The effect of ionic strength on the rheology of pH-induced bovine serum albumin/κ-carrageenan coacervates

Protein/polysaccharide coacervates are frequently applied to food products to control the rheology. This study investigated the effect of ionic strength (I) on the rheology of pH-induced protein/polysaccharide coacervates. Bovine serum albumin (BSA) and kappa-carrageenan were used as a model protein and a polysaccharide, respectively. As the formation of BSA/kappa-carrageenan coacervates increased the turbidity of an aqueous mixture, pH, pH(phi), and pH(max) values were identified corresponding to the pH of the formation of soluble coacervates, insoluble coacervates, and large insoluble coacervates respectively. Based on pH(c), pH phi, and pH(max), a state diagram of BSA/kappa-carrageenan coacervation versus pH and I was constructed. Involvement of salt in coacervation screened out the electrostatic interaction between BSA and K-carrageenan coacervation, resulting in the shift of pH(c), pH(phi), and pH(max) to lower pH. The shift was linearly changed to 1/I-1/2 that corresponded to the Debye length. BSA/K-carrageenan coacervates were more elastic than viscous. The transition from insoluble coacervates to large insoluble coacervates contributed to enhancement of the rheology, especially in elasticity. An increase in the I of a BSA/kappa-carrageenan mixture reduced the degree of coacervation and the elasticity, and the viscosity of BSA/kappa-carrageenan coacervates. (C) 2014 Elsevier Ltd. All rights reserved.