Characterization of the Zein Protein Composition in Maize Flour Extracts

Highly homogenous zein protein was isolated from maize kernels in an environment-friendly process using 95 % ethanol as solvent. High purity of the zein protein product was determined by SDS PAGE analysis and by 2 D gel electrophoresis followed by MALDI-ToF-MS peptide mass fingerprinting after in-gel chymotrypsin digestion. Being a natural product that is encoded by multiple gene copies, the polymorphic zein protein product revealed two rows of protein spots, one at 25 kDa and one at 20 kDa apparent molecular mass. MALDI-ToF-MS peptide mapping of the proteins from all spots indicated the presence of only alpha zein proteins. The most prominent ion signals in the MALDI mass spectra after in-gel digestion were recorded at m/z 1083.5 and m/z 1691.8. These ion signals have been found typical for zein proteins and may serve as marker ion signals which upon chymotryptic digestion reliably indicate the presence of zein protein in both hybrid corn products. Due to the given polyploidy and genetic polymorphism of the plant source the application of high resolution separation methods in conjunction with precise analytical methods, such as MALDI-ToF-MS, is required to accurately estimate homogeneity of products that contain natural zein protein.