Antioxidant-Impregnated Polymers / Antioxidant Ability and Interactions with Food

Abstract: Interactions between antioxidant-impregnated low-density polyethylene (LDPE) and polypropylene (PP), and oxygen-sensitive foods have been investigated. BHT and a-tocopherol are two antioxidants commonly used in both foods and polymers. In general, BHT was rapidly lost from LDPE film in contact with various foodstuffs. a-Tocopherol was completely retained in PP film, but some losses, although less pronounced than those of BHT, occurred from LDPE film, depending on the nature of the contact medium. In general, fatty foods, especially w/o emulsions, were more prone than water-based foods to interact with the film and, hence, to influence the retention of the antioxidant. While the losses from LDPE film in contact with fatty foods were ascribed to migration, those occurring for contact with water-based foods probably were the result of degradation of the antioxidant. Trace metals, e.g. iron and copper, present in the aqueous media may have caused accelerated degradation of the a-tocopherol, while the presence of ascorbic or citric acid seemed to inhibit this degradation. In food packaging applications where antioxidants have been incorporated into plastic materials, the antioxidants may have a dual function, i.e. to protect the polymer from oxidative degradation during processing, and to delay the onset of oxidation of the packaged foodstuff during storage. a-Tocopherol-impregnated LDPE film was found to enhance the stability of a linoleic acid emulsion stored at 6°C, while BHT-impregnated LDPE film seemed to reduce odour changes in an oatmeal product stored at 20°C. When investigating the antioxidant ability of impregnated films rather high levels of a-tocopherol were incorporated into the films. These levels were found to cause changes in physical and mechanical properties of the finished materials, e.g. discoloration, increasing oxygen transmission and decreasing impact strength. Thus, before using the concept of intended release of antioxidants from packaging materials to food several factors need to be considered, e.g. that the antioxidant and its degradation products are safe, how the food will benefit from the addition, and that the packaging material will not suffer from inferior properties due to the incorporation of the antioxidant.