Viscosity of guar gum

The viscosity of guar gum sols is unaffected by pH changes between 4 and 10.5. 

Grafting of polyacrylamide onto guar gum [431] and Ipomoea gum [178] in aqueous medium initiated by the potassium persulphate/ascorbic acid redox system was performed in the presence of atmospheric oxygen and Ag" " ions. After grafting, a tremendous increase of the viscosity of both gum solutions was achieved, and the grafted gums were found to be thermally more stable. 

The viscosity of natural gums, such as cellulose gums, mannogalactans, seaweed, pectin, locust bean gum, guar gum, and tragacanth has important industrial applications in the food, pharmaceutical, cosmetic, textile, adhesives, and paint fields. The characteristics of viscosity are related to specific uses and to the economics of the process. 

In a pseudoplastic mass the shear speed increases together with the shear stress and the viscosity decreases. This behaviour can be seen in solutions of guar gum and alginates. 

The viscosity of xanthan gum solutions is considerably increased, or gelation occurs, in the presence of some materials such as ceratonia, guar gum, and magnesium aluminum silicate. This effect is most pronounced in deionized water and is reduced by the presence of salt. This interaction may be desirable in some instances and can be exploited to reduce the amount of xanthan gum used in a formulation see Section 7. 

The efficacy of guar is probably dependent mainly on its capacity to hydrate rapidly and thus to increase viscosity in the small intestine postprandially. Measurement of the rate of hydration in vitro might therefore be a useful index of the effectiveness of guar formulations. A simple method for monitoring the hydration rate of guar gum has been developed (Ellis and Morris, 1991). Marked differences in hydration rate and ultimate (maximum) viscosity between the different guar samples were observed (Ellis and Morris, 1991). These results may explain why some guar gum preparations are clinically ineffective (Ellis and Morris, 1991). 

Figure 6. Viscosity of mnthan gum, guar gum solutions (0.5% total gum concentration) Brookfield LVT Viscometer, 60 rpm...

Ma X., Pawlik M. 2007. Intrinsic viscosities and Huggins constants of guar gum in alkali metal chloride solutions. Carhnhvdr. Polymers. 70,15-24. 

Haiju, E. Increases in meal viscosity caused by addition of guar gum decrease postprandial activity and rate of emptying of gastric contents in healthy subjects. Panmi-nervaMed, 27, 125-128(1985). 

As their name implies, hydrolysis is the preferred reaction for hydrolases in water under optimal conditions. Some exanq>les in the polysaccharide area include cellulolytic enzymes for biomass conversion (5), proteases for the degradation of guar gum (21), cellulase for viscosity reduction of xanthan gum (21), and P-D-galactosidase for pectin hydrolysis (21). 

Donnelly 13) describes the use of galactose oxidase in combination with catalase for the oxidation of guar gum to produce products with various viscosities or gels under mild conditions for food applications. Oxidized guar gum and locust bean gum can also be used as precursors for various chemically modified polysaccharides. Yalpani and Hall exploited the aldehyde functionality to attach various functional groups via reductive amination, oxidation, and reduction 14), Oxidized guar can also be further oxidized chemically to obtain a... 

The molecular weight of the galactomannan is close to 310kdal. Physical properties correspond to those of guar gum, except the viscosity of the solution is not as high (cf. Table 4.21). 

---