PREDICTING THE RHEOLOGY OF FOOD BIOPOLYMERS USING CONSTITUTIVE MODELS

Several constitutive models have been discussed to explain data for so me foods in diluted and concentrated systems. Firstly, the theories of Rouse and Zimm, as well as rod-like theory, were used to study the co nformation of the pectins in dilute solution. Among the dilute theorie s, the random coil theory of Zimm best explained the experimental data and suggested a certain level of intermolecular interaction present i n the dilute pectin solution. The Bird-Carreau constitutive theory wit h four empirical constants and zero shear limiting viscosity was used to describe the viscoelastic properties of the solutions of the guar, CMC/guar, glutenin, gluten and wheat flour doughs. The Bird-Carreau mo del was able to predict eta and eta' in the high and low frequency reg ions for 1% guar solution. In the case of CMC/guar blend, the Bird-Car reau model explained steady shear and dynamic properties very well in the higher shear rate or frequency region of 1-100 s(-1). However, eta ''/omega does not tend to a zero shear constant value. The Bird-Carrea u model also gave good predictions on the theological properties of gl uten and glutenin biopolymers in the free-flow region. The polydispers e type, Doi-Edwards model, fits the experimental G' and G'' better tha n the monodisperse model for 5% apple pectin dispersion. However, ther e is still a discrepancy between experimental and predicted values.