Dextran-coated silver nanoparticles for improved barrier and controlled antimicrobial properties of nanocellulose films used in food packaging

The effect of dextran-coated silver nanoparticles (Ag NPs 12.0 ± 1.9 nm) loading (0−0.42 wt%) on the mechanical, barrier, and antimicrobial properties of thin (50−60 μm) films prepared from cellulose nanofibrils by solvent casting method were studied as eco-friendly and food-preservative packaging materials. The presence of dextran was shown to act not only as a dispersing media for Ag NPs and controlling its release but also as a moisture-resistant sealable additive that, synergetically with reduced oxygen permeability, may preserve the food against bacteria growth. Thus, significantly reduced Oxygen Transmission Rates (from 2.07 to 1.40-0.78 cm3 m−2d−1) and hydrophilicity (from 20.8° to 52.4° for MilliQ water, and from 35-37° to 62-74° for 3 % acetic acid and 0.9 % NaCl simulant solutions), yielding a 99.9 % inhibition of Escherichia coli after five repeated cycles of 24 h exposure to 0.9 % NaCl solution was displayed, supported by a controlled release of Ag+ ions (below the toxicologically harmful threshold, <0.5 mg L-1)

Antibacterial ability of immobilized silver nanoparticles in agar-agar films co-doped with magnesium ions

The antibacterial ability of in situ prepared nanometer-sized silver particles, immobilized in agar-agar films, was studied as a function of the concentration of co-dopant, magnesium ions. Content of inorganic components in hybrid films was determined using inductively coupled plasma optic emission spectroscopy, and found to be low (<2 wt.-%). Morphology of prepared hybrid films, studied by transmission electron microscopy, revealed the presence of non-agglomerated and randomly distributed 10–20 nm silver nanoparticles (Ag NPs) within the agar-agar matrices. Fourier-transform infrared spectroscopy indicated the distinct chemical interaction between Ag NPs and polymer chains. Thermogravimetric analysis, as well as the determination of tensile strength, Young's modulus, and elongation at break showed improvement of thermal stability and mechanical properties of agar-agar matrices upon the incorporation of Ag NPs due to high compatibility between the hydrophilic organic component and inorganic components. The complete microbial reduction of Gram-positive bacteria Staphylococcus aureuswas observed for all agar-silver films, while satisfactory results were observed for Gram-negative bacteria Pseudomonas aeruginosa (≥99.6%). The release of Ag+ ions is suppressed by the increase of the concentration of Mg2+ ions and it was found to be significantly smaller (≤0.24 ppm) than the harmful ecological level (1 ppm). © 2019 Elsevier Lt