Synthesis of Antioxidant Polymers by Grafting of Gallic Acid and Catechin on Gelatin

A novel, simple, and cheap method to synthesize antioxidant-protein conjugates by grafting reaction was developed employing a hydrogen peroxide-ascorbic acid pair as radical initiator system. Our challenge was to covalently bind molecules with tested antioxidant activity, as gallic acid (GA) and catechin (CT) to a biomacromolecule, as gelatin, extensively used in the pharmaceutical, cosmetic, and food industry. In this way, two gelatin conjugates, bearing GA and CT covalently bounded to a side chain of protein, were synthesized. Calorimetric, UV-vis, and fluorescence analyses were performed to verify the covalent bond between antioxidant molecules and gelatin, and the antioxidant activity of conjugates was compared to that of a control polymer submitted to the same reaction conditions without antioxidant molecule. The ability of synthesized materials to inhibit 2,2'-diphenyl-1-picrylhydrazyl, hydroxyl radicals, and linoneic acid peroxidation was determined and, to well characterized antioxidant properties of grafted biomacromolecules, disposable phenolic equivalents and total antioxidant activity were calculated. The conjugates showed a good antioxidant activity, confirming the efficiency of the synthetic strategy proposed in this paper. The results clearly showed that antioxidant moieties covalently bounded to a natural polymer allow to introduce in the macromolecule peculiar features for specific industrial applications.