Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/12/2010
Publication Date: 2/16/2011
Citation: Selling, G.W. 2011. Degradation of Corn Protein During Extrusion Processing. Meeting Abstract.
Technical Abstract: Corn protein (zein) is one of the main co-products of corn bio-ethanol production. Extrusion processing of zein continues to be the preferred route to provide improved articles having lower cost and improved properties. There is a lack of information regarding the conditions which can be employed to melt process zein without inducing degradation. Extrusion processing has been carried out on corn protein (zein) where extrusion temperatures were varied between 100 and 300 degrees Celcius (C). The appearance of the extrudate across this range changed significantly. By differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) thermal degradation begins around 220 degree C. While the color of zein changed at higher extrusion temperatures, the rate of color change increases above 160 degrees C. Sodium dodecyl sulfate polyacrylamide gel electrohoresis (SDS-PAGE) analysis shows that zein begins cross-linking at 120 degrees C and chain cleavage begins above 180 degrees C. Examination of the structure of the extrudate using near and far-ultraviolet circular dichroism (UV CD) shows a slow loss in alpha-helix and beta-sheet content between 100 C and 240 degrees C; above 240 degrees C the rate of secondary structure loss is increased. Infrared (IR) spectroscopy displayed differences in the carbonyl absorption with the carbonyl peak becoming narrower and shifting towards higher wavenumber with increased extrusion temperature. The peak at 1533 cm-1 becomes slowly smaller with increased extrusion temperature until 220 degrees C where the rate of loss accelerates. Nuclear magnetic resonance (NMR) spectroscopy demonstrated the formation of new carbonyl peaks and the lost of alkoxyl carbons suggesting that in addition to protein backbone cleavage the alcohol moieties of serine and threonine are oxidizing to carboxylic acids. Tensile properties begin to deteriorate when extruding above 140 degrees C; extruding above 220 degrees C yields a material that cannot be molded.