Polysaccharide viscosity data

Viscosity data are reported in Table I for a number of the polysaccharide derivatives in 5% LiCl/N,N-dimethylacetamide solutions. At low concentrations of polymers, an upward curvature in the DSp/c (reduced viscosity) vs c (concentration) plot was observed. Additionally, nonlinear increases in solvent viscosity were observed for increased lithium ion concentrations in the absence of polymer. Therefore, reduced viscosities at 0.25 dl/g are reported. 

Dextran is perhaps one of the most extensively investigated polysaccharides, yet it has not achieved significant commercial success. It dissolves in cold water to produce viscous solutions, but the viscosity is low in comparison to the viscosity of many other polysaccharides used industrially. Viscosity data for a high molecular weight (5 to 40 x 10 Daltons) dextran and xanthan gum are shown in Table VII. 

Thermodynamically unfavourable interactions between two biopolymers may produce a significant increase in the surface shear viscosity (rf) of the adsorbed protein layer. This change in surface rheological behaviour is a consequence of the greater surface concentration of adsorbed protein. For instance, with p-casein + pectin at pH = 5.5 and ionic strength = 0.01 M (Ay = 2.6 x 10 m3 mol kg-2), the surface shear viscosity at the oil-water interface was found to increase by 20-30%, i.e., rp = 750 75 and 590 60 mN s m-1 in the presence and absence of polysaccharide. These values of rp refer to data taken some 24 hours following initial protein layer formation (Dickinson et al., 1998 Semenova et al., 1999a). 

Flaxseed powder and oat bran were utilized as a fat replacer in cake without any detrimental effects (Lee et al., 2004b). Flaxseed significantly decreased viscosity at 20% however, an increase in cake volume was observed, potentially due to the high lipid content which served as a shortening in the presence of nonstarch polysaccharides. However, more data are required to explain the observed phenomenon. Flaxseed powder addition significantly (p < 0.05) darkened crumb color and increased yellowness values. Results indicated that flaxseed was an acceptable additive when used with Nutrim oat bran. 

The viscosity obtained from the above equation in the linear region of a creep experiment can be used to extend the low-shear rate region of apparent viscosity versus shear rate data obtained in a flow experiment by about two decades (Giboreau et al., 1994 Rayment et al., 1998). The low shear rate region of about 10 -10 is often used for the characterization and differentiation of structures in polysaccharide systems through the use of stress controlled creep and non destructive oscillatory tests. The values of strain (y) from the creep experiment can be converted to shear rate from the expression y t) = y t)/t. 

The characteristic viscosity [qjg can be estimated either directly from experiment, or from Equation (16.1) under the condition that b = 0.5, which is valid at the point, if the constant in this equation is known. To test the relationship (16.11), we used the data of Pavlov and co-workers [4] for the polysaccharide rhodexman, for which the Mark-Kuhn-Houwink equation has the form ... 

In general, the polysaccharide is highly branched. The molecular weight is 50-70 kdal. The molecule is nearly spherical in shape, so its aqueous solution behaves like a Newtonian fluid. The viscosity is exceptionally low. At a temperature of 20 °C, the viscosity of a 10% solution is 1.74 cps, a 30% solution 7.8 cps at pH 4 or 8.15 cps at pH 11, and a 40% solution 23.5 cps. These data show that the viscosity is practically unaffected by pH. The solution acquires a thick paste consistency only at concentrations exceeding 60%. 

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