Foaming and Interfacial Properties of Polymerized Whey Protein Isolate

Yield stresses (τ) of whipped foams prepared from various ratios of native whey protein isolate (WPI) and polymerized whey protein isolate (pWPI) were characterized by means of vane rheometry Yield stress displayed a parabolic response to increasing concentrations of pWPI, peaking at 50%. Foam air phase volume steadily decreased with increasing pWPI content, whereas equilibrium surface tension steadily increased. Dynamic surface tension measurements revealed that native WPI adsorbed much more rapidly than pWPI, presumably because of the latter's larger size. Interfacial dilatational elasticity (E') displayed a parabolic trend with increasing pWPI content, peaking at 50%. This suggested that pWPI coadsorbs with native WPI, bolstering E' of native WPI interfaces. However, too much pWPI caused a weakening of the network. A positive, curvilinear relationship between E' and τ was observed, consistent with a previous observation for WPI foams formed at various pH levels and salt concentrations, further suggesting a general link between these parameters.