THE MOLECULAR STRUCTURE OF GELPROTEIN FROM BARLEY, ITS BEHAVIOUR IN WORT-FILTRATION AND ANALYSIS

Abstract

Gelproteins from barley and malt play a major role in the lauter tun filtration. These proteins (called glutenin in wheat) are partly broken down during malting and then aggregate during mashing. These aggregates form a part of the upper layer of the spent grains (the ‘oberteig’). To obtain more insight into this mechanism the composition of gelproteins of different cultivars of barley were analysed using various electrophoretic techniques. From this work a model can be proposed in which the protein, like its counterpart in wheat consists of high molecular weight (HMW) subunits as a backbone and low molecular weight (LMW) subunits as side chains, joined by inter-and intra-molecular disulphide bonds. During malting the disulphide bonds are reduced and subunits are broken down by proteolysis. During mashing a complex is formed between residual gelprotein in the malt and the glutelins, which gives rise to an impenetrable layer on the spent grains. The quantity of gelprotein as analysed by high pressure liquid chromatography (HPLC) or densitometry of Sodium dodecyl sulphate polyacrylamide electrophoresis (SDS—PAGE) patterns of HMW subunits showed a negative relationship to the lauter tun filtration rate.