Colloidal stability of bovine calcium caseinate suspensions. effect of protein concentration and the presence of sucrose and lactose

Abstract

Sodium caseinate suspensions (Cas) are stabilized as submicelles in a dynamic system consisting of caseins α, β, and κ. Their use in the food industry is quite widespread because of their functional properties and nutritional value. In the presence of calcium ions, Cas are able to form colloidal stable aggregates in suspension (CCA) at certain Ca2+ and Cas concentration ratios (Ca:Cas). The aim of this work was to study the effect of the protein concentration on the CCA solubility and viscosity at different Ca:Cas and to relate those two functional properties to protein composition and conformational changes. The stability of CCA was also evaluated in the presence of lactose and sucrose. The apparent solubility of the CCA was determined by applying a spectrophotometric method, and the stability test parameters were obtained using a model based on thermodynamic linked functions. The protein conformational changes were followed by using fluorescence techniques and were related to the partial specific volume and the intrinsic viscosity. The experimental data obtained allowed us to conclude that the stability of CCA depends on the initial protein concentration for the same Ca:Cas ratio. A model based on multiple-step equilibrium was proposed as an approach to explain the stability of Cas against Ca2+. Furthermore, it was observed that the addition of Ca2+ to Cas generates changes in the protein conformation, leading to more compact and symmetrical structures. The colloidal stability of the CCA was favored by the presence of sugars, especially by lactose.