Impact of ethanol on the air-water interfacial properties of enzymatically hydrolyzed wheat gluten

Studying the air-water (A-W) interfacial characteristics of enzymatically hydrolyzed wheat gluten proteins contributes to understanding their potential as alternatives to animal proteins as foaming agents in food products. In this paper, the impact of the presence of ethanol on the A-W interfacial behavior of gluten hydrolysates (GHs) was studied. Regardless of protein concentration, foaming capacity (FC), i.e. the initial amount of foam formed after a standardized whipping procedure, of four structurally different GHs was higher in a solution containing ethanol than in water. However, the rates of diffusion to and adsorption at the A-W interface of the GH constituents was lower in the presence of ethanol than in water. This suggests that the affinity of the GHs for the interface was lower when ethanol was present, which may be due to ethanol-induced conformation changes in the GH constituents or to some kind of competitive effect due to the surface activity of ethanol. It is hypothesized that the latter effect also contributes to the elevated FC values in the presence of ethanol. The strength of adsorbed GH films was generally lower in a in the presence of ethanol than in water. This was in line with the overall lower foam stability, which is the amount of foam remaining after one hour, of GH solutions containing ethanol compared to that in water. Thus, it is important to take the impact of other food constituents into account when evaluating the potential of plant protein hydrolysates as foaming agents in food systems.