Gelation of whey protein fractal aggregates induced by the interplay between added HCI, CaCl2 and NaCl

Gelation of whey protein fractal aggregates was induced by simultaneously adding salt (CaCl2 or NaCl) and acid (HCl). Further, simultaneous addition of both specifically binding (Ca2+) and non-binding (Na+) cations was studied at a fixed protein charge density. The effect of adding mixtures of ions on pH, gelation kinetics, elastic modulus and gel microstructure was investigated. For all studied systems the time of gelation (t(g)) had an Arrhenius dependence on temperature, characterised by an activation energy (E-a). The value of E-a depended on the type and concentration of added ions. The elastic modulus of gels was found to be independent of the ion composition, reaching 0.2-0.3 kPa at a protein concentration of 40 g L-1 and 1 kPa at 60 g L-1. At conditions of strong electrostatic repulsion between aggregates, addition of NaCl reduced t(g). However, when the repulsions were weak, further addition of NaCl increased t(g). (C) 2020 Elsevier Ltd. All rights reserved.