Kinetics of Ascorbic Acid/Hydrogen Peroxide-mediated Graft Polymerization of Whey Protein Isolate with EGCG
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Abstract:
Graft polymerization of (-)-epigallocatechin gallate (EGCG) onto whey protein isolate (WPI) was investigated using ascorbic acid (Asc) and hydrogen peroxide (H2O2) as a redox system. The effects of different reaction parameters on the graft yield; activation time, initiator concentration, monomer concentration, and temperature were determined, and the kinetic equation for the graft polymerization reaction was established from the reaction level and apparent activation energy. The results demonstrated that, in an Asc/H2O2 system, acid free radicals (Asc•-) mediate the graft polymerization of WPI and EGCG, with the graft yield reaching 42.08 mg/g under an ascorbic acid concentration of 0.014 mol/L, H2O2 concentration of 0.10 mol/L, pH 6, temperature of 35 ℃, and activation time of 120 min. Based on the above results, a calculation equation describing the WPI-EGCG polymerization rate was obtained for reactions under an Asc concentration range of 0.01~0.022 mol/L, H2O2 concentration range of 0.09~0.12 mol/L, EGCG concentration of 0.0012~0.0042 mol/L, and temperature of 298.15~308.15 K. An activation energy of 12.96 kJ/mol was obtained for polymerization. The results provide theoretical guidance for the structural design and controllable preparation of proteins, thus broadening the application of proteins in the food industry.
