Effect of electrostatic interactions on the percolation concentration of fibrillar beta-lactoglobulin gels

The effect of electrostatic interactions on the critical percolation concentration (c(p)) of fibrillar beta-lactoglobulin gels at pH 2 was investigated using rheological measurements, transmission electron microscopy (TEM), and performing conversion experiments. A decreasing c(p) with increasing ionic strength was found. The fraction of nonaggregated beta-lactoglobulin was independent of ionic strength in the regime of 0.01-0.08 M. TEM experiments showed long fibrils (2-7 microm) for ionic strengths between 0.01 and 0.08 M. Since both the conversion of monomers and the contour length of the fibrils were independent of ionic strength (0.01-0.08M), the linear increase of c(p) with the Debye length can be attributed purely to an increase of electrostatic repulsion between the fibrils. This increase is explained in terms of an adjusted random contact model which takes into account the charge and semiflexibility of the fibrils.