Review: Mechanical properties of dry cellular solid foods / Revisión: Propiedades mecánicas de alimentos celulares sólidos

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Abstract
The compressive stress-strain relationships of most cellular materials and solid foams have a char acteristic sigmoid shape that reflects three deformation mechanisms: primarily elastic distortion under small strains; collapse and/or fracture of cell walls; and densification. The exact shape of the relationship is mainly determined by the materials' composition including: moisture contents; the cells and cell wall size and geometry; and whether the cells are open or closed. Upon repeated compression the nature of the relationship may change as a result of irreversible changes in the solid matrix (especially rupture). When the cell wall material is very brittle the force-displacement curve can be extremely irregular and jagged, often concealing its underlying sigmoid shape. Characterization of such brittle products requires methods of jaggedness evaluation and smoothing procedures. These are now readily available and have been successfully applied to extruded puffed foods. Food particulates tested in bulk can show similar compressibility patterns even if they themselves do not have a cellular structure. Although tensile properties of spongy baked foods, like bread crumbs, can be determined experimentally they have not yet been proven useful as indicators of textural quality, primarily as it appears, because of structural non-uniformity.