摘要:

AbstractA new adaptive DO (dissolved oxygen) concentration control algorithm considering DO electrode dynamics with response time delay has been developed. A system model with two time‐varying parameters was used to relate the DO concentration with two control variables: air flow rate and agitation speed. Parameters of this model were estimated on‐line using a regularized constant trace recursive least‐squares method. An extended Kalman filter was used to remove the effect of noises from the DO concentration measurements and thus to improve control performance. A discrete one‐step ahead control scheme was adopted to determine control actions based on the parameter estimation results. Experimental results showed that the new adaptive DO concentration control algorithm performed better than other algorithms tested, a PID controller and adaptive algorithms without the DO electrode d

ISSN:0006-3592    

DOI:10.1002/bit.260370702

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe effect of the distribution of pore radii in the resin beads on protein binding was taken into account to analyze the elution profiles of proteins from the polymer‐packed column obtained by repetitive injection method. By assuming that the distribution of pore radii in the resin beads is logarithmic Gaussian, the theoretical curves obtained agreed well with the experimental dat

ISSN:0006-3592    

DOI:10.1002/bit.260370703

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

年代:1991

数据来源: WILEY

摘要:

AbstractA limited number of support matrices have so far been developed for use in magnetically stabilized fluidized bed (MSFB) applications. We have developed a versatile magnetic silica support which can be derivatized readily for both adsorption chromatography and enzyme immobilization by well‐known techniques. A magnetic pellicular bead is prepared by electrostatically depositing alternating layers of colloidal silica and cationic polymer onto macroscopic nickel core particles. The polymer is then burned out and the silica partially sintered to yield a porous shell with 5–80 m2/g of surface area. This magnetic composite was tested as a support for immobilizing invertase. Sucrose was continuously converted to its component monosaccharides with nearly constant activity over the first 8 days and retention of 50% of initial activity after 25 d

ISSN:0006-3592    

DOI:10.1002/bit.260370704

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

年代:1991

数据来源: WILEY

摘要:

AbstractWidespread commercial application of enzymes as catalysts for specialty or commodity chemical synthesis will require their use in nonaqueous systems. While a number of non‐aqueous enzyme applications have been demonstrated, the lack of useful rules for predicting enzyme–solvent interactions has hindered the development of this technology. Both Hildebrand and solvent hydrophobicity (octanol–water partition coefficient) parameters have been used previously to correlate and predict enzyme activity in nonaqueous systems, with some success, but any single‐parameter approach is inherently limited in its ability to reflect the spectrum of possible enzyme‐solvent interactions. Therefore, this study evaluates the three‐dimensional solubility parameter space, as proposed by Hansen, to correlate and predict enzyme activity in microaqueous, miscible, and biphasic nonaqueous systems. Preliminary results suggest that Hansen parameters may be useful for correlating nonaqueous enzyme activity, and that the dispersive and polar parameters may be disproportionately important in single‐phase microaqueous systems. The Hansen hydrogen‐bonding parameter appears to be the only parameter yet evaluated capable of correlating the water requirement for enzyme activity in microaqueous systems, suggesting that water affects protein structure through enthalpic rather than entropic processes in nonaqueous systems. Insufficient data are available for miscible and biphasic systems, but it is proposed that enzyme activity may correlate with the average solubility parameters of miscible systems and of the aqueous phase in b

ISSN:0006-3592    

DOI:10.1002/bit.260370705

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

年代:1991

数据来源: WILEY

摘要:

AbstractA variety of enzymes have been found to acylate sucrose in anhydrous pyridine. The enzymic reaction is highly selective; with trifluoroethylbutyrate as ester donor, enzyme‐catalyzed transesterification of sucrose yielded sucrose 1′‐butyrate and sucrose 6, 1′‐dibutyrate. No sucrose–tributyrates were formed. Using a similar technique, a long‐chain linear sucrose polyester has been prepared using Proleather, an alkaline protease from aBacillussp. This protease catalyzes the esterification of sucrose with bis(2, 2, 2‐trifluoroethyladipate) in a 1:1 ratio to yield a sucrose‐containing polyester withMw= 2100 andMn= 1600 for a polydispersity of 1. 31. Polymers with molecular weights in excess of 13, 000 have been prepared by this enzymic approach, indicating that molecules containing over 30 sucrose units have been produced. The polyester is extremely water soluble and soluble in polar organic solvents. As with the sucrose dibutyrate, the polyester has ester linkages at the C6 and C1′ positions on the sucrose. The polyester can be depolymerized using Proleather in aqueous buffer, pH7. After 9 days in aqueous buffer, Proleather catalyzed the breakdown of the polyester to anMwof ca. 900. This sucrose‐containing polyester may have applications as a water‐absorbent, biodegradable plastic for use as diapers and hygienic products, water‐treatment chemicals, and components

ISSN:0006-3592    

DOI:10.1002/bit.260370706

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

年代:1991

数据来源: WILEY

摘要:

AbstractBacterial chemotaxis, the directed movement of a cell population in response to a chemical gradient, plays a critical role in the distribution and dynamic interaction of bacterial populations in nonmixed systems. Therefore, in order to make reliable predictions about the migratory behavior of bacteria within the environment, a quantitative characterization of the chemotactic response in terms of intrinsic cell properties is needed.The design of the stopped‐flow diffusion chamber (SFDC) provides a well‐characterized chemical gradient and reliable method for measuring bacterial migration behavior. During flow through the chamber, a step change in chemical concentration is imposed on a uniform suspension of bacteria. Once flow is stopped, diffusion causes a transient chemical gradient to develop, and bacteria respond by forming a band of high cell density which travels toward higher concentrations of the attractant. Changes in bacterial spatial distributions observed through light scattering are recorded on photomicrographs during a 10‐min period. Computer‐aided image analysis converts absorbance of the photographic negatives to a digital representation of bacterial density profiles. A mathematical model (part II) is used to quantitatively characterize these observations in terms of intrinsic cell parameters: a chemotactic sensitivity coefficient, μ0, from the aggregate cell density accumulated in the band and a random motility coefficient, μ, from population dispersion in the absence of a chemical gradient.Using the SFDC assay and an individual‐cell‐based mathematical model, we successfully determined values for both of these population parameters forEscherichia coliK12 responding to fucose. The values obtained were μ = 1.1 ± 0. 4 × 10−5cm2/s and χo= 8 ± 3 ± 10−5cm2/s. We have demonstrated a method capable of determining these parameter values from the now validated mathematical model which will be useful for predicting bacterial migration

ISSN:0006-3592    

DOI:10.1002/bit.260370707

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

年代:1991

数据来源: WILEY

摘要:

AbstractA quantitative description of bacterial chemotaxis is necessary for making predictions about the migratory behavior of bacterial populations in applications such as biofilm development, release of genetically engineered bacteria into the environment, and in situ bioremediation technologies. The bacterial chemotactic response is characterized by a mathematical model which relates individual cell properties such as swimming speed and tumbling frequency to population parameters, specifically the random motility coefficient and the chemotactic sensitivity coefficient. Our model includes a nonlinear dependence of the chemotactic velocity on the attractant gradient as well as a dependence of the random motility coefficient on the temporal and spatial attractant gradients, both of which previous analyses have neglected. As we will show, these aspects are critical for interpreting the results from experiments like those performed in the stopped‐flow diffusion chamber (SFDC) because the initial temporal and spatial gradients are very steep. Our analysis demonstrates that values for the random motility coefficient and chemotactic sensitivity coefficient can be obtained from experimental plots of net cell redistribution from initial conditions versus the square root of time. Values for these parameters are determined from experimental measurements of bacterial population distributions in the SFDC as described in the companion article. Using parameter values determined from independent experiments, μ = 1.1 ± 0.4 ± 10−5cm2/s and χ0= 8 ± 3 ± 10−5cm2/s, excellent agreement is found between theoretically predicted bacterial density profiles and actual experimental profiles forEscherichia coliK12 responding to fucose over two orders of magnitude in initial attractant concentration. Thus, our model captures the concentration dependence of this behavioral response satisfactorily in terms of cell population parameters which are derived from individual cell properties and will therefore be useful for making predictions about the migratory behavior of bacterial populations in the

ISSN:0006-3592    

DOI:10.1002/bit.260370708

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

年代:1991

数据来源: WILEY

摘要:

AbstractCatharanthus roseushairy root cultures, genetically transformed withAgrobacterium rhizogenes, produce a wide variety of indole alkaloids. The effect of sucrose, phosphate, nitrate, and ammonia concentrations on growth and indole alkaloid production ofC. roseushairy root cultures were studied by using statistical experimental designs and linear regression analysis. Contradictory effects of these nutrients on growth and indole alkaloid production were found. The maximal growth was obtained by having 77. 8 mg NaH2PO4· H2O/L and 1. 311 g KNO3/L in the medium, whereas the specific production of alkaloids was highest at the lowest levels of all the nutrients studied. The maximal dry weight was obtained with high values of sucrose and ammonia, but clear optimum concentrations could not be found. When having enough nutrients to support reasonable growth, it appeared difficult to affect the specific alkaloid production rates considerably. The growth (dry wt.) with the optimized nutrient concentrations in the medium was more than 50% better than in the control medium with about the same alkaloid production

ISSN:0006-3592    

DOI:10.1002/bit.260370709

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

年代:1991

数据来源: WILEY

摘要:

AbstractA Baker–Perkins corotating twin screw extruder was used as a bioreactor to hydrolyze pregelantinized corn starch by themophilicBacillus licheniformisα‐amylase. The extruder was modeled as a tube, and characterized as a closed system. This characterization is not in the thermodynamic sense; rather, it relates to the profile of a tracer fluid upon entry to and exit from the reaction zone. The reaction kinetics were modeled by a modified first‐order equation, which allowed the dispersion equation to be solved analytically with the Danckwerts boundary condition. Data from several extrusion runs were super‐imposed to obtain a profile to evaluate the model. The dispersion number, determined from the first and second moments of the RTD curve, was primarily a function of the length of the reaction zone. There was good agreement between predictions and experimental data, especially at low dispersion numbers. In general, the axial dispersion model appears to be suitable for analysis of enzymatic reactions of up to 30% conversion. At a fixed flow rate and constant temperature, the extent of starch conversion depends significantly on moisture content, residence time and enzyme dosage, but not on scr

ISSN:0006-3592    

DOI:10.1002/bit.260370710

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

年代:1991

数据来源: WILEY

摘要:

AbstractDevelopment of bioengineering using such biomaterials as plant tissues or genetically produced microorganisms makes it important to accurately estimate the prevailing shear rate in bioreactors because they are generally sensitive to shear. Various authors have discussed ways to estimate the average shear rate in a bubble column or an airlift reactor.1This communication will explain the background consideration for the development of the expression as γav= 50ugby the present authors, and give suggestions for further discussions

ISSN:0006-3592    

DOI:10.1002/bit.260370711

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

年代:1991

数据来源: WILEY