Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/18/2008
Publication Date: 8/27/2008
Citation: Sessa, D.J., Mohamed, A., Byars, J.A. 2008. Chemistry and Physical Properties of Melt Processed- and Solution- Cross Linked Corn Zein. Journal of Agricultural and Food Chemistry. 56(1):7067-7075. Interpretive Summary: The demand for food service disposables which includes packaging products, cups, dinnerware and other products is projected to increase to $16.6 billion by 2011 based on a marketing report of the Freedonia Group Inc., Cleveland, OH. Zein, a protein co-product of the ethanol industry has the potential for use in those products. Previously reported "solution' chemistry demonstrated that chemical modification of zein with a bis-aldehyde improved zein's mechanical properties essential for constructing bio-based films. Our current research demonstrates that we can achieve plasticized zein products with properties similar to those developed previously, by melt processing zein modified with bis-aldehyde. This green process would eliminate the need for solvents and solvent recoveries, a major cost cutting benefit that is suitable for industrial scale-up. This finding not only will benefit the farmer and corn-ethanol producers but also the multi-billion dollar foodservice industry.
Technical Abstract: Corn zein was cross linked with the glutaraldehyde (GDA) using glacial acetic acid (HAc) as catalyst. The objectives are to enhance the mechanical properties of poured films and to compare them with compression molded tensile bars from melt processed zein. Chemistry of the cross linking reaction was based on the aldehyde binding characteristics defined by use of fluorescence spectroscopy; sodium dodecyl sulfate polyacrylamide gel electrophoreses (SDS-PAGE) to demonstrate the cross linking reaction; FTIR to observe absorption differences of the cross linked product; DSC, DMA and TGA to assess thermal properties; and the use of Instron Universal Testing Machine to evaluate mechanical properties. A reaction mechanism for acid catalyzed GDA cross linking of zein is proposed. Thermal and mechanical properties of tensile bars cut from either film or formed by compression molding were similar where both showed increased tensile strengths, ductility and stiffness when compared with unmodified controls. Samples that were reacted with 4% GDA by weight based on weight of zein from either process retained their integrity when tensile bars were subjected to boiling water for 10 min or soaking in either water or HAc for 24h. The melt processed, cross linked zein would be a more environmentally friendly method that would eliminate the need for HAc recovery.