摘要:

AbstractThe influence of polyhydric alcohols and carbohydrates on the thermostability, i.e., the heat inactivation kinetics, ofBacillus licheniformisα‐amylase was studied in the temperature range 96° to 130°C. High concentrations (from 9 to 60 weight percent) of glycerol, sorbitol, mannitol, sucrose, or starch can markedly decrease the inactivation rate constant,k, and in the studied cases, this stabilizing effect grows stronger with increasing additive concentration. Statements about stabilization should, however, be specified carefully with respect to temperature, becauseEAis mostly altered likewise. For dissolved enzymeEAwas almost always decreased in the presence of polyol or carbohydrate, whereas for immobilized enzyme it was augmented in each studied instance. The inactivation of dissolved enzyme can, in all the studied cases, be adequately described as a firstorder process. Immobilized enzyme, however, shows biphasic then first‐order inactivation kinetics, depending on the additive concentration and temperature. © 1994 John Wiley&So

ISSN:0006-3592    

DOI:10.1002/bit.260430202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe cell membrane permeability governs the rate of solute transport into and out of the cell, significantly affecting the cell's metabolic processes, viability, and potential usefulness in both biotechnological applications and physiological systems. Most previous studies of the cell membrane permeability have neglected the possible effects of suspending medium on membrane transport, even though there is extensive experimental evidence that suspending phase composition can significantly affect other properties related to the cell membrane (e.g., cell deformability, fragility, and aggregation rate). This study examined the effects of suspending phase composition (both proteins and electrolytes) on the permeability of human red blood cells to the metabolites creatinine and uric acid. Data were obtained using a stirred ultrafiltration device with direct cell‐ and proteinfree sampling through a semipermeable membrane. Both the uric acid and creatinine permeabilities were strongly affected by the suspending phase composition, with the permeabilities in different buffer solutions varying by as much as a factor of three. The predominant factors affecting the permeability were the presence (or absence) of chloride, phosphate/adenine, and proteins, although the magnitude and even the direction of these effects were significantly different for creatinine and uric acid transport. The dramatic differences in behavior for uric acid and creatinine reflect the different transport mechanisms for these solutes, with uric acid transported by a carrier‐mediated mechanism and creatinine transported by passive diffusion through the lipid bilayer. These results provide important insights into the effects of solution environment on cell membrane transport and other cell membrane‐mediated properties. © 1994 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260430203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe use of solvent‐free systems in the oil and fats industry is commonplace. Initial studies on interesterification were carried out in solvent systems because the lipase was immobilized solely by adsorption onto particles of diatomaceous earth. In this study, the mass transfer characteristics associated with the continuous interesterification of olive oil in a solvent‐free system have been examined, for lipase immobilized on the three ion‐exchange materials: Duolite ES562, Duolite ES568, and Spheroil DEA. The process of immobilization is influenced by the internal structure of the material and this in turn influences the interesterification activity of the catalyst. Individually prepared catalysts for the three support materials have shown that external mass transfer limitations are unlikely even at low flowrates.In the case of Spherosil DEA, with a mean pore diameter of 1480 Å, the wide pores would be expected to reduce internal mass transfer limitations; however, it is more likely that the reduction in activity with increased catalyst loading is due to the lipase molecules being immobilized in a tightly packed monolayer. In such a situation, some active sites of the lipase molecules would become inaccessible to substrate molecules leading to an observed reduction in activity. For Duolite ES568, the observed results are very similar to those seen for Spherosil DEA, however, the pore structure of this support material indicate that some internal mass transfer limitations may also be occurring. Yet the contribution of the individual effects cannot be determined. The results observed for the support Duolite ES562 are different than those observed for the other materials and reflect the heterogeneity of Duolite ES562. The large proportion of narrow pores in the support mean that, for the catalysts examined, immobilization is most likely to have occurred in the external pores of the particles, and as such no internal mass transfer limitation is observed.It is clear that for interesterification the material chosen for enzyme immobilization will have an important role in determining the catalyst efficiency. External mass transfer limitations are very minor and observed internal mass transfer limitations may be caused by both internal mass transfer and the manner in which the immobilization process occurs. © 1994 John Wiley&So

ISSN:0006-3592    

DOI:10.1002/bit.260430204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe rates of oxygen uptake and oxygen transfer during cell growth and citric acid production byCandida lipolyticaY 1095 were determined. The maximum cell growth rate, 1.43 g cell/L · h, and volumetric oxygen uptake rate, 343 mg O2/L · h, occurred approximately 21 to 22 h after inoculation. At the time of maximum oxygen uptake, the biomass concentration was 1.3% w/v and the specific oxygen uptake rate was slightly greater than 26 mg O2/g cell · h. The specific oxygen uptake rate decreased to approximately 3 mg O2/g cell · h by the end of the growth phase.During citric acid production, as the concentration of dissolved oxygen was increased from 20% to 80% saturation, the specific oxygen uptake and specific citric acid productivity (mg citric acid/g cell · h) increased by 160% and 71%, respectively, at a biomass concentration of 3% w/v. At a biomass concentration of 5% w/v, the specific oxygen uptake and specific citric acid productivity increased by 230% and 82%, respectively, over the same range of dissolved oxygen concentrations.The effect of dissolved oxygen on citric acid yields and productivities was also determined. Citric acid yields appeared to be independent of dissolved oxygen concentration during the initial production phase; however, volumetric productivity (g citric acid/L · h) increased sharply with an increase in dissolved oxygen. During the second or subsequent production phase, citric acid yields increased by approximately 50%, but productivities decreased by roughly the same percentage due to a loss of cell viability under prolonged nitrogen‐deficient conditions. © 1994 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260430205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA fresh quest is made of segregated cell models of microbial populations with a view to determine whether the multivarite distribution of physiological states, during transient growth, can attain self‐similar forms (i.e., become time invariant) when each physiological state variable is scaled with respect to its population average. Such self‐similar growth situations are believed to be more general than those of balanced growth. The conditions under which self‐similarity is possible are investigated. Thus conditions are stipulated on the synthesis rates of different physiological entities, cell division rate, and the partitioning of the parent cell's components among the daughter cells (assuming binary division) in order for self‐similar growth to be attained. Subject to the attainment of self‐similar growth, it is shown that cytometric data can be analyzed systematically to determine how the rates of syntheses of various biochemical entities and cell division rates vary with the physiological entities that are measured. Inverse problems, represented by algebraic systems, are identified which will potentially allow flow cytometric data to be inverted to yield quantitative information on the absolute rates of cellular growth and reproductory processes as a function of the cell states chosen for measurement. It is suggested that the methods become more effective when cytometry can be used to makedirectobservations on dividing cells so that the number of unknowns in the inverse problem can be reduced, thus facilitating its more complete solution. Preliminary analysis of cytometric data obtained in the literature show promise of self‐similarity and thus the possibility of application of the methods discussed here. © 1994 John Wil

ISSN:0006-3592    

DOI:10.1002/bit.260430206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA static method was developed that simultaneously determined the solubility of oxygen and the oxygen‐transfer coefficient in a stirred bioreactor. It was based on the static method developed by van Sonsbeek et al. to determine thekain a liquid‐impelled loop reactor. Only physical properties of the liquid were used to determine both parameters using a mass spectrometer. Data about the solubility of oxygen in water are available from the literature. Therefore, the solubility of oxygen in water was used to compare our data with published data. Furthermore, the solubility of oxygen in trypticase soy broth was compared to literature data. No significant deviations between our data and literature data could be observed. Our static method and the commonly applied dynamic method to determine the oxygen‐transfer coefficient yielded similar results. The effect of temperature on the oxygen‐transfer coefficient could be expressed as the activation energy needed for the transition of oxygen from the gas to the water phase. This was verified using the Arrhenius equation. © 1994 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260430207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIn high cell density batch fermentations,Zymomonas mobilisproduced 91 g L−1ethanol in 90 min but culture viability fell significantly. Similar viability losses in rapid fermentations by yeast have recently been shown to be attributable in part to the high rate of change of the extracellular ethanol concentration. However, in simulated rapid fermentations in which ethanol was pumped continuously to low cell densityZ. mobilissuspensions, increases in the rate of change of ethanol concentration in the range 21–83 g L−1h−1did not lead to accelerated viability losses. The lag phase ofZymomonascultures exposed to a 30‐g L−1step change in ethanol concentration was much shorter than that ofSaccharomyces cerevisiae, providing evidence that the comparative insensitivity ofZymomonasto high rates of change of ethanol concentration is due to its ability to adapt to changes in ethanol concentration more rapidly than yeast. © 1994 John Wil

ISSN:0006-3592    

DOI:10.1002/bit.260430208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA spinning cylindrical filter, known as a spinfilter, permits the mammalian cell bioreactor operation at high perfusion rates leading to very high cell densities (107mL−1). Filter screens with openings (25 μm) slightly larger than the average cell size have been used to retain single cells in suspension over a long period of operation without clogging. We have previously shown why it is necessary to optimize the rotational speed of the spinfilter in order to achieve efficient cell retention and avoid potential screen clogging. Effects of bulk mixing and perfusion rate on screen fouling and cell retention were also investigated. Based on this analysis, in this article, we suggest strategies for scaleup of spinfilters. Experimental data from 12‐ and 175‐L (working volume) bioreactors is shown in support of the scaleup analysis. © 1994 John Wiley&So

ISSN:0006-3592    

DOI:10.1002/bit.260430209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA visualization chamber has been developed to analyze potential correlations between osmotic step increase on yeasts and the resultant cell volume decreases. Image analysis was used to characterize the step increases in the center of the chamber and to measure the changes in the cell volume. Step increases of different intensities have been performed on the yeastSaccharomyces cerevisiae. This device has allowed the kinetics of the volumetric evolution of the cells to be observed. The water exit flow rate from the cell was found to occur in the first 10 s following the hypertonic step change. Comparison of the time constants of the chamber and of the cell volume variations allowed to conclude that the time constant of the water transfer across the membrane was short (about 1 s). © 1994 John Wiley&Sons, Inc

ISSN:0006-3592    

DOI:10.1002/bit.260430210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractKinetic data for lipase‐catalyzed interesterification reactions between free fatty acids and triglycerides were collected and the dynamics of the interesterification reactions were successfully modeled using tow rate experssions requiring a total of five adjustable parameters. One rate expression describes the disappearance of the free fatty acid (octanoic or linolenic acid), and the second describes the rate of release of fatty acid residues from the triglycerides (olive oil or milkfat). This model is able to account for the effects of the concentration of all chemical species participating in interesterification throughout the entire reaction. When the data for both milkfat and olive oil were subjected to nonlinear regression analyses using the same mathematical model, the parameter estimates for both systems were comparable. In addition to reproducing the tendencies observed experimentally, simulations of the interesterification system under a variety of initial conditions provided insight into the effects of several reaction variables which could not be examined experimentally. Among the most significant findings of the simulation work are (1) there is a limit beyond which increasing the initial concentration of water produces no further increase in the initial rate of the interesterification reaction; (2) an increase in the initial concentration of lower glycerides produces a concomitant increase in the rate of the interesterification reaction; (3) the free fatty acids inhibit the rate of hydrolysis of the fatty acid residues of the triglycerides; (4) there is a limit beyond which increasing the initial concentration of triglycerides produces no significant increase in the rate of either the hydrolysis reaction or the interesterification reaction. © 1994 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260430211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY