Calcium and chitosan-mediated clustering of whey protein particles for tuning their colloidal stability and flow behaviour

Whey protein microgel (WPM) particles were prepared by heating whey protein dispersions (40 mg mL⁻¹) at pH 5.8 and 80 °C for 15 min. Supplementation with 5 mM CaCl₂ at pH 6.0 increased the hydrodynamic diameter of WPMs, but did not influence the ζ-potential of the particles. The latter was attributed to clustering of WPMs by Ca²⁺ bridges. Supplementing WPM suspension with chitosan (0.5 mg mL⁻¹) at pH 5.0 caused formation of micron-sized clusters and a progressive increase in suspension viscosity over the subsequent 48 h. The latter was ascribed to development of a complexed lattice that inhibited sedimentation of WPMs. Immediately after chitosan supplementation, the WPM suspension changed from Newtonian to shear-thinning fluid. Fourier transform infra-red spectroscopy results suggested that microgelation proceeded by formation of inter-molecular β-sheets and loss of α-helix structure. It also indicated that chitosan may interact with WPMs at pH 6.0 through its acetyl groups.