GAS CELL STABILIZATION AND GAS RETENTION IN WHEAT BREAD DOUGH

Gas cell stabilisation and gas retention are of considerable interest because of their technological significance in bread making. We review recent studies in relation to the stabilisation of gas cells and the mechanisms of gas retention, and discuss how these may be affected by the liquid phase of dough. The possibility is discussed of the involvement of surface active materials, such as proteins and pentosans dissolved in the dough aqueous phase, and, perhaps more importantly, non-starch polar lipids in the formation and stabilisation of gas cells. There is accumulating evidence for the hypothesis that liquid films play a critical role in the mechanisms of gas retention in dough. The hypothesis proposes that two closely related, consecutive stages are involved in dough expansion. During the first stage, the expanding gas cells remain discrete until discontinuities develop in the starch-protein matrix, leaving areas containing only a liquid film. The timing and the degree to which such discontinuities occur is largely dependent on gluten proteins. The second stage involves an increase in the surface area of the liquid film as discontinuities become increasingly frequent during expansion. Failure of the lamellar film to maintain the rate at which new surface area is generated leads to the rupture of this film and, consequently, the loss of gas retention. Consideration is also given to the role of bakery fat in gas retention and to additional factors that affect gas retention in wholemeal doughs, in particular the physical disruption of the foam structure of such doughs by components of the outer layers of the grain.