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.