Rheological Properties of Hydrolysates of Proteins from Extracted Sunflower Flour Adsorbed at the Air-Water Interface

In this paper, we present surface dilatational properties of a sunflower protein isolate (SPI) and its hydrolysates at different degrees of hydrolysis (DH = 5.62%, 23.5%, and 46.3%) adsorbed on the air-water interface, as a function of adsorption time. The surface rheological parameters (surface dilatational modulus, E, its elastic, Ed, and viscous, Ev, components, and phase angle, (phi)) were measured as a function of protein concentration (ranging from 1 to 1 * 10^-5% w/w) at pH 7.0, ionic strength (I) 0.05 M, and 20 (degree)C. We found that the surface dilatational modulus, E, increases with time, (theta). This phenomenon has been related to protein adsorption, unfolding, and/or protein-protein interactions (at long-term adsorption). The dilatational properties of the adsorbed films depend on the degree of hydrolysis of the SPI and on the protein concentration in the aqueous phase. The adsorption kinetics at long-term adsorption is controlled by the penetration and unfolding of the protein at the interface. Sunflower protein isolate and its hydrolysates are adsorbed at the air-water interface with different degrees of association at different concentrations in the bulk phase.