Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/15/2012
Publication Date: 9/21/2012
Citation: Selling, G.W. 2102. Impact of various extrusion processes on zein. 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 ºC as well as carrying out multiple passes at 140 °C. In the temperature series, the appearance of the extrudate across this range changed significantly. By DSC and TGA thermal degradation begins around 220 ºC. While the color of zein changed at higher extrusion temperatures, the rate of color change increases above 160 ºC. SDS-PAGE analysis shows that zein begins cross-linking at 120 ºC and chain cleavage begins above 180 ºC. Examination of the structure of the extrudate using near and far-UV CD shows a slow loss in alpha-helix and beta-sheet content between 100 C and 240 ºC; above 240 ºC the rate of secondary structure loss is increased. 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 ºC where the rate of loss accelerates. 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 ºC; extruding above 220 ºC yields a material that cannot be molded. Regarding the impact that multiple passes has on zein, the molecular weight of the zein begins to increase after the second pass and continues to grow with subsequent passes. After the third pass the secondary structure begins to be altered. Color change can be seen after four extrusion passes. Physical properties did not change with additional passes through the extruder.