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  • 1
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Fermentation experiments were performed to obtain time-dependent data on broth rheology for three filamentous microorganisms, Streptomyces rimosus, Actinomadura roseorufa and Saccharopolyspora erythraea, cultivated under standard conditions in a mechanically stirred bioreactor. Rheological data were successfully analysed using Mitschka's technique and flow curves of the cultures described by the “power law” model in the range of shear rate between 5 and 100 s–1. Consistency coefficients of the cultures were found to vary continuously with fermentation time while flow behaviour index fell sharply within the first few hours of cultivation and then remained practically unchanged till the end of fermentation. The pH of the biomass was found to have a strong influence on both consistency coefficient and flow behaviour index.
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  • 2
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Measurements of oxygen transfer were made during cultivation of the yeast Saccharomyces cerevisiae in a 90–250 litre working volume concentric tube airlift fermenter. Results demonstrated that the rate of oxygen transfer varies with position in the fermenter, being higher in the riser and top-section than in the downcomer and lowest near the base of the fermenter. The time for liquid circulation was generally smaller than the time constant for oxygen transfer (1/kLa) indicating that the rate of oxygen transfer was slow compared to the rate of liquid movement. Measured dissolved oxygen concentrations therefore did not represent the equilibrium arising from the balance between the rates of oxygen transfer and oxygen depletion. Hence measuredk L a values were not representative of local oxygen transfer conditions but instead were indicators of the rate of mass transfer the liquid flow had encountered prior to reaching the point of measurement. Generally the individual rates of oxygen transfer in the vessel were found to increase with increasing vessel height.
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  • 3
    ISSN: 1432-5233
    Keywords: l-glucose ; Placenta ; Maternal-fetal exchange ; Streptozotocin diabetes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The placental transfer ofd- andl-glucose was investigated in anaesthetised non-diabetic and streptozotocin-induced diabetic rats. Maternal to fetal transfer was determined by perfusing the fetal side of one placenta in situ whilst infusing a mixture ofd-[3-3H]glucose andl-[1-14C]glucose into the maternal circulation. Backtransfer from the fetal to maternal circulation was assessed by determining the uptake of the radiolabelled glucoses from the perfusion fluid during a single passage through the placenta on the fetal side. Maternal diabetes resulted in a reduced utero-placental blood flow but an increased bidirectional transfer ofd-glucose. Non-specific maternal to fetal placental transfer ofl-glucose was greater in diabetic rats than in controls, and the loss ofl-glucose during placental perfusion of the fetal side was, again, greater in diabetic than in control rats. This increased bidirectional ‘leak’ of glucose possibly reflects a functionally compromised placenta, caused by its formation in a diabetic milieu, and may explain the greater fetal-maternal glucose ratios found in diabetic rats relative to controls.
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  • 4
    ISSN: 1432-0428
    Keywords: Keywords Vitamin E ; ascorbic acid ; oxidative stress ; isoprostanes ; nitric oxide ; vascular endothelium ; resistance artery ; diabetes mellitus.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Impaired endothelium-dependent relaxation could underlie many of the vascular complications associated with insulin-dependent diabetes mellitus, and may be mediated by increased oxidative stress. The effect of antioxidants on vascular endothelial function and oxidative stress of streptozotocin-diabetic rats was assessed by dietary supplementation with vitamins E and C. Diabetic (i. v. streptozotocin, 45 mg/kg) male Sprague-Dawley rats were fed one of six supplemented diets containing 75.9, 250, or 500 mg vitamin E/kg chow, 250 mg vitamin C/kg H20, 250 mg vitamin E/kg chow plus 250 mg vitamin C/kg H2O, or chow deficient in vitamin E, and then compared to standard-fed control rats. After 4 weeks, small mesenteric arteries were dissected and mounted on a small vessel myograph, concentration response curves were then constructed to noradrenaline, acetylcholine and sodium nitroprusside. Acetylcholine-mediated relaxation was impaired in arteries from diabetic rats (pEC50 6.701 ± SEM 0.120, n = 8) compared to controls (7.386 ± 0.078, n = 6; p 〈 0.05). The 500 mg/kg vitamin E diet further impaired maximum relaxation to acetylcholine (58.2 ± 10.5 vitamin E, n = 7 vs 84.4 ± 5.3 % standard, p 〈 0.05), and the combined vitamin E plus C diet impaired maximum relaxation to sodium nitroprusside (48.5 ± 4.1 in vitamin E + C, n = 8 vs 75.6 ± 3.9 % standard; p 〈 0.01). However, plasma 8-epi-prostaglandin (PG)F2α (measured as an estimate of oxidative stress) was dose-dependently decreased in rats on vitamin E supplemented diets. Dietary antioxidant supplementation did not reverse impaired endothelial function in this model of uncontrolled diabetes despite a concomitant decrease in oxidative stress. [Diabetologia (1998) 41: 148–156]
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  • 5
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Information about the bursting strength of animal cells is essential if the mechanisms of cell damage in bioreactors are to be understood, and if cell mechanical properties are ever to be related to cell structure and physiology. We have developed a novel cell compression technique that makes it possible to directly measure the bursting strength of single mammalian cells, and to infer information about cell mechanical properties.
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  • 6
    ISSN: 1432-0428
    Keywords: Keywords Diabetes mellitus ; vascular endothelium ; lipids ; antioxidants ; resistance artery ; isoprostanes ; nitric oxide ; acetylcholine ; probucol ; simvastatin.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Oxidative stress and dyslipidaemia are key features of diabetes mellitus and may be involved in mediating the vascular endothelial dysfunction associated with this disease. The aim of this study was to examine the effect of dietary lipid-lowering and antioxidant agents on vascular endothelial function and oxidative stress. Diabetic male Sprague-Dawley rats (i. v. streptozotocin, 45 mg/kg) were fed for 4 weeks on a standard diet or on a diet supplemented with either the lipid-lowering antioxidant probucol (1 % w/w in diet) or the 3-hydroxy 3-methylglutaryl coenzyme-A (HMG-CoA) reductase inhibitor simvastatin (0.01 % w/w in diet). Responses to noradrenaline, acetylcholine, and sodium nitroprusside were assessed in small mesenteric arteries (mean internal diameter 300 ± 5 μm, n = 80) mounted on a small vessel myograph. Plasma concentrations of total cholesterol and triglycerides were significantly raised in standard-fed diabetic rats and significantly reduced in probucol and simvastatin-fed diabetic rats. 8-epi-prostaglandin (PG)F2α, an indicator of oxidative stress, was raised in liver and aorta from diabetic rats compared to controls. Probucol supplementation reduced 8-epi-PGF2α in aorta and liver of diabetic rats but increased 8-epi-PGF2α content in plasma and aorta from control animals. The abnormal relaxation to acetylcholine in arteries from the diabetic rats (pEC50 diabetic 6.763 ± 0.172 vs control 7.541 ± 0.175; p 〈 0.05) was not improved by probucol or simvastatin. These data, therefore, do not support a role for oxidative stress or dyslipidaemia in mediating the impaired ACh-induced endothelium-dependent relaxation of small mesenteric arteries from the streptozotocin-diabetic rat. [Diabetologia (1998) 41: 157–164]
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  • 7
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The influence of mechanical forces resulting from the rotation of (multiple) turbine impellers on the morphology and penicillin production of Penicillium chrysogenum Panlabs P-1 was investigated in batch fermentations using semi-defined media. Experiments were carried out at three different scales of fermentation, 5 dm3,100 dm3 and 1000 dm3 working volume, with the impeller tip speed ranging from 2.5 to 6.3 m/s. Throughout all fermentations, the dissolved oxygen concentration never fell below the critical value for maximum penicillin production. Morphological measurements using image analysis showed that the mean main hyphal length and mean hyphal growth unit increased during the rapid growth period and then decreased to a relatively constant value dependent on the agitation intensity. The specific rate of penicillin production (q pen)and the average main hyphal length during the linear penicillin production phase were lower at high agitation speed, which promoted more rapid mycelial fragmentation and a higher branching frequency. Comparison of the results from the three scales showed that impeller tip speed is a poor scale up parameter whereas a term based on mycelial circulation through the zone of high energy dissipation fitted the data well.
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  • 8
    ISSN: 1432-0428
    Keywords: Keywords Shear stress ; diabetes mellitus ; endothelium ; nitric oxide ; vascular smooth muscle.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Acetylcholine-induced vasodilatation is impaired in animal models of insulin-dependent diabetes mellitus (IDDM), and may result from altered nitric oxide synthesis or release. The response to intraluminal flow, a more physiologically relevant stimulus for nitric oxide release, is unknown. This study examined flow-induced responses in isolated resistance arteries from male Sprague-Dawley control and streptozotocin-diabetic (45 mg/kg i.v, 4 week duration) rats. Mesenteric arteries (4–5th order) were dissected and cannulated on a pressure myograph (mean internal diameter ± SEM at 40 mmHg, control 223 ± 8, n = 9 vs diabetic 239 ± 12 μm, n = 8, NS). Arteries were preconstricted with noradrenaline (1 μmol/l) and intraluminal pressure raised and maintained at 80 mmHg. Luminal flow was raised in incremental steps (0–1.27 μl/s). Arteries from control animals dilated to flow while arteries from diabetic animals constricted (% change in internal diameter ± SEM at 0.79 μl/s: control 13.46 ± 6.52, n = 9 vs diabetic –7.44 ± 3.38 %, n = 8; p 〈 0.005). Incubation with Nω-nitro-l-arginine methyl ester (0.1 mmol/l) abolished flow responses in arteries from controls but not from diabetic rats. In conclusion, impaired flow-induced nitric oxide-mediated vasodilatation may contribute to vascular disease in IDDM. [Diabetologia (1998) 41: 34–39]
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  • 9
    ISSN: 0178-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  Measurements of oxygen transfer were made during cultivation of the yeast Saccharomyces cerevisiae in a 90–250 litre working volume concentric tube airlift fermenter. Results demonstrated that the rate of oxygen transfer varies with position in the fermenter, being higher in the riser and top-section than in the downcomer and lowest near the base of the fermenter. The time for liquid circulation was generally smaller than the time constant for oxygen transfer (1/k L a) indicating that the rate of oxygen transfer was slow compared to the rate of liquid movement. Measured dissolved oxygen concentrations therefore did not represent the equilibrium arising from the balance between the rates of oxygen transfer and oxygen depletion. Hence measured k L a values were not representative of local oxygen transfer conditions but instead were indicators of the rate of mass transfer the liquid flow had encountered prior to reaching the point of measurement. Generally the individual rates of oxygen transfer in the vessel were found to increase with increasing vessel height. Symbols a mean gas-liquid interfacial area per unit liquid volume (m-1) A cross-sectional area (m2) C* saturation concentration of dissolved oxygen (mol/m3) C L dissolved oxygen concentration (mol/m3) d BS Sauter mean bubble diameter (m) g acceleration due to gravity (m/s2) Δh distance between pressure measurement points (m) H Henry’s Law constant for water (Pa/mole fraction) H D height of gas-liquid dispersion from vessel base (m) H DT height of top of draft tube from vessel base (m) H L height of ungassed liquid from vessel base (m) k L liquid side mass transfer coefficient (m/s) k L a volumetric mass transfer coefficient (s-1) M W Molecular weight of water (g/mol) N A specific rate of oxygen transfer to the liquid phase (mol/m3/s) P absolute pressure (Pa) ΔP measured hydrostatic pressure difference (Pa) P 1 pressure at point of gas inlet to vessel (Pa) Q G 0 volumetric flowrate of gas through the sparger (m3/s) R universal gas constant (J/mol.K) T absolute temperature (K) t C liquid circulation time (s) v SG riser superficial gas velocity (m/s) V L ungassed liquid volume (m3) x vertical displacement from base of vessel (m) y 1, y2 mean oxygen mole fraction of inlet and exit gas streams respectively (mole fraction) y 02 oxygen composition of gas (mole fraction) ɛ mean gas hold-up (-) η factor to account for reduction in oxygen solubility in fermentation medium compared with that in water at the same conditions (-) ρ L density of liquid phase (kg/m3) ρ W density of water (kg/m3) Subscripts D downcomer section R riser section TS top-section
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  • 10
    ISSN: 0178-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  Fermentation experiments were performed to obtain time-dependent data on broth rheology for three filamentous microorganisms, Streptomyces rimosus, Actinomadura roseorufa and Saccharopolyspora erythraea, cultivated under standard conditions in a mechanically stirred bioreactor. Rheological data were successfully analysed using Mitschka’s technique and flow curves of the cultures described by the “power law” model in the range of shear rate between 5 and 100 s-1. Consistency coefficients of the cultures were found to vary continuously with fermentation time while flow behaviour index fell sharply within the first few hours of cultivation and then remained practically unchanged till the end of fermentation. The pH of the biomass was found to have a strong influence on both consistency coefficient and flow behaviour index.
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