摘要:

AbstractMost fermentation models presented in the literature are unstructured, i.e., the biomass composition is assumed constant during all operating conditions. These models are unable to simulate experiments carried out at widely different operating conditions. It is therefore interesting to examine simple structured models where knowledge of the cell physiology is taken into account in the modeling phase. In this article, a simple structured model is presented. The model is based on experimental work with the lactic acid bacteriaStreptococcus cremoris,but due to the similarities in basic metabolism for many microorganisms it is applicable also for other fermentation system. The basic assumption in the model is that the biomass can be divided into two parts (compartments)–an active part and a mainly inactive structural part. The size of the active part has a pivotal role in the mode

ISSN:0006-3592    

DOI:10.1002/bit.260380102

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

年代:1991

数据来源: WILEY

摘要:

AbstractA two‐compartment model for the lactic acid fermentation withStreptococcus cremorisis experimentally verified. The seven parameters of the model are determined using steady‐state chemostat data at varying values of dilution rate,D, but with a constant feed concentration,sf, of a single carbohydrate source (glucose, lactose, or galactose), and a constant feed concentration ofsNfof the N source. Steady‐state measurements of the RNA content at different exit concentrations,s, of the carbohydrate are included to calculate kinetic parameters that determine the cell composition for varying operating conditions. The model is tested using data from a large set of steady‐state and non‐steady‐state experiments: batch fermentations and step and pulse experiments in a chemostat. Both qualitatively and quantitatively the major features of the model are confirmed: the external substrates enter into intracellular high‐energy building blocks, and lactic acid is formed as a by‐product of these reactions. Cell growth depends on the fraction of active components (XA) of the cell and is not accompanied by lactic acid production. Possible model modifications are discussed, primarily to obtain a better description of lactic acid fermentation at nongr

ISSN:0006-3592    

DOI:10.1002/bit.260380103

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

年代:1991

数据来源: WILEY

摘要:

AbstractA two‐compartment model is extended to describe growth and product formation on a mixture of different carbohydrate sources. The open‐ended structure of the compartment model is utilized to include description of the basic mechanisms of catabolite repression. The model is used to simulate batch triauxic, steady‐state, and transient fermentation, and the simulations are compared with experimental results obtained with growth of the lactic acid bacteriaStreptococcus cremorison mixtures of glucose, galactose, and lactose. The model adequately describes characteristic experimental observations such as substrate preference and carbohydrate ado

ISSN:0006-3592    

DOI:10.1002/bit.260380104

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe authors measured the rate of hydrolysis of the homologs of 2‐naphtyl ester by using a Lewis cell with constant interfacial area to elucidate the kinetic mechanism of the lipase‐catalyzed hydrolysis in biphasic system. On the basis of the two‐film model, it was found from the analysis of experimental results that the hydrolysis of these substrates proceeds at the interface between the aqueous and organic phases. The interfacial reaction rate could be correlated by Michaelis–Menten mechanism. The values of the rate constant and the Michaelis constant were almost independent of the kinds of 2‐naphtyl ester. The values of the interfacial kinetic parameters for 2‐naphtyl ester were much greater than those for the hydrolysis in the aq

ISSN:0006-3592    

DOI:10.1002/bit.260380105

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

年代:1991

数据来源: WILEY

摘要:

AbstractFed‐batch cultures of recombinantE. coliHB101 harboring expression plasmid pTRLBT1 or pTREBT1, with acetate concentration monitoring, are investigated to obtain high cell density and large amounts of human epidermal growth factor (hEGF). The expression plasmid pTRlBT1 contains a synthetic hEGF gene attached downstream of the N‐terminal fragment of thetrpL gene preceded by thetrppromoter. The expression plasmid pTREBT1 contains the same coding sequence attached downstream of the N‐terminal fragment of thetrpE gene preceded by thetrppromoter,trpL gene, and attenuator region.E. coliharboring pTREBT1 produces 0.56 mg/L hEGE and immediately degrades it. On the other handE. coliharboring pTRLBT1 produces 6.8 mg/L hEGF and does not decompose it. Prominent inclusion bodies are observed inE. colicells harboring pTRLBT1 using an election microscope. To CultivateE. coliharboring pTRLBT1, a fed‐batch culture system, divided into a cell growth step and an hEGF production step, is carried out. The cells grow smoothly without acetate‐induced inhibition. Cell concentration and hEGF quantity reach the high values of 21 g/L and 60 mg/L, res

ISSN:0006-3592    

DOI:10.1002/bit.260380106

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

年代:1991

数据来源: WILEY

摘要:

AbstractInvestigations were carried out in a 9 m high, 4 m3volume, pilot plant airlift tower loop bioreactor with a draft tube. The reactor was characterized by measuring residence time distributions of the gas phase using pseudostochastic tracer signals and a mass spectrometer and by evaluating the mixing in the liquid phase with single‐pulse tracer inputs. The local gas holdup and the bubble size (piercing length) were measured with two‐channel electrical conductivity probes. The mean residence times and the intensities of the axial mixing in the riser and downcomer and the circulation times of the phases as well as the fraction of the recirculated gas phase were evaluated. The gas holdup in the riser is nearly uniform along the reactor. In the downcomer, it diminishes from top to bottom. The liquid phase dispersion coefficients,DL, are smaller than those measured in the corresponding bubble columns. In the pilot plant with tap water the following relationship was found:DLr=cw SGn; withc= 203.4;n= 0.5;DLr(cm2s−1;) andWSG(cm s−1) whereDLris the longitudinal dispersion coefficient in the riser andWSGis the superficial gas velocity. The gas phase dispersion coefficients in the riser of the pilot plant,DGr, are also enlarged with increasing superficial gas velocity,WSG, however, no simple relationship exists. ParameterDGris the highest in the presence of antifoam agents, intermediate in tap water, and the smallest in ethanol

ISSN:0006-3592    

DOI:10.1002/bit.260380107

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe local properties of the dispersed gas phase (gasholdup, bubble diamater, and bubble velocity) were measured and evaluated at different positions in the riser and downcomer of a pilot plant reactor and, for comparison, in a laboratory reactor. These were described in Parts I and II of this series of articles during yeast cultivation and with model media. In the riser of the pilot plant reactor, the local gas holdup and bubble velocities varied only slightly in axial direction. The gas holdup increased considerably, while the bubble velocity increased only slightly with aeration rate. The bubble size diminished with increasing distance from the aerator in the riser, since the primary bubble size was larger than the equilibrium bubble size. In the downcomer, the mean bubble size was smaller than in the riser. The mean bubble size varied only slightly, the bubble velocity was accelerated, and the gas holdup decreased from top to bottom in the downcomer. In pilot plant at constant aeration rate, the properties of the dispersed phase were nearly constant during the batch cultivation, i.e., they depended only slightly on the cell concentration. In the laboratory reactor, the mean bubble sizes were much larger than in the pilot plant reactor. In the laboratory reactor, the bubble velocities in the riser and downcomer increased, and the mean gas holdup and bubble diameter in the downcomer remained constant as the aeration rate was increased.

ISSN:0006-3592    

DOI:10.1002/bit.260380108

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

年代:1991

数据来源: WILEY

摘要:

AbstractWild‐typeAgrobacterium radiobacterNCIB 9042 has been cultivated in batch cultures on a synthetic medium which was adapted for growth and succinoglucan production. Experiments were carried out in a 4‐L stirred‐tank aerated reactor. Glucose, biomass, polysaccharide, protein, and inorganic‐ and organic‐nitrogen concentrations were measured, and oxygen consumption and CO2production rates were obtained by a gas‐balance technique. Nitrogen balance shows that inorganic nitrogen is entirely recovered into proteins. The carbon balance is satisfied with in ±5%. Stoichiometric equations for biomass growth and succinoglucan synthesis were established. The biosyntheticpolymer pathways including ATP and cofactor consumption were investigated. From previous studies, a(P/O)value of 1.66 is selected for oxygen sufficient cultures. The actual ATP requirements of 25.4 mmol ATP/g succinoglucan (38.5 mol ATP/mol succinoglucan), determined by a metabolic analysis, is 2.39 times the stoichiometric value. Experimental results were modeled by a system of differential equations. The exponential growth phase was described by a nitrogen‐limited Monod equation. Subsequent succinoglucan synthesis followed a slightly modified Luedeking–Piret relation partitioning internal and external polysaccharide. Experimentally determined coefficients are compared with published results for continuous culture ofA. radio

ISSN:0006-3592    

DOI:10.1002/bit.260380109

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe morphology of mycelial fungi in liquid culture effects culture rheology and this in turn may affect product yield. It is therefore important to understand how environmental factors influence mycelial morphology and this paper describes the effect of dilution rate on two strains ofFusarium graminearum,the relatively sparsely branched parental strain (A3/5) and a relatively highly branched “colonial” variant (C106). At any given dilution rate, the concentration of mycelial fragments present at steady state of both strains remained approximately constant with time, suggesting that mycelial fragmentation occurred in a regular manner. However, for both strains fragment concentration decreased with increasing dilution rate. The strains had a similar morphology at a dilution rate of 0.07 h−1. The length of the hyphal growth unit of A3/5 increased with increase in dilution rate, while that of C106 decreased with increase in dilution rate. At all dilution rates, C106 produced up to ten times more macroconidia than

ISSN:0006-3592    

DOI:10.1002/bit.260380110

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

年代:1991

数据来源: WILEY

摘要:

AbstractCleaning of an inorganic ultrafiltration membrane has been quantified through hydraulic, physicochemical, and spectroscopic (infrared and x‐photoelectron spectroscopy) analyses. An efficient cleaning sequence of nitric acid followed by sodium hypochlorite has been proposed for cleaning of defatted whey protein concentrate and milk ultrafiltration membranes. The influence of reversed sequence and time reduction are discussed together with the action of both cleaning chemicals. In spite of residual fouling left after every cleaning sequence studied, hydraulic cleanliness of the membrane was achieved, particularly after the standard procedur

ISSN:0006-3592    

DOI:10.1002/bit.260380111

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

年代:1991

数据来源: WILEY