Rheology and microstructure of dispersions of protein fibrils and cellulose microfibrils

Mixtures of protein based fibrils and bacterial cellulose based microfibrils (BC) were investigated for macroscopic stability, rheology and microstructure, prepared under different conditions. The protein based fibrils are obtained after prolonged heating of whey protein isolate (WPI) at 80 °C at pH 2. Mixtures of WPI and BC microfibrils at pH 2 were stable at BC microfibril concentrations of 0.2 wt% and above. The mixtures were thixotropic showing hysteresis upon the reversal of the shear flow. Upon prolonged heating, the rheological properties and microstructure of the mixtures at pH 2 were modified. It is concluded that the order of mixing and heating only has an effect on G′ when the BC concentration is low. For the viscosity as a function of shear rate the effect of order of mixing and heating is much smaller.