An example is given in Figure 17.19. It is seen that a gel was formed
after about 30%of the protein had been denatured, i.e., at a denatured
protein concentration of about 1.4%. Then a permeability and a shear
modulus could be measured. However, the permeability soon reached a kind
of plateau value, although it kept slowly decreasing, until almost all protein
had been denatured. The modulus, however, strongly increased with time.
This can most likely be interpreted as the formation of a space-filling
network that is initially more or less fractal, after which denatured protein
molecules or protein particles are deposited onto the existing network. The
network then will keep about the same overall geometry, although the pores
become somewhat smaller, whereas the junctions between the particles will
be greatly strengthened, and the network strands will become much stiffer.
FIGURE17.19 Changes occurring when keeping a 4.5%solution of a whey protein
isolate (in 0.4 M NaCl) at 68.5 8 C for various timest(h). Shown are fraction of the
protein undenatured (crel), gel permeability (B/10^15 m^2 ), and dynamic shear
modulus (G^0 /Pa). (From results by M. Verheul, S. P. F. M. Roefs. Food
Hydrocolloids 12 (1998) 17.)