Emulsifying behaviour and rheological properties of the extracellular polysaccharide produced by Pseudomonas oleovorans grown on glycerol byproduct

The functional properties of a novel extracellular polysaccharide (EPS) produced by Pseudomonas oleovorans grown on glycerol byproduct, generated by the biodiesel industry, were investigated. The EPS is a high molecular weight (4.6 × 10⁶) heteropolysaccharide, composed by neutral sugars (galactose, 68%; mannose, 17%; glucose, 13%; rhamnose, 2%; fucose, 4%) and acyl groups (3.04%). This biopolymer has pseudoplastic fluid behaviour in aqueous media. The apparent viscosity was stable for the pH range 2.9–7.1 and NaCl concentrations up to 1.0 M. Though the apparent viscosity decreased at high temperatures, at alkaline conditions and at NaCl concentrations of 2.0 M, pseudoplastic fluid behaviour was retained. The EPS was capable of stabilizing water emulsions with several hydrophobic compounds, including hydrocarbons, vegetable and mineral oils. It retained its emulsifying activity during exposure to wide temperature (30–50 °C) and pH (2–12) variations, as well as to the presence of NaCl at concentrations as high as 2.0 M.     

Characteristics of a novel high viscosity polysaccharide,methylan, produced byMethylobacterium organophilum

Summary A new anionic high molecular weight polysaccharide, Methylan, was produced byMethylobacterium organophilum from methanol as a sole source of carbon and energy under the specific culture conditions. By GPC and light scattering, the molecular weight was determined to be 2–4×10⁶ dalton and the distribution of molecular weight was very homogeneous. Methylan was composed of carbohydrate (80%), uronic acid (12%), protein (6%) and pyruvic acid (5%). The sugar composition of Methylan was identified as glucose, galactose and mannose with the approximate molar ratio of 232. Methylan solution showed a pseudoplastic non-Newtonian fluid property at the concentration above 0.05%. At the concentration of 1% Methylan solution, the consistency index was 18,000 centipoise which was almost 10 times higher than that of Xanthan and the flow behavior index was 0.15.     

New Culture Medium to Xanthan Production by <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv<Emphasis Type="Italic">. campestris</Emphasis>

Xanthan is a important biopolymer for commercial purpose and it is produced in two stages by Xanthomonas campestris. In the first one, the bacterium is cultivated in the complex medium enriched in nitrogen and the biomass produced is used as inoculum for the next stage in which the gum is produced in another medium. In this work a new medium for the first stage is proposed in place of currently used YM medium. Different formulated growth media were studied and the correspondent biomass produced was analysed as inoculum for the second stage. The inoculum and gum were produced by batch process in shaker at 27°C in pH 6.0 and at 30°C in pH 7.0, respectively. The gum was precipitated with ethanol (3:1 v/v). The dryed biomass and xathan gum produced were determined by drying in oven at 105 and 40°C, respectively. The viscosity of the fermentation broth and 1% gum solution in water were determined in Brookfield viscometer. The formulated medium presented the increase in gum production (30%), broth (136%) and 1% gum solution viscosity (60%) compared to YM, besides the inferior cost. The results showed the importance of the quality of the inoculum from the first stage of the culture which influenced on the gum viscosity in the second stage.     

Rheological Behaviour of Instant Hot Chocolate Beverage: Part 1. Optimization of the Effect of Different Starches and Gums

In this study, effects of different starches (tapioca (TS), wheat (WS), corn (CS), potato (PS), modified corn (MCS) and modified potato (MPS)) and gums (xanthan gum (XG), guar gum (GG), alginate (A), salep (S), locust bean gum (LBG) and carrageen (C)) on the rheological properties of model hot chocolate beverage were studied. Swelling power (SP) of the starches and water absorption capacity (WAC) of the gums were determined. Hot chocolate beverages showed pseudoplastic behaviour. Ostwald de Waele model accurately described flow behaviour of each beverage sample. K, n, R ² values for Ostwald model were in the range of 4.8–160.3 mPa.sⁿ, 0.5117–0.9745, 0.9972–0.9998, respectively. The highest synergic effect in the model was observed between the interaction of MCS and XG. The XG-PS, XG-TS, XG-CS combinations showed the highest K and viscosity values, respectively.     

Rheological properties of polysaccharides produced by a Zoogloea sp.

A newly isolated marine bacterium, identified as Zoogloea sp., produced two different polysaccharides: one was water-soluble and the other was cell-bound. Both had non-Newtonian, pseudoplastic fluid behaviour and the solutions had low activation energies. The solutions of these polysaccharides showed rheological behaviour over a wide range of pH (2–12) and temperature (20–80 °C), and compatibility with NaCl.     

The influence of the non-Newtonian properties of blood on the flow in large arteries: unsteady flow in a 90 degrees curved tube.

A numerical and experimental investigation of unsteady entry flow in a 90 degrees curved tube is presented to study the impact of the non-Newtonian properties of blood on the velocity distribution. The time-dependent flow rate for the Newtonian and the non-Newtonian blood analog fluid were identical. For the numerical computation, a Carreau-Yasuda model was employed to accommodate the shear thinning behavior of the Xanthan gum solution. The viscoelastic properties were not taken into account. The experimental results indicate that significant differences between the Newtonian and non-Newtonian fluid are present. The numerical results for both the Newtonian and the non-Newtonian fluid agree well with the experimental results. Since viscoelasticity was not included in the numerical code, shear thinning behavior of the blood analog fluid seems to be the dominant non-Newtonian property, even under unsteady flow conditions. Finally, a comparison between the non-Newtonian fluid model and a Newtonian fluid at a rescaled Reynolds number is presented. The rescaled Reynolds number, based on a characteristic rather than the high-shear rate viscosity of the Xanthan gum solution, was about three times as low as the original Reynolds number. Comparison reveals that the character of flow of the non-Newtonian fluid is simulated quite well by using the appropriate Reynolds number.     

Kinetics and physico-chemical characterization of exopolysaccharides produced by the cyanobacterium Oscillatoria formosa

Exopolysaccharides of the cyanobacterium Oscillatoria formosa have been physico-chemically characterized and kinetics of their production studied. The organism produced 334.8 μg EPS per ml culture in 24 days with the maximum rate of production obtained during initial days of growth. HPLC analysis of the EPS hydrolysate revealed that besides three unidentified sugars, EPS contained ribose, mannose, and galacturonic acid. FT-IR spectrum of EPS revealed the presence of methyl, carboxyl and C–N groups. Elemental analysis indicated the presence of 4.7% nitrogen in EPS. The organism produced 75.6% more EPS when incubated at 35°C compared to cultures at 28°C. Under varied nutritional conditions, though the growth of the organism was less yet it produced enhanced amounts of EPS. Aqueous dispersions of EPS showed non-Newtonian, pseudoplastic behaviour. The viscosity of the aqueous solution of EPS was quite stable over a wide range of pH and temperature but it was observed to be affected by CaCl_2.     

Characterization and production of a new extracellular polymer from Pseudomonas sp. GSP-910

Summary A new strain, Pseudomonas sp. GSP-910 has been isolated from soil and has been found to produce large quantities of an extracellular, highly viscous polysaccharide in a simple salt medium. Good polymer production (6.16 g·l^-1) occurs on a sucrose-containing medium (2%) at high phosphate concentration (80 mM·l^-1) and 0.5 g·l^-1 of nitrogen source NH₄Cl. The relative proportions of sugars in the polymer are: glucuronic acid 8.8%, glucose 28.07%, galactose 56.8%, and it is partially acetylated (6.32%). The isolated polymer exhibits higher viscosity at dilute concentrations than xanthan gum and it is stable at different temperatures, over a wide range of pH and in the presence of monovalent salt. In the presence of divalent cation (CaCl₂ 0.5%), 910-gum in aqueous solution (1%) solidifies to a resilient gel.     

Concentration and shear rate dependence of viscosity in random coil polysaccharide solutions

The concentration (c) and shear rate (γ) dependence of viscosity (η) has been studied for a wide range of random coil polysaccharide solutions, and the following striking generalities are observed:

1. 1. The transition from dilute to concentrated solution behaviour occurs at a critical concentration , when ‘zero shear’ specific viscosity (η_sp) ≈ 10. η_sp varies as c^1.4 for dilute solutions, and as c^3.3 for concentrated solutions.

2. 2. The shear rate dependence of viscosity, and frequency dependence of dynamic (oscillatory) viscosity are closely superimposable.

3. 3. Double logarithmic plots of against (where η₀ is ‘zero shear’ viscosity, and is the shear rate at which ) are essentially identical for all concentrated solutions studied, and thus the two parameters η₀ and completely define the viscosity at all shear rates of practical importance.

Departures from points 1 and 2, but not 3, are observed for concentrated solutions of locust bean gum, guar gum, and hyaluronate at low pH and high ionic strength and are attributed to specific intermolecular associations (‘hyperentanglements’) of longer timescale than non-specific physical entanglements.     

Xanthan gum production under several operational conditions: molecular structure and rheological properties*

Xanthan gum production under several operational conditions has been studied. Temperature, initial nitrogen concentration and oxygen mass transfer rate have been changed and average molecular weight, pyruvilation and acetylation degree of xanthan produced have been measured in order to know the influence of these variables on the synthesised xanthan molecular structure. Also, xanthan gum solution viscosity has been measured, and rheological properties of the solutions have been related to molecular structure and operational conditions. The Casson model has been employed to describe the rheological behaviour. The parameter values of the Casson model, tau(0) and K(c), have been obtained for each polysaccharide synthesised under different operational conditions. Both pyruvilation and acetylation degrees and average molecular weight of xanthan increase with fermentation time at any operating conditions. Xanthan molecules with the highest average molecular weight have been obtained at 25 degrees C. Nevertheless, at this temperature acetate and pyruvate radical concentration are lowest. Nitrogen concentration in broth does not show any clear influence over xanthan average molecular weight, although with high nitrogen source concentration xanthan with low pyruvilation degree is produced.     

Rheology and Shear Stress of Centaurea calcitrapa Cell Suspension Cultures Grown in Bioreactor

Centaurea calcitrapa suspension cultures were grown either in Erlenmeyer flasks or in a mechanically stirred bioreactor. Its rheological behaviour, when fitted to the Oswald–de Waele model (power law), showed pseudoplastic characteristics in both cases. The flow behaviour index (n) decreased over the course of a growth cycle and the consistency index (K) increased, reached a value of 1.81 N sⁿ m⁻² run on 2 l bioreactor. Bioreactor cultivation of C. calcitrapa cells at different agitation rates (30, 60, 100 and 250 rpm), highlighted the influence of shear forces on cell viability loss (90–34%) and phenol accumulation (74–140 μg l⁻¹), due to increased stirring speeds. Analysis of these results suggests that this cell line is shear-sensitive. An empirical exponential correlation was defined between apparent viscosity and biomass concentration, under the studied conditions, giving the possibility to estimate the prevailing broth regime and to optimize bioreactor design. Revisions requested 10 October 2005; Revisions received 19 December 2005     

Influence of Guar Gum on the In Vitro Starch Digestibility—Rheological and Microstructural Characteristics

The present study investigates the effect of guar gum on the digestibility of a waxy maize starch in vitro under simulated gastric and intestinal conditions. A detailed rheology and confocal scanning laser microscopy of the digesta were performed in order to study the possible mechanisms of interactions involved during in vitro hydrolysis of starch. No starch hydrolysis was observed under simulated gastric conditions, whereas more than 90% hydrolysis was observed at the end of digestion under simulated intestinal conditions. In the presence of guar gum, the starch hydrolysis was reduced by nearly 25% during the first 10 min and by 15% at the end of in vitro intestinal digestion. The rheological behavior of the digesta was significantly affected in the presence of the gum. The viscosity of digesta decreased during intestinal digestion; however, the extent of decrease was quite low in the presence of guar gum. The consistency index increased and flow behavior index of digesta decreased in the presence of gum after 1 min of intestinal digestion. All the samples (digested or undigested) displayed a pseudoplastic behavior as their apparent viscosity (η _a) decreased with an increase in shear rate. A negative correlation between the starch hydrolysis (%) and storage modulus for the starch sample without gum and a positive correlation for the starch sample with gum were found. Large granule remnants observed through confocal micrographs have shown that the solubilization of starch granule remnants during in vitro digestion is significantly reduced in the presence of gum.     

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     

Investigations into the rheological characteristics of bovine amniotic fluid

The rheological characteristics of bovine amniotic fluid have been studied at different shear rates. The viscosity of bovine amniotic fluid at 20°C was found to increase with time at a constant low shear rate during the measurement. Additionally, the viscosity was observed to decrease with increasing shear rate, indicating that a shear thinning behaviour of the fluid was occurring. The log-log plot of shear stress versus shear rate yielded a straight line, consistent with non-Newtonian behaviour of the fluid and characteristic of pseudoplastic liquids. The data of shear stress versus shear rate could be represented by a power law model. The treatment of amniotic fluid with cetylpyridinium chloride (CPC) resulted in the precipitation of a mixture of components, including complex sulphated polysaccharides and extracellular proteoglycans, with the viscosity of the resulting liquid similar to that of water at 20°C. In addition, the viscosity of the CPC-pretreated fluid did not increase with time at constant shear rate and remained constant with the increase in shear rate. The apparent increase in viscosity with time and the shear thinning behaviour of the amniotic fluid can thus be attributed to pseudoplastic liquid behaviour associated with the presence of structurally complex polysaccharides and extracellular proteoglycans. The implications of this fluid viscosity behaviour are discussed in terms of their impact on the operation of packed or expanded (fluidized) chromatographic bed systems when amniotic fluid biofeed-stocks are used as a source of commercially important proteins.     

Structural elucidation, modification and characterization of seed gum from Cassia javahikai seeds: A non-traditional source of industrial gums

A water-soluble seed gum was isolated from seed endosperm of Cassia javahikai. The acid-catalyzed fragmentation, methylation, selective enzymatic degradation and periodate oxidation suggested a heteropolymeric structure for the polysaccharide. The polysaccharide was shown to have a linear chain of β(1 → 4) linked d-mannopyranosyls units with side chains of α(1 → 6) d-galactopyranosyl units. Grafting of polyacrylamide onto the gum was performed using K₂S₂O₈/ascorbic acid redox system in presence of Ag⁺ as catalyst at 35 ± 2 °C. The viscosity of the gum solution increased on grafting and the grafted gum was observed to resist biodegradation for more than 256 h. Thermogravimetric analysis revealed that grafted gum was more thermally stable than native gum.     

Rheological behaviour of some antibiotic biosynthesis liquids

This paper prsents the results of teh study of rheological behaviour of antibiotic biosynthesis liquids obtained by submerged aerobic cultivation of microorganisms belonging to the actinomycete and fungi classes, in stirred tank bioreactors with turbine impellers. These liquids have a non-Newtonian behaviour which follows the power-law rhcological model with a correlation index of over 0.95. The studied liquids are pseudoplastic, and alter their rheological properties, such as consistency index, (K), flow index, (n), apparent viscosity, (η_a), maximum Newtonian viscosity (η₀), with the culture age, microrganism strain and batch conditions. Also, these liquids are time dependent, exhibiting thixotropy. The most viscous liquids are produced by Streptomyces aureofaciens and Streptomyces rimosus cultivation, while that produced by Streptomyces griseus is the least viscous. A higher pseudoplasticity appears after 30 hours culture age. Since all these biosynthesis are aerobic, a careful observation of the rhelogical behaviour dynamics is necessary to avoid the oxygen culture supply limitation and the decrease of the bioreactor performance during biosynthesis.     

Relationship between the Rheological Properties of Thickener Solutions and Their Velocity through the Pharynx as Measured by the Ultrasonic Pulse Doppler Method

The dependence of the dynamic viscoelastic parameters of carboxymethylcellulose (CMC), xanthan gum, and guar gum solutions on the angular frequency (ω) was compared with that of their viscosity (μ) on the shear rate (γ). In addition, the effect of these rheological properties on the maximum velocity through the pharynx, V _max, as measured by the ultrasonic pulse Doppler method, was investigated. The CMC and guar gum solutions examined were taken as a dilute solution and a true polymer solution, respectively. The xanthan gum solution was taken as a weak gel above 0.5% and a true polymer solution below 0.2%. The maximum velocity, V _max, of the thickener solutions correlated well with μ, the dynamic viscosity η′, and the complex viscosity η^*, especially those measured at γ or ω of 20–30 s^?1 (or rad/s) and above, suggesting that μ, η′, and η^* are suitable indexes for care foods of the liquid type for dysphagic patients.     

Hydrodynamic characteristics and mixing behaviour of Sclerotium glucanicum culture fluids in an airlift reactor with an internal loop used for scleroglucan production

The filamentous fungus, Sclerotium glucanicum NRRL 3006, was cultivated in a 0.008 m³ airlift bioreactor with internal recirculation loop (ARL-IL) for production of the biopolymer, scleroglucan. The rheological behaviour of the culture fluid was characterised by measurement of the fluid consistency coefficient (K) and the flow behaviour index (n). Based on these measurements, the culture fluid changed from a low viscosity Newtonian system early in the process, to a viscous non-Newtonian (pseudoplastic) system. In addition, reactor hydrodynamics and mixing behaviour were characterised by measurement of whole mean gas hold-up (ɛ _g), liquid re-circulation velocity (U _ld) and mixing time (t _m). Under identical process conditions, the effects of the viscosity of the culture fluid and air flow rate on ɛ _g, U _ld and t _m were examined and empirical correlations for ɛ _g, U _ld and t _m with both superficial velocity U _g and consistency coefficient K were obtained and expressed separately. The correlations obtained are likely to describe the behaviour of real fungal culture fluids more accurately than previous correlations based on Newtonian or simulated non-Newtonian systems. Journal of Industrial Microbiology & Biotechnology (2001) 27, 208–214. Received 05 June 2000/ Accepted in revised form 18 March 2001     

Rheological properties of cashew gum

Solubilities and rheological properties of dissolved fractions of cashew gum from Anacardium occidentale were investigated. A fraction of gum (64.2%) dissolved in water at 30 °C. A further 13.4% dissolved when the remaining suspension was heated. The fraction that dissolved at 30 °C produced greater solution viscosity than the other fraction or the whole gum. When the pH was raised above 5.5, the solution viscosity dropped sharply.     

Viscoelastic properties of an exopolysaccharide: Aeromonas gum, produced by Aeromonas nichidenii 5797

The viscoelastic properties of Aeromonas (A) gum in water were investigated by using the Rheometric Scientific ARES controlled strain rheometer. An intrinsic viscosity of 8336 ml/g was obtained according to the Fuoss-Straus equation. The effect of salt concentration on intrinsic viscosity revealed that the A gum exists as semiflexible chain. Typical shear-thinning (pseudoplastic) behavior was observed at concentrations higher than 0.52%. The zero shear viscosity (eta(0)) increased with increasing polysaccharide concentration (c) showing a gradient of approximately 1.0, 2.9 and 4.8 in different concentration domains. The critical concentrations c* and c**, at which the transitions from a dilute solution of independently moving chains to semidilute and then concentrated domains occurred, were determined roughly to be 1.2% and 3.5%. The results from dynamic experiments revealed that the A gum solution shows characteristics of polymer solutions without any evidence of gel-like character. All the results from steady and dynamic tests suggest that the A gum is a non-gelling polysaccharide. The temperature dependence of apparent viscosity was described by Arrhenius equation and the flow activation energy was estimated to be 45.2 kJ/mol, which is independent on polymer concentration.