Changes occurring in protein body structure and α-zein during cornflake processing

Zeins, which comprise the majority of proteins in corn, are located in spherical organelles called protein bodies. Changes in protein body shape and release of encapsulated alpha-zeins as a result of cornflake processing (conventional pressed or extrusion flaking) were investigated. Size-exclusion chromatography, SDS-PAGE, and protein solubility tests showed that, upon cooking, zein proteins form large, disulfide-bound polymers, many of which were insoluble in nonreducing solvents. Transmission electron microscopy with immunogold staining revealed that cooking had no effect on protein body structure in corn, but after processing to cornflakes, protein body structure was altered. In conventional pressed cornflakes, the protein bodies were flattened, partially fused together, and alpha-zeins were to some degree released, whereas in the extruded flakes, protein bodies were completely disrupted and alpha-zeins dispersed. These results suggest that zeins in cornflakes, particularly extruded ones, are not confined to rigid protein bodies but can interact with each other and other components in the system. The disruption of protein bodies, zein release, and the chemical changes that proteins undergo during processing are speculated to be determinants of texture in ready-to-eat corn-based breakfast cereals.