2001 AACC Annual Meeting Charlotte, North Carolina October 14-18, 2001 Charlotte Convention Center

The effect of gas cell size and concentration on the breadcrumb structure is important to cereal scientists because the gas cells affect the structural integrity of bread and hence its textural quality. We have used ultrasonic techniques to investigate the changes in the mechanical properties of freeze-dried breadcrumb that occur as the concentration and size of gas cells was varied. The volume fraction of voids, phi, in the breadcrumb was varied from 0.85 to 0.95 by proofing the dough at various times. For 54 kHz longitudinal waves transmitted through the breadcrumb, we found that both the ultrasonic velocity and amplitude decreased with phi as the size of the gas cells increased. To extend the data to lower phi, a uniaxial stress was applied to the breadcrumb prior to freeze-drying, thereby increasing its density. In addition, however, the shape of the cells changed from spheres to elongated ellipsoids. As a result, the velocity became anisotropic, with the velocity parallel to the compression direction showing a remarkably large decrease as phi was lowered. Thus the phi-dependence of the velocity is opposite for the compressed and uncompressed cases, a clear indication of the differences in their structures. The results demonstrate the potential for using ultrasound as a non-destructive, cheap and accurate tool in the baking industry for studying the structure of breadcrumb.