Immobilization of caffeic acid on a polypropylene film: synthesis and antioxidant properties

The immobilization of caffeic acid (CA) on a polypropylene (PP) film was successfully performed through the covalent binding of the caffeoyl chloride on a modified polymeric surface of PP films grafted with hydroxyethyl methacrylate as monomer (PP-g-HEMA). The different reaction steps were monitored by FT-IR spectroscopy. The synthesized films were characterized by Folin−Ciocalteu method by measuring the available phenolic groups as caffeic acid equivalents linked to the surface. The antioxidant efficiency of the modified polymers was evaluated by typical spectrophometric methods, such as the bleaching of radicals DPPH^• and ABTS^•+, and the inhibition of the enzymatically induced coupled oxidation of linoleic acid and betacarotene. The available phenolic groups on the modified film presented a good correlation with the antiradical activity toward DPPH^•. Moreover, the polymer synthesized in this work showed a good protective activity against ascorbic acid oxidation in real samples of orange juice.