Home About us Contact
|
Home About us Contact | ||
|
|
||
First-order Kinetic Model (first-order + kinetic_model)
Selected AbstractsPredicting world health organization toxic equivalency factor dioxin and dioxin-like polychlorinated biphenyl levels in farmed atlantic salmon (Salmo salar) based on known levels in feedENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2007Marc H. G. Berntssen Abstract Assimilation and elimination rate constant of dietary polychlorinated dibenzo- p -dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DLPCBs) with a World Health Organization toxic equivalency factor (WHO-TEF) were estimated in market-size Atlantic salmon (Salmo salar) using fish that were previously fed vegetable oil,based (low in PCDD/Fs and DLPCBs) or fish oil,based (high in PCDD/Fs and PCBs) diets. At the start of the kinetic trial, half the fish that were fed fish oils were fed vegetable oil feeds and inverted (cross-over design) for five months. The assimilation efficiencies of the PCDD/F congeners were more variable (3,89%) and, generally, were lower than those of the DLPCBs (70,80%). Among the PCDD/F congeners, the assimilation efficiency of the most toxic tetra- and pentachlorinated PCDD/Fs was greater than that of higher-chlorinated PCDD/Fs. Elimination rates for DLPCBs were higher than those for PCDD/Fs. Lower-chlorinated PCDDs had a lower elimination rate than the higher-chlorinated PCDDs, but no differences were observed among PCDF congeners or DLPCB congeners. Kinetic parameters were used to predict the level of WHO-TEF dioxins and DLPCBs in Atlantic salmon reared in a large-scale facility under commercial conditions. Predictions were based on preanalyzed levels of these organochlorines in feeds with three different replacement levels (0, 30, and 60%) of vegetable oil. A simple one-compartmental, first-order kinetic model was used to predict the level of sum WHO toxic equivalents for PCDD/Fs and DL-PCBs. The predicted values varied by 0 to 11% from the measured values in the commercially reared salmon. [source] Addition of activated carbon to batch activated sludge reactors in the treatment of landfill leachate and domestic wastewaterJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2001Özgür Akta Abstract Leachate from a municipal landfill was combined with domestic wastewater and was treated in batch activated sludge systems. The effectiveness and applicability of the addition of Powdered Activated Carbon (PAC) to activated sludge reactors was investigated. Isotherm tests were carried out with PAC in order to estimate the extent of adsorption of organic matter onto PAC. Then, in activated sludge reactors COD (Chemical Oxygen Demand) removal and nitrification were studied both in the absence and presence of PAC for comparison purposes. In both cases, Oxygen Uptake Rates (OUR) were measured with respect to time in order to investigate substrate removal and change in microbial activity. Addition of PAC to activated sludge increased COD removal by removing mainly the non-biodegradable fraction in leachate. The COD decreases in batch reactors were best expressed by a first-order kinetic model that incorporated this non-biodegradable leachate fraction. With added PAC, nitrification was also enhanced. But in all of the batch runs a significant accumulation of NO2 -N took place, indicating that the second step of nitrification was still inhibited. © 2001 Society of Chemical Industry [source] THERMAL AND HIGH-PRESSURE STABILITY OF PURIFIED PECTIN METHYLESTERASE FROM PLUMS (PRUNUS DOMESTICA)JOURNAL OF FOOD BIOCHEMISTRY, Issue 2 2006CLÁUDIA S. NUNES ABSTRACT Pectin methylesterase (PME) from greengage plums (Prunus domestica) has been extracted and purified using affinity chromatography. Only one band on sodium dodecyl sulfate,polyacrylamide gel electrophoresis was obtained, with an estimated molecular weight of 31 kDa. On isoelectric focusing electrophoresis, two bands with neutral isoelectric points (6.8 and 7.0) were detected. The optimal pH and temperature for plum PME activity were 7.5 and 65C, respectively. A study of purified plum PME thermostability was performed at pH 7.5 and 4.0, indicating a higher thermostability at pH 7.5 than at pH 4.0. A biphasic inactivation behavior was observed for thermal treatments (54,70C), whereas its pressure inactivation could be described by a first-order kinetic model in a pressure range of 650,800 MPa at 25C. Purified plum PME was found to be relatively stable to thermal and pressure (,600 MPa) treatments, compared to PME from other fruits. [source] CLARIFICATION OF WATERMELON (CITRULLUS LANATUS) JUICE BY MICROFILTRATIONJOURNAL OF FOOD PROCESS ENGINEERING, Issue 6 2008Ch. CHHAYA ABSTRACT Microfiltration of watermelon juice was conducted using stirred membrane cell in continuous mode. The experiments were conducted at operating pressures of 136.5, 204.7 and 276 kPa, and stirring speeds 1,200 rpm (Re = 1.40 × 105), 1,400 rpm (Re = 1.63 × 105) and 1,600 rpm (Re = 1.87 × 105). Permeate flux decline was analyzed using a first-order kinetic model, and correlations were developed for the steady-state polarized layer resistance with the operating conditions, e.g., transmembrane pressure difference, Reynolds number and membrane resistance. The permeate flux was calculated based on the developed correlation, and found to be in good agreement with the actual experimental flux. The change in quality parameters of clarified juice was marginal compared to that of original juice. PRACTICAL APPLICATIONS The application of membrane technology is one of the emerging areas in food industry. The major application includes fruit juice clarification and concentration. Because of the nonthermal nature of membrane separation, the juice can be clarified at room temperature and packed aseptically for a longer shelf life without the loss of its initial quality parameters. The major problem during clarification is decline in permeate flux of fruit juice with time. Identification of causes for flux decline is essential for designing of membrane modules to make the clarification process commercially viable. The quality of juice during storage is vital, and therefore, determination of variation of its physicochemical properties during storage is also important. [source] High-Pressure Processing of Orange Juice: Kinetics of Pectinmethylesterase InactivationJOURNAL OF FOOD SCIENCE, Issue 2 2001U. Nienaber ABSTRACT: A kinetic study of pectinmethylesterase (PME) inactivation in orange juice was conducted. Juice samples were subjected to combinations of high pressure (400, 500, 600 MPa) and thermal (25, 37.5, 50 °C) treatments for various time periods. PME inactivation followed a first-order kinetic model with a residual activity of pressure-resistant enzyme remaining. Calculated D-values ranged from 4.6 min to 117.5 min at 600 MPa/50 °C and 400 MPa/25 °C, respectively. Pressures in excess of 500 MPa resulted in sufficiently fast inactivation rates for economic viability of the process. [source] C. botulinum inactivation kinetics implemented in a computational model of a high-pressure sterilization processBIOTECHNOLOGY PROGRESS, Issue 1 2009Pablo Juliano Abstract High-pressure, high-temperature (HPHT) processing is effective for microbial spore inactivation using mild preheating, followed by rapid volumetric compression heating and cooling on pressure release, enabling much shorter processing times than conventional thermal processing for many food products. A computational thermal fluid dynamic (CTFD) model has been developed to model all processing steps, including the vertical pressure vessel, an internal polymeric carrier, and food packages in an axis-symmetric geometry. Heat transfer and fluid dynamic equations were coupled to four selected kinetic models for the inactivation of C. botulinum; the traditional first-order kinetic model, the Weibull model, an nth-order model, and a combined discrete log-linear nth-order model. The models were solved to compare the resulting microbial inactivation distributions. The initial temperature of the system was set to 90°C and pressure was selected at 600 MPa, holding for 220 s, with a target temperature of 121°C. A representation of the extent of microbial inactivation throughout all processing steps was obtained for each microbial model. Comparison of the models showed that the conventional thermal processing kinetics (not accounting for pressure) required shorter holding times to achieve a 12D reduction of C. botulinum spores than the other models. The temperature distribution inside the vessel resulted in a more uniform inactivation distribution when using a Weibull or an nth-order kinetics model than when using log-linear kinetics. The CTFD platform could illustrate the inactivation extent and uniformity provided by the microbial models. The platform is expected to be useful to evaluate models fitted into new C. botulinum inactivation data at varying conditions of pressure and temperature, as an aid for regulatory filing of the technology as well as in process and equipment design. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Trypsin Inhibition Activity of Heat-Denatured Ovomucoid: A Kinetic StudyBIOTECHNOLOGY PROGRESS, Issue 1 2004Iesel Van der Plancken A kinetic study was conducted on the effect of heating in the temperature range of 75,110 °C on the trypsin inhibition activity of ovomucoid. Heat treatment of isolated ovomucoid resulted in a time-dependent decrease in trypsin inhibition activity that could accurately be described by a first-order kinetic model. The magnitude and the temperature dependence of the rate constants was affected by the pH during heat treatment. The heat stability of ovomucoid was the lowest at pH 7.6. Heat treatments intended to decrease the trypsin inhibition activity should therefore be carried out as soon as possible after laying, because the ovomucoid was inactivated faster at the pH of fresh egg white (pH 7.6). The presence of the other egg white constituents decreased the heat stability of ovomucoid compared to that of the model system of ovomucoid in buffer, presumably by the formation of ovomucoid-lysozyme complexes in the former. [source] Interaction of Flavin Adenine Dinucleotide (FAD) with a Glassy Carbon Electrode SurfaceCHEMISTRY & BIODIVERSITY, Issue 8 2008Haizhen Wei Abstract The interaction of flavin adenine dinucleotide (FAD) with a glassy carbon electrode (GCE) surface was investigated in terms of the FAD adsorption thermodynamics and kinetics, the subsequent electroreduction mechanism, and the corresponding electron-transfer rate. The kinetics of FAD electroreduction at the GCE was found to be an adsorption-controlled process. A set of electroreduction kinetic parameters was calculated: the true number of electrons involved in the FAD reduction, n=1.76, the apparent transfer coefficient, ,app=0.41, and the apparent heterogeneous electron-transfer rate constant, kapp=1.4,s,1. The deviation of the number of exchanged electrons from the theoretical value for the complete reduction of FAD to FADH2 (n=2) indicates that a small portion of FAD goes to a semiquinone state during the redox process. The FAD adsorption was well described by the Langmuir adsorption isotherm. The large negative apparent Gibbs energy of adsorption (,Gads=,39.7 ±0.4,kJmol,1) indicated a highly spontaneous and strong adsorption of FAD on the GCE. The energetics of the adsorption process was found to be independent of the electrode surface charge in the electrochemical double-layer region. The kinetics of FAD adsorption was modeled using a pseudo -first-order kinetic model. [source] | |||||||||||||