Antimicrobial Properties of Palladium and Platinum Nanoparticles: A New Tool for Combating Food-Borne Pathogens

Although some metallic nanoparticles (NPs) are commonly used in the food processing plants as nanomaterials for food packaging, or as coatings on the food handling equipment, little is known about antimicrobial properties of palladium (PdNPs) and platinum (PtNPs) nanoparticles and their potential use in the food industry. In this study, common food-borne pathogens Salmonella enterica Infantis, Escherichia coli, Listeria monocytogenes and Staphylococcus aureus were tested. Both NPs reduced viable cells with the log₁₀ CFU reduction of 0.3–2.4 (PdNPs) and 0.8–2.0 (PtNPs), average inhibitory rates of 55.2–99% for PdNPs and of 83.8–99% for PtNPs. However, both NPs seemed to be less effective for biofilm formation and its reduction. The most effective concentrations were evaluated to be 22.25–44.5 mg/L for PdNPs and 50.5–101 mg/L for PtNPs. Furthermore, the interactions of tested NPs with bacterial cell were visualized by transmission electron microscopy (TEM). TEM visualization confirmed that NPs entered bacteria and caused direct damage of the cell walls, which resulted in bacterial disruption. The in vitro cytotoxicity of individual NPs was determined in primary human renal tubular epithelial cells (HRTECs), human keratinocytes (HaCat), human dermal fibroblasts (HDFs), human epithelial kidney cells (HEK 293), and primary human coronary artery endothelial cells (HCAECs). Due to their antimicrobial properties on bacterial cells and no acute cytotoxicity, both types of NPs could potentially fight food-borne pathogens.     

Performance of La1−xSrxAl1−y−y′FeyMgy′O3−δ perovskites in methane combustion: effect of aluminum and magnesium content

Perovskites of different La_1−xSr_xAl_1−y−y′Fe_yMg_y′O_3−δ compositions (x=0, 0.1, 0.15, 0.2 and y=0.1, 0.3, 0.5, 0.8) were prepared from a reactive precursor slurry of hydrated oxides. Each sample was aged between 16 and 26 h up to 1473 K. Activity in methane combustion (1%/air) was determined in a plug-flow reactor, with 1 g catalyst and 24 l/h flowrate. Gradual decrease in activity due to thermal aging was observed, the degree of activity loss being composition dependent. Nevertheless, activity of samples aged at 1370 K was nearly independent of composition. The best thermal stability showed LaAl_0.65Fe_0.15Mg_0.2O₃ perovskite. None of the magnesium substituted perovskites performed better than a La_0.85Sr_0.15Al_0.87Fe_0.13O₃ reference sample.     

Materials for catalytic gas combustion

Catalytic combustion, which permits to burn lean fuel/air mixtures is the key to environmentally preferable utilization of natural gas as an energy source and to removal of organic combustible gases from industrial effluents. The range of potential applications of catalytic combustion is large and can vary in temperatures of operation. Successful wide implementation of existing and of new catalytic combustion technologies will largely depend on the availability of suitable low cost catalytic materials. Since no single material can meet all demands, development of new catalysts needs to be orchestrated with the specific requirements of a given technology. The challenge is to combine existing knowledge and expertise in the area of combustion catalysts with innovations in their synthesis, improved formulations and applications in new specific composite forms. This paper outlines the current state of art and then focuses on perovskites for applications below 1,000 K. Examples of highly active formulations and of further enhancement of their activity through controlled synthesis and suitable support combinations are given. Criteria for the design of highly performing materials for high temperature catalytic combustion are also presented.     

The influence of different niobium pentoxide precursors on the solid-state synthesis of potassium sodium niobate

Two batches of K_0.5Na_0.5NbO₃ were prepared from the orthorhombic and monoclinic Nb₂O₅ polymorphs and potassium and sodium carbonates. The influence of the different Nb₂O₅ precursors on the solid-state synthesis of K_0.5Na_0.5NbO₃ was studied. To reduce the particle size, both types of Nb₂O₅ were milled prior to use. XRD and TEM analyses showed that the milled orthorhombic Nb₂O₅ was single phase; however, after milling the monoclinic Nb₂O₅ consisted of large monoclinic particles and orthorhombic nanocrystals. The latter reacted with the carbonates to form (K_xNa_1-x)NbO₃ solid solutions with varying K/Na molar ratios, while the orthorhombic Nb₂O₅ reacted to form a homogeneous solid solution of K_0.5Na_0.5NbO₃. Sintering of the two powder compacts resulted in different densification behavior and microstructure. This study shows the important influence of the Nb₂O₅ precursor phase and the particle size distribution on the homogeneity and further densification of the potassium sodium niobate solid solution.     

Comparison of UV/H(2)O(2) and UV/TiO(2) for the degradation of metaldehyde: Kinetics and the impact of background organics

The kinetics of photodegradation of the pesticide metaldehyde by UV/H₂O₂ and UV/TiO₂ in laboratory grade water and a natural surface water were studied. Experiments were carried out in a bench scale collimated beam device using UVC radiation. Metaldehyde was efficiently degraded by both processes in laboratory grade water at identical rates of degradation (0.0070 and 0.0067 cm² mJ⁻¹ for UV/TiO₂ and UV/H₂O₂ respectively) when optimised doses were used. The ratio between oxidant and metaldehyde was significantly higher for H₂O₂ due to its low photon absorption efficiency at 254 nm. However, the presence of background organic compounds in natural water severely affected the rate of degradation, and whilst the pseudo first-order rate constant of degradation by UV/H₂O₂ was slowed down (0.0020 cm² mJ⁻¹), the degradation was completely inhibited for the UV/TiO₂ process (k′ = 0.00007 cm² mJ⁻¹) due to the blockage of active sites on TiO₂ surface by the background organic material.     

Antibacterial polyvinyl chloride/antibiotic films: The effect of solvent on morphology,antibacterial activity,and release kinetics

Medical‐grade polyvinyl chloride was modified with sodium ampicillin in a concentration range from 0 to 5 wt % by solvent casting technique using cyclohexanone and N,N‐dimethylformamide. The obtained polymeric systems were characterized by optical microscopy, tensile test, and scanning electron microscopy. In addition, in vitro antibacterial activity against Gram‐negative and Gram‐positive bacteria was determined by an agar diffusion test. Antibiotic release experiments were performed in distilled water and physiological saline solution, which were monitored by UV‐vis spectroscopy. The results showed a crucial role of the solvent on the morphology, antibacterial activity, and releasing characteristic of the ampicillin. Furthermore, a mathematical model was applied to data obtained from release study, to characterize the release kinetics of the ampicillin from the polyvinyl chloride‐antibiotic systems. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Phenolic acid contents of kale (Brassica oleraceae L. var. acephala DC.) extracts and their antioxidant and antibacterial activities

Nine phenolic acids were identified and quantified by HPLC–MS in leaves and 10 in seeds of kale (black cabbage). The free, ester (methanol-soluble), glycoside and ester-bound (methanol-insoluble) phenolic acid contents of the leaves were 487, 532, 4989 and 6402 ng/g fresh weight, respectively. Ferulic and caffeic acids (total contents; 4269 and 4887 ng/g, respectively) were the most abundant. The seed contents of these fractions were 1993, 1477, 1231 and 4909 ng/g dry weight (DW), respectively, and sinapic acid was the most abundant (5037 ng/g DW). The fractions’ total phenolic contents, determined colorimetrically, were highly correlated with their DPPH scavenging capacity, and in antimicrobial activity assays, with nine test organisms representing a wide array of taxa, all of the fractions were effective against Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis and (most strongly) Moraxella catarrhalis. Antimicrobial and antioxidant activities of kale phenolics in free and conjugated forms are discussed.     

Effect of some manufacturing variables on formaldehyde release from particleboard: Relationship between different test methods

Different standard methods were used to determine the formaldehyde emission (FE) from particleboard; some of them were defined as European, Japanese and American standards. This study aimed to determine the effect of some manufacturing variables on FE of particleboards produced using melamine–urea–formaldehyde (MUF) adhesive with low content of free formaldehyde. The FE from the two types of particleboard (uncoated and laminated of 16–19 mm thickness) was measured with gas analysis method (EN 717-2) as well as the formaldehyde content (FC) with perforator method (EN 120). The European chamber (EN 717-1), Japanese desiccator method (JIS A 1460) and American large chamber (ASTM E 1333-96) values were measured by the conversion factor. The two types of particleboard studies showed differences in their formaldehyde parameters. It was concluded that the amount of formaldehyde emitted from the most of the manufactured boards resulted in the emission class El. In addition, laminating and decreasing the board thickness had a highly significant effect (p < 0.001) on decreasing the formaldehyde parameters. The particleboard E1-emission class had approximately the same value according to the test methods and similar behavior was observed in the relationship between the EN 120 values and EN 717-1, JIS A 1460, the proposed California Air Resource Board (CARB) Phase 1 and 2. This article considers how to estimate the FE values of the international test methods using the conversion factor to eliminate the need for time consuming and expensive equipment.