A proposed reaction mechanism is shown in Fig. 2. The initial step is oxidation of EGCG to its corresponding o-quinone under alkaline conditions with free exposure to air. Then EGCG dimerization occurs prior to the interaction with proteins, and such reactions have been reported by Sang, Yang, Buckley, Ho, and Yang (2007). Afterwards, these highly reactive dimer quinones can irreversibly react with the nucleophilic side chains of proteins such as lysine and cysteine residues. As a result of Schiff Bases and Michael addition reactions, covalent protein–EGCG complexes are synthesized.