Structure and Mechanics of Starch Bread

Abstract

The mechanical properties of breads made of potato or wheat starch were measured in two successive compression/decompression cycles. From the shape of the stress–strain curves, the initial modulus and the critical stress and strain could be derived; the critical stress and strain are those at which the crumb structure starts to collapse. The magnitude of the stress–strain related parameters changed markedly during storage. The initial modulus, as well as the critical stress for structural collapse, increased, and the critical strain decreased. Moreover, the resistance of bread crumb to collapse of structure in compression decreased. The mechanical properties of potato starch bread changed more rapidly than those of wheat starch bread. The results are discussed in relation to the structure of the starch breads on different levels, i.e. from molecular (amylopectin recrystallisation) to macroscopic (sponge structure). It is concluded that the mechanical properties of the starch breads are determined by the mechanical properties of the condensed lamellae and beams consisting of irregularly shaped, partly swollen starch granules as well as by the distribution of the thickness of the lamellae and beams.