Bread properties and crumb structure

The relationship between bread-crumb cellular structure and many aspects of quality in a loaf of white bread justifies investigations of how the structure arises during processing of the dough. Following a brief over-view of the development of bread cellular structure in the dough, three parts of the literature pertaining to crumb appearance (visual texture) and bread quality are reviewed, with emphasis on the mechanical properties (physical texture) of the crumb. The importance of an objective segmentation of the two macroscopic phases (crumb cells and cell walls solids) is emphasised in digital image analysis studies of bread-crumb structure. A review of studies where mechanical properties have been measured in fundamental units has sections on the mechanical properties of the composite structure and on recent analyses of the mechanical properties of the solid phase. Finally, models which have been used to relate structure to mechanical properties will be reviewed with emphasis on the work of Gibson and Ashby [Gibson, L.J., & Ashby, M.F., 1988. Cellular solids: structure & properties. Oxford: Pergamon Press; Gibson, L.J., & Ashby, M.F., 1997. Cellular solids: structure and properties (2nd ed.). Cambridge: University Press]. It is shown that experimental values of Young's modulus of bread crumb reside within the Hashin-Shtrikman bounds. Compared with the rule of mixtures, these bounds represent a good (52%) improvement in the ability to predict values for bread crumb moduli (crumb firmness). Using information provided by digital image analysis, Gibson and Ashby's relationships between structure (relative density) and mechanical properties can be modified to incorporate dough processing effects such as dough strain hardening and the effect of gas cell coalescence. (C) 2001 Elsevier Science Ltd. All rights reserved.