Improvement of antioxidant activity of egg white protein by phosphorylation and conjugation of epigallocatechin gallate.

Egg white protein (EWP) was phosphorylated by dry heating in the presence of pyrophosphate. The antioxidant activity of phosphorylated EWP (PP-EWP) was then investigated before and after conjugation of epigallocatechin gallate (EGCG). The binding interaction between EWPs and EGCG was investigated by UV and FTIR, which indicated that more EGCG bound to PP-EWP than to native EWP and dry-heated EWP. The antioxidant activities including ABTS+ free-radical scavenging capacity, oxygen radical antioxidant capacity, reducing power, chelating capacity, and superoxide anion scavenging activity of EWP were remarkably improved by phosphorylation before and after conjugation of EGCG. The improved antioxidant property of PP-EWP can be attributed to the introduced phosphate group, more exposed hydrophobic group, increased surface thiol group of protein, and more EGCG bound to EWP. The secondary structure of PP-EWP decreased with more bound EGCG. This study is the first to describe an improvement in the antioxidant property of EWP by phosphorylation and conjugation of EGCG, thereby providing insight into the design of food protein antioxidant.