The Staling of Bread and the Maintainance of its Freshness.
In this survey the processes occurring in the course of the staling of wheat bread and rye bread are extensively examined. Especially the physico‐chemical changes in the starch as well as its interaction with the other constituents of the bread, above all gluten and water are discussed. Apart from literature data results of works of the author and his associates are discussed with special reference to experiments with pure starch.
The starch is the principal origin for the staling of bread. With storing the macromolecules of the starch as well as the water molecules lose their mobility between about + 50 °C and –7°C forming a structured system which leads to the staling of bread.
With storing of white bread with little in‐baked starch sacks it was shown that the water content of the starch decreased despite the higher water content of the crumb at a similar rate, i. e. from 31.3% (after 4 hrs) to 28.9% (after 8 days) in the starch, and from 42.2% to 39.0% in the crumb. Thus no considerable redistribution of water from the well‐watered crumb to the more arid starch takes place.
The author suggests a model, according to which the pore walls of the crumb consisting of starch and denaturized proteins represents a swelled system in which part of the water is thermodynamically bound and partly distributed in the intermolecular spaces of protein and the swollen partially gelatinized starch. Here the molecules of water, starch and protein form a uniform structure system. During refreshening of staled bread by heating the structure of water in the micropores of the crumb is disturbed. Thus, the macromolecules of starch and protein can return to that state which is characteristic for fresh bread.
