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Inactivation Kinetics (inactivation + kinetics)
Kinds of Inactivation Kinetics Selected AbstractsTHERMAL INACTIVATION KINETICS OF ALKALINE PHOSPHATASE IN BUFFER AND MILKJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 3 2006S. 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] Microbial Inactivation Kinetics during High-Pressure Carbon Dioxide Treatment: Nonlinear Model for the Combined Effect of Temperature and Pressure in Apple JuiceJOURNAL OF FOOD SCIENCE, Issue 8 2008G. Ferrentino ABSTRACT:, Isobaric and isothermal semi-logarithmic survival curves of natural microflora in apple juice treated with high-pressure carbon dioxide at 7, 13, and 16 MPa pressures and 35, 50, and 60 °C temperatures were fitted with a nonlinear equation to find the values of the coefficient b(P ), b(T ), n(P ), and n(T ). Profiles of the model parameters were obtained as a function of pressure and temperature. The model fitted with good agreement (R2 > 0.945), the survival curves. An empirical equation was proposed to describe the combined effects of pressure and temperature. The equation, derived from a power law model, was written in the form: . The proposed model fitted the experimental data well. At 7 MPa and 50 and 60 °C, 13 MPa and 35 and 60 °C, 16 MPa and 35 °C, the model provided log10 reduction residual values (observed value , fitted value) lower than 0.284 showing a good agreement between the experimental and the predicted survival levels. [source] The Effect of Electric Field on Important Food-processing Enzymes: Comparison of Inactivation Kinetics under Conventional and Ohmic HeatingJOURNAL OF FOOD SCIENCE, Issue 9 2004I. Castro ABSTRACT: This work deals with the determination of the inactivation kinetics of several enzymes, most of them used as time-temperature integrators in the food industry. The tested enzymes were polyphenoloxidase, lipoxygenase, pectinase, alkaline phosphatase, and p-galactosidase, and the inactivation assays were performed under conventional and ohmic heating conditions. The thermal history of the samples (conventional and ohmically processed) was made equal to determine if there was an additional inactivation caused by the presence of an electric field, thus eliminating temperature as a variable. All the enzymes followed 1st-order inactivation kinetics for both conventional and ohmic heating treatments. The presence of an electric field does not cause an enhanced inactivation to alkaline phosphatase, pectinase, and ,- galactosidase. However, lipoxygenase and polyphenoloxidase kinetics were significantly affected by the electric field, reducing the time needed for inactivation. The results of the present work can be used industrially to determine processing effectiveness when ohmic heating technology is applied. [source] Thermal Inactivation Kinetics of Peroxidase and Lipoxygenase from Broccoli, Green Asparagus and CarrotsJOURNAL OF FOOD SCIENCE, Issue 1 2002E.F. Morales-Blancas ABSTRACT: Thewermal inactivation curves for peroxidase (POD) and lipoxygenase (LOX) in broccoli (florets), green asparagus (tip and stem), and carrots (cortex and core) extracts were determined in the range of 70 to 95 °C for 0 to 600 s. The capillary tube method was used to obtain quasi-isothermal conditions. The kinetics of both enzymes showed a biphasic first-order model, while at 70 °C, LOX in asparagus showed a monophasic first-order behavior. LOX activity was not detected for carrots. Kinetic parameters, k and Ea, were determined for heat-labile and heatresistant isoenzyme fractions. Additionally, initial and residual activities for both enzymes within tissue sections showed a different distribution and heat stability. [source] Thermal Inactivation Kinetics of Salmonella and Listeria in Ground Chicken Breast Meat and Liquid MediumJOURNAL OF FOOD SCIENCE, Issue 4 2000R.Y. Murphy ABSTRACT: Thermal inactivation of Listeria innocua and 6 Salmonella serotypes in ground chicken breast meat was compared to that in peptone (0.1%) - agar (0.1%) solution. Inoculated samples were packed in a thin-wall metal tube and submerged in a water bath at temperatures ranging from 55.0 to 70.0 °C. For Salmonella and Listeria, the D values in ground chicken breast meat at 55 to 70 °C were higher (p < 0.0001) than those in peptone-agar solution; however, the z values were not significantly different. Complete first-order inactivation models, with Arrhenius temperature dependency, were developed for each inoculum and medium. [source] Inactivation Kinetics of Foodborne Spoilage and Pathogenic Bacteria by OzoneJOURNAL OF FOOD SCIENCE, Issue 3 2000J.-G. Kim ABSTRACT: Ozone was tested against Pseudomonas fluorescens, Escherichia coli O157:H7, Leuconostoc mesenteroides, and Listeria monocytogenes. When kinetic data from a batch reactor were fitted to a dose-response model, a 2-phased linear relationship was observed. A continuous ozone reactor was developed to ensure a uniform exposure of bacterial cells to ozone and a constant concentration of ozone during the treatment. Survivors plots in the continuous system were linear initially, followed by a concave downward pattern. Exposure of bacteria to ozone at 2.5 ppm for 40 s caused 5 to 6 log decrease in count. Resistance of tested bacteria to ozone followed this descending order: E. coli O157:H7, P. fluorescens, L. mesenteroides, and L. monocytogenes. [source] Calorimetric Studies on Dry Pectinlyase Preparations: Impact of Glass Transition on Inactivation KineticsBIOTECHNOLOGY PROGRESS, Issue 4 2001Viviana M. Taragano The glass transition temperature (Tg) of a dry ultrafiltrated pectinlyase (PL) preparation decreased from 56 to 24 °C when water content increased to 20%. The thermal transition temperature (Tp) for protein denaturation decreased greatly up to 40% moisture; above 40% no further changes in Tp were observed. In the glassy state, a lag period of approximately 7 days with no PL activity loss was observed; after that, PL activity was lost. Above Tg, the rates of PL inactivation greatly increased. In the glassy state Ea was 16.6 kJ/mol. When the system was in a higher mobility state (rubbery), Ea increased to 66.5 kJ/mol. [source] Molecular determinants of inactivation in voltage-gated Ca2+ channelsTHE JOURNAL OF PHYSIOLOGY, Issue 2 2000Steffen Hering Evolution has created a large family of different classes of voltage-gated Ca2+ channels and a variety of additional splice variants with different inactivation properties. Inactivation controls the amount of Ca2+ entry during an action potential and is, therefore, believed to play an important role in tissue-specific Ca2+ signalling. Furthermore, mutations in a neuronal Ca2+ channel (Cav2.1) that are associated with the aetiology of neurological disorders such as familial hemiplegic migraine and ataxia cause significant changes in the process of channel inactivation. Ca2+ channels of a given subtype may inactivate by three different conformational changes: a fast and a slow voltage-dependent inactivation process and in some channel types by an additional Ca2+ -dependent inactivation mechanism. Inactivation kinetics of Ca2+ channels are determined by the intrinsic properties of their pore-forming ,1 -subunits and by interactions with other channel subunits. This review focuses on structural determinants of Ca2+ channel inactivation in different parts of Ca2+ channel ,1 -subunits, including pore-forming transmembrane segments and loops, intracellular domain linkers and the carboxyl terminus. Inactivation is also affected by the interaction of the ,1 -subunits with auxiliary ,-subunits and intracellular regulator proteins. The evidence shows that pore-forming S6 segments and conformational changes in extra- (pore loop) and intracellular linkers connected to pore-forming segments may play a principal role in the modulation of Ca2+ channel inactivation. Structural concepts of Ca2+ channel inactivation are discussed. [source] Protein kinase A modulates A-type potassium currents of larval zebrafish (Danio rerio) white muscle fibresACTA PHYSIOLOGICA, Issue 2 2009C. A. Coutts Abstract Aims:, Potassium (K+) channels are involved in regulating cell excitability and action potential shape. To our knowledge, very little is known about the modulation of A-type K+ currents in skeletal muscle fibres. Therefore, we sought to determine whether K+ currents of zebrafish white skeletal muscle were modulated by protein kinase A (PKA). Methods:, Pharmacology and whole-cell patch clamp were used to examine A-type K+ currents and action potentials associated with zebrafish white skeletal muscle fibres. Results:, Activation of PKA by a combination of forskolin + 3-isobutyl-1-methylxanthine (Fsk + IBMX) decreased the peak current density by ,60% and altered the inactivation kinetics of A-type K+ currents. The specific PKA inhibitor H-89 partially blocked the Fsk + IBMX-induced reduction in peak current density, but had no effect on the change in decay kinetics. Fsk + IBMX treatment did not shift the activation curve, but it significantly reduced the slope factor of activation. Activation of PKA by Fsk + IBMX resulted in a negative shift in the V50 of inactivation. H-89 prevented all Fsk + IBMX-induced changes in the steady-state properties of K+ currents. Application of Fsk + IBMX increased action potential amplitude, but had no significant effect on action potential threshold, half width or recovery rate, when fibres were depolarized with single pulses, paired pulses or with high-frequency stimuli. Conclusion:, PKA modulates the A-type K+ current in zebrafish skeletal muscle and affects action potential properties. Our results provide new insights into the role of A-type K+ channels in muscle physiology. [source] Androgen modulates the kinetics of the delayed rectifying K+ current in the electric organ of a weakly electric fishDEVELOPMENTAL NEUROBIOLOGY, Issue 12 2007M. Lynne McAnelly Abstract Weakly electric fish such as Sternopygus macrurus utilize a unique signal production system, the electric organ (EO), to navigate within their environment and to communicate with conspecifics. The electric organ discharge (EOD) generated by the Sternopygus electric organ is quasi-sinusoidal and sexually dimorphic; sexually mature males produce long duration EOD pulses at low frequencies, whereas mature females produce short duration EOD pulses at high frequencies. EOD frequency is set by a medullary pacemaker nucleus, while EOD pulse duration is determined by the kinetics of Na+ and K+ currents in the electric organ. The inactivation of the Na+ current and the activation of the delayed rectifying K+ current of the electric organ covary with EOD frequency such that the kinetics of both currents are faster in fish with high (female) EOD frequency than those with low (male) EOD frequencies. Dihydrotestosterone (DHT) implants masculinize the EOD centrally by decreasing frequency at the pacemaker nucleus (PMN). DHT also acts at the electric organ, broadening the EO pulse, which is at least partly due to a slowing of the inactivation kinetics of the Na+ current. Here, we show that chronic DHT treatment also slows the activation and deactivation kinetics of the electric organ's delayed rectifying K+ current. Thus, androgens coregulate the time-varying kinetics of two distinct ion currents in the EO to shape a sexually dimorphic communication signal. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007 [source] Development of ionic currents of zebrafish slow and fast skeletal muscle fibersDEVELOPMENTAL NEUROBIOLOGY, Issue 3 2006Christopher A. Coutts Abstract Voltage-gated Na+ and K+ channels play key roles in the excitability of skeletal muscle fibers. In this study we investigated the steady-state and kinetic properties of voltage-gated Na+ and K+ currents of slow and fast skeletal muscle fibers in zebrafish ranging in age from 1 day postfertilization (dpf) to 4,6 dpf. The inner white (fast) fibers possess an A-type inactivating K+ current that increases in peak current density and accelerates its rise and decay times during development. As the muscle matured, the V50s of activation and inactivation of the A-type current became more depolarized, and then hyperpolarized again in older animals. The activation kinetics of the delayed outward K+ current in red (slow) fibers accelerated within the first week of development. The tail currents of the outward K+ currents were too small to allow an accurate determination of the V50s of activation. Red fibers did not show any evidence of inward Na+ currents; however, white fibers expressed Na+ currents that increased their peak current density, accelerated their inactivation kinetics, and hyperpolarized their V50 of inactivation during development. The action potentials of white fibers exhibited significant changes in the threshold voltage and the half width. These findings indicate that there are significant differences in the ionic current profiles between the red and white fibers and that a number of changes occur in the steady-state and kinetic properties of Na+ and K+ currents of developing zebrafish skeletal muscle fibers, with the most dramatic changes occurring around the end of the first day following egg fertilization. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2006 [source] Improving thermostability and catalytic activity of pyranose 2-oxidase from Trametes multicolor by rational and semi-rational designFEBS JOURNAL, Issue 3 2009Oliver Spadiut The fungal homotetrameric flavoprotein pyranose 2-oxidase (P2Ox; EC 1.1.3.10) catalyses the oxidation of various sugars at position C2, while, concomitantly, electrons are transferred to oxygen as well as to alternative electron acceptors (e.g. oxidized ferrocenes). These properties make P2Ox an interesting enzyme for various biotechnological applications. Random mutagenesis has previously been used to identify variant E542K, which shows increased thermostability. In the present study, we selected position Leu537 for saturation mutagenesis, and identified variants L537G and L537W, which are characterized by a higher stability and improved catalytic properties. We report detailed studies on both thermodynamic and kinetic stability, as well as the kinetic properties of the mutational variants E542K, E542R, L537G and L537W, and the respective double mutants (L537G/E542K, L537G/E542R, L537W/E542K and L537W/E542R). The selected substitutions at positions Leu537 and Glu542 increase the melting temperature by approximately 10 and 14 °C, respectively, relative to the wild-type enzyme. Although both wild-type and single mutants showed first-order inactivation kinetics, thermal unfolding and inactivation was more complex for the double mutants, showing two distinct phases, as revealed by microcalorimetry and CD spectroscopy. Structural information on the variants does not provide a definitive answer with respect to the stabilizing effects or the alteration of the unfolding process. Distinct differences, however, are observed for the P2Ox Leu537 variants at the interfaces between the subunits, which results in tighter association. [source] Effect of water activity on the inactivation kinetics of Escherichia coli O157:H7 by electron beam in ground beef, chicken breast meat, and trout filletsINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 4 2008Jennifer Leah Black Summary Water activity (aw) of ground beef, chicken breast meat, and trout fillets was modified to intermediate (aw 0.98,0.99) and lowest (aw 0.94,0.96) levels. The meat samples with modified and unaltered (native, aw 1.00) aw were inoculated with Escherichia coli O157:H7 and subjected to electron beam (e-beam). Survivor curves were plotted and the D10 -values were calculated. The D10 -values ranged from 0.22 kGy for trout at native aw to 0.33 kGy for beef at intermediate, and chicken and trout at lowest aw. Regardless of the species, aw reduction increased E. coli resistance to e-beam, suggesting that even small depletion of unbound water from food increases survival. The difference of the D10 -values between the samples at intermediate and lowest aw was insignificant. E-beam could be used before aw -reducing techniques are applied to food products. However, this would require stringent microbial control following e-beam processing. The ,tailing' of survivors was observed for some samples with reduced aw. [source] Relationship between inactivation kinetics of a Listeria monocytogenes suspension by chlorine and its chlorine demandJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2004R. Virto Abstract Aims:, Chlorine demand by Listeria monocytogenes cells and inactivation of L. monocytogenes by chlorine (0·6,1·0 mg l,1) at different temperatures (4, 20 and 30°C) have been investigated in a batch reactor. Methods and Results:, Chlorine demand depended on the microbial concentration and was independent on the initial chlorine concentration and temperature. Chlorine decay was modelled by the addition of two first-order decay equations. Inactivation of L. monocytogenes by chlorine depended on the initial microbial concentration, initial chlorine concentration and temperature. A mathematical model based on a biphasic inactivation properly described survival curves of L. monocytogenes and a tertiary model was developed that satisfactorily predicted the inactivation of L. monocytogenes by different concentrations of initial chlorine at different temperatures. Conclusions:, Both available chlorine decay and inactivation of L. monocytogenes by chlorine were biphasic and can be modelled by a two-term exponential model. Significance and Impact of the Study:, The biphasic nature of survival curves of L. monocytogenes did not reflect the effect of a change of available chlorine concentration during the treatment. The microbial inactivation was caused by successive reactions that occur after the consumption of the chlorine by the bacterial cell components. [source] INACTIVATION OF STAPHYLOCOCCUS AUREUS EXPOSED TO DENSE-PHASE CARBON DIOXIDE IN A BATCH SYSTEMJOURNAL OF FOOD PROCESS ENGINEERING, Issue 1 2009HUACHUN HUANG ABSTRACT The inactivation of Staphylococcus aureus exposed to dense-phase carbon dioxide (DPCD) was investigated, and the kinetics of come-up time (CUT) in pressurization was monitored with come-down time (CDT) and temperature fluctuation in depressurization. CUT was about 2.5, 3.5, 4.0 and 4.0 min; CDT was 3.4, 3.7, 4.5 and 4.5 min; lowest temperature of samples in depressurization was 4, ,1, ,15 and ,22C, corresponding to 10, 20, 30 and 40 MPa at 37C. The inactivation behavior of S. aureus was closely related to the variables of process pressure, holding-pressure time (HPT), process temperature and process cycling. The log reduction of S. aureus at 40 MPa for 30-min HPT was significantly greater (P < 0.05), but the inactivation effect at 10, 20 and 30 MPa was similar. The log reduction of S. aureus at 30 and 40 MPa for 60-min HPT was similar and significantly greater (P < 0.05), while the inactivation effect at 10 and 20 MPa was similar. The inactivation of S. aureus against HPT conformed to a fast,slow biphase kinetics; the two stages were well fitted to a first-order model with higher regression coefficients R2 = 1.000 and 0.9238; their respective D values (decimal reduction time) were 16.52 and 70.42 min. As the process temperature increased, the log reduction of S. aureus increased significantly (P < 0.05); the inactivation kinetics of S. aureus versus process temperature was characterized with a fast inactivation rate from 32 to 45C and a slow inactivation rate from 45 to 55C. As compared to one-process cycling for a total of 60-min HPT, four-process cycling resulted in a significant reduction of S. aureus, and its maximal reduction was near to 5 log cycles, indicating that more process cycling caused more inactivation of S. aureus under identical pressure and temperature with equal HPT. However, the maximal reduction was 0.09 and 0.12 log cycles for two- and four-process cyclings with 0-min HPT, indicating that pressurization and depressurization had a lesser effect on the inactivation of S. aureus, while HPT was significant in DPCD to inactivate S. aureus. PRACTICAL APPLICATIONS Dense-phase carbon dioxide (DPCD) is a novel technology to achieve cold pasteurization and/or sterilization of liquid and solid materials, and is likely to replace or partially substitute currently and widely applied thermal processes. This study showed that DPCD effectively inactivated Staphylococcus aureus inoculated in 7.5% sodium chloride broth, and the inactivation behavior of S. aureus was closely related to the pressure, holding-pressure time, temperature and process cycling. Based on this observation, the technology of DPCD can be applied in the pasteurization of foods such as milk and various fruit juices, especially thermal-sensitive materials. [source] Inactivation of Food Spoilage Microorganisms by Hydrodynamic Cavitation to Achieve Pasteurization and Sterilization of Fluid FoodsJOURNAL OF FOOD SCIENCE, Issue 9 2007P.J. Milly ABSTRACT:, Hydrodynamic cavitation is the formation of gas bubbles in a fluid due to pressure fluctuations induced by mechanical means. Various high-acid (pH , 4.6) fluid foods were processed in a hydrodynamic cavitation reactor to determine if commercial sterility can be achieved at reduced processing temperatures. Sporicidal properties of the process were also tested on a low-acid (pH < 4.6) fluid food. Fluid foods were pumped under pressure into a hydrodynamic cavitation reactor and subjected to 2 rotor speeds and flow rates to achieve 2 designated exit temperatures. Thermal inactivation kinetics were used to determine heat-induced lethality for all organisms. Calcium-fortified apple juice processed at 3000 and 3600 rpm rotor speeds on the reactor went through a transient temperature change from 20 to 65.6 or 76.7 °C and the total process lethality exceeded 5-log reduction of Lactobacillus plantarum and Lactobacillus sakei cells, and Zygosaccharomyces bailii cells and ascospores. Tomato juice inoculated with Bacillus coagulans spores and processed at 3000 and 3600 rpm rotor speeds endured a transient temperature from 37.8 to 93.3 or 104.4 °C with viable CFU reductions of 0.88 and 3.10 log cycles, respectively. Skim milk inoculated with Clostridium sporogenes putrefactive anaerobe 3679 spores and processed at 3000 or 3600 rpm rotor speeds endured a transient temperature from 48.9 to 104.4 or 115.6 °C with CFU reductions of 0.69 and 2.84 log cycles, respectively. Utilizing hydrodynamic cavitation to obtain minimally processed pasteurized low-acid and commercially sterilized high-acid fluid foods is possible with appropriate process considerations for different products. [source] The Effect of Electric Field on Important Food-processing Enzymes: Comparison of Inactivation Kinetics under Conventional and Ohmic HeatingJOURNAL OF FOOD SCIENCE, Issue 9 2004I. Castro ABSTRACT: This work deals with the determination of the inactivation kinetics of several enzymes, most of them used as time-temperature integrators in the food industry. The tested enzymes were polyphenoloxidase, lipoxygenase, pectinase, alkaline phosphatase, and p-galactosidase, and the inactivation assays were performed under conventional and ohmic heating conditions. The thermal history of the samples (conventional and ohmically processed) was made equal to determine if there was an additional inactivation caused by the presence of an electric field, thus eliminating temperature as a variable. All the enzymes followed 1st-order inactivation kinetics for both conventional and ohmic heating treatments. The presence of an electric field does not cause an enhanced inactivation to alkaline phosphatase, pectinase, and ,- galactosidase. However, lipoxygenase and polyphenoloxidase kinetics were significantly affected by the electric field, reducing the time needed for inactivation. The results of the present work can be used industrially to determine processing effectiveness when ohmic heating technology is applied. [source] Quinacrine Enhances Vesicular Stomatitis Virus Inactivation and Diminishes Hemolysis of Dimethylmethylene Blue,phototreated Red Cells,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2002Stephen J. Wagner ABSTRACT Several photodynamic methods for virus inactivation in red blood cell (RBC) suspensions have resulted in unwanted hemolysis during extended 1,6°C storage. To explore the possibility that hemolysis may be mediated by a membrane-bound dye, a molecule similar in structure to yet different in light absorption properties from the photosensitizer was used as an inhibitor for RBC membrane binding in virus photoinactivation and photohemolysis studies. The addition of 500 ,M quinacrine to oxygenated RBC before treatment with 3.6 ,M dimethylmethylene blue (DMMB) and 219 mJ/cm2 red light resulted in an increased extracellular concentration of the sensitizer, increased extracelluar viral inactivation kinetics, and decreased hemolysis during 1,6°C storage without alteration of quinacrine absorption properties. These results collectively suggest that despite its recognized affinity for viral nucleic acid, DMMB also binds to RBC membranes and that the bound dye is, in part, responsible for photoinduced hemolysis. [source] Modulation of Ca2+ signalling in rat atrial myocytes: possible role of the ,1c carboxyl terminalTHE JOURNAL OF PHYSIOLOGY, Issue 2 2003Sun-Hee Woo Ca2+ influx through L-type Cav1.2 (,1c) Ca2+ channels is a critical step in the activation of cardiac ryanodine receptors (RyRs) and release of Ca2+ via Ca2+ -induced Ca2+ release(CICR). The released Ca2+, in turn, is the dominant determinant of inactivation of the Ca2+ current (ICa) and termination of release. Although Ca2+ cross-signalling is mediated by high Ca2+ fluxes in the microdomains of ,1c -RyR complexes, ICa -gated Ca2+ cross-signalling is surprisingly resistant to intracellular Ca2+ buffering and has steeply voltage-dependent gain, inconsistent with a strict CICR mechanism, suggesting the existence of additional regulatory step(s). To explore the possible regulatory role of the carboxyl (C)-terminal tail of ,1c in modulating Ca2+ signalling, we tested the effects of introducing two ,1c C-terminal peptides, LA (1571,1599) and K (1617,1636) on the central ,1c -unassociated Ca2+ -release sites of atrial myocytes, using rapid (240 Hz) two-dimensional confocal Ca2+ imaging. The frequency of spontaneously activating central sparks increased by approximately fourfold on dialysing LA- but not K-peptide into myocytes voltage-clamped at -80 mV. The rate but not the magnitude of caffeine (10 mM)-triggered central Ca2+ release was significantly accelerated by LA- but not K-peptide. Individual Ca2+ spark size and flux were larger in LA- but not in K-peptide-dialysed myocytes. Although LA-peptide did not change the amplitude or inactivation kinetics of ICa, LA-peptide did strongly enhance the central Ca2+ transients triggered by ICa at -30 mV (small ICa) but not at +20 mV (large ICa). In contrast, K-peptide had no effect on either ICa or the local Ca2+ transients. LA-peptide with a deleted calmodulin-binding region (LM1-peptide) had no significant effects on the central spark frequency but suppressed spontaneous spark frequency in the periphery. Our results indicate that the calmodulin-binding LA motif of the ,1c C-terminal tail may sensitize the RyRs, thereby increasing their open probability and providing for both the voltage-dependence of CICR and the higher frequency of spark occurrence in the periphery of atrial myocytes where the native ,1c -RyR complexes are intact. [source] High gas pressure effects on yeastBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2008V. Espinasse Abstract Dried microorganisms are particularly resistant to high hydrostatic pressure effects. However, exposure to high pressures of nitrogen proved to be effective in inactivating dried yeasts. In this study, we tried to elucidate this mechanism on Saccharomyces cerevisiae. High-pressure treatments were performed using different inert gases at 150 MPa and 25°C with holding time values up to 12 months. The influence of cell hydration was also investigated. For fully hydrated cells, pressurized gases had little specific effect: cell inactivation was mainly due to compression effects. However, dried cells were sensitive to high pressure of gases. In this latter case, two inactivation kinetics were observed. For holding time up to 1 h, the inactivation rate increased to 4 log and was linked to a loss of membrane integrity and the presence of damage on the cell wall. In such case cell inactivation would be due to gas sorption and desorption phenomena which would rupture dried cells during a fast pressure release. Gas sorption would occur in cell lipid phases. For longer holding times, the inactivation rate increased more slightly due to compression effects and/or to a slower gas sorption. Water therefore played a key role in cell sensitivity to fast gas pressure release. Two hypotheses were proposed to explain this phenomenon: the rigidity of vitrified dried cells and the presence of glassy solid phases which would favor intracellular gas expansion. Our results showed that dried microorganisms can be ruptured and inactivated by a fast pressure release with gases. Biotechnol. Bioeng. 2008;101: 729,738. © 2008 Wiley Periodicals, Inc. [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] Characterization of two Bunodosoma granulifera toxins active on cardiac sodium channelsBRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2001Cyril Goudet Two sodium channel toxins, BgII and BgIII, have been isolated and purified from the sea anemone Bunodosoma granulifera. Combining different techniques, we have investigated the electrophysiological properties of these toxins. We examined the effect of BgII and BgIII on rat ventricular strips. These toxins prolong action potentials with EC50 values of 60 and 660 nM and modify the resting potentials. The effect on Na+ currents in rat cardiomyocytes was studied using the patch-clamp technique. BgII and BgIII slow the rapid inactivation process and increase the current density with EC50 values of 58 and 78 nM, respectively. On the cloned hH1 cardiac Na+ channel expressed in Xenopus laevis oocytes, BgII and BgIII slow the inactivation process of Na+ currents (respective EC50 values of 0.38 and 7.8 ,M), shift the steady-state activation and inactivation parameters to more positive potentials and the reversal potential to more negative potentials. The amino acid sequences of these toxins are almost identical except for an asparagine at position 16 in BgII which is replaced by an aspartic acid in BgIII. In all experiments, BgII was more potent than BgIII suggesting that this conservative residue is important for the toxicity of sea anemone toxins. We conclude that BgII and BgIII, generally known as neurotoxins, are also cardiotoxic and combine the classical effects of sea anemone Na+ channels toxins (slowing of inactivation kinetics, shift of steady-state activation and inactivation parameters) with a striking decrease on the ionic selectivity of Na+ channels. British Journal of Pharmacology (2001) 134, 1195,1206; doi:10.1038/sj.bjp.0704361 [source] High Pressure Processing , a Database of Kinetic InformationCHEMIE-INGENIEUR-TECHNIK (CIT), Issue 8 2008R. Buckow Abstract Hydrostatic high pressure technology is relatively new to food industry and is more and more considered as an alternative to traditional preservation methods like heat processing. The inactivation of bacteria, spores, viruses and enzymes has been demonstrated in numerous papers, and various schemes for modelling the experimental inactivation data have been suggested. Although there are similarities to heat inactivation kinetics it is generally agreed that the heat process safety assessment with its typical indicator organisms cannot simply be transferred to high pressure treatment. In this paper a database is introduced which aims at the comparison of published kinetic high pressure inactivation data by using suitable mathematical modelling tools. For the sake of clarity, the functional associations of pressure, temperature and exposure time is presented by means of pressure-temperature diagrams (pT -diagrams), which show pressure-temperature combinations yielding to a desired reaction (e.g. inactivation) rate constant. Thus, the database software was particularly designed to enable the user to call up pressure-temperature dependent function equations for a number of micro-organisms, enzymes and food constituents and to visualize them in pT -diagrams for predetermined treatment times or as kinetics under predetermined p - T conditions. In addition, the database also features a simple calculator tool which allows the user to make an entry in three of the four process conditions (pressure level, temperature level, inactivation level, dwell time) and calculate the remaining forth process condition. The database is accessible through the internet and is continuously updated on the basis of the most recent publications and own experimental data. [source] From Time Temperature Integrator Kinetics to Time Temperature Integrator Tolerance Levels: Heat-Treated MilkBIOTECHNOLOGY PROGRESS, Issue 1 2004Wendie L. Claeys Six milk compounds were studied as potential intrinsic time temperature integrators (TTIs) for the assessment of heat-treated milk. These include the enzymes alkaline phosphatase and lactoperoxidase, the whey protein ,-lactoglobulin and the chemical compounds hydroxymethylfurfural, lactulose and furosine. In previous research the inactivation/denaturation/formation kinetics of these compounds were analyzed under isothermal and nonisothermal conditions and evaluated for variability of the milk composition. The present paper focuses on the implementation of the TTIs. TTIs are validated with respect to microbiological indices and quality attributes, and a quantitative relationship between the denaturation, inactivation or formation of the TTIs and technological processes is established by construction of general time temperature tolerance (TTT) diagrams. In these diagrams temperature time combinations are presented, which lead to the same formation, inactivation or denaturation of TTIs, or result in the same level of microbiological destruction or quality degradation of the product. TTT-diagrams are very informative since they allow visualization of the impact of a thermal process on milk and evaluation of criteria for evaluating milk authenticity (conformity of the product with the terminology applied). Moreover, the optimum combination of temperature and time of heating may be readily deduced from these diagrams. [source] | |||||||||||||