Ligands affecting silver antimicrobial efficacy on Listeria monocytogenes and Salmonella enterica.

Although silver is being extensively used in food or other applications as the key component to control microbial proliferation, many factors affecting its real potential are still unknown. In the present work, the presence of specific ligands or the contents in organic matter was correlated with silver speciation and its antibacterial performance. Silver was found to be only active in form of free silver ions (FSI). The presence of chloride ions produced an equilibrium of stable silver chloride complexes which were void of antimicrobial efficacy. However, even at relatively high concentrations of chlorides, a small fraction of FSI may still be present, producing a bactericidal effect with concentrations at the nanomolar level under optimum conditions. Low concentrations of thiol groups completely inactivated silver, while methylsulphur groups only affected its efficacy at very high concentrations. Antibacterial performance revealed differences of about 1000-fold between results for environments with high organic matter content and results for aqueous salt buffers. Thiol groups were nonetheless not found directly associated with the decrease in antimicrobial performance in a nutrient rich environment. These results point out the complexity of the antimicrobial systems based on silver and can have relevance in food or other applications of silver as an antimicrobial.

Development and characterization of silver-based antimicrobial ethylene-vinyl alcohol copolymer (EVOH) films for food-packaging applications.

The use of silver as an antimicrobial in the food area has raised wide interest in recent years. In the present work, 0.001-10 wt % silver ions was satisfactorily incorporated into an ethylene-vinyl alcohol (EVOH) copolymer matrix by a solvent casting technique. The antibacterial efficacy of the composite was evaluated under laboratory conditions and in contact with some foods. The ionic compound did not affect the crystallinity or the water-induced plasticization of the materials and was homogeneously distributed across the surface and thickness of the films. When immersed in water, sorption-induced release of 50-100% of the silver ions took place in <30 min. In the bacterial minimal growth medium M9, the minimal inhibitory concentration (MIC) of the film was in the range of 0.01-0.1 ppm. High protein content food samples displayed low susceptibility to the films (<1 log reduction in any case), whereas low protein content food samples exhibited no detectable bacterial counts for films with 1 and 10 wt % silver and about 2 log reduction for films with 0.1 wt % silver. These results represent a step forward in the understanding of silver antimicrobial efficacy and its possible application in the food-packaging industry, most likely as food coatings.

Stabilization of a nutraceutical omega-3 fatty acid by encapsulation in ultrathin electrosprayed zein prolamine.

Docosahexaenoic acid (DHA) is a long chain polyunsaturated fatty acid of the omega-3 series (omega-3), which exerts strong positive influences on human health. The target of this study was the stabilization by encapsulation of this bioactive ingredient in zein ultrathin capsules produced by electrospraying. The zein ultrathin DHA encapsulation was observed by ATR-FTIR spectroscopy to be more efficient against degradation under both ambient conditions and in a confined space (so-called headspace experiment). In the latter case, that more closely simulates a sealed food packaging situation, the bioactive DHA was considerably more stable. By fitting the degradation data to a specific auto-decomposition food lipids kinetic model, it was seen that the encapsulated omega-3 fatty acid showed a 2.5-fold reduction in the degradation rate constant and also had much higher degradation induction time. Moreover, the ultrathin zein-DHA capsules resulted to be more stable across relative humidity and temperature. Finally, headspace analysis by gas chromatography coupled with mass spectrometry showed that the presence of 3 main flavor-influencing aldehydes in the headspace was much lower in the zein encapsulated DHA, suggesting that the encapsulated bioactive also releases much less off-flavors. Electrosprayed ultrathin capsules of zein are shown to exhibit potential in the design of novel functional foods or bioactive packaging strategies to enhance the stability of functional ingredients. Practical Application: This article presents a novel methodology for the stabilization by encapsulation of omega 3 nutraceuticals via electrospraying and has potential application in the development of functional foods.

Novel silver-based nanoclay as an antimicrobial in polylactic acid food packaging coatings.

This paper presents a comprehensive performance study of polylactic acid (PLA) biocomposites, obtained by solvent casting, containing a novel silver-based antimicrobial layered silicate additive for use in active food packaging applications. The silver-based nanoclay showed strong antimicrobial activity against Gram-negative Salmonella spp. Despite the fact that no exfoliation of the silver-based nanoclay in PLA was observed, as suggested by transmission electron microscopy (TEM) and wide angle X-ray scattering (WAXS) experiments, the additive dispersed nicely throughout the PLA matrix to a nanoscale, yielding nanobiocomposites. The films were highly transparent with enhanced water barrier and strong biocidal properties. Silver migration from the films to a slightly acidified water medium, considered an aggressive food simulant, was measured by stripping voltammetry. Silver migration accelerated after 6 days of exposure. Nevertheless, the study suggests that migration levels of silver, within the specific migration levels referenced by the European Food Safety Agency (EFSA), exhibit antimicrobial activity, supporting the potential application of this biocidal additive in active food-packaging applications to improve food quality and safety.

Comparative performance of electrospun collagen nanofibers cross-linked by means of different methods.

Collagen, as the major structural protein of the extracellular matrix in animals, is a versatile biomaterial of great interest in various engineering applications. Electrospun nanofibers of collagen are regarded as very promising materials for tissue engineering applications because they can reproduce the morphology of the natural bone but have as a drawback a poor structural consistency in wet conditions. In this paper, a comparative study between the performance of different cross-linking methods such as a milder enzymatic treatment procedure using transglutaminase, the use of N-[3-(dimethylamino)propyl]-N'-ethylcarbodiimide hydrochloride/N-hydroxysuccinimide, and genipin, and the use of a physical method based on exposure to ultraviolet light was carried out. The chemical and enzymatic treatments provided, in this order, excellent consistency, morphology, cross-linking degree, and osteoblast viability for the collagen nanofibers. Interestingly, the enzymatically cross-linked collagen mats, which are considered to be a more biological treatment, promoted adequate cell adhesion, making the biomaterial biocompatible and with an adequate degree of porosity for cell seeding and in-growth.

Using ATR-FTIR spectroscopy to design active antimicrobial food packaging structures based on high molecular weight chitosan polysaccharide.

ATR-FTIR spectroscopy has been used in this study to characterize the molecular mechanisms and kinetic processes that take place when a chitosonium acetate thin coating is put in contact with water solutions, Staphylococcus aureus solutions, microbial nutrient solutions, and with a high water activity TSA hydrogel medium to simulate the effect of direct contact with high moisture foods such as fresh meats, fish, and seafood products or beverages. The results of this work suggest that the biocide carboxylate groups that form when chitosan is cast from acetic acid solutions are being continuously evaporated from the formed film in the form of acetic acid (mechanism I) in the presence of environmental humidity, rendering weak biocide film systems. On the other hand, upon direct contact of the cast chitosonium acetate film with liquid water, water solutions, or the high moisture TSA hydrogel, a positive rapid migration, with a diffusion coefficient faster than 3.7 x 10(-12) m2/s, of protonated glucosamine water soluble molecular fractions (mechanism II) takes place from the film into the liquid phase, yielding strong antimicrobial performance and leaving in the remaining cast film only the non-water soluble chitosan fractions. Finally, this study describes a refined spectroscopic methodology to predict the antimicrobial properties of chitosan and gives insight into the capacity of chitosan as a natural biocide agent.

Thermal Resistance of Bacillus stearothermophilus Spores Heated in Acidified Mushroom Extract.

The thermal resistance of Bacillus stearothermophilus spores was studied in bidistilled water as the reference medium, mushroom extract and acidified mushroom extract. Citric acid and glucono-δ-lactone were used as acidulants. Results indicated that mushroom extract affects the heat resistance of spores; D values were lower than for those in bidistilled water. The pH effect was lower with higher treatment temperatures. Acidification reduced the thermal resistance of spores, the reduction being similar for both types of acidulants, and in general it also had the effect of increasing the z values. It has been confirmed that acidification of the canned mushrooms could actually help to control the thermophilic spoilage. This acidification could also be obtained by the use of glucono-δ-lactone, which has been shown to be as effective as citric acid in reducing the heat resistance of spores.