Characterization of self-assembled monolayers of iron and cobalt octaalkylthiosubstituted phthalocyanines and their use in nitrite electrocatalytic oxidation

Cobalt and iron phenylthiosubstituted phthalocyanines have been deposited on Au electrode surfaces through the self-assembled monolayer (SAM) technique. The so formed layers were studied using voltammetric and impedance techniques. These SAMs blocked a number of Faradic processes and electrocatalyzed the oxidation of nitrite. The electrocatalytic parameters of the cobalt and iron phenylthiosubstituted phthalocyanines deposited on Au electrodes in nitrite solution were studied. Nitrite overpotentials which are lower than ever reported were obtained in this work for the iron phenylthiosubstituted phthalocyanines with very high stability.     

Quantitative risk assessment on the dietary exposure of Finnish children and adults to nitrite

Nitrite intake from the consumption of cured meat and tap water was estimated for Finnish children of 1, 3 and 6 years as well as Finnish adults of 25–74 years. Nitrite content in the foods was measured by capillary electrophoresis, and was then used together with individual food consumption data from the FINDIET 2007 and DIPP studies in a stochastic exposure assessment by a Monte Carlo Risk Assessment (MCRA) program. Nitrite intake from additive sources and tap water was assessed, and more than every 10th child between the ages 3 and 6 years was estimated to have a nitrite intake exceeding the acceptable daily intake (ADI) of nitrite. The high exposure levels were caused by frequent consumption of large portions of sausages, up to 350 g day^–1 or 750 g in 3 days, among the children. Median nitrite intake from cured meat was 0.016, 0.040, 0.033 and 0.005 mg kg^–1 body weight day^–1 for children of 1, 3 and 6 years and adults, respectively. Bayesian estimation was employed to determine safe consumption levels of sausages and cold cuts for children, and these results gave rise to new national food consumption advice.     

Parallel enzymatic and non-enzymatic formation of zinc protoporphyrin IX in pork

Zinc protoporphyrin is formed in pork homogenates in both enzymatic and non-enzymatic reactions. Ferrochelatase is active in formation of the highly fluorescent pigment known from Parma ham as demonstrated by inhibition with N-methylmesoporphyrin and by thermal inactivation. A non-enzymatic transmetallisation reaction, exchange of iron in myoglobin by zinc(II), is demonstrated by Pb(II) inhibition of zinc protoporphyrin formation at low Pb(II) concentrations, but promoted at higher Pb(II) concentrations. The non-enzymatic reaction is characterised as a slow bimolecular reaction between protoporphyrin IX and zinc(II) with a second-order rate constant of 0.63 l mol⁻¹ s⁻¹ at 35 °C and a high energy of activation of 98 kJ mol⁻¹ for acetone:water (3:1, v/v) as solvent. Zinc protoporphyrin formation is concluded to be thermodynamically controlled with a formation constant of 4 × 10⁵ M (35 °C, acetone:water (3:1)). An efficient inhibition of formation of zinc protoporphyrin by nitrite is related to myoglobin as substrate and involves both enzymatic and non-enzymatic reactions.     

Interactive inhibition of meat spoilage and pathogenic bacteria by lysozyme,nisin and EDTA in the presence of nitrite and sodium chloride at 24 degrees C

To develop a nisin- and lysozyme-based antimicrobial treatment for use with processed ham and bologna, in vitro experiments were conducted to determine whether inhibition enhancing interactions occur between the antimicrobials lysozyme, chrisin (a commercial nisin preparation), EDTA, NaCl and NaNO₂. Inhibitory interactions were observed between a number of agents when used against specific pathogenic and spoilage bacteria. The observed interactions included lysozyme with EDTA (Enterococcus faecalis and Weissella viridescens), chrisin with EDTA (all Gram-positive organisms), EDTA with NaCl (Escherichia coli, Salmonella enterica serovar Typhimurium, Serratia grimesii), EDTA with nitrite (E. coli, Lactobacillus curvatus, Leuconostoc mesenteroides, Listeria monocytogenes, S. Typhimurium), chrisin with nitrite (Lc. mesenteroides, L. monocytogenes), and NaCl with nitrite (S. Typhimurium, Shewanella putrefaciens). Previous reports have described interactions between nisin with EDTA that resulted in enhanced antimicrobial effect against Gram-negative bacteria, or lysozyme with nisin against Gram-positive bacteria. These interactions were not observed in these experiments. We observed that unlike previous studies, these experiments were conducted on growing cells in nutrient broth, rather than under conditions of nutrient limitation. We propose that screening of antimicrobials for use in food systems in nutrient-deficient systems is inappropriate and that new protocols should be developed.     

Nitrous oxide generation in full-scale biological nutrient removal wastewater treatment plants

International guidance for estimating emissions of the greenhouse gas, nitrous oxide (N₂O), from biological nutrient removal (BNR) wastewater systems is presently inadequate. This study has adopted a rigorous mass balance approach to provide comprehensive N₂O emission and formation results from seven full-scale BNR wastewater treatment plants (WWTP). N₂O formation was shown to be always positive, yet highly variable across the seven plants. The calculated range of N₂O generation was 0.006-0.253 kgN₂O-N per kgN denitrified (average: 0.035 ± 0.027). This paper investigated the possible mechanisms of N₂O formation, rather than the locality of emissions. Higher N₂O generation was shown to generally correspond with higher nitrite concentrations, but with many competing and parallel nitrogen transformation reactions occurring, it was very difficult to clearly identify the predominant mechanism of N₂O production. The WWTPs designed and operated for low effluent TN (i.e. <10 mgN L⁻¹) had lower and less variable N₂O generation factors than plants that only achieved partial denitrification.     

Evaluating operating conditions for outcompeting nitrite oxidizers and maintaining partial nitrification in biofilm systems using biofilm modeling and Monte Carlo filtering

In practice, partial nitrification to nitrite in biofilms has been achieved with a range of different operating conditions, but mechanisms resulting in reliable partial nitrification in biofilms are not well understood. In this study, mathematical biofilm modeling combined with Monte Carlo filtering was used to evaluate operating conditions that (1) lead to outcompetition of nitrite oxidizers from the biofilm, and (2) allow to maintain partial nitrification during long-term operation. Competition for oxygen was found to be the main mechanism for displacing nitrite oxidizers from the biofilm, and preventing re-growth of nitrite oxidizers in the long-term. To maintain partial nitrification in the model, a larger oxygen affinity (i.e., smaller half saturation constant) for ammonium oxidizers compared to nitrite oxidizers was required, while the difference in maximum growth rate was not important for competition under steady state conditions. Thus, mechanisms for washout of nitrite oxidizing bacteria from biofilms are different from suspended cultures where the difference in maximum growth rate is a key mechanism. Inhibition of nitrite oxidizers by free ammonia was not required to outcompete nitrite oxidizers from the biofilm, and to maintain partial nitrification to nitrite. But inhibition by free ammonia resulted in faster washout of nitrite oxidizers.     

Electrochemical nitrite nanosensor developed with amine- and sulphate-functionalised polystyrene latex beads self-assembled on polyaniline

Aniline doped with polyvinyl sulphonate (PV-SO₃⁻) was electropolymerised on screen printed carbon (SPCE) and glassy carbon (GCE) electrodes. Then nano-structured polystyrene (PS_NP) latex beads functionalised with amine (PS_NP-NH₂) and sulphate (PS_NP-OSO₃⁻) were self-assembled on the modified SPCE and GCE. The resultant polyaniline nanocomposites (PANI|PS_NP-NH₂ or PANI|PS_NP-OSO₃⁻) were characterised by cyclic voltammetry (CV), UV-vis spectroscopy and scanning electron microscopy (SEM). Brown-Anson analysis of the multi-scan rate CV responses of the various PANI films gave surface concentrations of the order of 10⁻⁸ mol cm⁻². UV-vis spectra of the PANI films dissolved in dimethyl sulphoxide showed typical strong absorbance maxima at 480 and 740 nm associated with benzenoid π-π* transition and quinoid excitons of polyaniline, respectively. The SEM images of the PANI nanocomposite films showed cauliflower-like structures that are <100 nm in diameter. When applied as electrochemical nitrite sensor, sensitivity values of 60, 40 and 30 μA/mM were obtained for electrode systems containing PANI|PS_NP-NH₂, PANI and PANI|PS_NP-SO₃⁻, respectively. The corresponding limits of detection of the sensors were 7.4, 9.2 and 38.2 μM NO₂⁻.     

一些果蔬对活性自由基和亚硝酸盐的消除作用

对29种新鲜水果和蔬菜的一般营养成分和过氧化物酶、过氧化氢酶活性以及对H_2O_2和NaNO_2的消除能力进行了测定。结果表明,在模拟胃液条件下,各种供试的新鲜果蔬对活性氧自由基和亚硝酸盐均具有不同程度的消除能力,其消除量与新鲜果蔬中的蛋白质含量呈极显著正相关。谷胱甘肽、还原型辅酶Ⅰ、维生素E、维生素C和半胱氨酸等还原性食品成分对NaNO_2和H_2O_2都有良好的线性消除关系。煮沸处理后,有机酸含量高的果蔬对NaNO_2和H_2O_2的消除能力增强,有机酸含量低时,其消除能力下降。提示果蔬对活性氧自由基和亚硝酸盐的消除能力取决于果蔬中还原性食品成分的种类、含量及其氧化还原特性。     

Determination of nitrite and nitrate levels in meat and vegetable products by high performance liquid chromatography

A range of fresh and processed meat and vegetable products was analysed by h.p.l.c. for nitrite and nitrate contents. Satisfactory results were obtained for vegetable products and most meats, but some meat products were subject to matrix interference. Sucrose, sulphate and phosphate did not affect results. Added sodium chloride decreased retention time of nitrite and increased apparent levels of both nitrite and nitrate. Ascorbic and erythorbic acids decreased apparent nitrite levels and correspondingly increased apparent nitrate levels.