Effect of Kappa carrageenan on acid-induced gelation of whey protein aggregates. Part I: Potentiometric titration, rheology and turbidity

Gelation of suspensions of whey protein aggregates (WPA) was induced by lowering the pH in-situ using GDL. The effect of adding kappa-carrageenan (KC) on the relationship between the net charge density of the proteins (alpha) and the pH was determined by potentiometric titration. It showed that complexes were formed for alpha > -2. The effect of adding KC on the storage shear modulus and the turbidity was studied by oscillatory shear rheology and UV-Vis spectrometry. The KC concentration dependence was investigated up to 6 g/L at a fixed protein concentration of 20 g/L. Gels were formed for alpha > -3 in the absence of KC and alpha > -3.7 with 2 g/L KC, which was accompanied by an increase of the turbidity starting at the same alpha. The elastic modulus and the turbidity of the gels at steady state increased with increasing alpha. For a given alpha, a strong decrease of the elastic modulus and a strong increase of the turbidity were observed with increasing KC concentration. The effect of the gelation temperature was studied between 20 degrees C and 80 degrees C. The gelation rate increased strongly with increasing temperature and was controlled by the degradation rate of GDL, but it was not influenced by the KC concentration. Increasing the gelation temperature led to an increase of the elastic modulus and the turbidity at steady state.