Model studies on precursor system generating blue pigment in onion and garlic

Reactions involved in blue-green discoloration in a mixture of onion (Allium cepa L.) and garlic (Allium sativum L.) were investigated. Vivid-blue color was successfully reproduced by using a defined model reaction system comprising only trans-(+)-S-(1-propenyl)-L-cysteine sulfoxide (1-PeCSO) from onion, S-allyl-L-cysteine sulfoxide (2-PeCSO) from garlic, purified alliinase (EC 4.4.1.4), and glycine (or some other amino acids). Four reaction steps identified and factors affecting the blue color formation were in good agreement with those suggested by earlier investigators. When crude onion alliinase was used in place of garlic alliinase, less pigment was formed. This result was explained by a difference in the amount of thiosulfinates, colorless intermediates termed color developers, yielded from 1-PeCSO by these enzymes.     

Predicting the Concentration of Total Mercury in Mineral Horizons of Forest Soils Varying in Organic Matter and Mineral Fine Fraction Content

In this study, an artificial neural networks (ANN) model was developed to predict the removal of a polycyclic aromatic hydrocarbon (PAH), namely, naphthalene from marine oily wastewater by using UV irradiation. The removal rate was used as model output and simulated as a function of five independent input variables, including fluence rate, salinity, temperature, initial concentration and reaction time. The configuration of the ANN model was optimized as a three-layer feed-forward Levenberg–Marquardt backpropagation network with log-sigmoid and linear transfer functions at the hidden (12 hidden neurons) and output layers, respectively. By considering goodness-of-fit and cross validated predictability, the ANN model was trained to provide good overall agreement with experimental results with a slope of 0.97 and a correlation of determination (R ²) of 0.943. Sensitivity analysis revealed that fluence rate and temperature were the most influential variables, followed by reaction time, salinity and initial concentration. The findings of this study showed that neural network modeling could effectively predict the behavior of the photo-induced PAH degradation process.     

Quantification of Oxidant Demand and Consumption for In Situ Chemical Oxidation Design: in the Case of Potassium Permanganate

Accurate estimation of oxidant consumption during in situ chemical oxidation (ISCO) is the key to determining the treatment effectiveness in contaminated sites. We established the estimation model of soil oxidant demand (SOD) and simulation equations of potassium permanganate (KMnO₄) dynamic consumption based on the reaction equation of KMnO₄ with reductive minerals and the estimation model of SOD. Model validation, model application, and simulation assessment had been accomplished. Results indicated that the simulations are in good agreement with measured data. The confidence level of the SOD estimation model of KMnO₄ was over 80%, with sensitivity in decreasing order as follows: organic matter content > initial KMnO₄ concentration > reductive minerals (RMs). Particularly, the organic matter played a dominate role in the SOD model estimation. The coefficient of determination (R²) of the SOD dynamic consumption simulation equation was above 0.9. Among the various types of soils, the overall trend of SOD value and reaction period decreased as follows: clay > loam > sand. However, the consumption rate of KMnO₄ decreased in the order of clay > sand > loam. In addition, SOD value, reaction period, and reaction rate all increased as the initial concentration of KMnO₄ went up. This work can provide a methodology and reference for selecting and estimating of the optimal oxidant doses and reaction period during field application.     

Emission of groundwater‐derived nitrous oxide into the atmosphere: model simulations based on a 15N field experiment

Indirect emissions of the major greenhouse gas nitrous oxide (N₂O) occurring from aquatic ecosystems are considered to be a highly uncertain component in the global N₂O budget. In this study, we investigated the fate of N₂O produced by denitrification in a sandy shallow aquifer in northern Germany. The experimental data from a previous ¹⁵N field study and site‐specific diffusion coefficients were used to simulate upward fluxes of groundwater‐derived (¹⁵N‐)N₂O in the soil as well as its ultimate emission into the atmosphere. The one‐dimensional simulation model considered gas diffusion and gas retardation by dissolution in the water phase. The modelled concentration gradients and emissions were in good agreement with the experimental data, indicating that diffusion was the dominant transport process in the soil, and that our model approach was thus suitable for simulating N₂O fluxes from the unsaturated zone to the atmosphere. Furthermore, the results revealed that there was no evidence for consumption of ¹⁵N‐N₂O during upward diffusion from the surface groundwater to the atmosphere. Simulated concentrations and emissions of groundwater‐derived N₂O were found to be very small and a negligible component of total N₂O.     

基于化学动力学的生物质颗粒燃烧排放NO特性模拟与验证

为研究生物质颗粒燃料燃烧NO排放规律及其生成机理,采用CFD和Chem Kin联合仿真,建立试验锅炉燃烧筒CFD网络模型,应用Chem Kin接口导入简化的17组分58基元反应机理,建立Chem Kin-PSR反应模拟网络,选用Reaction Design C2_NOx详细机理,对棉秆、玉米秸秆、木质3种生物质颗粒NO排放进行模拟。结果表明,NO生成量:棉秆玉米秸秆木质;NO排放量随过量空气系数的增加先增大后减小,在过量空气系数为1.7附近达到峰值。将模拟结果与试验结果进行比较,证明了模型和化学反应机理的正确性,为生物质燃料燃烧NO排放的预测与控制提供参考。     

Role of glucose in the maillard browning of maltose and glycine: a radiochemical approach

We followed the contribution of released glucose to the formation of melanoidins in the maltose-glycine reaction by adding (14)C glucose to the maltose-glycine mixture, after it already had undergone some reaction. This approach allowed us to confirm the turnover of glucose in this reaction and hence the role of glucose in forming melanoidins. A comparison of the total amount of glucose converted into the melanoidins with the total concentration of melanoidins formed from maltose and glycine showed that the concentration of melanoidins originating from the released glucose was relatively small in comparison to the total melanoidins concentration. Hence, the parallel glucose-glycine reaction is considered to be only a minor pathway in the formation of maltose-glycine melanoidins. The incorporation of glucose into the nondialyzable melanoidins in the maltose-glycine reaction was in excellent agreement with the amount estimated from a kinetic model for the reaction of maltose with glycine. The rate constants were estimated by nonlinear regression, via multiresponse modeling.     

Development of a stable isotope dilution assay for the quantitation of glycidamide and its application to foods and model systems

On the basis of a stable isotope dilution assay and derivatization with 2-mercaptobenzoic acid, the presence of the carcinogenic glycidamide ( 2) in processed foods was verified for the first time. Using (13)C-labeled 2 as the internal standard and the formation of the thioether derivatives, a new stable isotope dilution assay for the quantitation of 2 was developed. Application of the method on several potato samples revealed amounts between 0.3 and 1.5 mug/kg depending on the processing conditions. In a model experiment, the formation of 2 by an epoxidation of the double bond in acrylamide, that is, by a reaction with linoleic acid hydroperoxides, was established. This result was in good agreement with data showing that French fries processed in sunflower oil, which is high in linoleic acid, contained more 2 as compared to fries prepared in coconut oil. The derivatization procedure allows the simultaneous quantitation of acrylamide and glycidamide in foods.     

Comparative studies on the delignification of pine kraft-anthraquinone pulp with hydrogen peroxide by binucleus Mn(IV) complex catalysis

Pine kraft-anthraquinone (kraft-AQ) pulp was bleached in alkaline solution with hydrogen peroxide catalyzed by either [L(1)Mn(IV)(micro-O)(3)Mn(IV)L(1)](PF(6))(2)] (C1) or [LMn(IV)(2)(micro-O)(3)] (ClO(4))(2) (C2) at 60 and 80 degrees C for 120 min with a catalyst charge of 10 ppm on pulp. The resulting bleached pulp was hydrolyzed with cellulase to obtain insoluble and soluble residual lignins. The alkaline bleaching effluents were acidified to precipitate alkaline-soluble lignins. These lignin preparations were then characterized by 2D heteronuclear multiple-quantum coherence (HMQC) NMR spectroscopic techniques. The results showed that biphenyl (5-5) and stilbene structures of the residual lignin in the pulp are preferentially degraded in both the C1- and C2-catalyzed bleachings, whereas beta-O-4, beta-5, and beta-beta structures undergo degradation to a lesser extent. In both cases, the degradation of the residual lignin increased with the increase in reaction temperature from 60 to 80 degrees C. Thus, the result of C1-catalyzed delignification is not in agreement with the observed decrease in the disappearance rate for substrates in the C1-catalyzed oxidation of lignin model compounds with hydrogen peroxide when the reaction temperature is increased from 60 to 80 degrees C. In addition, the resulting residual lignins in the C2-catalyzed bleaching at 80 degrees C are less degraded than the corresponding lignins in the C1-catalyzed bleaching at both 60 and 80 degrees C. Thus, C1 is more effective than C2 as catalyst in the binucleus Mn(IV) complex-catalyzed bleaching of pine kraft-AQ pulp with hydrogen peroxide.     

Evaluation of binary solvent mixtures for efficient monoacylglycerol production by continuous enzymatic glycerolysis

This study was aimed at evaluating different binary solvent mixtures for efficient industrial monoacylglycerol (MAG) production by enzymatic glycerolysis. Of all investigated cases, the binary mixture of tert-butanol:tert-pentanol (TB:TP) 80:20 vol % was the most suitable organic medium for continuous enzymatic glycerolysis, ensuring high MAG formation in a short time, reasonable solvent price, and easy handling during distillation/condensation processing. A minimum solvent dosage of 44-54 wt % of the reaction mixture was necessary to achieve high MAG yields of 47-56 wt %, within 20 min. The melting and boiling points of the TB:TP mixture were estimated to be 7 and 85 degrees C, respectively, using thermodynamic models. These predictions were in good agreement with experimentally determined values. In spite of the high reaction efficiency in the binary TB:TP system, the mixture of glycerol and sunflower oil (containing 97.1% triacylglycerol) yielded surprisingly a liquid/liquid phase split behavior even at high temperatures (>80 degrees C). This in contrast to thermodynamic model calculations suggested full miscibility in all proportions. These findings suggest that enhanced reaction efficiency in organic solvent also depends upon aspects other than the system homogeneity such as reduced viscosity, reduced mass transfer limitations, and the accessibility of the substrate to the active site of the enzyme.     

雪荷载作用下几字型钢日光温室极限承载力分析

雪灾是导致日光温室倒塌的主要原因之一。为探明几字型钢日光温室在雪荷载作用下的失稳机理,该研究采用有限单元法,以8 m跨日光温室为研究对象,模拟其在雪荷载（均匀分布雪荷载和非均匀分布雪荷载）作用下的失稳破坏过程,计算其极限承载力,并探究纵向系杆、初始几何缺陷、截面参数对极限承载力的影响。结果表明：对于净截面面积、上翼缘宽度、腹板高度和壁厚均相同的几字型钢和空心矩形钢管,几字型钢日光温室极限承载力稍高于空心矩形钢管日光温室极限承载力;相较于均匀分布雪荷载,日光温室拱架对非均匀分布雪荷载更为敏感,非均匀分布雪荷载作用下的极限承载力约是均匀分布雪荷载作用下的28%,在日光温室结构设计中,应重点考虑非均匀分布雪荷载工况;在非均匀分布雪荷载作用下,屋脊和后屋面支座处为危险截面,最先进入全截面屈服状态;纵向系杆的设置可有效抑制结构平面外变形,进而提高结构极限承载力,有纵向系杆约束条件下的结构极限承载力约是无纵向系杆约束条件下的1.25倍;该日光温室拱架对初始几何缺陷敏感度较低,当最大初始几何缺陷幅值从5 mm增加到20 mm时,极限承载力降低约2%;在几字型钢截面选取时,在满足规范要求宽厚比前提下,建议上翼缘宽度与翻边宽度之比控制在4.17左右,腹板高度与翻边宽度之比不大于9.25,下翼缘宽度与翻边宽度之比不大于1.7,上翼缘宽度与下翼缘宽度之比控制在3.33左右,腹板高度与下翼缘宽度之比控制在4.67左右。该研究结果可为开口冷弯薄壁型钢日光温室拱架抗雪设计提供参考。     

Kinetic modeling of reactions in heated monosaccharide-casein systems

In the present study, a kinetic model of the Maillard reaction occurring in heated monosaccharide-casein systems was proposed. Its parameters, the reaction rate constants, were estimated via multiresponse modeling. The determinant criterion was used as the statistical fit criterion instead of the familiar least squares to avoid statistical problems. The kinetic model was extensively tested by varying the reaction conditions. Different sugars (glucose, fructose, galactose, and tagatose) were studied regarding their effect on the reaction kinetics. This study has shown the power of multiresponse modeling for the unraveling of complicated reaction routes as occur in the Maillard reaction. The iterative process of proposing a model, confronting it with experiments, and criticizing the model was passed through four times to arrive at a model that was largely consistent with all results obtained. A striking difference was found between aldose and ketose sugars as suggested by the modeling results: not the ketoses themselves but only their reaction products were found to be reactive in the Maillard reaction.     

High-pressure liquid chromatographic determination of vitamin D3 in resins, oils, dry concentrates, and dry concentrates containing vitamin A.

A high-pressur liquid chromatographic (HPLC) procedure has been developed for the determination of vitamin D3 in resins, oils, dry concentrates, and dry concentrates containing vitamin A. Specificity of the method for vitamin D3 in the presence of isomers and other related constituents was shown by ultimate recovery of the vitamin D3 and the individual constituents and their characterization by other methods such as ultraviolet spectrophotometry. Precision and accuracy are within 2%, and as many as 20 determinations may be completed in a working day. Excellent agreement with the official AOAC biological assay was found. A comparison of the response of isomers of vitamin D3 by the HPLC method vs. other instrumental and chemical procedures shows HPLC to be the most specific method for determining the bioactive isomers.     

Short-term temporal changes of bare soil CO2 fluxes after tillage described by first-order decay models

To further understand the impact of tillage on carbon dioxide (CO₂) emission, we compare the performance of two conceptual models that describe CO₂ emission after tillage as a function of the non-tilled emission plus a correction resulting from the tillage disturbance. The models assume that C in the readily decomposable organic matter follows a first-order reaction kinetics equation as     and that soil C-CO₂ emission is proportional to the C decay rate in soil, where C _soil( t ) is the available labile soil C (g m⁻²) at any time ( t ) and k is the decay constant (time⁻¹). Two possible relationships are derived between non-tilled ( F _NT) and tilled ( F _T) soil fluxes:     (model 1) and     (model 2), where t is time after tillage. The difference between these two models comes from an assumption related to the k factor of labile C in the tilled plot and its similarity to the k factor of labile C in the non-till plot. Statistical fit of experimental data to conceptual models showed good agreement between predicted and observed CO₂ fluxes based on the index of agreement (d-index) and with model efficiency as large as 0.97. Comparisons reveal that model 2, where all C pools are assigned the same k factor, produces a better statistical fit than model 1. The advantage of this modelling approach is that temporal variability of tillage-induced emissions can be described by a simple analytical function that includes the non-tilled emission plus an exponential term, which is dependent upon tillage and environmental conditions.     

Solvent-free enzymatic preparation of feruloylated monoacylglycerols optimized by response surface methodology

The ability of immobilized lipase B from Candida antarctica (Novozym 435) to catalyze the direct esterification of glyceryl ferulate (FG) and oleic acid for feruloylated monoacylglycerols (FMAG) preparation in a solvent-free system was investigated. Enzyme screening and the effect of glycerol on the initial reaction rate of esterification were also investigated. Response surface methodology (RSM) was used to optimize the effects of the reaction temperature (55-65 degrees C), the enzyme load (8-14%; relative to the weight of total substrates), oleic acid/(FG + glycerol) (6:1-9:1; w/w), and the reaction time (1-2 h) on the conversion of FG and yield of FMAG. Validation of the RSM model was verified by the good agreement between the experimental and the predicted values of FG conversion and FMAG yield. The optimum preparation conditions were as follows: temperature, 60 degrees C; enzyme load, 8.2%; substrate ratio, 8.65:1 (oleic acid/(FG + glycerol), w/w); and reaction time, 1.8 h. Under these conditions, the conversion of FG and yield of FMAG are 96.7 +/- 1.0% and 87.6 +/- 1.2%, respectively.     

Study of Pyrene Adsorption on Two Brazilian Soils

This study investigated pyrene adsorption on two contrasting Brazilian soils: a Kandiudult and a Vertisol. It was found that the time taken to reach thermodynamic equilibrium depended on the soil type. The curves for different pyrene-to-soil mass ratios for Vertisol soil showed significant differences. This is probably related to the presence of 2:1 clays that may increase the adsorption of pyrene due to the resulting interlamellar space. The adsorption of pyrene on the Kandiudult showed, in general, good agreement with the Langmuir isotherm. In the case of the Vertisol, there was good agreement with the linear isotherm. The kinetic model that best explains the adsorption in Kandiudult was the pseudo second-order model. For the Vertisol, the Morris Weber model best explains the behavior of pyrene.     

Modification of casein by the lipid oxidation product malondialdehyde

The reaction of malondialdehyde with casein was studied in aqueous solution to evaluate the impact of this lipid oxidation product on food protein modification. By using multiresponse modeling, a kinetic model was developed for this reaction. The influence of temperature and pH on protein browning and malondialdehyde degradation was evaluated. The hypothesis that one malondialdehyde unit leads to the cross-linking of two casein-bound lysine residues was in accordance with the data. At higher malondialdehyde concentrations, a different reaction mechanism was operative, probably involving a dihydropyridine cross-link. The results obtained were compared with the reaction of casein with 2-oxopropanal, a well-studied alpha-dicarbonyl compound. The reaction of casein with 2-oxopropanal followed a different reaction pathway. Comparison of the degree of browning of casein by reaction with malondialdehyde and 2-oxopropanal showed a considerably higher degree of browning induced by malondialdehyde. This research has shown that kinetic modeling is a useful tool to unravel reaction mechanisms. Clearly, the contribution of lipid oxidation products, such as malondialdehyde, to protein modification (both in food and in vivo) can be substantial and needs to be taken into account in future studies.     

Simulation Model for Composting Cellulosic (Bagasse) Substrates

A dynamic model of aerobic composting with solid substrates was developed as a first step to predict the rate of decomposition of cellulosic materials. The model was based on heat and mass transfer principles and reaction kinetics of biological processes. The relations describing the rates of reaction and the degradability potential of the substrates were determined based on laboratory-scale experiments. The model was developed using a graphical software package, Stella II® (which was able to solve feedback loops encountered in actual composting processes.

The model was validated with temperature, oxygen distribution and mass degradation accompanying the composting of bagasse. Experimental setups consisted of 30 gallon drum reactors, continuously aerated. Temperature and oxygen in exhaust gases were monitored on an hourly basis and measurements of moisture content, pH and volatile solids were done on a weekly basis.

The data fit with the model was excellent for mass degraded and temperatures for the first 10 days. From day 10 to 14, the deviations between model predictions (as solved with Stella II®) and actual measurements did not exceed 2.6 percent. The concentrations of oxygen in outlet gases showed fair agreement between predicted and experimental values. Simulating the model with varying airflow rates showed that the maximum mass breakdown rates occurred for airflow rates of 0.12 kg dry air/(kg dry compost.hr) while maintaining the temperatures below 50°C, through a temperature feedback control strategy.     

Formation of pyrazines and a novel pyrrole in Maillard model systems of 1,3-dihydroxyacetone and 2-oxopropanal

Alkylpyrazines are a very important class of Maillard flavor compounds, but their mechanism of formation is complex and consists of different pathways. The model reaction of 20 different amino acids with 1,3-dihydroxyacetone, as a precursor of 2-oxopropanal, was studied by means of SPME-GC-MS to investigate the involvement of the amino acid side chain in the substitution pattern of the resulting pyrazines. 2,5-Dimethylpyrazine was quantitatively the most important pyrazine formed from all of the amino acids. The amino acid side chain is not involved in its formation. The substituents of other less abundant pyrazines resulted mainly from the incorporation of the Strecker aldehyde or aldol condensation products in the intermediate dihydropyrazine. The importance of different reaction mechanisms was evaluated, taking into account the pattern of pyrazines identified. In the solvent extracts of aqueous model reactions of 2-oxopropanal with amino acids, the main reaction product was not a pyrazine but a novel pyrrole. This pyrrole was identified as 2,5-diacetyl-3-methyl-1 H-pyrrole by means of spectral analysis, secured by chemical synthesis. A reaction mechanism for its formation was proposed and evaluated. The influence of various reaction conditions on the formation of 2,5-diacetyl-3-methyl-1 H-pyrrole and 2,5-dimethylpyrazine in the model reaction of alanine with 2-oxopropanal was studied. These results underscore the importance of the ratio of the different reagents and the presence of water in the resulting flavor formation in the Maillard reaction.     

Heterogeneous Activation of Persulfate by Graphene Oxide-TiO<Subscript>2</Subscript> Nanosheet for Oxidation of Diclofenac: Optimization by Central Composite Design

In this study, the performance of oxidation with actived persulfate (PS) by graphene oxide-TiO₂ nanosheet (GO-TiO₂) was investigated for diclofenac (DCF) removal, an anti-inflammatory analgesic being widely used in human health care and veterinary treatment. GO-TiO₂ containing oxygen functional groups is employed as an activator for the activation of PS used as the oxidizing agent. Modeling and optimization of the process were performed by central composite design (CCD) as a response surface methodology (RSM). The effects of various factors, including PS concentration, GO-TiO₂ amount, initial pH of DCF solution, and reaction time on DCF oxidation, were evaluated. When the estimated values of the full quadratic model obtained with CCD were compared with the actual experimental results, a strong agreement was obtained with an R² value of 0.9553. Besides, the model consistency was verified by analysis of variance (ANOVA) with a value of 20.17 of F value and P value of less than 0.05. After the optimization run, maximum DCF removal of 93.06% occurred with contact time of 14 min, pH of 5.54, PS concentration of 10 g/L, and 0.1 g of GO-TiO₂ as optimal variable values.     

Mechanisms of flavor release in chewing gum: cinnamaldehyde

Recently we reported that the release profile of cinnamaldehyde from a sugar-free chewing gum was correlated to the release of the sugar alcohol phase or was not in agreement with the log P model. The objective of this study was therefore to investigate mechanisms of cinnamaldehyde release from a sugar-free chewing gum; p-cresol (similar log P value) was also analyzed for comparison. Breath analysis of the chewing gum samples over an 8 min consumption period reported that the maximum concentration of cinnamaldehyde was 2- to 3-fold higher during the initial phase of mastication in comparison to the later phase, whereas the concentration of p-cresol was relatively constant over these two time periods. By contrast the release profile of cinnamaldehyde from a flavored gum base (no sugar alcohol phase) was constant over the 8 min consumption period and similar to the release of cresol from the flavored gum base. On the basis of tandem mass spectrometry, cinnamaldehyde was reported to react with sorbitol and generate hemiacetal reaction products that were not stable under slight alkaline conditions; it was suggested to revert back to free cinnamaldehyde and sugar alcohol in the oral cavity. The increased polarity of these transient cinnamaldehyde-sorbitol hemiacetal reaction products would result in a more rapid release rate of cinnamaldehyde than would be typically predicted based on the affinity of cinnamaldehyde for the gum base.