Abstract:

A comparative analysis of 2 rheological models such as the Cross model and the Carreau model as well as their separate modified expressions and transmission electron microscopic (TEM) examinations were carried out for elucidating the microstructures of pure whey protein isolate (WPI), pure pectin and WPI/pectin mixture in aqueous solutions at pH 7 without added salts. The concentrations (m/m, %) employed for the solutions were: pure WPI, 5%; pure pectin, 0.8%, 5%and WPI/ 0.8% pectin mixture (5%/0.8%). Both the models were obtained from a shear strain-controlled rheometer over the shear rate range of 0.09s-1 to 600 s-1 and at 80 ℃. The pure WPI and the pure pectin solutions showed Newtonian behaviors, which could be well described by the modified Carreau model. The WPI/pectin mixture, on the other hand, showed shear thinning behaviors and the Carreau model provided a best fit.

Key words: Cross model, Carreau model, shear viscosity, whey protein isolate, pectin