97 Effect of glycerol and moisture on bread staling: A mechanical and thermal study.

M. Y. BAIK and P. Chinachoti. Dept. of Food Science, University of Massachusetts, Amherst, MA 01003.

Bread has a sponge like structure containing amorphous and crystalline regions and change of both regions greatly influence the bread quality during storage. Moisture redistribution affects the change of amorphous and crystalline regions but its mechanism is not well known. To investigate the role of glycerol, white bread with or without glycerol (10%, w/w starch basis) was packed with or without crust in a tri- laminated pouch and their mechanical, thermal and thermomechanical properties were monitored. The stress-strain relationship showed typical sigmoidal shape. Added glycerol resulted in a decrease in moisture content and a(w) of intact bread, but all breads were equally soft initially. Although moisture loss was the same and the amylopectin recrystallization was less than the control bread, glycerol bread firmed at a faster rate. Glycerol had no influence on recoverable work, which decreased initially (3 days) and then remained constant. Fracture of hardened bread was a significant factor. In DMA, fresh bread showed only a main transition near 0 C, possibly due to overlapped ice melting and glass transition, but aged bread showed a main and a transition at 60 C (possibly due to amylopectin melting transition). From this study, changes of amorphous as well as the crystalline components play both important roles in bread staling. Both are expected to be manifested by water migration and water mobility.