Composition, surface-active and foaming properties of the aqueous phase of fermented cereal doughs

There is currently much interest in breads containing non-wheat cereals because of their nutritional profile. However, partial replacement of wheat flour by non-wheat alternatives reduces the gas-holding capacity of dough, which has a detrimental effect on bread loaf volume and crumb structure. In the initial steps of the classical wheat bread making process, the viscoelastic gluten network stabilizes the gas cells. The gas cells remain discrete until discontinuities develop in the gluten-starch matrix, leaving areas surrounded with only an aqueous film. This film is believed to originate from the dough aqueous phase and mainly consists of surface-active and viscosifying constituents. Today, the composition and functional properties of the aqueous phase of non-wheat cereal doughs are still very poorly understood. In this work, the aqueous phase (further referred to as dough liquor [DL]) of fermented dough from wheat, rye, barley, and oat flour was isolated using ultracentrifugation. DL composition showed high protein levels for wheat and rye, while lipid levels were unexpectedly high in oat DL. The non-starch polysaccharide fractions of wheat and rye DL were rich in arabinoxylan (AX), whereas β-glucans were the major polysaccharides of barley and oat DL. Surface tension and dilatational interfacial rheology measurements were performed at constant DL protein levels using a pendant drop tensiometer and foaming experiments also conducted at constant protein level using a standardized whipping test. Enzymes specifically targeting non-starch polysaccharides were used to study how AX and β-glucan affect DL surface-active and foaming properties. Overall, the data indicated that the interface in fermenting wheat dough is composed of a mixture of proteins and lipids without any associative interactions between AX and the adsorbed interfacial layer. In contrast, the interfacial region in fermenting rye dough seems to be dominated by proteins with AX acting as secondary stabilizing layer. The interface in fermenting barley dough presumably consists of proteins. Barley β-glucans did not seem to interact with the primary adsorbed protein layer. The interfacial layer in fermenting oat dough appears to be dominated by both proteins and lipids. In contrast to what was observed with wheat, the mixed interface was remarkably resistant to dilatation already at high dilution. Oat β-glucans determined the stability of the interfacial region, but to a lower extent than with rye AX.status: accepte