Adsorption of whey protein isolate at the oil-water interface as a function of processing conditions: A rheokinetic study

In this paper we present surface dynamic properties (interfacial tension an d surface dilational properties) of a whey protein isolate with a high cont ent of beta-lactoglobulin (WPI) adsorbed on the oil-water interface as a fu nction of adsorption time. The experiments were performed at constant tempe rature (20 degrees C), pH (5), and ionic strength (0.05 M). The surface rhe ological parameters and the interfacial tension were measured as a function of WPI concentration (ranging from 1 x 10(-1) to I x 10(-5)% w/w) and diff erent processing factors (effect of convection and heat treatment). We foun d that the interfacial pressure, pi, and surface dilational modulus, E, inc rease and the phase angle, phi, decreases with time, theta, which should be associated with WPI adsorption. These phenomena have been related to diffu sion of the protein toward the interface (at short adsorption time) and to the protein unfolding and/or protein-protein interactions (at long-term ads orption) as a function of protein concentration in solution and processing conditions.