Protein adsorption at solid-liquid interfaces: Part III--Adsorption from ternary protein mixture.
Simultaneous adsorption of bovine serum albumin (BSA), beta-lactoglobulin and gelatin from aqueous solutions of their ternary mixture to the alumina-water interface has been studied as a function of protein concentration at different values of pH, ionic strength, temperature and weight fraction ratios of proteins. At a fixed weight fraction of beta-lactoglobulin, preferential adsorption (gamma w(lac)) of this protein significantly depends on the amounts of BSA and gelatin present in the solution before adsorption. At higher ranges of protein concentrations, extent of adsorption (gamma w(ser)) of BSA decreases sharply with increase of gamma w(lac) until gamma w(ser) becomes significantly negative, thereby indicating that beta-lactoglobulin and water preferentially adsorbed at the interface are responsible for complete displacement of BSA from the surface. On the other hand, adsorption (gamma w(gel)) of gelatin under similar situation increases mutually with increase in the values of gamma w(lac) in many systems. In few systems, gamma w(gel) also decreases with increase of gamma w(lac) depending upon solution parameters. At pH 5.2, increase of ionic strength and temperature, respectively, increases the extent of adsorption of each protein in the mixture considerably. Extents of adsorption of all proteins are observed to increase when pH is changed from 5.2 to 6.4. The affinities of different proteins in the mixture are expressed in unified scales either in terms of maximum extents of total adsorption or in terms of standard free energies of adsorption of protein mixtures with respect to surface saturation.