Viscoelastic characterization of solid-like structure in aqueous colloids of globular proteins

The relationship between viscoelastic properties and the colloidal structure of aqueous colloids of globular proteins, such as ovalbumin (OA), bovine serum albumin (BSA), and rat serum albumin (RSA), has been studied. The OA colloidal systems show a remarkable yield stress sigma(y) and dynamic modulus G', due to a solid-like structure, even in very dilute systems of 0.03 wt.%. The yield stress and rigidity increase sharply with gelation due to the heat denaturation of the OA molecule. They increase with increasing ionic concentration and then decrease, passing through a maximum. The serum albumin systems also have a certain solid-like structure and the values of sigma(y) and G', which are approximately equal to 0.1 Pa for the BSA and 0.08 Pa for the RSA system, remain almost constant over a wide concentration range from about 0.01-10 wt.%. Although this rheological behavior is very characteristic, it seems to be a common property for the colloidal systems of the various globular proteins. The solid-like structure can be strongly related to the electrostatic interaction between the dispersing particles and the size of the particles.