Mesostructure of fibrillar protein gels

We investigated the mesostructure of three different food proteins (ß-lactoglobulin (ß-lg), bovine serum albumin (BSA), and ovalbumin), after protein assembly at pH 2, using rheology and transmission electron microscopy (TEM). TEM micrographs showed fibrils with a contour length of about 2-7 µm for ß-lg, 100-300 nm for BSA, and 150-300 nm for ovalbumin. Using the results of rheological measurements, the critical percolation concentration (cp) was determined as a function of ionic strength. A decrease of cp with increasing ionic strength was found for all three proteins. All proteins studied in this work assemble into fibrils that form a homigeneoous isotropic network at low protein concentrations. The aggregation process was reversible for BSA, bus irreversible for ß-lg and ovalbumin, which may be due to the formation of intermolecular ß-sheets in these proteins. The linear decrese of cp with the Debye screening length is explained by an adjusted random contact model for charged semiflexible fibrils. Using this model we can estimate a persistence length for each of the proteins. The persistence length was 1.6 ± 0.4 µm for ß-lg, 16 ± 4 nm for BSA, and 300 ± 75 nm for ovalbumin