The Relationship Between D Hordein and Malting Quality in Barley

Abstract

The contribution of grain protein to the malting quality of barley (Hordeum vulgareL.) was investigated by comparing the hordein composition and the malting quality in barley produced under a range of field conditions. Two malting cultivars, Schooner and Arapiles, and one feed cultivar, Galleon, were grown under five nitrogen regimes in each of two years. Hordein composition of the grain was determined at maturity using a combination of sodium dodecyl sulphate-polacrylamide gel electrophoresis and laser densitometry. Malt extract was determined on all samples after micromalting. Variation in growth conditions resulted in a wide range of grain protein contents and malt extract values, as well as variation in the proportions of the individual B, C and D hordeins in the grain. D hordein in particular varied over a 10-fold range. High levels of all protein fractions were associated with low malt extract. Total protein, as expected, displayed a strong, negative correlation with malt extract. The relationship was cultivar specific and separate regression lines were generated for each cultivar. Of the individual hordein fractions, D hordein displayed the strongest negative correlation with malt extract and its relationship to malt extract was independent of cultivar. A consistent relationship between D hordein and malt extract was observed across seasons, treatments and cultivars that was indicative of a causal relationship between D hordein and malting quality. D hordein therefore offers an alternative measurement to total protein for the prediction of malting quality over a wide range of environmental conditions and cultivars.