Fabrication of Surface-Active Antioxidant Food Biopolymers: Conjugation of Catechin Polymers to Egg White Proteins

The oxidation of unsaturated lipids commonly occurs at oil-water interfaces in heterogeneous foods (such as emulsions), and so there is a need for surface-active antioxidants to inhibit lipid oxidation. In this study, catechin was oxidatively polymerized by horseradish peroxidase to obtain catechin polymers (CTP). An amphiphilic antioxidant was then produced by conjugating CTP with egg white proteins (EWP) using a hydrogen peroxide-ascorbic acid pair as a radical initiator system. The covalent attachment of CTP to EWP was confirmed by electrophoresis, liquid chromatography-mass spectrometry, and fluorescence analyses. The antioxidant capacity of CTP-EWP conjugates was evaluated using several in vitro models. The conjugates exhibited strong scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (79% at 1 mg/mL), 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (97% at 0.5 mg/mL), and had a high ferric reducing power. Furthermore, CTP-EWP conjugates exhibited an inhibitive effect on lipid peroxidation in linoleic acid oil-in-water emulsions, indicating that the conjugates may have potential applications in food, pharmaceutical and cosmetic industries.