ABSTRACT
High-temperature, short-time extrusion is used to create expanded foods that have a porous, open structure. Many snack products and ready-to-eat cereals, which share a characteristic “crunchy” texture, are formed by this process. The degree of expansion achieved during extrusion, as well as the exact product structure, is quite variable and depends on both the process parameters employed and the physical properties of the extrusion formula. Cellularity defines the perception of extruded products from visual, auditory, and tactile perspectives. While microscopy can provide a general assessment of the size and configuration of cells, and also of the thickness and relative intactness of cell walls, quantification of cell size distributions by an image analysis technique is usually necessary for a complete and accurate description of structure. Many process and formulation parameters will affect extrudate structure. Chief among these are variables that change the rheology of the extrusion melt or ingredients that serve as nucleating agents for expansion.
