Abstract :
Rheology modifiers are widely used in the food industry as thickeners, gelling agents and emulsifiers. Under investigation are the effects of the additive xanthan on an idealised suspension of ‘hard-sphere’ monodisperse polystyrene latex. The flow curves of a variety of these systems are measured using a controlled stress Carri-med rheometer. As the suspending medium is non-Newtonian, the xanthan-modified suspensions do not obey the usual, simple, scaling laws seen with latex and pure water. When the apparent viscosity is reduced relative to that of the medium at zero shear rate, a single reduced flow curve is obtained, irrespective of xanthan concentration. This scaling approach is currently being extended to be used with an approximation to a real food system, of starch and glucose syrup, and a variety of modifiers including pectin, alginate and guar gum. The preliminary results from these experiments indicate that there is a general reduced flow curve for suspensions of particles in various non-Newtonian media which, when obtained for one medium concentration, could be used to interpret the flow curves of suspensions of the same particles in different non-Newtonian media. This will lead to a technique of simplifying complex non-Newtonian flow curves and therefore predicting the rheological flow curves and fluid mechanics when different modifiers are added to food suspensions.
