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

- pH and ionic strength (I) influence the rheology of coacervates.
- Involvement of salt in coacervation reduced the pH of coacervation to lower pH.
- The pH of coacervation was linearly proportional to 1/I1/2.
- Formation of large insoluble coacervates increased the elasticity of 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 κ-carrageenan were used as a model protein and a polysaccharide, respectively. As the formation of BSA/κ-carrageenan coacervates increased the turbidity of an aqueous mixture, pHc, pHϕ, and pHmax values were identified corresponding to the pH of the formation of soluble coacervates, insoluble coacervates, and large insoluble coacervates respectively. Based on pHc, pHϕ, and pHmax, a state diagram of BSA/κ-carrageenan coacervation versus pH and I was constructed. Involvement of salt in coacervation screened out the electrostatic interaction between BSA and κ-carrageenan coacervation, resulting in the shift of pHc, pHϕ, and pHmax to lower pH. The shift was linearly changed to 1/I1/2 that corresponded to the Debye length. BSA/κ-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/κ-carrageenan mixture reduced the degree of coacervation and the elasticity, and the viscosity of BSA/κ-carrageenan coacervates.