Analysis of Zein by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS) was used to analyze the protein composition of corn prolamine (zein). Mass spectra were obtained from commercial zein and zein extracted with aqueous 2-propanol and aqueous ethanol from consumer corn meal. For the commercial zein, three major zein fractions with m/z 26.8k, 24.1k, and 23.4k were clearly seen with two minor fractions (m/z 14.5k and 20.4k) also present. As compared with the results from sodium dodecyl sulfate−polyacrylamide gel electrophoresis (SDS−PAGE), these three fractions were identified as α-zeins (24.1k and 23.4k combined as Z19; 26.8k as Z22). When extracted with 55% aqueous 2-propanol, three α-zein fractions with m/z 26.8k, 24.1k, and 23.4k were predominant. When extracted with ethanol, extraction temperature had an effect on the final products. When extracted with 75% aqueous ethanol at room temperature, α-zein and some 17−18k species were observed, whereas at 60 °C, a small amount of δ-zein was also present. Comparison of the MALDI/MS results with SDS−PAGE and gene sequence analysis shows that the MALDI/MS method is superior to SDS−PAGE in having higher resolution and mass accuracy. Keywords: Zein; molecular weight; matrix-assisted laser desorption/ionizatin (MALDI); mass spectrometry