Proteomics Study of Silica Eluent Proteins in Beer

The aim of this study was to identify the silica eluent (SE) proteins generated in beer during the brewing process, using a proteomics approach. In this study, we found that the distribution and amino acid composition of SE proteins depended on the raw materials and technology used for beer production. The protein and amino acid contents were significantly different in samples taken at various stages of the process. Coomassie blue-stained sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting revealed SE proteins of approx. 40, 25-29, and 6.5-17 kDa that originated primarily from malt water-soluble protein, but also from hordein. SDS-PAGE and two-dimensional electrophoresis (2-DE) analysis in combination highlighted the malt protein modification that occurred during the brewing process. Using mass spectrometry (MS), major 2-DE gel protein spots were identified as barley trypsin inhibitor CMe precursor germin E (Hordeum vulgare) and protein Z. These proteins were resistant to proteolysis and heat denaturation during the brewing process and might be important contributors to beer haze formation.