Study of the shear effects on the mixture of whey protein/polysaccharides—2: Application of flow models in the study of the shear effects on WPI/polysaccharide system

The comparison of the pectin/whey protein isolate (WPI) mixtures and the κ-carrageenan/WPI mixtures were performed using a shear strain-controlled rheometer at pH 7 and at 80 °C. No salts were used in this work. The samples were first pre-sheared for 2 min with a constant shear rate, ranging from 0 to 200 s−1, and then submitted to a sweep of shear rate starting from 0.05 to 600 s−1 for the purpose of obtaining the shear-viscosity flow curves. These curves were analyzed using two shear-viscosity flow models, the Carreau model and its modified expression, through a fitting procedure. When the mix ratio was found to be higher than 0.08 for the pectin/WPI, and 0.06 for the κ-carrageenan/WPI, the viscosities and the hydrodynamic size of the microgel particles of both systems significantly increased, and the systems showed pseudoplastic behaviour. Furthermore, it was found that the viscosity and the hydrodynamic size of the κ-carrageenan/WPI system increased at a more rapid rate than that in the pectin/WPI system under the same conditions. The present work indicated that the above models were very useful to study the sheared system at high temperature.