ABSTRACT
Zein, the prolamine of corn, has been investigated for its potential as an industrial biopolymer. In previous research, zein was plasticized with oleic acid and formed into sheets/films. Physical properties of films were affected by film structure and controlled in turn by zein-oleic acid interactions. The nature of such interactions is not well understood. Thus, protein-fatty acid interactions were investigated in this work by the use of surface plasmon resonance (SPR). Zein adsorption from 75% aqueous 2-propanol solutions, 0.05% to 0.5% w/v, onto hydrophilic and hydrophobic self-assembled monolayers (SAMs) formed by 11-mercaptoundecanoic acid and 1-octanethiol, respectively, was monitored by high time resolution SPR. Initial adsorption rate and ultimate surface coverage increased with bulk protein concentration for both surfaces. The initial slope of plotted adsorption isotherms was higher on 11-mercaptoundecanoic acid than on 1-octanethiol, indicating higher zein affinity for hydrophilic SAMs. Also, maximum adsorption values were higher for zein on hydrophilic than on hydrophobic SAMs. Flushing off loosely bound zein in the SPR cell allowed estimation of apparent monolayer values. Differences in monolayer values for hydrophobic and hydrophilic surfaces were explained in terms of zein adsorption footprint.
Subject(s)
Surface Plasmon Resonance/methods , Zein/chemistry , Adsorption , Hydrogen-Ion Concentration , Hydrophobic and Hydrophilic Interactions , Microscopy, Atomic Force/methods , Surface Properties , Time Factors , Viscosity , Zea mays/chemistry , Zein/analysisABSTRACT
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 alpha-zeins (24.1k and 23.4k combined as Z19; 26.8k as Z22). When extracted with 55% aqueous 2-propanol, three alpha-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, alpha-zein and some 17-18k species were observed, whereas at 60 degrees C, a small amount of delta-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.
