Structure and rheology of heat-set gels of globular proteins - I. Bovine serum albumin gels in isoelectric conditions

The structure and the rheology of systems resulting from heating at 80 degrees C isoelectric solutions of bovine serum albumin (BSA) in the concentration range 10-200 mg/ mi were studied. Small-angle neutron scattering measurements view the systems as being formed of large aggregates of micrometric size with a close packed arrangement of denatured protein molecules. No indication of a fractal structure stands out. The viscoelastic behaviour is linear up to about 5% strain, except in the BSA concentration range 30-90 mg/ml where the linearity limit is below 1% strain. The viscoelastic response was analysed in the Linear domain, or as close as possible to it, by combining the results of dynamic and creep recovery measurements. The dependence on concentration of the steady state viscosity, of the steady state compliance, and of the average retardation time shows a marked change around a concentration C(0) similar to 50 mg/ml, corresponding probably to a percolation threshold.