Proteomic identification of technologically modified proteins in malt by combination of protein fractionation using convective interaction media and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A method for the fast separation of proteins and identification of their modifications based on the use of monolithic chromatographic media and mass spectrometric techniques is described. This method has been developed and applied to the analysis of malt proteins and its posttranslational modifications (glycation). Glycation, one of the most common forms of posttranslational modifications (PTM), can be detected in both biological and industrial samples. Our attention was focused on the investigations of possible chemical modifications of water-soluble barley proteins during malting process by combination of anion-exchange chromatography with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The malt extract was directly fractioned by anion-exchange chromatography using short monolithic columns and a linear gradient from 0 to 700 mM NaCl. Sufficient fractionation was obtained for malt sample, which demonstrates the potential of anion-exchange chromatography on this type of column. Proteins in separated fractions were identified by MALDI-TOF/TOF MS. Our proteomic analysis provided the identification of the major proteins present in the malt that were found to be heterogeneously glycated after malting. One of these proteins: nonspecific lipid transfer protein 1 (LTP1) can be used as a marker for characterization of glycation during malting. This protein and its modifications can be easily determined by the developed method.