Abstract
A study of the adsorption of β-lactoglobulin at the air/water interface was made in order to resolve some fundamental aspects of protein interfacial behaviour. Measurements of adsorption rates at constant area, ( A) and constant surface pressure (ψ) were compared. The results demonstrated that dψ/d t can only be used as a measure of the relative rate (d n/d t) in a restricted range of pressure. On this basis, some previous interpretations of protein adsorption kinetics in terms of two separated processes of adsorption and molecular rearrangement are shown to be invalid. A well-defined adsorption isotherm was obtained for β-lactoglobulin up to the highest concentration measured (0.1%). The surface pressure was a linear function of the logarithm of the bulk concentration, in agreement with the simple form of the Gibbs adsorption equation. From the slope, a value of 2.1 nm 2 was calculated for the area per molecule. A comparison of the bulk concentrations calculated from the adsorption isotherm and from the rate of desorption at a fixed pressure, confirmed that desorption is a hindered process with a large activation energy barrier.
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