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This study aims to develop antimicrobial films consisting of chitosan and silver nanoparticles that are homogeneously distributed throughout the polymer matrix. Nanoparticles were generated in situ during the neutralization of the chitosan acetate film with sodium hydroxide. The temperature of neutralization and the concentration of silver in the film were crucial determinants of the shape and size of the nanoparticles. Neutralized films exhibited antimicrobial activity against Escherichia coli and Staphylococcus aureus in liquid growth media. However, the effectiveness of the films was considerably greater in diluted growth media. Furthermore, no significant differences were found either in the antimicrobial capacities of films incorporating different amounts of silver or in the amount of silver that migrated into the liquid media after 18 h of immersion of the film. Neutralized films maintained their activity after 1 month of immersion in deionized water, which can be attributed to the slow sustained release of silver ions and thus efficacy over time.

11In this work, active packaging films for antimicrobial food with materials derived from 12 renewable resources and biodegradable nature have been developed and 13 The antimicrobial effect of the films was tested against pathogen bacteria (S. aureus 20 and E. coli) and pasteurized milk inoculated with L. monocytogenes. 21Sensory evaluation by a panel of untrained judges was carried out to determine 22 whether the release of the active component into pasteurized milk changed its odor 23 appreciably and if so, to estimate whether this modification was acceptable by 24 consumers. 25The results show that all films with cinnamaldehyde showed antimicrobial effect against 26 bacteria studied model, being more effective against Gram positive bacteria. The films 27 provided a highly effective antimicrobial effect with both mild but sustained heat 28 treatment or short but more intense heat treatments, being possible to achieve a high 29 reduction of microbial load or even complete. The application of the films developed in 30 pasteurized milk inhibits the growth of L. monocytogenes for 12 days under 31 refrigeration conditions which may lengthen the segurity of such products. Sensory 32 analysis of pasteurized milk in contact with the films has shown that cinnamon smell 33 does not cause any rejection among potential consumers, being preferred over the 34

Chitosan/cyclodextrin films (CS:CD) incorporating carvacrol were obtained by casting, and conditioned at 23°C and 75% relative humidity prior to being immersed in liquid carvacrol until they reached sorption equilibrium. In a previous work, the in vitro antimicrobial activity of these films was studied. In this work, active films were used to inhibit microbial growth in packaged chicken breast fillets. Samples of CS:CD films loaded with carvacrol, of different sizes and thus with different quantities of antimicrobial agent, were stuck to the aluminium lid used to seal PP/EVOH/PP cups containing 25g of chicken fillets. These samples were stored for 9days at 4°C. The packages were hermetically sealed and it was confirmed that they provided an infinite barrier to carvacrol. The partition of the antimicrobial agent within the food/packaging system was analysed. The antimicrobial devices rapidly released a large percentage of the agent load, amounts that were gained by the adhesive coating of the lid and especially by the chicken fillets. The latter were the main sorbent phase, with average concentrations ranging between 200 and 5000mg/Kg during the period of storage. The microbiota of the packaged fresh chicken fillets - mesophiles, psychrophiles, Pseudomonas spp., enterobacteria, lactic acid bacteria and yeasts and fungi - were analysed and monitored during storage. A general microbial inhibition was observed, increasing with the size of the active device. Inhibition with a 24cm(2) device ranged from 0.3 log reductions against lactic acid bacteria to 1.8logs against yeasts and fungi. However, the large amount of antimicrobial that was sorbed or that reacted with the fillet caused an unacceptable sensory deterioration. These high sorption values are probably due to a great chemical compatibility between chicken proteins and carvacrol.

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