The preparation of alginate films with suitable properties requires a two-step contact with reticulating agents: initially a weakly structured pre-film is formatted which is further crosslinked in a second stage by immersion in a more concentrated solution. The present work evaluated the effects of a combined crosslinking procedure using calcium and barium ions on the physical and morphological properties of alginate-based films containing natamycin as antimicrobial agent. The release behavior of natamycin in water was evaluated as well as the antimicrobial activity against four target microorganisms, which are common cheese product contaminants. Films attributes were affected by the type of ion used in the second stage while the natamycin release rate and the antimicrobial activity were influenced by the ion used in the first stage. Films crosslinked with Ba 2þ in the first and Ca 2þ in the second stage (BaeCa films) exhibited physical properties very similar to films crosslinked with calcium in both stages. Release kinetics of natamycin in water fitted well to Fick's second law diffusional model, with effective diffusivity values ranging from 0.40 Â 10 À11 to 1.74 Â 10 À11 cm 2 /s. BaeCa films presented the lowest natamycin diffusion coefficient and the smallest inhibition zone diameter against the four microorganisms tested.

Chitosan cross-linked pentasodium tripolyphosphate particles were produced by ionotropic gelation. The aim of this study was to evaluate the influence of the molar mass and deacetylation degree of chitosan and of the concentration of pentasodium tripolyphosphate in the production of chitosan micro/nanoparticles. The obtained charge ratio (R±), mean particle size, surface electrical charge, polydispersity index, and tendency of particle aggregation were selected as dependent variables. Results demonstrated that stable particles exhibited a high zeta potential value, between ?62 and ?68 mV. Particles were produced in different size ranges controlling the R± between the positively charged chitosan and negatively charged pentasodium tripolyphosphate. Chitosan micro/ nanoparticles were successfully prepared via the ionic gelation method controlling R±, therefore the association of an active ingredient to a micro/nanoparticle allows the molecule to intimately interact with specific structures, to overcome barriers and to prolong its residence time in the target. Chitosan cross-linked pentasodium tripolyphosphate particles are expected to be a good approach for active ingredients formulation in the agrofood sector and related industries.

a b s t r a c tNatamycin, an antimicrobial agent sparingly soluble in water, was incorporated into alginate films in order to produce antimicrobial packaging, using three different approaches: the conventional loading method, when natamycin is added directly to the polymeric aqueous film-forming solution; the immersion procedure, by which a previously prepared films is contacted with natamycin solution, and by the supercritical solvent impregnation (SSI) method, with loading tests performed in CO 2 containing natamycin, with and without addition of cosolvent (ethanol, 10% molar). The loading capacities were evaluated, as well as the influence on physical attributes of the films and on the release behavior of natamycin in water. The conventional method led to films heterogeneities with high surface roughness, and the immersion technique evinced several disadvantages like low incorporation yields, and negative influence on water vapor permeability and on the swelling degree of the film. The supercritical method showed that longer contact times and the use of ethanol as a cosolvent increased the natamycin loading yields and led to homogeneous films, where SSI (CO 2 + EtOH) process produced visually attractive and tranlucent films.

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