[en] The present thesis dissertation has focused on the use of natural antioxidants as active agents both to protect the polymer against its own oxidative degradation and as active ingredients into antioxidant active packaging to preserve the packaged food. Several chromatographic and electrophoretic methods were developed and compared for separation and quantification of the studied antioxidants into natural samples and food simulants. Molecularly imprinted polymers were also developed and tested aimed to purify and concentrate catechins from those natural samples. To delay food deterioration caused by oxidative processes, catechins, quercetin, tocopherols and extracts of green tea were selected as natural antioxidants and incorporated as active agents by extrusion into polypropylene matrix, highly used into packaging sector. The use of polypropylene in active packaging is limited by its low or null capacity for the release of antioxidants. Therefore, this doctoral thesis concerns the development and assessment of two suitable strategies to modify the polymeric matrix and the mechanism by which antioxidants were released: use of chain extenders/plasticizers and polypropylene with modified surface trough reactive extrusion. The physicochemical properties of the materials, the effect of the incorporation of several antioxidants (catechins, quercetin, tocopherols and extracts of green tea), the modifications over the controlled release mechanisn within the polymer packaging to gradually deliver effective antioxidants into different food simulants, as well as the antioxidant activity after the release process were also evaluated

[gl] Nesta tese doutoral abordouse o emprego de antioxidantes naturais como axentes activos para o seu uso tanto na protección de polímeros fronte a súa degradación oxidativa, como en envases activos co obxectivo de protexer tanto ó polímero como ó alimento envasado. Desenvolvéronse varios sistemas cromatográficos e electroforéticos para a identificación e cuantificación de catequinas e quercetina tanto en mostras naturais como nos simulantes alimentarios, e sistemas de purificación e preconcentración de catequinas mediante o uso de polímeros impresos molecularmente. Derivado do seu alto uso no sector do envase e da embalaxe, empregouse o polipropileno como material base para o desenvolvemento dos sistemas activos por extrusión, incorporando catequinas, quercetina, tocoferois e extractos de té verde como antioxidantes naturais co obxectivo de retrasalos procesos oxidativos. A escasa ou nula capacidade de liberación dos antioxidantes dende a matriz de polipropileno limita o seu uso en envases activos, polo que nesta tese proponse o emprego de dous sistemas como modificadores da matriz polimérica: extensores de cadea/plastificantes e polipropileno modificado superficialmente mediante extrusión reactiva. Caracterizáronse as propiedades físico-químicas de interese dos materiais desenvolvidos, o efecto da incorporación de varios antioxidantes naturais (catequinas, quercetina, tocoferoles e extractos de té verde) e as modificacións na capacidade de liberación dos antioxidantes provocadas por cada unha das modificacións introducidas en diferentes simulantes alimentarios, así como a actividade antioxidante tralo proceso de liberación.