Interfacial properties of whey protein foams as influenced by preheating and phenolic binding at neutral pH

The impact of preheating and phenolic treatment on the adsorption behavior at the air–water interface and subsequent foaming properties of whey proteins isolate (WPI) was investigated. Native WPI (NWPI) and heat-unfolded (80 °C for 9 min) WPI (HWPI) were interacted with gallic acid (GA) or epigallocatechin gallate (EGCG) at pH 7.0. Phenolic treatment slightly increased the unordered secondary structure and significantly decreased the surface hydrophobicity of proteins whereas the effect of EGCG was more remarkable. The protein–phenolic binding was further confirmed by isothermal titration calorimetry. NWPI and HWPI (10 mg/mL) were able to adsorb at the air–water interface to form an elastic film and the adsorption process was dominated by protein unfolding and rearrangement at the interface. Preheating significantly improved the dynamic surface pressure (π) and depressed the dilatational elasticity (E_d) of whey proteins adsorbed at the air–water interface. The heat-induced protein aggregation led to an enhanced foam stability. GA and EGCG induced different patterns of time-dependent π evolution, which were closely related to the phenolic concentration. Both phenolics suppressed the E_d of protein film via weakening protein interactions at the interface. However, foaming properties were significantly enhanced at all phenolic concentrations except for the 240 μmol/g EGCG-treated HWPI, which was corroborated by the foam image.