The interaction of chitosan with whey proteins (WPI) was studied by isothermal titration calorimetry (ITC) and turbidity measurements, at different pHs (3.0–6.0) and ionic strengths (100 and 250 mM). ITC results showed that electrostatics is the main driving force for chitosan:WPI interaction, as an increase in ionic strength lead to a smaller interaction. A pH and chitosan:WPI ratio dependence of aggregate formation was clearly observed by turbidimetry. At pH 3.0, there was no change in turbidity upon addition of chitosan, whereas at pH 4.0 and 6.0, the turbidity values varied with chitosan:WPI ratio and were smaller at 250 mM than those at 100 mM.
The rheology of chitosan:WPI coacervates was studied in acetate buffer (100 and 250 mM), at pH 5.5, mixing ratios of 0.25:1 and 0.10:1. Time dependent flow behaviour, higher G′ and G″ values and higher elasticity were observed for the coacervates, originating mainly from the electrostatic interactions between the protein and the polysaccharide chains.