Potential of wheat gluten hydrolysates as foaming agents in food

In many foods and beverages, such as meringues, chocolate mousses or beers, foams play important structural and textural roles. Animal proteins, such as those of egg white, are often used in this context because of their excellent functionality but their production is expensive and has a substantial environmental impact. Plant proteins can be a valid alternative, but they often lack functionality or have low solubility in aqueous media. A notable example are wheat gluten proteins, a co-product of the industrial wheat starch isolation process. Controlled enzymatic hydrolysis increases the solubility of gluten proteins in aqueous media but also enhances their foaming properties. In current literature, a thorough evaluation of the air-water (A-W) interfacial and foaming characteristics of such hydrolysates is only rarely considered. Furthermore, as protein hydrolysate functionality is usually assessed in relatively simple aqueous solutions, the complexity of food products is often underestimated. Here, we conducted a stepwise evaluation of the potential of enzymatically hydrolyzed wheat gluten proteins as foaming agents in food. In a first part, the relationship between the structural, A-W interfacial and foaming characteristics of gluten hydrolysates were studied in depth. Foaming capacity, i.e. the initial amount of foam formed, was related to the rates of diffusion to and adsorption at the A-W interface. Foam stability, i.e. the amount of foam remaining after one hour, was related to the strength of adsorbed gluten hydrolysates protein films at the A-W interface. The structural features of the gluten hydrolysates responsible for their interfacial behavior were studied by performing a foam fractionation process. In a second part, the A-W interfacial and foaming properties of gluten hydrolysates were assessed in gradually more complex systems to obtain an image of how such hydrolysates would behave in food relevant media. Firstly, the impact of a varying pH was investigated. Secondly, the impact of the presence of sucrose and ethanol, which commonly occur in food foams, on the A-W interfacial characteristics of gluten hydrolysates was studied. Finally, the impact of the presence of egg white proteins, which can stabilize foams by themselves, on the interfacial behavior of gluten hydrolysates was investigated. All these steps have yielded fundamental knowledge on interfacial behavior of wheat gluten hydrolysates in more complex systems, and contribute to their possible use as foaming agents in food.status: publishe