JOURNAL OF FOOD BIOCHEMISTRY, Issue 2 2008
VERONICA S. CHEDEA
ABSTRACT The kinetic patterns of pure soy lipoxygenase LOX-1 and crude or defatted soybean extracts containing LOX isoenzymes (LOX-1, LOX-2 and LOX-3) were studied by UV spectrometry at 234 and 280 nm, depending on their extraction and measurement conditions. Different pHs (from 6.0 to 9.0), corresponding to specific activation of LOX isoenzymes and the ratios of enzyme protein per substrate were used in order to evaluate the enzyme rates, as indicators of its affinity for substrate in different environments. The crude soy extract contained mainly LOX-1 activity (measured at 234 nm, at pH 9.0) and LOX-3, in an approximate ratio of 3:1. The LOX-2 activity was very low. The defatted extracts buffered at pH 6.8 and 7.1 showed a low LOX-1 and LOX 2 activity, but mostly LOX-3 activity (measured at 280 nm, at pH 7.1), with a mirror-type relation between the enzyme/substrate ratio and their enzymatic specific activity. The results suggest that defatting inhibits specifically the LOX-1 activity and indicate the possibility to modulate LOX activity by modifications of enzyme/substrate ratios and modifications of pH in the enzyme environment. PRACTICAL APPLICATIONS Because of the specific kinetic behaviors of the three different LOXs found in crude soy extracts involved in off-flavor generation, one can modulate the inhibition of these isoenzymes during soybean processing. Our experiments showed that pH variation could be a simple solution to inhibit the LOX isoenzymes, and therefore, the off-flavor generation. From the analytical point of view, the techniques described in this article are designed to be as simple as possible, and easy to use at large-scale level in food industry (food chain control). The idea is to minimize the number of separate chemical manipulations and, thereby, minimize errors. These studies can offer the background of further inhibition experiments in vitro using natural extracts. The LOX inhibition by natural antioxidants is related as well to pH and other factors influencing the enzyme's activity; this idea can be also valorized practically in the future. [source]

KINETICS AND HYDROLYSIS PARAMETERS OF TOTAL FRUCTOOLIGOSACCHARIDES OF ONION BULBS: EFFECTS OF TEMPERATURE REGIMES AND CULTIVARS

JOURNAL OF FOOD BIOCHEMISTRY, Issue 1 2007
NOUREDDINE BENKEBLIA
ABSTRACT This work studied the percentage of hydrolysis, observed hydrolysis rate constant (kobs), half-life time (t1/2) and kinetics of degradation of the total fructooligosaccharides (FOS) of three different onion bulb cultivars (Yellow Spanish, Red Amposta and Tenshin) kept during 6 months under three temperature regimes, 10, 15 and 20C. The percentage of hydrolysis of FOS was higher at 20C than at 10C and ranged from 47 to 58% at 10C, from 63 to 68% at 15C and from 74 to 83% at 20C. The kobs ranged from 27 × 10,3 to 36 × 10,3/week at 10C and from 41 × 10,3/week to 47 × 10,3/week at 15C, while at 20C, it was high and was about kobs 56 × 10,3/week.. The t1/2 decreased when temperature increased, and varied from 19.5 to 26.0 weeks at 10C, from 14.6 to 16.8 weeks at 15C and from 9.4 to 12.3 weeks at 20C, indicating that high degree of polymerization (DP) FOS have shorter lives than low DP FOS. Linear regression and kinetics of hydrolysis have shown that FOS hydrolysis is higher at 20C, with a coefficient of regression ranging between 0.87 and 0.99. Apparently, FOS hydrolysis is temperature independent, and storage time had more effect on the higher DP FOS than on the lower DP FOS. [source]

THIN-LAYER DRYING KINETICS OF SESAME HULLS UNDER FORCED CONVECTION AND OPEN SUN DRYING

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2007
MAJDI A. AL-MAHASNEH
ABSTRACT Sesame hulls are a useful by-product of the sesame processing industry. The sesame hulls are produced at a high moisture content (68% wet basis) and need further drying to prevent deterioration. In this study, both open sun drying (OSD) and forced convection drying (FCD) at 42, 55, and 76C and 1.2 m/s air velocity were investigated. Six common thin-layer drying models were fitted to the experimental data. Several statistical parameters were used to evaluate the performance of thin-layer drying models, including r2, x2, root mean square error (RMSE) and residuals. Sesame hull drying was found to take place completely in the falling rate region. The modified Page model was found to describe OSD data well, while the Wang and Singh model was the best model for describing FCD. Effective diffusivity was found to be 1.89 × 10 - 8 m2/s and 7.36 × 10 - 10 to 1.20 × 10 - 9 m2/s for OSD and FCD, respectively. Activation energy was also found to be 12.95 kJ/mol for FCD. [source]

THERMAL DEGRADATION KINETICS OF SUCROSE, GLUCOSE AND FRUCTOSE IN SUGARCANE MUST FOR BIOETHANOL PRODUCTION

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2006
J. NOLASCO JR.
ABSTRACT Thermal degradation of sugars contained in sugarcane must (21.5°Brix, pH 6.14) was evaluated at temperatures of 110, 120, 130 and 140C, using the thermal-death-time tube method, determining remaining sugars by high-pressure liquid chromatography. The study analyzed thermal degradation kinetics of both the total reducing sugars (TRS) and glucose and fructose individually. All curves of remaining sugars presented strong nonlinearity, with initial shoulder and final tail adjusted by an extended logistic model that was adapted for two species for TRS, and a simple logistic model for the monosaccharides. It was shown that rate constants are influenced by temperature according to two irreconcilable methods: the Arrhenius and the Bigelow methods. Obtained activation energies for fructose and glucose were quite coincident, 140.37 and 140.23 kJ/mol, respectively. Thermal resistance parameters were 21.59 and 21.61C, respectively. Comparison of the rate constants revealed that fructose degraded approximately 9,10 times faster than glucose. [source]

KINETICS OF ACRYLAMIDE FORMATION DURING TRADITIONAL AND VACUUM FRYING OF POTATO CHIPS

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2005
CLAUDIA GRANDA
ABSTRACT Acrylamide is considered a carcinogen in animals and a possible carcinogen in humans. It has been found in starch-rich foods cooked at high temperatures. Vacuum frying (10 Torr) was investigated as a possible alternative to reduce acrylamide formation in potato chips. The cultivar Atlantic was used to determine the kinetics of acrylamide formation during traditional and vacuum frying at different temperatures. There was a 94% decrease in acrylamide content when potatoes were fried to the same final moisture content (1.5% ± 0.3% w.b.) under vacuum compared to those fried under atmospheric conditions. Acrylamide accumulation under vacuum frying was modeled using first-order kinetics (during traditional frying, the logistic kinetic model was used). The behavior of the kinetics of acrylamide content in potato chips fried under the two processes was different mainly because of the different temperatures used. During traditional frying, higher temperatures are used (150 to 180C) and acrylamide after some time is produced but starts degrading, producing a constant level of acrylamide content at longer times. During vacuum frying (10 Torr), acrylamide increased exponentially (but at lower levels) for all frying times. [source]

KINETICS of QUALITY CHANGE DURING COOKING and FRYING of POTATOES: PART I. TEXTURE

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 4 2003
F. NOURIAN
ABSTRACT Kinetics of texture change during cooking and frying of potatoes were evaluated in this study. Potatoes were cut into cylinders (diameter × height: 20 mm × 20 mm for cooking, and 10 mm × 20 mm for frying) and cooked in a temperature controlled water bath at 80,100C or fried in a commercial fryer at 160,190C for selected times. the cooked samples were water cooled while the fried samples were air cooled immediately after the treatment. Test samples were then subjected to a single cycle compression test in a computer interfaced Universal Testing Machine and three textural properties (hardness, stiffness and firmness) were derived from the resulting force-deformation curves. Texture parameters of cooked potatoes decreased with progress of cooking time and the rate of texture changes associated with each temperature was found to be consistent with two pseudo first-order kinetic mechanisms, one more rapid than the other. Textural values of fried potatoes were found to increase with frying time and also followed a first order kinetic model. Temperature sensitivity of rate constants was adequately described by Arrhenius and z-value models. [source]

APPLICATION OF WLF AND ARRHENIUS KINETICS TO RHEOLOGY OF SELECTED DARK-COLORED HONEY

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2001
KAMAL I.M. AL-MALAH
ABSTRACT The rheological properties of Common Black Horehound, Globe Thistle, and Squill types of dark-colored Jordanian honey were examined. The types of honey used were identified via assessing the source of nectar using pollen analysis (Melissopalynology). The apparent viscosity, ,, was measured as a function of the shear rate, ,. In addition, the apparent viscosity was measured, at constant shear rate (6.12 s,1), as a function of shearing time. Newton's law of viscosity (i.e., ,=,,) was found to adequately (R2, 0.99) describe the flow behavior of honey samples. The apparent viscosity was found to decrease with temperature, and the temperature dependence of viscosity was contrasted versus both Arrhenius model (,=,oeEa/RT) and WLF model (,/,G= 10 (C1(T,T)/C2+(T,TG))). Although Arrhenius kinetics may fit the viscosity versus temperature data for the examined types of honey, nevertheless, it gives a relatively high value of activation energy that is quite comparable with, if not even larger than, that of a typical chemical reaction. On the other hand, WLF-model was found to adequately describe the data while at the same time it gives quite reasonable values of both TG and ,G, which are in agreement with those cited in literature. [source]

KINETICS OF OSMOTIC DEHYDRATION IN ORANGE AND MANDARIN PEELS

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 4 2001
M. CHÁFER
ABSTRACT The nutritional and health properties of some citrus peel components such as pectin, flavonoids, carotenoids or limonene make interesting developing processing methods to obtain peel stable products, maintaining its quality attributes, increasing its sweetness and improving its sensory acceptability. In this sense, osmotic dehydration represents a useful alternative by using sugar solutions at mild temperature. Kinetics of osmotic treatments of orange and mandarin peels carried out at atmospheric pressure and by applying a vacuum pulse at the beginning of the process were analysed at 30, 40 and 50C, in 65 °Brix sucrose, 55 °Brix glucose and 60 °Brix rectified grape must. Vacuum pulse greatly affected mass transfer behavior of peels due to the greatly porous structure of albedo. So, PVOD treatments greatly accelerate the changes in the product composition in line with an increase in the peel sample thickness. In osmotic processes at atmospheric pressure, sample impregnation occurs coupled with osmotic process, but much longer treatments are required to achieve a reasonable concentration degree which assures sample stability. Low viscosity osmotic solutions seems recommendable in order to promote both diffusional and hydrodynamic transport, in vacuum pulsed pretreatments at mild temperatures. [source]

KINETICS OF HYDROXYMETHYLFURFURAL ACCUMULATION AND COLOR CHANGE IN HONEY DURING STORAGE IN RELATION TO MOISTURE CONTENT

JOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 1 2009
L. BULUT
ABSTRACT Quality reduction in honey during storage is indicated by hydroxymethylfurfural (HMF) accumulation and darkening of color. The effects of moisture content and temperature on HMF accumulation and color change in honey during storage were investigated. HMF accumulation and color change followed first- and zero-order reaction kinetics, respectively. The moisture content affected the rate of the two degradation reactions depending on the storage temperature. Reduction in moisture content caused an increase in rate constant for HMF accumulation at 20 and 30C, but there was no significant effect of moisture content at 40C. Rate constants for change in lightness and total color change values increased with increasing moisture content at 20 and 30C. The highest rate constant for change in color values was obtained at a moisture content of 18% at 40C. PRACTICAL APPLICATIONS Hydroxymethylfurfural accumulation and color change are two major quality degradations in honey during storage. This study shows that the rates of these two degradations are dependent on moisture content of honey. In addition, effect of moisture content on the rates of reactions was dependent on temperature of storage. Therefore, producers need to consider the effects of both moisture content and storage temperature in reducing quality loss in honey during storage. [source]

EFFECT OF OSMOTIC TREATMENT WITH CONCENTRATED SUGAR AND SALT SOLUTIONS ON KINETICS AND COLOR IN VACUUM CONTACT DRYING

JOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 6 2007
S.M.A. RAHMAN
ABSTRACT An experimental study of osmotic dehydration (OD) of selected heat-sensitive products was carried out in a laboratory-scale vacuum contact dryer. Cubes of potato and apple were examined as model heat-sensitive objects. Experiments were conducted at different conduction heat input levels with wall temperatures in the range 35,45C under vacuum and also in pure vacuum without any external heat input. Detailed investigations were carried out of OD on drying performance, product temperature and color of the dried product. PRACTICAL APPLICATIONS Osmotic treatment of potato and apple samples using concentrated sugar solution shows better osmotic dehydration as well as drying rate in a vacuum contact drying system. This information may help to select the osmotic agent in any industrial application for faster drying rate in vacuum contact drying specially for food products. Moreover this work shows the analysis to find out the starting point of precipitation of osmotic agent inside the products in terms of drying time, temperature and moisture content. This information will be helpful for critical analysis in osmotic dehydration technique which in turns may help for optimum design. [source]

DEGRADATION KINETICS OF ANTHOCYANIN IN ETHANOLIC SOLUTIONS

JOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 5 2006
KUO-CHAN TSENG
ABSTRACT The objective of this study was to investigate the degradation kinetics of anthocyanin in ethanolic model solutions simulating wine and liqueur in aging or long-term storage. Malvidin-3-glucoside, as the predominant anthocyanin in many cultivars of grape, was chosen to represent anthocyanins. The results from high performance liquid chromatography analysis show that the disappearance of malvidin-3-glucoside follows apparent first-order kinetics, and accelerates with the increase in ethanol concentration. The Ea values were found to be 22.80, 24.45, 24.35 and 22.75 kcal/mole at 0, 10, 30 and 50% ethanol concentrations, respectively. We propose that the decreased stability of anthocyanin at an elevated ethanol concentration is a result of a decreased extent of self-association in the solution. [source]

THERMAL INACTIVATION KINETICS OF ALKALINE PHOSPHATASE IN BUFFER AND MILK

JOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 3 2006
S. FADILO
ABSTRACT A detailed kinetic study on the thermal inactivation of alkaline phosphatase (ALP) added into buffer and pasteurized milk and for ALP naturally present in raw cow's milk has been performed. Kinetic parameters (rate constant, k; decimal reduction time, D; activation energy, Ea; and z value) were evaluated based on the first-order rate model at 50,80C. The temperature sensitivity of the kinetic parameters was evaluated considering the Arrhenius-type Ea model. All kinetic behaviors were well described by the first-order model (r2 > 0.91). The D values increased with increasing temperature. Higher temperatures resulted in higher rates of enzyme inactivation as indicated by lower D values and higher k values. There are significant differences (P < 0.01) among the D values for ALP in buffer and milk at treated temperatures. The rate of enzyme inactivation was much more rapid in buffer than in pasteurized milk. The evaluated Ea values for ALP added into the buffer and pasteurized milk, and for ALP naturally present in raw milk were 97.2, 149.9 and 207.8 kJ/mol, respectively. The inactivation kinetics of ALP during heat treatment was found to be dependent on the composition of the medium, and the time and temperature of the heat treatment. [source]

GROWTH KINETICS OF CLOSTRIDIUM PERFRINGENS IN COOKED BEEF,

JOURNAL OF FOOD SAFETY, Issue 2 2003
LIHAN HUANG
ABSTRACT The objective of this work was to investigate the growth kinetics of a three-strain cocktail of Clostridium perfringens in cooked beef. The study was conducted by growing the heat-activated spores in ground beef under isothermal conditions between 17,50C. A four-parameter Gompertz equation was used as a primary model to fit the growth curves along with a modified Ratkowsky model to analyze the temperature dependence of the bacterial growth. Results indicated that the Gompertz model could accurately describe the growth of C. perfringens in cooked beef. The estimated theoretical minimum, optimum, and maximum growth temperatures of this organism in cooked beef were 9.8, 47.1, and 50.8C, respectively. A linear relationship between the durations of the lag and exponential phases of growth curves was observed in this study. Such a linear relationship can be used to generate a linear isothermal growth curve complete with the lag, exponential, and stationary phases without complex mathematical computation. The kinetic models and growth parameters obtained from this study potentially can be applied to the food industry to design appropriate cooling schedules and estimate the growth of C. perfringens in thermally processed beef products under temperature abuse conditions. [source]

VARIATIONS IN COMPOSITION, PETROLEUM POTENTIAL AND KINETICS OF ORDOVICIAN , MIOCENE TYPE I AND TYPE I-II SOURCE ROCKS (OIL SHALES): IMPLICATIONS FOR HYDROCARBON GENERATION CHARACTERISTICS

JOURNAL OF PETROLEUM GEOLOGY, Issue 1 2010
H. I. Petersen
Lacustrine and marine oil shales with Type I and Type I-II kerogen constitute significant petroleum source rocks around the world. Contrary to common belief, such rocks show considerable compositional variability which influences their hydrocarbon generation characteristics. A global set of 23 Ordovician , Miocene freshwater and brackish water lacustrine and marine oil shales has been studied with regard to their organic composition, petroleum potential and generation kinetics. In addition their petroleum generation characteristics have been modelled. The oil shales can be classified as lacosite, torbanite, tasmanite and kukersite. They are thermally immature. Most of the shales contain >10 wt% TOC and the highest sulphur contents are recorded in the brackish water and marine oil shales. The kerogen is sapropelic and is principally composed of a complex of algal-derived organic matter in the form of: (i) telalginite (Botryococcus-, Prasinophyte- (Tasmanites?) or Gloeocapsomorpha-type); (ii) lamalginite (laminated, filamentous or network structure derived from Pediastrum- or Tetraedron-type algae, from dinoflagellate/acritarch cysts or from thin-walled Prasinophyte-type algae); (iii) fluorescing amorphous organic matter (AOM) and (iv) liptodetrinite. High atomic H/C ratios reflect the hydrogen-rich Type I and Type I-II kerogen, and Hydrogen Index values generally >300 mg HC/g TOC and reaching nearly 800 mg HC/g TOC emphasise the oil-prone nature of the oil shales. The kerogen type and source rock quality appear not to be related to age, depositional environment or oil shale type. Therefore, a unique, global activation energy (Ea) distribution and frequency factor (A) for these source rocks cannot be expected. The differences in kerogen composition result in considerable variations in Ea -distributions and A-factors. Generation modelling using custom kinetics and the known subsidence history of the Malay-Cho Thu Basin (Gulf of Thailand/South China Sea), combined with established and hypothetical temperature histories, show that the oil shales decompose at different rates during maturation. At a maximum temperature of ,120°C reached during burial, only limited kerogen conversion has taken place. However, oil shales characterised by broader Ea -distributions with low Ea -values (and a single approximated A-factor) show increased decomposition rates. Where more deeply buried (maximum temperature ,150°C), some of the brackish water and marine oil shales have realised the major part of their generation potential, whereas the freshwater oil shales and other brackish water oil shales are only ,30,40% converted. At still higher temperatures between ,165°C and 180°C all oil shales reach 90% conversion. Most hydrocarbons from these source rocks will be generated within narrow oil windows (,20,80% kerogen conversion). Although the brackish water and marine oil shales appear to decompose faster than the freshwater oil shales, this suggests that with increasing heatflow the influence of kerogen heterogeneity on modelling of hydrocarbon generation declines. It may thus be critical to understand the organic facies of Type I and Type I-II source rocks, particularly in basins with moderate heatflows and restricted burial depths. Measurement of custom kinetics is recommended, if possible, to increase the accuracy of any computed hydrocarbon generation models. [source]

KINETICS OF HYDROCARBON GAS GENERATION FROM MARINE KEROGEN AND OIL: IMPLICATIONS FOR THE ORIGIN OF NATURAL GASES IN THE HETIANHE GASFIELD, TARIM BASIN, NW CHINA

JOURNAL OF PETROLEUM GEOLOGY, Issue 4 2007
Yunpeng Wang
In this paper we derive kinetic parameters for the generation of gaseous hydrocarbons (C1-5) and methane (C1) from closed-system laboratory pyrolysis of selected samples of marine kerogen and oil from the SW Tarim Basin. The activation energy distributions for the generation of both C1-5 (Ea = 59-72kcal, A = 1.0×1014 s,1) and C1 (Ea = 61-78kcal, A = 6.06×1014 s,1) hydrocarbons from the marine oil are narrower than those for the generation of these hydrocarbons from marine kerogen (Ea = 50-74kcal, A = 1.0×1014 s,1 for C1-5; and Ea = 48-72kcal, A=3.9×1013 s,1 for C1, respectively). Using these kinetic parameters, both the yields and timings of C1-5 and C1 hydrocarbons generated from Cambrian source rocks and from in-reservoir cracking of oil in Ordovician strata were predicted for selected wells along a north-south profile in the SW of the basin. Thermodynamic conditions for the cracking of oil and kerogen were modelled within the context of the geological framework. It is suggested that marine kerogen began to crack at temperatures of around 120°C (or 0.8 %Ro) and entered the gas window at 138°C (or 1.05 %Ro); whereas the marine oil began to crack at about 140 °C (or 1.1 %Ro) and entered the gas window at 158 °C (or 1.6%Ro). The main geological controls identified for gas accumulations in the Bachu Arch (Southwest Depression, SW Tarim Basin) include the remaining gas potential following Caledonian uplift; oil trapping and preservation in basal Ordovician strata; the extent of breaching of Ordovician reservoirs; and whether reservoir burial depths are sufficiently deep for oil cracking to have occurred. In the Maigaiti Slope and Southwest Depression, the timing of gas generation was later than that in the Bachu Arch, with much higher yields and generation rates, and hence better prospects for gas exploration. It appears from the gas generation kinetics that the primary source for the gases in the Hetianhe gasfield was the Southwest Depression. [source]

KINETICS OF NITRATE, AMMONIUM, AND UREA UPTAKE BY FOUR INTERTIDAL SEAWEEDS FROM NEW ZEALAND,

JOURNAL OF PHYCOLOGY, Issue 3 2004
Julia C. Phillips
The competitive ability for N uptake by four intertidal seaweeds, Stictosiphonia arbuscula (Harvey) King et Puttock, Apophlaea lyallii Hook. f. et Harvey, Scytothamnus australis Hook. f. et Harvey, and Xiphophora gladiata (Labillardière) Montagne ex Harvey, from New Zealand is described by the uptake kinetics for NO3,, NH4+, and urea. This is the first study to report uptake kinetics for N uptake by a range of southern hemisphere intertidal seaweeds in relation to season and zonation. Species growing at the highest shore positions had higher NO3, and urea uptake at both high and low concentrations and had unsaturable NH4+ uptake in both summer and winter. Although there was evidence of some feedback inhibition of Vmax for NO3, uptake by Stictosiphonia arbuscula growing at the lower vertical limits of its range, rates were high compared with species growing lower on the shore. Our results highlight the superior competitive ability for N uptake of certain high intertidal seaweeds, and consistent with our previous findings we can conclude that intertidal seaweeds in southeast New Zealand are adapted to maximizing N acquisition in a potentially N-limiting environment. [source]

Part 1: Kinetics and mechanism of the crystallization process

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2006
Oleg D. Linnikov
Abstract The kinetics of spontaneous crystallization of sodium chloride from aqueous-ethanol solutions were studied. During the crystallization the electrical conductance and optical transmission of the supersaturated solutions were measured automatically. For monitoring of the total surface of growing potassium chloride crystals at the crystallization the turbidimetric method was used. The growth rate and activation energy were determined. The crystal growth rate was proportional to supersaturation. When the volume fraction of ethanol in solution increased from 14.85 to 29.72%, the activation energy of the growth process did not change and was about 50 kJ· mol -1. Aggregation of the crystals was found. The aggregation kinetics of the crystals may be described approximately by the famous Smoluchowski equation for coagulation of colloidal particles. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Kinetics and Mechanism of Ni(II) Chelation in Model and Real Solutions of Xylem Sap of Quercus ilex

ELECTROANALYSIS, Issue 22 2007
Margarida, Maria Correia, Santos
Abstract The kinetics of formation and dissociation of Ni(II) complexes with oxalic and citric acids was studied by cyclic voltammetry in model solutions of xylem sap of Q. ilex (the dominant tree growing on serpentine soils of Northeast Portugal) using representative concentrations, pH and ionic strength. The role of magnesium on complex formation was analyzed from solutions where Mg is present at concentration levels found in the xylem sap of Q. ilex growing on both nonserpentine and serpentine soils. Kinetics studies were also done in diluted solutions of real xylem sap samples, spiked with increasing amounts of magnesium. The values obtained for the apparent rate constants were those anticipated by the proposed model. To test the validity of the methodology and mechanisms, formation rate constants, kf (M,1 s,1) of Ni(II) complexes with citrate and oxalate were evaluated that compare with the values from Eigen mechanism. [source]

Probing Biomolecular Interactions at Conductive and Semiconductive Surfaces by Impedance Spectroscopy: Routes to Impedimetric Immunosensors, DNA-Sensors, and Enzyme Biosensors

ELECTROANALYSIS, Issue 11 2003
Eugenii Katz
Abstract Impedance spectroscopy is a rapidly developing electrochemical technique for the characterization of biomaterial-functionalized electrodes and biocatalytic transformations at electrode surfaces, and specifically for the transduction of biosensing events at electrodes or field-effect transistor devices. The immobilization of biomaterials, e.g., enzymes, antigens/antibodies or DNA on electrodes or semiconductor surfaces alters the capacitance and interfacial electron transfer resistance of the conductive or semiconductive electrodes. Impedance spectroscopy allows analysis of interfacial changes originating from biorecognition events at electrode surfaces. Kinetics and mechanisms of electron transfer processes corresponding to biocatalytic reactions occurring at modified electrodes can be also derived from Faradaic impedance spectroscopy. Different immunosensors that use impedance measurements for the transduction of antigen-antibody complex formation on electronic transducers were developed. Similarly, DNA biosensors using impedance measurements as readout signals were developed. Amplified detection of the analyte DNA using Faradaic impedance spectroscopy was accomplished by the coupling of functionalized liposomes or by the association of biocatalytic conjugates to the sensing interface providing biocatalyzed precipitation of an insoluble product on the electrodes. The amplified detections of viral DNA and single-base mismatches in DNA were accomplished by similar methods. The changes of interfacial features of gate surfaces of field-effect transistors (FET) upon the formation of antigen-antibody complexes or assembly of protein arrays were probed by impedance measurements and specifically by transconductance measurements. Impedance spectroscopy was also applied to characterize enzyme-based biosensors. The reconstitution of apo-enzymes on cofactor-functionalized electrodes and the formation of cofactor-enzyme affinity complexes on electrodes were probed by Faradaic impedance spectroscopy. Also biocatalyzed reactions occurring on electrode surfaces were analyzed by impedance spectroscopy. The theoretical background of the different methods and their practical applications in analytical procedures were outlined in this article. [source]

Electron Transfer Kinetics of Ferrocene at Microcrystalline Boron-Doped Diamond Electrodes: Effect of Solvent and Electrolyte

ELECTROANALYSIS, Issue 4 2003
Shannon Haymond
Abstract Cyclic voltammetric measurements were made using well-characterized microcrystalline boron-doped diamond thin-film electrodes to test the material's responsiveness for ferrocene as a function of scan rate, solvent, and electrolyte composition. Apparent heterogeneous electron transfer rate constants, k°app, of 0.042±0.015, 0.048±0.015, and 0.008±0.002,cm/s were observed in 0.1,M NaClO4/CH3CN, 0.1,M TBAClO4/CH3CN, and 0.1M TBAClO4/CH2Cl2, respectively. These rate constants, obtained using electrodes without any type of pretreatment, are similar to those observed for freshly polished glassy carbon. The results demonstrate that boron-doped diamond is a viable material for the electrochemical analysis of nonaqueous analytes. [source]

Optimization of Operating Temperature for Continuous Immobilized Glucose Isomerase Reactor with Pseudo Linear Kinetics

ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 5 2004
N.M. Faqir
Abstract In this work, the optimal operating temperature for the enzymatic isomerization of glucose to fructose using a continuous immobilized glucose isomerase packed bed reactor is studied. This optimization problem describing the performance of such reactor is based on reversible pseudo linear kinetics and is expressed in terms of a recycle ratio. The thermal deactivation of the enzyme as well as the substrate protection during the reactor operation is considered. The formulation of the problem is expressed in terms of maximization of the productivity of fructose. This constrained nonlinear optimization problem is solved using the disjoint policy of the calculus of variations. Accordingly, this method of solution transforms the nonlinear optimization problem into a system of two coupled nonlinear ordinary differential equations (ODEs) of the initial value type, one equation for the operating temperature profile and the other one for the enzyme activity. The ODE for the operating temperature profile is dependent on the recycle ratio, operating time period, and the reactor residence time as well as the kinetics of the reaction and enzyme deactivation. The optimal initial operating temperature is selected by solving the ODEs system by maximizing the fructose productivity. This results into an unconstrained one-dimensional optimization problem with simple bounds on the operating temperature. Depending on the limits of the recycle ratio, which represents either a plug flow or a mixed flow reactor, it is found that the optimal temperature of operation is characterized by an increasing temperature profile. For higher residence time and low operating periods the residual enzyme activity in the mixed flow reactor is higher than that for the plug flow reactor, which in turn allows the mixed flow reactor to operate at lower temperature than that of the plug flow reactor. At long operating times and short residence time, the operating temperature profiles are almost the same for both reactors. This could be attributed to the effect of substrate protection on the enzyme stability, which is almost the same for both reactors. Improvement in the fructose productivity for both types of reactors is achieved when compared to the constant optimum temperature of operation. The improvement in the fructose productivity for the plug flow reactor is significant in comparison with the mixed flow reactor. [source]

Sulphur-containing compounds in food plants: Kinetics, biological activity, and mechanisms of action

ENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 3 2009
Evelyn Lamy
No abstract is available for this article. [source]

Kinetics of cadmium accumulation in periphyton under freshwater conditions,

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2009
Philippe Bradac
Abstract The aim of the present study was to investigate the kinetics of cadmium (Cd) accumulation (total and intracellular) in periphyton under freshwater conditions in a short-term microcosm experiment. Periphyton was precolonized in artificial flow-through channels supplied with natural freshwater and then exposed for 26.4 h to nominal Cd concentrations of 5 and 20 nM added to natural freshwater. Labile Cd in water determined with diffusion gradient in thin films was 60 to 69% of total dissolved Cd in the exposure channels and 11% in the control channel. Intracellular Cd concentrations in periphyton increased rapidly and linearly during the first 71 min. Initial intracellular uptake rates were 0.05 and 0.18 nmol of Cd/g of dry weight × min in the 5 nM and 20 nM exposures, respectively. The subsequent intracellular uptake was slower, approaching steady state at the end of Cd exposure. Uptake kinetics of Cd was slower when compared to experiments with planktonic algal cultures, probably due to diffusion limitations. Intracellular Cd uptake during the entire exposure was modeled with a nonlinear, one-compartment model from which uptake and clearance rate constants, as well as bioconcentration factors, were obtained. The release of Cd from periphyton after the end of Cd exposure was slow when compared to the initial uptake rates. [source]

Kinetics of the reduction of chromium(VI) by vitamin C

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2005
Xiang-Rong Xu
Abstract The kinetics of the reduction of Cr(VI) to Cr(III) by vitamin C was studied using potassium dichromate solution as the model pollutant. Effects of the concentration of vitamin C, pH, temperature, and irradiation on the reduction of Cr(VI) were examined. The kinetics of Cr(VI) reduction by vitamin C can be described as - d[Cr(VI)]/dt = 0.0156 (,M s,1).[Cr(VI)][vitamin C] (pH 5), where dt is the differential function (d) of time (t). The activation entropy (,S,) and enthalpy (,H,) are 42.4 kJ mol,1 and -71.0 J mol,1 K,1, respectively, and the activation energy at 298 K is 63.5 kJ mol,1. The advantages of vitamin C as a reductant are as follows: It is an important biological reductant in humans and animals, and it is not toxic. Toxic Cr(VI) can be reduced by vitamin C not only in acidic conditions but also in alkaline solutions (pH 9); furthermore, the reduction was shown to occur both under the irradiation and in the dark. The present results suggest that vitamin C could be used effectively in the remediation of Cr(VI)-contaminated soil and groundwater in a wide range of pH, with or without sunlight. [source]

Kinetics of toluene sorption and desorption in Ca- and Cu-montmorillonites investigated with Fourier transform infrared spectroscopy under two different levels of humidity

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2004
Yang-Hsin Shih
Abstract Clays in soils or groundwater aquifer materials play roles in the sorption of organic pollutants. The intrinsic sorption kinetics of toluene in dry and humid clay films was investigated by tracking the change of infrared absorbance. Under the humid condition, similar toluene-sorbed intensities were found in Ca- and Cu-montmorillonites. However, a higher intensity of sorbed toluene was found in the Cu-form than in the Ca-form under the dry condition, which indicates a stronger interaction occurring in dry Cu-montmorillonite. The general time scale of sorption of toluene on clays is around 100 s. In both forms of montmorillonite, some portion of toluene was desorbed at an extremely slow rate under the dry condition. Some newly identified peaks were persistent against desorption from montmorillonites, suggesting the existence of irreversibly sorbed species and the possibility of toluene transformation occurring in clay systems. [source]

Oral bioavailability and toxicokinetics of 3,3,,4,4,,5-pentachlorobiphenyl in northern leopard frogs, Rana pipiens

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2000
Yue-wern Huang
Abstract This study is the first report on oral bioavailability, whole-body elimination, and distribution of a specific polychlorinated biphenyl (PCB) congener on an amphibian species, northern leopard frogs. Each frog was orally dosed once with either 0.35 or 5.0 mg/kg PCB 126 (based on frog wet wt), including tracer 14C-PCB 126 (3,,4,,5,-phenyl-ring- 14C) by force feeding it a cricket injected with the PCB. We found no statistical difference (t = 0.917, df = 5, p = 0.401) in the average 48-h oral bioavailabilities of 0.35- and 5.0-mg/kg dosage groups, which were 84.6 ± 5.8% (mean ± SE, n = 4) and 90.9 ± 1.5% (n = 3), respectively. Statistical analysis indicated that time was the only independent variable affecting the retention of whole-body 14C content. Kinetics were apparently first order because elimination rate was independent of dose. Assuming a single pool and one elimination rate, the t1/2 value for whole-body elimination of PCB-derived 14C was 763 d. Liver, fat bodies (corpora adiposa), carcass (head, bone, cartilage materials, and residues of other tissues), skin, and muscle were the major organs for PCB 126 retention in both dosage groups. The concentrations of 14C residue in fat bodies were relatively constant throughout the experiment. However, total residues in fat bodies declined throughout the experiment in both dosage groups in correlation with declining masses of fat bodies. Gonad, kidney, stomach, intestine, and a tissue pool including esophagus, lung, spleen, heart, and cloacal materials each accumulated <1% of the initial total 14C residue. The egg follicles in 19 females contained 1 to 23% of the initial total 14C residue, with an average of 10.0 ± 9.2% (mean ± SE, n = 19). [source]

Metabolism of cholesterol ester of apolipoprotein B100-containing lipoproteins in dogs: evidence for disregarding cholesterol ester transfer

EUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 8 2004
E. Bailhache
Abstract Background, It has been shown that dogs exhibit no cholesterol ester transfer protein (CETP) activity in vitro, in contrast to humans. The aim of our study was to determine modalities of in vivo plasma cholesterol ester turnover in this species, using a kinetic approach with stable isotopes. Materials and methods, Kinetics of very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) were studied in seven adult male Beagle dogs using a dual isotope approach through endogenous labelling of both their cholesterol moiety and their protein moiety. A primed constant infusion of both [1,213C]acetate and [5,5,5- 2H3]leucine enabled us to obtain measurable deuterium enrichments by gas chromatography-mass spectrometry for plasma leucine and apoB100, as well as measurable 13C enrichment by gas chromatography-combustion-isotopic ratio mass spectrometry for unesterified cholesterol and cholesterol ester in the VLDL and LDL. Two identical multicompartmental models (SAAM II) were used together for the analysis of tracer kinetics' data of proteins and cholesterol. Results, Characterization of the apoB100-containing lipoprotein cholesterol ester model allowed determination of kinetic parameters of VLDL and LDL cholesterol ester metabolism. We succeeded in modelling VLDL and LDL cholesterol ester metabolism and apoB100 metabolism simultaneously. Fractional catabolic rate (FCR) of apoB100 and CE had the same values. Introducing cholesterol ester transfer between lipoproteins in the model did not significantly improve the fit. Total VLDL FCR was 2·97 ± 01·47 h,1. Approximately one-quarter corresponded to the direct removal of VLDL (0·81 ± 00·34 h,1) and the remaining three-quarters corresponded to the fraction of VLDL converted to LDL, which represented a conversion of VLDL into LDL of 2·16 ± 01·16 h,1. Low-density lipoproteins were produced exclusively from VLDL conversion and were then removed (0·031 ± 0·004 h,1) from plasma. Conclusion, These kinetic data showed that VLDL cholesterol ester and LDL cholesterol ester metabolism followed VLDL and LDL apoB100 metabolism, and that consequently there is no in vivo transfer of cholesterol ester in dogs. [source]

Kinetics of stem cell engraftment and clearance of leukaemia cells after allogeneic stem cell transplantation with reduced intensity conditioning in chronic myeloid leukaemia

EUROPEAN JOURNAL OF HAEMATOLOGY, Issue 1 2002
Karl-Anton Kreuzer
Abstract: It is hypothesised that an effective graft-vs.-leukaemia reaction contributes substantially to the therapeutic effect of reduced intensity conditioning stem cell transplantation in chronic myeloid leukaemia. However, kinetic data on eradication of leukaemia cells and stem cell engraftement which could support this assumption are lacking . Thus, we investigated bcr/abl fusion transcripts and haematopoietic chimerism in 14 patients undergoing such a transplantation protocol. Ten of them obtained a complete molecular remission, and two patients achieved haematologic remissions but remained bcr/abl positive. Weekly determinations of bcr/abl transcript numbers by qualitative and quantitative polymerase chain reaction and donor chimerism revealed that 10 responders cleared bcr/abl positive cells from the peripheral blood within a median of 9 wk (range 3,22 wk). The close relation (P = 0.0075) between the firstoccurrence of graft-vs.-host disease and the complete clearance ofbcr/abl positive blood cells argues in favour of an effective graft-vs.-leukaemia reaction. [source]

Kinetics of CD8+ effector T cell responses and induced CD4+ regulatory T cell responses during Friend retrovirus infection

EUROPEAN JOURNAL OF IMMUNOLOGY, Issue 10 2006
Gennadiy Zelinskyy
Abstract Cytolytic CD8+ T cells are critical for the control of acute Friend virus (FV) infection yet they fail to completely eliminate the virus during chronic infection because they are functionally impaired by regulatory T cells (Treg). We performed a kinetic analysis of T cell responses during FV infection to determine when dysfunction of CD8+ T cells and suppressive activity of CD4+ regulatory T cells develops. At 1,week post infection, virus-specific CD8+ T cells with effector phenotype and cytolytic potential expanded. Peak expansion was found at 12,days post infection, correlating with peak viral loads. After 2,weeks when viral loads dropped, numbers of activated CD8+ T cells started to decline. However, a population of virus-specific CD8+ T cells with effector phenotype was still detectable subsequently, but these cells had lost their ability to produce granzymes and to degranulate cytotoxic molecules. Contemporaneous with the development of CD8+ T cell dysfunction, different CD4+ T cell populations expressing cell surface markers for Treg and the Treg-associated transcription factor Foxp3 expanded. Transfer as well as depletion experiments indicated that regulatory CD4+ cells developed during the second week of FV infection and subsequently suppressed CD8+ T cell functions, which was associated with impaired virus clearance. [source]

Kinetics of costimulatory molecule expression by T cells and dendritic cells during the induction of tolerance versus immunity in vivo

EUROPEAN JOURNAL OF IMMUNOLOGY, Issue 4 2005
Kristin Hochweller
Abstract Steady-state dendritic cells (DC) present peptide-MHC complexes to T cells in a tolerogenic manner, presumably because of deficient costimulation. However, it is clear that the path to tolerance involves initial T cell activation, suggesting that the deficit may lie in late-acting costimulatory molecules. With this in mind we have investigated the kinetics of expression of several costimulatory pairs on DC and OVA-reactive T cells after i.v. injection of mice with peptide and LPS (immunity), or peptide alone (tolerance). We find that T cells up-regulate CD154, OX40, RANKL and PD-1 whether they are destined for tolerance or immunity, although there are some differences in the levels and length of expression. In contrast, when analyzing DC, we found that up-regulation of CD80, CD86, CD40, RANK and PDL-1 occurred only when peptide was co-administered with LPS. These data give a picture of the T cell looking for costimulatory cues that are not forthcoming when pMHC is presented by steady-state DC, leading to tolerance. However, we did see a strong and rapid up-regulation of RANKL on T cells that occurred specifically when peptide was given in the absence of LPS, suggesting a possible positive signal influencing the decision between tolerance and immunity. [source]