INVESTIGATION OF THE RELATIONSHIP OF MALT PROTEIN AND BEER HAZE BY PROTEOME ANALYSIS

Abstract

ABSTRACT The changes in malt proteins during the brewing process and the roles of malt proteins in the formation of beer haze were investigated in this study. Coomassie blue stained sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) revealed that proteins with molecular weights of ∼40, 25–29 and 6.5–17 kDa were the major components of beer haze protein, originating primarily from malt water-soluble protein, partly from hordein. Two-dimensional electrophoresis and mass spectrometry analysis highlighted malt protein modification occurring during the brewing process. It was found that most of the malt hordeins disappeared during the brewing process, except B and γ3 hordein and storage protein (Hordeum vulgare). The results also suggested that the heat- and proteolysis-stable hydrophobic proteins such as barley trypsin inhibitor CMe protein, germin E (H. vulgare) and protein Z might be the important haze-promoting proteins, and that B and γ3 hordein might be the minor haze-active proteins in beer but were a critical factor in the formation of beer haze. PRACTICAL APPLICATIONS Haze stability is of great importance to brewers as it is the first characteristics by which a consumer judges the quality of their beer. It is conventionally accepted that proline-rich hordeins from malt play a major role in the formation of haze. In this study, it was found that B and γ3 hordein might be the minor haze-active proteins, but the heat- and proteolysis-stable hydrophobic proteins such as barley trypsin inhibitor CMe (BTI-CMe) protein, germin E (Hordeum vulgare) and protein Z might be the important haze-promoting proteins. This study made a further confirmation on this issue that nonhordein proteins are regarded as haze-active and laid the theoretical foundation for further investigations to determine the mechanism of the formation of beer haze. An improved understanding of the impact of brewing on malt proteins could potentially provide further scope for optimizing beer quality.