Influence of Water Activity on the Acoustic Properties of Breakfast Cereals

Abstract

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 (Aw). The flakes differed essentially in their ability to propagate vibrations. At low Aw's, both types of flakes were alike, but at higher Aw's, corn flakes damped high‐frequency waves while wheat bran flakes did not show this property.

Effect of water activity on the crispiness of a biscuit (Crackerbread): Mechanical and acoustic evaluation

“…Thus the partially plasticised matrix deforms when compressed rather than break, thus offering a more resistant to fracture (Harris & Peleg, 1996). Similar antiplasticisation resulting in an increase in hardness of crispy products with increasing moisture content or a w has been reported in extruded products such as breads (Roudaut et al, 1998), starches (Gondek et al, 2006;Pamies et al, 2000) and rice crisps (Heidenreich et al, 2004).…”

“…(1)). The Fermi equation and its modified forms have been extensively used to describe the sigmoid curve obtained from plotting parameters associated with crispiness as a function of a w (Gondek et al, 2006;Harris & Peleg, 1996;Heidenreich et al, 2004;Pamies, Roudaut, Dacremont, Le Meste, & Mitchell, 2000;Peleg, 1994aPeleg, , 1994b.…”

“…Several studies have been conducted on loss of crispiness due to hydration by mechanical and acoustic evaluation (Duizer, 2001;Gondek, Lewicki, & Ranachowski, 2006;Heidenreich et al, 2004;Roudaut, Dacremont, & Le Meste, 1998;Sauvageot & Blond, 1991). Despite these and more other studies, there is no standard method to determine crispiness (Castro-Prada, Luyten, Lichtendonk, Hamer, & Van Vliet, 2007).…”

Extruded Bread Classification on the Basis of Acoustic Emission Signal With Application of Artificial Neural Networks

“…The study of the acoustic properties of extruded bread and other crispy foods in relation to its water content is complex because these properties are affected by several extra factors in addition to the fracture properties of the crispy food surface, as pore size for example (Primo Marin et al, 2009;Salvador et al, 2009). Nevertheless, it is generally accepted that the number of acoustic events is strongly affected by the water activity and increasing aw causes a decrease in the number of acoustic events (Gondek et al, 2006;Primo-Martin et al, 2009). As the number of sound events is correlated negatively with the water content, a range of analyzed water activities was selected to ensure maintenance of crispiness of the extruded bread (Marzec et al, 2007b).…”

Modulation of the physico-chemical and functional properties of bread by applying surface treatments

“…Crust has very low water content (Wählby and Skjöldebrand, 2002), because of that it is relatively dry, crisp and brittle in the fresh state . Water migration from the crumb and the atmosphere surroundings to the crust induces a transition from the glassy to the rubbery state of the main crust macromolecules (Gondek et al, 2006;. As consequence, the mechanical properties of the crust associated to crispness changes and crust becomes very soft and leathery , which causes consumer's rejection.…”