Dextran viscosity

Dextrans are particularly useful and are employed as a plasma substitute. A concentration of about 6% dextran (50,000-100,000 relative molecular weight) has equivalent viscosity and colloid-osmotic properties to blood plasma. Dextran can also be used as non-irritant absorbent wound dressings, an application also suited to alginate gels. 

A prehminary study of the use of larch AGs in aqueous two-phase systems [394] revealed that this polysaccharide provides a low-cost alternative to fractionated dextrans for use in aqueous two-phase, two-polymer systems with polyethylene glycol (PEG). The narrow molecular-weight distribution (Mw/Mn of 1-2) and low viscosity at high concentration of AG can be exploited for reproducible separations of proteins under a variety of conditions. The AG/PEG systems were used with success for batch extractive bioconversions of cornstarch to cyclodextrin and glucose. 

Aqueous standard solutions are a source of certain difficulties In electrothermal atomic absorption spectrometry of trace metals In biological fluids The viscosities and surface tensions of aqueous standard solutions are substantially less than the viscosities and surface tensions of serum, blood and other proteln-contalnlng fluids These factors Introduce volumetric disparities In pipetting of standard solutions and body fluids, and also cause differences In penetration of these liquids Into porous graphite tubes or rods Preliminary treatment of porous graphite with xylene may help to minimize the differences of liquid penetration (53,67) A more satisfactory solution of this problem Is preparation of standards In aqueous solutions of metal-free dextran (50-60 g/llter), as first proposed by Pekarek et al ( ) for the standardization of serum chromium analyses This practice has been used successfully by the present author for standardization of analyses of serum nickel The standard solutions which are prepared In aqueous dextran resemble serum In regard to viscosity and surface tension Introduction of dextran-contalnlng standard solutions Is an Important contribution to electrothermal atomic absorption analysis of trace metals In body fluids. 

This enzymically synthesized dextran differed from that formed by L. mesenteroides organisms only in its lower relative viscosity. Both types of dextran are serologically similar (see page 215). Each reacts with antisera of Leuconostoc and of pneumococcus Types II, XX, and XII, and comparable ratios of activity against these antisera were observed. 

Agarose/ Alginate Dextran/Calcium Chloride Agarose is the thermally gelled precast polmer Dextran adjusts the viscosity. 10... 

Recently, it has been reported that a low molecular weight alternan, with lowered viscosity, can be produced by conducting the s3mthesis of alternan in the presence of D-glucose and endodextranase (23). The latter prevents the formation of dextran by contaminating dextransucrase and the former decreases the molecular size of the alternan by acceptor reactions that terminates alternan polymerization. 

They are most commonly used plasma expanders. It is polysaccharide isolated from beet sugar which is formed by the action of Leuconstec mesenteroides. It is available in mainly two forms depending upon the molecular weight. Dextran 70 (mol. wt. 70,000) available in 6% solution and Dextran 40 (mol. wt. 40,000) available in 10% solution. They are infused intravenously in the treatment of shock. Dextran 40 acts more rapidly than dextran 70. It decreases the blood viscosity and prevents the sludging of RBC s. Dextran 70 remains in circulation for longer period (upto 24 hrs) and is slowly excreted by glomerular filtration. 

Fig. 11. Variation ofTc of [3H]PVP360 transport in solutions of dextran of varying molecular weight as a function of the specific viscosity of the dextran solution (n5PM). Dextran M 1.04 x 10 ( ) Klw 2.04xl(P (O) M - 6.94 x 10 (A) Klw = 15.4x 10 (A) 511...

Figure 8.12 illustrates the effect of complex formation between protein and polysaccharide on the time-dependent surface shear viscosity at the oil-water interface for the system BSA + dextran sulfate (DS) at pH = 7 and ionic strength = 50 mM. The film adsorbed from the 10 wt % solution of pure protein has a surface viscosity of t]s > 200 mPa s after 24 h. As the polysaccharide is not itself surface-active, it exhibited no measurable surface viscosity (t]s < 1 niPa s). But, when 10 wt% DS was introduced into the aqueous phase below the 24-hour-old BSA film, the surface viscosity showed an increase (after a further 24 h) to a value around twice that for the original protein film. Hence, in this case, the new protein-polysaccharide interactions induced at the oil-water interface were sufficiently strong to influence considerably the viscoelastic properties of the adsorbed biopolymer layer. 

Figure 8.12 Time-dependent surface shear viscosity rjS of bovine serum albumin (BSA) + dextran sulfate (DS) at the /7-tetradecane-water interface (pH = 7, ionic strength = 50 mM, 25 °C) ( ) 10 3 wt% DS ( ) 10 3 wt% BSA (A) 10"3 wt% DS added (11) to aqueous sub-phase below the BSA film after 24 h. Reproduced from Dickinson (1995) with permission.

There is currently little understanding of the influence of interfacial composition and (nano)structure on the kinetics of enzymatic hydrolysis of biopolymers and lipids. However, a few preliminary studies are beginning to emerge (McClements et al., 2008 Dickinson, 2008). Thus, for example, Jourdain et al. (2009) have shown recently that, in a mixed5 sodium caseinate + dextran sulfate system, the measured interfacial viscosity increased from qs = 220 mN s m 1 without enzyme to qs = 950 mN s m 1 with trypsin present. At the same time, the interfacial elasticity was initially slightly reduced from (7S = 1.6 mN m 1 to (h = 0.7 mN m, although it later returned to close to its original value. Conversely, in the... 

PGSE measurements on polyethylene oxide) in aqueous dextran solutions were performed by Brown and Stilbs A2) as function of the concentrations of both polymers. The results for D(PEO) depend on the product of the concentration and the intrinsic viscosity of the dextran (host) component, and suggest that coil overlap in the concentrated host solution is the principal impediment to PEO diffusion. 

Cultured milk products are manufactured by fermentation of milk or cream by lactic culture microorganisms that produce desirable flavor and rheological properties which are influenced by the composition of the milk or cream, and by the processing conditions used (Richter 1977 Foster et al. 1957 Marth 1974). Cultured buttermilk may be made from skim milk but is sometimes made from milk containing 1.0 to 3.5% milk fat. Some cultured milk products often contain added MSNF and plant gum or modified starch stabilizers to increase viscosity and control whey syneresis. Dextran-producing culture microorganisms are sometimes used to provide needed viscosity to the cultured milk product without the need to add MSNF or stabilizers. Up to 0.1% citric acid or sodium citrate is commonly added as a substrate for... 

Figure 1. Effects of the concentration of dextrans with various molecular weights on three indices of BBC aggregation (16). MAI indicates the average number of RBCs in each aggregation unit counted under the microscope. ESR is the maximum rate of sedimentation of erythrocytes in a calibrated tube, with corrections made for changes in viscosity and density of the suspending medium following the addition of dextrans. The relative viscosity (t)r) is the ratio of the viscosity of RBC suspension to that of the suspending medium at a shear rate fo 0.1 sec 1. The RBC concentration of the suspension was 1% for MAI and 45% for ESR and r)r measurements. The vertical bars represent SEM. (A), Dx 40 (O), Dx 80 (M), Dx 150 (A), Dx 500 ( ), Dx 2000.

The of normal RBCs suspended in dextran solutions can be determined from measurements of electrophoretic mobility (u), fluid viscosity (Tf), and the dielectric constant (c) (29). 

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