The fate of added nitrate used in the manufacture of Emmental cheese

The aim of this study was to observe the dynamics of nitrates and nitrites during the six stages of manufacture of Emmental cheeses. Samples were taken of untreated milk, of pasteurized milk, of milk with nitrates added, of pressed cheese curd, of whey, of maturing cheese and of the final product. The samples were drawn from a commercial operation in a cheese factory in the eastern part of Slovakia. The mean NaNO₂ content in untreated and in pasteurised milk was 0.2 and 0.1 mg kg^-1, respectively and the mean NaNO₃ content was 0.9 and 0.9 mg kg^-1 respectively. Nitrates were added to the milk to prevent 'blowing' of hard cheese by micro organisms. In milk with nitrate added the mean content was 81.2 mg kg^-1 NaNO₃; the maximum value being 90.0 mg kg¹ NaNO₃. After pressing, the mean value of nitrate was found to be 20.6 mg kg^-1 NaNO₃. A considerable quantity of nitrates passed into the whey, where the mean nitrate content was 67.0 mg kg^-1 NaNO₃. The final product had a markedly decreased content of nitrates (3.3 mg kg^-1 NaNO₃) and nitrites (0.2 mg kg^-1 NaNO₂) when compared with the values in cheese during maturation (11.3 mg kg^-1 NaNO₃; 0.4 mg kg^-1 NaNO₂).     

Nitrate and nitrite quantification from cured meat and vegetables and their estimated dietary intake in Australians

High dietary nitrate and nitrite intake may increase the risk of gastro-intestinal cancers due to the in vivo formation of carcinogenic chemicals known as N-nitroso compounds. Water and leafy vegetables are natural sources of dietary nitrate, whereas cured meats are the major sources of dietary nitrite. This paper describes a simple and fast analytical method for determining nitrate and nitrite contents in vegetables and meat, using reversed-phase HPLC-UV. The linearity R² value was >0.998 for the anions. The limits of quantification for nitrite and nitrate were 5.0 and 2.5 mg/kg, respectively. This method is applicable for both leafy vegetable and meat samples. A range of vegetables was tested, which contained <23 mg/kg nitrite, but as much as 5000 mg/kg of nitrate. In cured and fresh meat samples, nitrate content ranged from 3.7 to 139.5 mg/kg, and nitrite content ranged from 3.7 to 86.7 mg/kg. These were below the regulatory limits set by food standards Australia and New Zealand (FSANZ). Based on the average consumption of these vegetables and cured meat in Australia, the estimated dietary intake for nitrate and nitrite for Australians were 267 and 5.3 mg/adult/day, respectively.     

电化学传感器测定食品中亚硝酸盐的研究进展

综述了近年来电化学传感器测定食品中痕量亚硝酸盐的研究进展,着重介绍了应用于肉制品、乳制品和蔬菜亚硝酸盐检测中的电位型电化学传感器和电流型电化学传感器等电化学传感器,对其测定原理、测定参数及其使用范围等进行了详细的阐述,并分析比较了各种传感器的优劣;展望了电化学传感器测定食品中痕量亚硝酸盐的应用前景.     

Modeling Enhanced In Situ Denitrification in Groundwater

A two-dimensional numerical solute transport model was developed for simulating an enhanced in situ denitrification experiment performed in a nitrate-contaminated aquifer on Cape Cod, Massachusetts. In this experiment, formate (HCOO?) was injected for a period of 26 days into the carbon-limited aquifer to stimulate denitrification. Calibration of the vertical-profile site model was demonstrated through error analysis and comparison with formate, nitrate, and nitrite concentration data monitored along a transect of three multilevel groundwater sampling wells for 75 days after initial injection. Formate utilization rates were approximately 142 and 38 μM/day for nitrate and nitrite reduction, respectively. Nitrate and nitrite utilization rates were approximately 29 and 8 μM/day, respectively. Nitrate utilization rates under enhanced conditions were 1 order of magnitude greater than previously reported naturally occurring rates. The nitrite production rate was approximately 29 μM/day. Persistence of nitrite was attributed to a combination of factors, including electron donor (formate) limitation late in the experiment, preferential utilization of nitrate as an electron acceptor, and greater nitrite production relative to nitrite utilization.     

Endogenous levels of nitrites and nitrates in wide consumption foodstuffs: Results of five years of official controls and monitoring

The massive introduction of nitrogen fertilisers, necessary to maximise the global food production, has brought about an increase of the residual amounts of nitrites and nitrates in the products. Notoriously, these compounds may exercise toxic effects.     

导数伏安法测定肉类食品中的亚硝酸盐

在盐酸介质中,痕量亚硝酸根对溴酸钾氧化中性红的反应有极强的催化作用,研究了最佳反应条件,发现在氨缓冲溶液中中性红具有良好的导数电流峰,通过悬汞电极跟踪催化反应过程中中性红浓度的变化,建立了测定痕量亚硝酸根的新方法。方法的线性范围为1.2×10~(-7)～5.0×10(~-4)μg·mL~(-1)。检出限为5.4×10~(-8)μg·mL~(-1),应用于肉类食品中亚硝酸根的测定,结果满意。     

Identification of Neutral and Charged NxOy Surface Species by IR Spectroscopy

The infrared spectral performance of the N_xO_y species observed on oxide surfaces [N₂O, NO^-, NO, (NO)₂, N₂O₃, NO⁺, NO₂^- (different nitro and nitrito anions), NO₂, N₂O₄, N₂O₅, NO₂, and NO₃^- (bridged, bidentate, and monodentate nitrates)] is considered. The spectra of related compounds (N₂, H-, and C-containing nitrogen oxo species, C─N species, NH_x species) are also briefly discussed. Some guidelines for spectral identification of N_xO_y adspecies are proposed and the transformation of the nitrogen oxo species on catalyst surfaces are regarded.     

Fractals in Heterogeneous Catalysis

In a recent review on the influence of particle size on catalytic properties of supported metals [l], evidently a most important aspect of heterogeneous catalysis by any account, the authors end on a fairly discouraging note since they suggest doing even more work — with ever more sophisticated techniques and methods as well as normalized procedures — on top of an already formidable amount of literature. At such a state of the art it may be appropriate to reflect and to ask whether full pursuit of reductionism as scientific method needs fresh thinking in order to progress more effectively. Perhaps the difficulties are rooted in emphasis on mere data collection, the lack of a good empirical guiding principle, inappropriate models; in brief, the frequent simplification of a vastly complicated object — the real catalyst — into the sum of phenomena of better-understood idealized subsets. It might even be argued that a thorough knowledge of a well-characterized prototype or a particular model catalyst would be actually of little help in seeing the real world where catalysts are of irregular shape, suffer sintering, become poisoned; in other words, lose their ideal state after some time of operation. Also, we realize that a change in “quantity” often engenders a change in “quality”: For instance, a material with a BET area of hundreds of square meters per gram can hardly be considered to have a surface like a huge tennis court or ball field: it is rather “convoluted” in some very irregular fashion, having a shape that is difficult to realistically construct as a linear combination of planar portions.     

食品中亚硝酸盐含量的测量不确定度评定

目的分析和评定影响食品中亚硝酸盐含量的测量不确定度分量,建立数学模型。方法测量不确定度评定与表示(JJF1059—1999)。结果当食品中亚硝酸盐含量为158mgkg时,合成不确定度为078mgkg,扩展不确定度为16mgkg。结论掌握亚硝酸盐含量的测量不确定度评定方法,能帮助检验人员确定测定结果的可靠程度,确保测定结果准确可靠。