DISULFIDE-BONDED GEL PROTEIN AGGREGATES IN BARLEY - QUALITY-RELATED DIFFERENCES IN COMPOSITION AND REDUCTIVE DISSOCIATION

The relationship between the content and composition of disulphide-bonded protein aggregates that were unextractable in sodium dodecyl sulphate (SDS) and malting quality was studied using protein assays, electrophoresis and high-performance liquid chromatography. Initial experiments using 32 samples of a single cultivar grown at different sites and a set of seven cultivars grown at two sites confirmed that there were greater amounts of SDS-unextractable protein in poor malting samples. Densitometry of SDS-polyacrylamide gel electrophoregrams of reduced SDS-unextractable protein revealed a specific elevation of B1 and B2-hordeins in poor-malting samples. Within a cultivar, hordein subunits differed in their extents of extraction from the aggregate at any given reductant concentration as sulphydryl reducing agent concentrations were increased. D-hordeins were slowest to be extracted, suggesting that they formed the `backbone' of the gel. Hordein subunits were also more readily extracted from an aggregate in good-malting than in poor-malting cultivars. We did not observe a relationship between the amount of gel protein total disulphide plus sulphydryl groups and malting quality. These studies instead raise the possibility that differences in the number and orientation of disulphide bonds between subunits in barley grain protein complexes may influence malting quality. © 1992, Academic Press Limited. All rights reserved.