Texture and structure of crispy-puffed food products - Part II: Mechanicalproperties in puncture

A puncture test was used to describe the mechanical and textural behavior o f crispy-puffed food extrudates. Four criteria were identified from the for ce-time curves: (1) the average puncturing force, F-m, (2) the spatial freq uency of structural ruptures, N-wr, (3) the average specific force of struc tural ruptures, f(wr), and (4) the crispness work, W-c. The discriminating power of these criteria was shown through the effects of moisture content a nd recipe composition in the extrusion-cooking process. Relationships betwe en puncture criteria were also studied. The effect of water activity showed that the force related criteria described well the mechanical behavior of expanded extrudates.