Foaming and air-water interfacial characteristics of mixed egg white – gluten hydrolysate protein solutions

Hen egg white (EW) protein is used in a range of food systems inter alia because of its excellent foaming characteristics. However, its production is more expensive and has a more significant environmental impact than that of plant protein. Thus, a shift towards plant protein-based food systems is beneficial both from economic and environmental perspectives. Enzymatically produced gluten hydrolysates (GHs) can be considered for (partial) EW protein replacement. We here investigated the air-water interfacial characteristics of solutions containing EW or GH protein or mixtures thereof. GH solutions had much higher foaming capacities than EW solutions, while foams from the latter had much higher stability than those of the former. The foaming capacity of a solution with GH and EW protein in a 1:5 ratio was at least as high as that of solutions containing only GH. Furthermore, even when half of the EW proteins were replaced by GH proteins, foam stability remained high. Thus, solutions containing both GH and EW protein had both high foaming capacity and foam stability. This suggests that both GH and EW protein contribute positively to foaming of their mixtures. Maximum bubble pressure and oscillatory drop shape tensiometry measurements indicated that both at early and later stages of protein adsorption and rearrangement, the composition of the interface is dominated by the average wise smaller and more flexible GHs, rather than by the larger and bulkier EW proteins. Measurements assessing coalescence of bubbles stabilized by EW and GH protein containing solutions showed that EW proteins improve the resistance of bubbles against coalescence. We hypothesize that these EW proteins form a secondary layer at the air-water interface which is maintained by interactions with the primarily adsorbed GHs. This secondary layer results in increased resistance to coalescence probably by electrostatically or sterically hindering gas bubbles from approaching each other.status: publishe