the covalent bonding process of ternary complexes. Structural characterization revealed that the fluorescence quenching and surface hydrophobicity of the covalent complexes were higher than those of the non-covalent complexes. Compared with β-LG-EGCG-Glc con, β-LG-Glc-EGCG con had stronger fluorescence quenching and higher surface hydrophobicity, while there was no obvious change between β-LG-EGCGGlc mix and β-LG-Glc-EGCG mix. In addition, compared with the non-covalent complexes, the covalent complexes were superior in functional properties. The emulsification and emulsion stability, foaming and foaming stability of β-LG-Glc- EGCG con were superior to those of β-LG-EGCG-Glc con, but there was little difference between the non-covalent complexes.

Key words: β-lactoglobulin, ternary complex, functional properties, structure, covalent bonding, non-covalent binding