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Mentus S.,University of Belgrade | Mentus S.,Serbian Academy of Science and Arts | Abu Rabi A.,Serbian Institute of Chemistry | Jasin D.,Technical School Zrenjanin
Electrochimica Acta | Year: 2012

By multiple potentiodynamic polarization of polished titanium surface in an aqueous PdCl 2 solution, a thin composite Pd/TiO 2 layer was formed, consisting of Pd submicron particles grown through a nanometer-thin surface TiO 2 layer. The real surface area of Pd was determined by cyclic voltammetry in nitrogen purged 0.1 mol dm -3 HClO 4. The oxygen reduction reaction on the Pd/TiO 2 layer in 0.1 mol dm -3 KOH and 0.1 mol dm -3 HClO 4 solutions has been studied using rotating disc electrode (RDE) voltammetry. Comparing to the best palladium or palladium based catalysts published thus far, the Pd/TiO 2 composite yielded similar or higher (in acidic solution) or discernible higher (in alkaline solution) rate of oxygen reduction. This was found to be mostly due to the high surface area of Pd particles, but, to some extent, due to the influence of TiO 2 support itself. © 2012 Elsevier Ltd.

Gorjanovic S.Z.,Serbian Institute of General and Physical Chemistry | Novakovic M.M.,Serbian Institute of Chemistry | Potkonjak N.I.,Serbian Institute of General and Physical Chemistry | Ida L.-C.,University of Belgrade | Suznievic D.Z.,Serbian Institute of General and Physical Chemistry
Journal of Agricultural and Food Chemistry | Year: 2010

A novel antioxidative assay based on direct current polarography has been developed. Quantification of antioxidative (AO) activity has been based on a decrease of hydrogen peroxide anodic current in the presence of antioxidants. An efficient experimental procedure, without any special pretreatment of analyzed samples, has been applied. Antioxidative activity of different kinds of commercial beers (dark, blond, and alcohol-free), some small-scale made special beers with medicinal herbs and mushroom extracts, extracts themselves, as well as individual phenolic components present in beer has been measured. In addition, changes of AO activity during the full-scale industrial process of beer production have been monitored. A strong correlation between results obtained and total phenolics content has been observed. The assay can be recommended for application in brewing industry, either to survey a process with the aim to optimize relevant technological factors or to analyze quality of final product. © 2009 American Chemical Society.

Andjelkovic U.,Serbian Institute of Chemistry | Picuric S.,Goethe University Frankfurt | Vujcic Z.,University of Belgrade
Food Chemistry | Year: 2010

Four external invertase isoforms (EINV1, EINV2, EINV3 and EINV4) from Saccharomyces cerevisiae were highly purified by isoelectric precipitation, ethanol precipitation, ion-exchange on QAE-Sephadex and gel filtration using Sephacryl S-200. Unlike previously published procedures for external invertase purification, a specially designed step elution was applied on QAE-Sephadex which enabled the separation of four isoforms. The isoforms have the same molecular mass and catalytic properties: Km for sucrose (25.6 mM), pH optimum (3.5-5.0) and temperature optimum (60 °C), but they exhibit significant difference in pI values, thermal stability and chemical reactivity. Deglycosylation studies showed that the observed differences between isoforms arise from posttranslational modifications. Results showed that external invertase is a mixture of at least four isoforms, but in order to improve the efficiency of food industry processes, only the most stable isoform (EINV1) should be purified and utilised. Substantially different chemical reactivity of the isoforms could be used to improve the yield of covalent immobilization procedures. © 2009 Elsevier Ltd. All rights reserved.

Gorjanovic S.Z.,Serbian Institute of General and Physical Chemistry | Alvarez-Suarez J.M.,Marche Polytechnic University | Novakovic M.M.,Serbian Institute of Chemistry | Pastor F.T.,University of Belgrade | And 3 more authors.
Journal of Food Composition and Analysis | Year: 2013

Hydrogen peroxide scavenging (HPS) activity of honey of different floral sources and its constituents such as predominant honey flavonoids, phenolic acids, amino and organic acids, and carbohydrates have been assessed by direct current (DC) polarographic assay. The assay was based on decrease of anodic current of hydrogen peroxide complex, formed in alkaline solution, at the potential of mercury dissolution. High correlations between honey HPS activity, its total phenolic content (FC-GAE), antioxidant activity measured by four standard methods (DPPH, TEAC, FRAP and ORAC), and also the relative antioxidant capacity index, were obtained. Statistical evaluation by ANOVA and F-test further confirmed the assay validity. The results for individual compounds showed that HPS activity of honey reflects an integrated action of a wide range of constituents, both phenolics and non-phenolics. The polarographic assay applied is a fast, reliable and low cost alternative to spectrophotometric antioxidant assays commonly applied in analysis of honey and can serve as an indicator of honey quality. © 2013 Elsevier Inc.

Dojcinovic B.P.,Serbian Institute of Chemistry | Roglic G.M.,University of Belgrade | Obradovic B.M.,University of Belgrade | Kuraica M.M.,University of Belgrade | And 2 more authors.
Journal of Hazardous Materials | Year: 2011

Decolorization of reactive textile dyes Reactive Black 5, Reactive Blue 52, Reactive Yellow 125 and Reactive Green 15 was studied using advanced oxidation processes (AOPs) in a non-thermal plasma reactor, based on coaxial water falling film dielectric barrier discharge (DBD). Used initial dye concentrations in the solution were 40.0 and 80.0mg/L. The effects of different initial pH of dye solutions, and addition of homogeneous catalysts (H2O2, Fe2+ and Cu2+) on the decolorization during subsequent recirculation of dye solution through the DBD reactor, i.e. applied energy density (45-315kJ/L) were studied. Influence of residence time was investigated over a period of 24h. Change of pH values and effect of pH adjustments of dye solution after each recirculation on the decolorization was also tested. It was found that the initial pH of dye solutions and pH adjustments of dye solution after each recirculation did not influence the decolorization. The most effective decolorization of 97% was obtained with addition of 10mM H2O2 in a system of 80.0mg/L Reactive Black 5 with applied energy density of 45kJ/L, after residence time of 24h from plasma treatment. Toxicity was evaluated using the brine shrimp Artemia salina as a test organism. © 2011 Elsevier B.V.

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