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 sc attering measurements view the systems as being formed of large aggreg ates of micrometric size with a close packed arrangement of denatured protein molecules. No indication of a fractal structure stands out. Th e viscoelastic behaviour is linear up to about 5% strain, except in th e BSA concentration range 30-90 mg/ml where the linearity limit is bel ow 1% strain. The viscoelastic response was analysed in the Linear dom ain, or as close as possible to it, by combining the results of dynami c 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 thre shold.