Hydrocolloids as Rheology Modifiers

The rheological behaviour of a very common class of hydrogels, namely polysaccharides are described. Here we concentrate on three polysaccharides, namely xanthan, guar and scleroglucan, as the first two are commonly used thickeners and scleroglucan is a relatively new and underused polysaccharide, which has some advantages over the other two at high temperatures. This review describes the chemical and structural nature of xanthan, guar and scleroglucan. Outlines the methods which can be used to investigate the mechanical, (rheological) behaviour of solutions of these polymers, which is then followed by a description of their rheological behaviour. We demonstrate that the rheological behaviour of Xanthan and scleroglucan are similar, but that scleroglucan is much more stable than xanthan with regards temperature, where the rheology oof scleroglucan is stable up to around 150°C, whereas xanthan starts to deteriorate at around 80°C. Both these polysaccharides have a low but significant yield value making them suitable to prevent sedimentation. Guar on the other hand does not have a significant yield value, and at high shear rates has a significantly higher viscosity, giving the appearance of having a higher viscosity, but it has the advantage of inhibiting ice crystal formation.