The rheological behaviour of starches and gums is of special importance when they are used to modify textural attributes. These properties could be measured as an indicator of product quality (Marcotte et al., 2001). Yield stress, a well recognized rheological parameters (Liddell & Boger, 1996) plays a vital role in their production.
Six thickeners (starch-based and gum-based) were first characterized for their particle size, true and bulk density and their water absorption kinetics. Thickeners that have smaller particles sizes absorbed more water than thickeners with larger particle sizes. Thickeners that are starch based are more sensitive to temperature and have the highest water absorption abilities.
The yield stress of thickeners was compared using different types of analytical methods, the vane method and the extrapolation of shear-stress data. Thickeners were investigated with concentration from 1.2% to 7.4% (wt/wt). There was a close agreement between vane yield stress and those obtained by extrapolation, however the vane yield stress was much larger than the extrapolated yield stress.
As expected, yield stress increased as concentration increased for all methods. Viscosity decreased as shear rate increased indicating that the thickeners are susceptible to shear thinning behaviour.