State diagrams to help describe wheat bread processing

Abstract

Physical changes in wheat bread processing can be described by the use of state diagrams and phase transition. State diagrams were constructed from real experimental results that described the glass transition and melting curves for starch and proteins as a function of water content. Wheat gluten protein is the main component responsible for bread dough structural formation, while starch is mainly involved in final textural properties and stability. During processing, hydration of wheat flour induces the glass transition of wheat gluten proteins. The input of mechanical energy during the mixing allows the development of continuous viscoelastic dough due to interactions between rubbery proteins. During baking, irreversible modifications of starch and proteins at high temperatures (> 200 °C) and superficial dehydration are responsible for bread crust formation. In the central part of the mixture, starch gelatinization and protein coagulation induce breadcrumb formation. After cooling, the low water content of the crust (3-7%) is sufficient for the transition of bread components from the rubbery to the glassy state. Consequently, structural hardening occurs and is responsible for crust crispness. The higher final water content of the crumb (35-40%) is responsible for rubbery behaviour, which gives structural mobility, smooth breadcrumb behaviour and explains the sensitiveness to starch retrogradation during storage.