Bread crumb is a cellular solid or sponge 1. On a macroscopic level, it is a two phase system at a high volume
fraction ( ≥0.8) of dispersed gas in a matrix with cell walls
of thickness 20 to 200 mm, that are more open than closed
2
,3. The cell walls themselves consist of semi-swollen starch
granules interlinked by a complex mixture of aggregated
starch and gluten proteins 4. Bread quality decreases during
storage, because the physical properties of bread crumb
change 5. Indeed, it firms and loses resilience 6. Since
mainly starch, protein and water contribute to the structural
architecture and the mechanical strength of bread, they are
assumed to play an important role in the change in cell wall
properties during bread storage. However, there is still controversy about the exact role of the different flour components in bread firming 7. Starch polymer crystallization with
the formation of supermolecular structures is certainly involved and research to date has focussed on the changes in
starch during heating, cooling and storage 8. While the role
of gluten proteins in bread crumb firming is still under
debate, both the rate and extent of starch (re)crystallization
have been related to the texture and acceptability of bread. A
plausible hypothesis is that amylopectin retrogradation