Structure, mechanics and texture of a food sponge

Abstract

The mechanical properties of sponge cake, representative of an aerated cereal based food, have been examined instrumentally in compression tests and the results related to structure and perceived texture. It was found that the form of the stress-strain relationship was such that an initial modulus and critical stress for structural collapse could be defined. For material conditioned to a given water activity (Aw), the variation of initial modulus with bulk density was consistent with recent theoretical developments concerning the deformation behaviour of solid foams. Material was examined over a range of water activity and, as Aw increased from ~0 to 0·75, both initial modulus and critical stress fell by an order of magnitude and there was a transition from structural collapse by brittle fracture to structural collapse by elastic buckling. The variation of the critical stress for elastic buckling with bulk density was consistent with theory. However, the data for the critical stress for brittle crushing showed less agreement with theory, possibly due to the influence of structural imperfections. Both initial modulus and critical stress values correlated (r>0·90) with a trained panel's assessment of sensory hardness. It is concluded that initial modulus and critical stress are important mechanical parameters which predict sensory hardness and which, since they are basic mechanical parameters, allow comparison with the general class of solid foam type materials.