Foaming and air-water interfacial characteristics of solutions containing both gluten hydrolysate and egg white protein

Enzymatically hydrolyzed wheat gluten can be a viable alternative for traditional animal-based foam stabilizing proteins in food systems. Gluten hydrolysates (GHs) can be considered for (partially) replacing surface-active food proteins such as those of egg white (EW). We here studied the foaming and air-water (A-W) interfacial characteristics of mixed GH + EW protein solutions. GH solutions had much higher (P < 0.05) foaming capacities than EW solutions, while the latter had much higher (P < 0.05) foam stability than the former. When only one sixth of EW proteins was replaced by GHs, the foaming capacity of the mixtures was as high as or higher than that of the GH solutions. Furthermore, when half of the EW protein was replaced by GH, the mixtures still had high foam stability. It thus seems that both GH and EW proteins contribute positively to the foaming characteristics of the mixtures. However, measurements of the early stages of diffusion to and adsorption at the interface, plus measurements of surface dilatational moduli at the interface, both suggested that the adsorbed protein film consists primarily of GHs rather than of EW proteins. Nonetheless, FS was higher when EW proteins were present. Mixed GH + EW solutions have a higher resistance to coalescence than GH solutions. Therefore, it is hypothesized that EW proteins form a secondary protein layer below the A-W interface which is maintained by interactions with adsorbed GH constituents, thereby providing bubbles with an additional resistance to coalescence.