Covalent complexation and functional evaluation of (−)-epigallocatechin gallate and α-lactalbumin

The covalent complexation between (−)-epigallocatechin gallate (EGCG) and α-lactalbumin (α-La), and the effect of EGCG on the antioxidative activity and emulsifying properties of α-La were investigated. The turbidity of a solution of 1% α-La and 0.2% EGCG decreased after 24 h reaction at pH 8.0 and 60 °C, less than the value of α-La alone. The interaction between α-La and EGCG at pH 8.0 was more pronounced than that at pH 6.0 or 7.0, as evidenced by the reduced amplitude of amide A, and I, and II bands of α-La by FT-IR and the increase in the total phenolic content and denaturation temperature. These results implied that EGCG was covalently linked to α-La at pH 8.0. In addition, compared with the control of α-La, α-La–EGCG complexes had significantly increased antioxidative activity. The emulsions stabilized by α-La–EGCG complexes, compared with that by α-La alone, had much smaller droplet sizes, which indicated the emulsifying property of α-La was improved.