Fermentation ofCandida utilis for uricase production

Summary Conditions for the production of microbial uricase byCandida utilis were studied. For the selected strain, hypoxanthine proved to be the most effective inducer of uricase formation. The highest values of biomass as well as uricase activity in the mechanically agitated fermentor were obtained under the following conditions: 50 h, rotation impeller speed 7 s^–1, air flow rate 1.25×10^–5 m³s^–1, concentration of inducer 0.1%.List of symbols b width of baffle, m - c length of baffle, m - D diameter of cylindrical fermentor, m - d diameter of impeller, m - d ₁ diameter of impeller disc, m - Fr _m impeller Froud number - g gravitional acceleration, ms^–2 - H height of batch surface above bottom, m - H ₂ height of impeller disc above bottom, m - h height of impeller blade, m - Kp _g flow rate number - L length of impeller blade, m - N rotational speed of impeller, s^–1 - Re _m impeller Reynolds number - T time, h - V volume of batch, m³ - V _g air (gas) flow rate, m³s^–1 - x mass fraction of the dry matter of cells - x ₀ initial value of the mass fraction of the dry matter of cells - _r volume fraction of the dry matter of cells - <eta<₁ viscosity of pure liquid, Pa s - viscosity of batch (suspension of microbial suspension), Pa s - density of batch, kg m^–3     

Performance of cell immobilized packed bed bioreactor for continuous fermentation of alcohol

Experiments were conducted in a packed bed bio-reactor consisting of entrapped yeast cells in alginate matrix for continuous production of alcohol. The variables include initial substrate level, reactor diameter, diameter of the bead and residence time. The influence of these parameters on the conversion of substrate was studied. The film and pore diffusional effects were observed by varying the column and bead diameters, respectively. The pseudo first order reaction rate constant was calculated and correlated with the bead diameter. The effectiveness factor and the Thiele modulus were estimated. A correlation was proposed for fractional conversion in terms of operating variables. It is possible to predict the residence time required and volumetric productivity achieved in a bioreactor for any given initial substrate concentration at any fractional conversion obtained.List of Symbols a _m m²/kg surface are per unit mass of catalyst particle - D m diameter of the reactor - D _e m²/s effective diffusivity - d m particle diameter - h m bed height - k m/s first order reaction rate constant - k m³/(kg · s) pseudo first order reaction rate constant - k _in m³/(kg · s) intrinsic reaction rate constant, (=K/gh) - k _m m/s mass transfer coefficient - P kmol/(m³ · s) volumetric productivity - Q m³/s flow rate of the feed - S kmol/m³ substrate concentration at any time - S _o kmol/m³ initial substrate concentration - S _p kmol/m³ substrate concentration on the gel bead surface - t s reaction time - T (kg · cat · s)/m³ space time (weight of the biocatalyst/flow rate of the feed) - v kmol/(kg · cat · s) reaction rate - V _pfr m³ volume of the packed bed reactor - X [1-(S/S _o)] fraction of the substrate converted in to product Greek Symbols effectiveness factor - Thiele modulus - kg/m³ density of the catalyst particle - s residence time, (= D² h/4Q) - voidage     

The disruption ofSaccharomyces cerevisiae cells and release of glucose 6-phosphate dehydrogenase (G6PDH) in a horizontal dyno bead mill operated in continuous recycling mode

Baker’s yeast was disrupted in a 1.4-L stainless steel horizontal bead mill under a continuous recycle mode using 0.3 mm diameter zirconia beads as abrasive. A single pass in continuous mode bead mill operation liberates half of the maximally released protein. The maximum total protein release can only be achieved after passaging the cells 5 times through the disruption chamber. The degree of cell disruption was increased with the increase in feeding rate, but the total protein release was highest at the middle range of feeding rate (45 L/h). The total protein release was increased with an increase in biomass concentration from 10 to 50% (w/v). However, higher heat dissipation as a result of high viscosity of concentrated biomass led to the denaturation of labile protein such as glucose 6-phosphate dehydrogenase (G6PDH). As a result the highest specific activity of G6PDH was achieved at biomass concentration of 20% (ww/v). Generally, the degree of cell disruption and total protein released were increased with an increase in impeller tip speed, but the specific activity of G6PDH was decreased substantially at higher impeller tip speed (14 m/s). Both the degree of cell disruption and total protein release increased, as the bead loading increased from 75 to 85% (v/v). Hence, in order to obtain a higher yield of labile protein such as G6PDH, the yeast cell should not be disrupted at biomass concentration and impeller tip speed higher than 20% (w/v) and 10 m/s, respectively.     

The influence of bakers’ yeast cells on protein adsorption in anion exchange expanded bed chromatography

Baker’s yeast was disrupted in a 1.4-L stainless steel horizontal bead mill under a continuous recycle mode using 0.3 mm diameter zirconia beads as abrasive. A single pass in continuous mode bead mill operation liberates half of the maximally released protein. The maximum total protein release can only be achieved after passaging the cells 5 times through the disruption chamber. The degree of cell disruption was increased with the increase in feeding rate, but the total protein release was highest at the middle range of feeding rate (45 L/h). The total protein release was increased with an increase in biomass concentration from 10 to 50% (w/v). However, higher heat dissipation as a result of high viscosity of concentrated biomass led to the denaturation of labile protein such as glucose 6-phosphate dehydrogenase (G6PDH). As a result the highest specific activity of G6PDH was achieved at biomass concentration of 20% (ww/v). Generally, the degree of cell disruption and total protein released were increased with an increase in impeller tip speed, but the specific activity of G6PDH was decreased substantially at higher impeller tip speed (14 m/s). Both the degree of cell disruption and total protein release increased, as the bead loading increased from 75 to 85% (v/v). Hence, in order to obtain a higher yield of labile protein such as G6PDH, the yeast cell should not be disrupted at biomass concentration and impeller tip speed higher than 20% (w/v) and 10 m/s, respectively.     

Production of a high viscosity polysaccharide, methylan, in a novel bioreactor

The effect of shear stress on the production of a high viscosity polysaccharide, methylan, from methanol by Methylobacterium organophilum was investigated by using a multidisk mixer. It was observed in the multidisk mixer with defined shear stresses that the specific production rate of methylan increased gradually with increasing shear stress up to 30 Pa, and the production rate was constant beyond 30 Pa. This result suggested that the limited mass transfer from the medium into cells reduced methylan production. A novel bioreactor that provided the large volume of a high shear region was used to increase methylan production. Fed-batch cultures in the novel bioreactor were performed by the dissolved oxygen-stat method of methanol. When 1.13 g/L ammonium ion was added, the concentrations of cells of methylan were 31 and 20.6 g/L, respectively. The productions of cells and methylan in our designed bioreactor were 20 and 50% higher than those obtained in a conventional fermentor. The methylan content reached a maximum of 20.7 g/L in the bioreactor and the viscosity of the fermentation broth was 127 Pa . s, which corresponds to 68 g/L as a xanthan. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 115-121, 1997.     

Anchorage-dependent animal cell culture by using a porous microcarrier

CHO-K1 cells were cultured by using a porous microcarrier. The effects of microcarrier concentration and agitation rate on cell growth in porous microcarrier cultures were investigated. The specific growth rate of 0.041 h^–1 in porous microcarrier cultures was independent of both microcarrier concentration and agitation rate. By estimating the total surface area occupied by cells from the maximum cell number, it was found that not all the surface area of the porous microcarrier was utilizable for cell growth.The maximum cell number decreased with increasing the microcarrier concentration and the agitation rate. From this result, it was also found that not all the cells grown on the interior surface of the porous microcarrier were protected against mechanical damage due to agitation. The protection capacity of the porous microcarrier was estimated to be 300 cells/carrier. The direct gas sparging into the culture broth in porous microcarrier cultures improved the cell density without mechanical damage to animal cells.List of Symbols d m microcarrier diameter - d _i m impeller diameter - d _p m mean pore diameter - n _i s^–1 agitation rate - p Pa pressure difference - v m/s velocity of microcarrier - v _p m/s average velocity flowing through cyclinder - Pa · s viscosity of medium - angle measured from stagnant point - Pa average shear stress - Pa shear stress distribution     

Experiences with a 20 litre industrial bead mill for the disruption of microorganisms

Suspensions of several yeast strains and bacterial species were disrupted in a continuously operating industrial agitator mill of 22.7 litre internal working volume. The influence of agitator speed, flow rate, concentration of microorganisms in the slurry, packing density of glass beads and bead diameter on the disruption process was studied using baker's yeast (Saccharomyces cerevisiae). Cell disintegration was followed by assaying the appearance of protein and the activities of d-glucose-6-phosphate dehydrogenase [d-glucose-6-phosphate:NADP⁺ oxidoreductase, EC 1.1.1.49] and α-d-glucosidase [α-d-glucoside glucohydrolase, EC 3.2.1.20] in the soluble fraction. The best operating conditions for the disintegration of baker's yeast with respect to activity yield appeared to be at a rotational speed of 1100 rev/min, a flow rate of 100 litre h^?1 and a cell concentration of 40% (w/v). The location of the desired enzyme in the cell is of importance for the choice of bead diameter and packing density of the glass beads. Temperature increase and power consumption during disintegration are also strongly influenced by the bead loading in the mill. With optimized parameters, 200 kg baker's yeast can be processed per hour with a degree of disintegration >85%. The disruption process in the mill was found to be very effective for several yeast species tested, e.g. Saccharomyces cerevisiae, Saccharomyces carlsbergensis, and Candida boidinii. The usefulness of the Netzsch LME 20-mill for the disruption of bacteria species was demonstrated with Escherichia coli, Brevibacterium ammoniagenes, Bacillus sphaericus and Lactobacillus confusus. As expected, the mill capacity for bacterial disruption was significantly smaller than for the yeast. Between 10 and 20 kg per h bacteria may be processed, depending on the organism.     

Tracking of single fluorescent particles in three dimensions: use of cylindrical optics to encode particle position.

We present a novel optical technique for three-dimensional tracking of single fluorescent particles using a modified epifluorescence microscope containing a weak cylindrical lens in the detection optics and a microstepper-controlled fine focus. Images of small, fluorescent particles were circular in focus but ellipsoidal above and below focus; the major axis of the ellipsoid shifted by 90 degrees in going through focus. Particle z position was determined from the image shape and orientation by applying a peak detection algorithm to image projections along the x and y axes; x, y position was determined from the centroid of the particle image. Typical spatial resolution was 12 nm along the optical axis and 5 nm in the image plane with a maximum sampling rate of 3-4 Hz. The method was applied to track fluorescent particles in artificial solutions and living cells. In a solution of viscosity 30 cP, the mean squared distance (MSD) traveled by a 264 nm diameter rhodamine-labeled bead was linear with time to 20 s. The measured diffusion coefficient, 0.0558 +/- 0.001 micron2/s (SE, n = 4), agreed with the theoretical value of 0.0556 micron2/s. Statistical variability of MSD curves for a freely diffusing bead was in quantitative agreement with Monte Carlo simulations of three-dimensional random walks. In a porous glass matrix, the MSD data was curvilinear and showed reduced bead diffusion. In cytoplasm of Swiss 3T3 fibroblasts, bead diffusion was restricted. The water permeability in individual Chinese Hamster Ovary cells was measured from the z movement of a fluorescent bead fixed at the cell surface in response osmotic gradients; water permeability was increased by > threefold in cells expressing CHIP28 water channels. The simplicity and precision of this tracking method may be useful to quantify the complex trajectories of fluorescent particles in living cells.     

A new technique for the production of immobilized biocatalyst in large quantities

A new technique is presented for the production of immobilized biocatalysts in large quantities. It consists of breaking up a jet of the biocatalyst/presupport mixture in uniform droplets by means of a resonance technique. Entrapment of yeast and plant cells in calcium alginate has been used as the model. The production capacity of the nozzles used (0.5, 0.8, and 1.1 mm exit diameters) is two orders of magnitude larger than the production capacity of the conventional techniques (maximum capacity with a 1.1-mm nozzle diameter is 24 L/h). Depending on frequency, nozzle diameter, and volumetric flow rate, the bead size varies between 1 and 2 mm, with standard deviations of 3-5% for yeast immobilization and 10-15% for plant cells. The deactivation of both yeast and plant cells is small and comparable to that found in the corresponding conventional procedures.     

Growth and death rates of bovine embryonic kidney cells in turbulent microcarrier bioreactors

Bead-bead collisions have been characterized using the velocity of the smallest turbulent eddies to calculate a turbulent collision severity (defined as the energy of collisions times their frequency), but a shear-based collision mechanism with a different dependence on the system variables is also applicable. This shearbased mechanism and the ratio of smallest eddy size to microcarrier diameter can explain the beneficial effects of both smaller diameter microcarriers and higher viscosity of the medium on the growth rate of bovine embryonic kidney cells. Death rates of these cells have also been measured at several levels of agitation. The decrease in apparent growth rate from increasing agitation is caused both by a higher rate of cell death as well as a lower intrinsic growth rate.List of Symbols B unspecified biological variable - d cm bead diameter - d _i cm impeller diameter - e error in estimate of power number - F _n , F _s (g·cm)/s² normal and shear forces on a cell - Fr Froude number - g 980cm/s² acceleration of gravity - k k^–1 first order death rate constant - m g mass of a bead - n s^–1 impeller rotational rate - n _b number of impeller blades - N _p impeller power number - R _i cm impeller leading edge radius - TCS (g·cm²)/s³ turbulent collision severity - V cm³ reactor volume - v _br cm/s rms relative velocity between beads - v _e cm/s velocity in smallest eddies - X number of cells/cm₃ cell population Greek Symbols volume fraction microcarriers - s^–1 shear rate - cm²/s³ turbulent power dissipation rate - cm size of smallest eddies - g/(cm·s) dynamic viscosity - h^–1 apparent growth rate of cells - ₀ h^–1 intrinsic growth rate of cells in absence of death - v cm²/s kinematic viscosity - _b g/cm³ bead density - _f g/cm³ fluid density - g/(cm·s²) shear stress     

The rotational diffusion of chloroplast phosphate translocator and of lipid molecules in bilayer membranes

The rotational mobility of the phosphate translocator from the chloroplast envelope and of lipid molecules in the membrane of unilamellar azolectin liposomes has been investigated. The rotational dynamics of the liposome membrane were investigated by measuring the rotational diffusion of eosin-5-isothiocyanate(EITC)-labeled L-alpha-dipalmitoylglycerophosphoethanolamine (Pam2 GroPEtn) in the lipid phase of the vesicles, either in the presence or absence of the reconstituted phosphate translocator. The temperature dependence of the anisotropy decay showed that above 25 degrees C the main contribution to the anisotropy decay was caused by uniaxial anisotropic rotation of the labelled lipid molecules around the axis normal to the membrane plane. The rate of rotation of the labelled lipid molecules was strongly dependent on the viscosity of the medium (eta 1). Extrapolation to eta 1 = 0 Pa.s yielded a correlation time of phi = 20 +/- 5 ns, t = 30 degrees C, for lipid rotation with respect to the membrane normal. The rotational diffusion coefficient of the lipid molecules was calculated to be Dr = 2.0 x 10(9) rad2.s-1 and the apparent microviscosity in the vesicle membrane, as derived from the rotational correlation time, was eta 2 approximately 12 mPa.s. The rotational correlation time of the phosphate translocator in the membrane was only slightly dependent on the viscosity of the medium. The temperature dependence of the protein rotation also indicated that the rotation of the protein in the membrane was largely restricted and occurred mainly about the axis normal to the membrane plane. Measurements at a medium viscosity of eta 1 = 1 mPa.s yielded a value of phi r approximately 450 ns corresponding to Dr = 8.8 x 10(7) rad2.s-1 for protein rotation with respect to the membrane normal. From this value and the data of the lipid rotation, the cross-sectional area of the protein part embedded in the membrane was calculated to be approximately 9 nm2. This cross-sectional area is large enough to include at most 14 membrane-spanning helices. Our results also indicated that at lipid/protein molar ratios greater than or equal to 1.5 x 10(4): 1 aggregation occurred in the model membranes below 30 degrees C. However, above 30 degrees C and at a high dilution of the protein in the membrane it appeared that the membrane viscosity monitored by lipid and protein rotational diffusion were identical.     

Forces and Straw Cutting Performance of Double Disc Furrow Opener in No-Till Paddy Soil

Conservation tillage is an energy efficient and low cost tillage system to improve soil environment compared with conventional tillage systems. However, the rice residue management becomes an “impossible to achieve” task due to high soil moisture content at harvest time and the thickness of rice straw. Disc type furrow openers are used for both seed drilling as well as straw cutting during no tillage sowing. A study was conducted to evaluate the draft requirement and straw cutting performances of different sized furrow openers in no-till paddy soil conditions. Double disc furrow opener was tested on an in-field traction bench for three working depths, i.e. 30, 60 and 90 mm, and three forwarding speeds, i.e. 0.1, 0.2 and 0.3 m/s. The draft and vertical forces on the disc were recorded with load cells. These sensors were connected to a data acquisition system developed with hardware and software. The results revealed that the size of the furrow opener, operating depth and the forwarding speed had significant effects (P<0.05) on the horizontal and vertical forces, and the straw cutting performance. Mean values of the draft were 648.9, 737.2 and 784.6 N for the opener with diameters of 330, 450 and 600 mm respectively, and the vertical forces for similar openers were 904.7, 1553.9 and 1620.4 N, respectively. Furthermore, the mean straw cutting efficiencies for the double disc opener with diameters of 330, 450 and 600 mm were 39.36, 78.47 and 65.46%, respectively. The opener with 450 mm diameter provided higher straw cutting efficiency as compared to 600 mm diameter disc, while lowest straw cutting efficiency was observed with 330 mm diameter disc. The 450 mm diameter opener provided the highest straw cutting efficiency (88.6%) at 90 mm working depth and expressed optimum performance compared with other furrow openers.     

Cross-flow filtration as a method of separating fungal cells and purifying the polysaccharide produced

Cross-flow filtration (CFF) has been investigated as a method of separating filamentously growing fungal cells and purifying the polysaccharide produced. The effects of transmembrane pressure, module geometry (e.g. channel height or tube diameter), tangential feed velocity and cell as well as polysaccharide concentration are discussed. Apart from these experiments, influences by the recirculation pump used are shown.List of Symbols b _f fouling index - b factor refering to the behaviour of the sublayer - C kg · m^–3 concentration - C _g kg · m^–3 solute concentration at the membrane - C _b kg · m^–3 solute concentration in the bulk phase - D s_-1 shear rate - k m · s^–1 mass-transfer coefficient - K mPa · sⁿ consistency index - n flow behaviour index - P _w m³ · s^–1 · m^–2 rate of permeation - P _w1 m³ · s^–1 · m^–2 rate of permeation at 1 minute - P _w m³ · s^–1 · m^–2 rate of permeation at the beginning - p Pa pressure - Q m² largest cross-section of a particle - q m² smallest cross-section of a particle - Re Reynolds number - R _f ^–1 fouling resistance - R _m m^–1 membrane resistance - t s time - w m · s^–1 tangential feed velocity Greek Symbols friction factor - pTM Pa transmembrane pressure - mPa · s shear viscosity - _sp specific viscosity (rel. increase of viscosity _sp=_rel-1) - [] m³· kg^–1 intrinsic viscosity - _w m² · s^–1 kinematic viscosity - kg · m^–3 density Indices b bulk - cell cells - f fouling - g gelling - PS polysaccharide - rel relative - sp specific - w water     

Process optimization of an auger pyrolyzer with heat carrier using response surface methodology

A 1 kg/h auger reactor utilizing mechanical mixing of steel shot heat carrier was used to pyrolyze red oak wood biomass. Response surface methodology was employed using a circumscribed central composite design of experiments to optimize the system. Factors investigated were: heat carrier inlet temperature and mass flow rate, rotational speed of screws in the reactor, and volumetric flow rate of sweep gas. Conditions for maximum bio-oil and minimum char yields were high flow rate of sweep gas (3.5 standard L/min), high heat carrier temperature (∼600 °C), high auger speeds (63 RPM) and high heat carrier mass flow rates (18 kg/h). Regression models for bio-oil and char yields are described including identification of a novel interaction effect between heat carrier mass flow rate and auger speed. Results suggest that auger reactors, which are rarely described in literature, are well suited for bio-oil production. The reactor achieved liquid yields greater than 73 wt.%.     

Process and molecular data of branched 1,3-β-D-glucans in comparison with Xanthan

Bioreactor cultivations were carried out with Schizophyllum commune and Xanthomonas campestris. Influence of process parameters and downstream processing on molecular data (molecular weight, intrinsic and shear viscosity) of the secreted exopolysaccharide are shown. Glucan formation of S. commune was enhanced by oxygen limitation. Depending on the type of agitator used, a maximum glucan formation rate of 0.12 kg/(m³ · h) was reached. During cultivation molecular weight and intrinsic viscosity went through a broad maximum with maximum data of 1.3 10⁷ g/mol and 15,400 cm³/g, respectively. After substrate consumption glucan degrading enzymes (glucananses) were released by S. commune. For washing out low molecular substances and concentrating cellfree glucan solutions cross-flow filtration technique with hollow fiber cartridges (molecular cut-off 100,000) were used. After this procedure the shear and intrinsic viscosity were decreased. In contrast to Xanthan, shear viscosity of glucan solutions was not affected by a change in pH from 2 to 12. The intrinsic viscosity of aqueous Xanthan and glucan solutions was opposingly altered by adding salt.List of Symbols A number of capillaries - C ^*g/(dm³ · h) formation rate - D ^–1 shear rate - k Pa/sⁿ consistency index - n flow behaviour index - MW g/mol molecular weight - R m radius - t h time - V dm³ volume - Y yield coefficient - mPas shear viscosity - [] cm³/g intrinsic viscosity - Pa shear stress Indices PS polysaccharide - X cell mass - S substrate - m maximum Dedicated to Prof. Dr. Fritz Wagner on his 60th birthday     

Optimal conditions for hepatitis B core antigen production in shaked flask fermentation

The effects of various environmental factors such as pH (5, 6, 7, 8 and 9), temperature (30, 37 and 40°C) and rotational speed (150, 200 and 250 rpm) on the growth and the hepatitis B core antigen (HBcAg) production ofEscherichia coli W3110IQ were examined in the present study. The highest growth rate is achieved at PH 7, 37°C and at a rotational speed of 250 rpm which is 0.927 h⁻¹. The effect of pH on cell growth is more substantial compared to other parameters; it recorded a 123% different between the highest growth rate (0.927 h⁻¹) at pH 7 and lowest growth at pH 5. The highest protein yield is achieved at pH 9, rotational speed of 250 rpm and 40°C. The yield of protein at pH 7 is 154% higher compared to the lowest yield achieved at pH 5. There is about 28% different of the protein yield for theE. coli cultivated at 250 rpm compared to that at 150 rpm which has the lowest HBcAg yield. The yield of protein at 40°C is 38% higher compared to the lowest yield achieved, at 30°C.     

Preparation of bead-tailed actin filaments: estimation of the torque produced by the sliding force in an in vitro motility assay.

By coating covalently the surface of a polystyrene bead (diameter = 1 micron) with gelsolin, we have succeeded in attaching the bead selectively at the barbed end of an actin filament and forming a 1:1 bead-actin filament complex. On a layer of heavy meromyosin on a nitrocellulose-coated coverglass, this bead-actin filament complex slid smoothly, trailing the bead at its end. Therefore we called this preparation "bead-tailed" actin filaments. The sliding velocity was indistinguishable from that of nonbeaded filaments. With use of this system, we tried to detect the axial rotation (rotation around the filament axis) in a sliding actin filament. Although a single bead at the tail end did not serve as the marker for the axial rotation, we occasionally found another bead bound to the tail bead. In this case, the orientation of the bead-aggregate could be followed continuously with a video monitor while the filament was sliding over heavy meromyosin. We observed that actin filaments slid over distances of many tens of micrometers without showing a complete turn of the bead-aggregates. On the basis of the calculation of rotational friction drag on the bead-aggregate, we estimate that the rotational component of the sliding force and the torque produced on a sliding actin filament (length < or = 10 microns) did not accumulate > 1 pN and 5 pN.nm, respectively. In the present system of randomly oriented heavy meromyosin lying on a nitrocellulose film without an external load.     

Effects of agitator configuration and rotational speed on the production of extracellular polysaccharide by Xanthomonas cucurbitae PCSIR B-52

A strain of Xanthomonas cucurbitae PCSIR B-52, efficiently produced extracellular polysaccharide using partially deproteinized low-acid cheese whey without hydrolysis. The effects of the agitator configuration and rotational speed on the viscosity of the fermented broth and the productivity of extracellular polysaccharide based on bacterial growth were evaluated in a batch process. Agitation was performed by a six-bladed disc turbine impeller and by a similar agitator, equipped with six vertically attached stabilizing fins. Comparatively, the magnitude of the decrease in the DO tension resulting from increased viscosity of the broth was less with the stabilizing-fin agitator due to increased system damping. A drastic increase in the mechanical agitation speed after 30-h fermentation, however, increased the broth viscosity and the accumulation of polysaccharide. Moreover, the volume of the macromixing region decreased with increasing rotational speed of agitator.     

Batch fermentations with a mixed culture of lactic acid bacteria immobilized separately in κ-carrageenan locust bean gum gel beads

Summary Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus were immobilized separately in -carrageenan-locust bean gum gel beads. The beads were prepared by a dispersion process in a two-phase system (water in oil) and two ranges of bead diameter selected by sieving (0.5–1.0 mm and 1.0–2.0 mm). Fermentations with the two strains were conducted in bench bioreactors in a supplemented whey permeate medium. Free and entrapped cells (two ranges of bead diameter and two levels of initial bead cell load) were grown in mixed culture, and carbohydrate utilization, acid production and cell growth or cell release rate measured. Fermentation rates were influenced by bead diameter and initial cell load of the beads. Beads with high initial cell density increased fermentation rates compared to low cell density beads or free cells. Smaller diameter beads (0.5–1.0 mm) showed a stable tendency (not statistically significant p _a > 0.05) towards higher cell release rates, lactose utilization, galactose accumulation and lactic acid production than did larger diameter beads (1.0–2.0 mm). Immobilization of S. salivarius subsp. thermophilus and L. delbrueckii subsp. bulgaricus in separate beads did not seem to affect protocooperation during batch fermentation, and allowed for high cell release rates into the medium.     

Flow behaviour of a POSS biopolymer solution

A non-biodegradable polyhedral oligomeric silsesquioxane (POSS) nanocomposite biopolymer has been developed for fabrication of medical devices and for tissue engineering human organs. The polymer in solution, containing 2 wt% of POSS, has been synthesized, characterized and investigated to determine its key rheological properties. Thus, the variation of shear stress and viscosity as a function of shear rate has been determined at ambient temperature to estimate yield stress and the index of pseudoplasticity, respectively. The temperature dependence of viscosity and the effect of ageing on the viscosity of the polymer have also been investigated. Results are compared with those of a conventional polycarbonate urethane (PCU) polymer solution. The POSS-PCU polymer solution shows near-Newtonian behaviour in the shear rate range to 1000 s(-1), having an apparent viscosity of approximately 3000 mPa s and a pseudoplasticity index of 0.90, decreasing slightly as the polymer solution is aged over 9 months. The temperature dependence of viscosity of the POSS polymer is extremely low and does not change with ageing but the yield strength increases from 2.7 Pa to 8.3 Pa.