As previously mentioned, the jaggedness of the signal is often used to
assess “crispness.” This variable was measured for the mechanical signal by
1 - r2), but no significant correlation was found here with CVA1. This apparent
contradiction can first be due to the use of the Kramer cell, which has a
large volume, and that fluctuations are limited by averaging and cushioning
effects. However, the testing volume (about 100 cm3) is close to the one
leading to the largest jaggedness obtained in the study by Nixon and Peleg
(1995). The explanation may rather rely on the fact that, in our study, the
samples only exhibit tiny differences in moisture content (Table 1). In most
studies on crispness of cereal products, the samples are equilibrated at different
moisture contents in order to emphasize the changes of this sensory
property. Thereby, crispness variations and the associated variations of jaggedness
are interpreted by modifications of the temperature of glass transition,
Tg. Differences between mechanical behaviors are mostly due to material
matrix and its components as the amount of glassy starch, or the one of water,
having influenced by lowering the Tg (Attenburrow et al. 1992; Le Meste
et al. 1996). In our case, the samples are all from commercial brands that were
expected to have satisfactory sensory properties, so changes in crispness are
not so significant, although sufficient to be recognized by the sensory panel.
These tinier variations of crispness may not rely on changes of Tg. Texture
behavior cannot be predicted only from the knowledge of the glass transition
temperature alone (Nicholls et al. 1995). Differences on mechanical properties
measured for flakes beds may also be due to the intrinsic properties of
the constitutive material of the flakes. The brittle behavior of starch–zein
systems has been shown not to depend on the Tg of components, but rather on the microstructural morphology of the matrix/particles biopolymer blends
(Chanvrier et al. 2005).