Factors affecting rheological characteristics of fibril gels: the case of beta-lactoglobulin and alpha-lactalbumin.

Some of the factors that affect the rheological characteristics of fibril gels are discussed. Fibrils with nanoscale diameters from beta-lactoglobulin (beta-lg) and alpha-lactalbumin (alpha-la) have been used to create gels with different rheological characteristics. Values of the gelation time, t(c), the critical gel concentration, c(0), and the equilibrium value of the storage modulus, G, such as at long gelation times, derived from experimental rheological data, are discussed. Fibrils created from beta-lg using solvent incubation and heating result in gels with different rheological properties, probably because of different microstructures and fibril densities. Partial hydrolysis of alpha-la with a serine proteinase from Bacillus licheniformis results in fibrils that are tubes about 20 nm in diameter. Such a fibril gel from a 10% (w/v) alpha-la solution has a higher modulus than a heat-set gel from a 10% (w/w) beta-lg, pH 2.5 solution; it is suggested that one reason for the higher modulus might be the greater stiffness of alpha-la fibrils. However, the gelation times of alpha-la fibrils are longer than those of beta-lg fibrils.