STRUCTURE AND MECHANICS OF STARCH BREAD

The mechanical properties of breads made of potato or wheat starch wer e measured in two successive compression/decompression cycles. From th e shape of the stress-strain curves, the initial modulus and the criti cal stress and strain could be derived; the critical stress and strain are those at which the crumb structure starts to collapse. The magnit ude of the stress-strain related parameters changed markedly during st orage. The initial modulus, as well as the critical stress for structu ral 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 mo re 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 t he starch breads are determined by the mechanical properties of the co ndensed lamellae and beams consisting of irregularly shaped, partly sw ollen starch granules as well as by the distribution of the thickness of the lamellae and beams. (C) 1996 Academic Press Limited