Ethylene vinyl alcohol copolymer (EVOH) films containing green tea extract were successfully produced by extrusion. The films were brown and translucent, and the addition of the extract increased the water and oxygen barrier at low relative humidity but increased the water sensitivity, the glass transition temperature, and the crystallinity of the films and improved their thermal resistance. An analysis by HPLC revealed that the antioxidant components of the extract suffered partial degradation during extrusion, reducing the content of catechin gallates and increasing the concentration of free gallic acid. Exposure of the films to various food simulants showed that the liquid simulants increased their capacity to reduce DPPH(•) and ABTS(•+) radicals. The release of green tea extract components into the simulant monitored by HPLC showed that all compounds present in the green tea extract were partially released, although the extent and kinetics of release were dependent on the type of food. In aqueous food simulants, gallic acid was the main antioxidant component released with partition coefficient values ca. 200. In 95% ethanol (fatty food simulant) the K value for gallic acid decreased to 8 and there was a substantial contribution of catechins (K in the 1000 range) to a greatly increased antioxidant efficiency. Kinetically, gallic acid was released more quickly than catechins, owing to its faster diffusivity in the polymer matrix as a consequence of its smaller molecular size, although the most relevant effect is the plasticization of the matrix by alcohol, increasing the diffusion coefficient >10-fold. Therefore, the materials here developed with the combination of antioxidant substances that constitute the green tea extract could be used in the design of antioxidant active packaging for all type of foods, from aqueous to fatty products, the compounds responsible for the protection being those with the higher compatibility with the packaged product.

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The widespread use of antibiotics has led to the emergence of multidrugresistant bacterial strains, and therefore a current concern for food safety and human health. The interest for new antimicrobial substances has been focused toward metal oxide nanoparticles. Specifically, titanium dioxide (TiO 2) has been considered as an attractive antimicrobial compound due to its photocatalytic nature and because it is a chemically stable, non-toxic, inexpensive, and Generally Recognized as Safe (GRAS) substance. Several studies have revealed this metal oxide demonstrates excellent antifungal and antibacterial properties against a broad range of both Gram-positive and Gram-negative bacteria. These properties were significantly improved by titanium dioxide nanoparticles (TiO 2 NPs) synthesis. In this chapter, latest developments on routes of synthesis of TiO 2 NPs and antimicrobial activity of these nanostructures are presented. Furthermore, TiO 2 NPs favor the inactivation of microorganisms due to their strong oxidizing power by free radical generation, such as hydroxyl and superoxide anion radicals, showing reductions growth against several microorganisms, such as Escherichia coli and Staphylococcus aureus. Understanding the main mechanisms of antimicrobial action of these nanoparticles was the second main purpose of this chapter.

The search for new antimicrobial substances has increased in recent years. Antimicrobial nanostructures are one of the most promising alternatives. In this work, titanium dioxide nanotubes were obtained by an atomic layer deposition (ALD) process over electrospun polyvinyl alcohol nanofibers (PVN) at different temperatures with the purpose of obtaining antimicrobial nanostructures with a high specific area. Electrospinning and ALD parameters were studied in order to obtain PVN with smallest diameter and highest deposition rate, respectively. Chamber temperature was a key factor during ALD process and an appropriate titanium dioxide deposition performance was achieved at 200 °C. Subsequently, thermal and morphological analysis by SEM and TEM microscopies revealed hollow nanotubes were obtained after calcination process at 600 °C. This temperature allowed complete polymer removal and influenced the resulting anatase crystallographic structure of titanium dioxide that positively affected their antimicrobial activities. X-ray analysis confirmed the change of titanium dioxide crystallographic structure from amorphous phase of deposited PVN to anatase crystalline structure of nanotubes. These new nanostructures with very large surface areas resulted in interesting antimicrobial properties against Gram-positive and Gram-negative bacteria. Titanium dioxide nanotubes presented the highest activity against Escherichia coli with 5 log cycles reduction at 200 μg/mL concentration.

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Active films (AFs) using polylactic acid (PLA) as a polymeric matrix containing various propolis concentrations (5, 8.5 and 13%) as the active agent (AA) were developed using a casting method. The purpose was to determine the effects of the incorporation of AA on the physical properties of the films and to evaluate the antioxidant and antimicrobial activities. Tensile strength and elastic modulus of the AFs decreased relative to the control (PLA without AA). Introducing the active substances from propolis into the PLA also affected its thermal properties (glass transition). Adding AAs to the polymer generated more opacity with a green-yellowish colour compared to the control. In addition, AFs exhibited reduced water vapor permeability as the AA concentration increased. Biodegradation assay showed that the AFs degraded faster than the control. AFs exhibited antioxidant activity, which was measured as the ability to scavenge free radicals (DPPH and ABTS), due to the presence of bioactive compounds (phenolics). Antimicrobial activity was evaluated against Escherichia coli and showed a reduction over 2 4-log cycles. Therefore, incorporation of propolis is a useful strategy for the development of active packaging with antioxidant and antimicrobial effects, which increase the shelf-life of food products.