Effect of specific mechanical energy on protein bodies and α-zeins in corn flour extrudates

Zeins, the storage proteins of corn, are located in spherical entities called protein bodies. The disruption of protein bodies and zein release during extrusion may influence the texture of corn-based extruded foods. In this work, chemical and microscopic studies were conducted on corn flour that had been extruded under mild to extreme conditions to determine the specific mechanical energy (SME) required to break apart protein bodies and release alpha-zein, and to assess changes in protein-protein interactions. Transmission electron microscopy with immunolocalization of alpha-zein revealed that starch granules and protein bodies remained intact under mild processing conditions (SME 35-40 kJ/kg), but under harsher conditions, protein bodies were disrupted and alpha-zein was released, At SME approximate to 100 kJ/kg, protein bodies appeared highly deformed and fused together with the alpha-zein released, whereas at higher SME, protein bodies were completely disrupted and alpha-zein was dispersed and may have formed protein fibrils. Protein in extrudates was less soluble in urea and SDS than in unprocessed corn flour, but it was readily extracted with urea, SDS, and 2-ME. This was likely due to protein aggregation upon processing due to a prevalence of hydrophobic interactions and disulfide bonds. This research directly relates SME during extrusion to chemical and structural changes in corn proteins that may affect the texture of corn-based, ready-to-eat food products.