Air/water interfacial properties and thin film drainage dynamics of compositionally diverse wheat flour water extracts

Abstract

The role of water-extractable (WE) wheat flour constituents and their interactions in determining the stability of wheat-based foam-type foods remain largely unexplored. Additionally, the contribution of drainage dynamics of the thin liquid films (TLFs) between gas bubbles to food foam stabilization is often overlooked. We here investigated the air/water (A/W) interfacial, TLF drainage, and foaming properties of compositionally diverse wheat flour aqueous extracts. Such extracts were prepared and then either used as such or modified by dialyzing out (i) low molecular mass constituents or (ii) both low molecular mass constituents and enzymatically hydrolyzed carbohydrates. This approach resulted in extracts with gradually increasing protein contents and distinct carbohydrate compositions. Wheat extract constituents created highly elastic A/W interfaces, regardless of the type of extract modification, suggesting a significant contribution from WE wheat proteins. TLFs stabilized by wheat extracts from which low molecular mass constituents were removed had significantly greater stability. This was ascribed to an increased disjoining pressure caused by steric repulsive forces, which in turn were attributed to the interaction between high molecular mass arabinoxylan in the bulk and adsorbed proteins at the A/W interfaces. All extracts showed similarly good foaming properties, implying a dominant role for WE wheat proteins in determining foaming. The strongly elastic A/W interfaces formed by WE wheat proteins likely reduced liquid drainage to such extent that coalescence and disproportionation were largely delayed. The findings of this study could facilitate further investigations on the possibility of tuning protein-AX interactions toward improved foam stability.