Importance of Gluten and Starch for Structural and Textural Properties of Crumb from Fresh and Stored Bread

Abstract

Bread crumb cellular structure and elasticity were monitored during aging and their relation to the main flour constituents, gluten and starch, was studied. The linear relation between the time-dependent slope of the linear part of the force-deformation curve, obtained in a static compressive test, and the shear modulus, obtained in quasi-static shear wave measurements, allowed calculating the Poisson’s ratio of bread crumb. This ratio and, thus, cell geometry remain unaffected during bread storage. While the elastic modulus of bread crumb strongly increased upon storage, image analysis and ultrasonic inspection, interpreted in the framework of the Biot-Allard model for porous structures, further confirmed that its cellular structure parameters did not change. Changing gluten properties in dough by means of redox agents had a profound impact on bread crumb density and its foam structure without affecting the rheological properties of the crumb cell walls. In agreement with the theory for cellular solids with open cells, bread with a lower density and a uniform crumb structure initially had a lower elastic modulus, which was maintained during aging, while bread with a higher density showed the opposite. Inclusion of an antifirming maltogenic exo-amylase in the recipe altered neither bread density, nor its macroscopic cellular structure parameters, but strongly affected the impact of storage on crumb texture. It was concluded that, without affecting starch properties or moisture content, the bread density, which is inter alia related to gluten properties, is a major determinant of bread crumb structure and texture during storage. In breads with a similar density and crumb foam structure, the evolution of crumb modulus during storage is determined by the changes in starch.