Microstructural changes in zein proteins during extrusion

Changes in proteins during extrusion may influence the texture of ready-to- eat (RTE) corn-based extruded foods. This study focused on microstructural changes and dispersal patterns of corn storage proteins, zeins, that occur during extrusion processing. Model systems were used that consisted of two type's of corn protein: commercial zein and corn gluten meal (CGM), combine d with corn starch. Commercial zein is not encased in protein bodies, where as CGM is comprised of zeins encapsulated in protein bodies. Mixtures were extruded under conditions that resulted in different specific mechanical en ergy (SME). The microstructure of the resulting extrudates was analyzed usi ng transmission electron microscopy (TEM) with immunogold labeling of the a -zein storage protein. The micrographs showed that the greatest zein disper sal occurred in CGM/starch extrudates, especially under high SME conditions . The micrographs also showed that, at both mild and harsh extrusion condit ions, commercial zein/starch extrudates contained large protein aggregates. Under mild extrusion conditions, protein bodies in the CGM/starch extrudat es partially retained their spherical shapes, but during harsher processing , protein bodies were disrupted and dispersed zein appeared to form fibrils . Such protein fibrils may influence texture and/or quality of extruded cor n-based snacks and breakfast foods.