Influence of water activity on the acoustic properties of breakfast cereals

Corn and wheat bran flakes were compressed in a plastic cylinder and the generated vibrations were measured by a piezoelectric accelerometer. Amplitude-time records were thoroughly analyzed and the total acoustic energy in arbitrary units, number of acoustic events and energy of a single acoustic event were calculated. Relationships between the time of compression, frequency and sound intensity are presented as acoustograms. All parameters, except the energy of a single acoustic event, were strongly dependent on water activity (A(w)). The flakes differed essentially in their ability to propagate vibrations. At low A(w)'s, both types of flakes were alike, but at higher A(w)'s, corn flakes damped high-frequency waves while wheat bran flakes did not show this property.