Potential for the Improvement of Malting Quality of Barley by Genetic Engineering

Abstract

Barley quality encompasses a range of chemical and physical attributes which depend on whether the grain is to be used in the preparation of malt for the brewery, as a component of stockfeed formulations, or in human nutrition. Currently, specifications for barley quality are tailored primarily for the malting and brewing industries, although agronomic properties such as yield and disease resistance are also important selection criteria in breeding programs. Thus, parameters such as grain size, dormancy, malt extract, grain protein content, development of hydrolytic enzymes for starch degradation (diastatic power), apparent attenuation levels, (1 → 3, 1 → 4)-β-glucanase potential and (1 → 3, 1 → 4)-β-glucan content represent commonly used quality indicators. Many of these quality characteristics are determined by the expression of several or many individual genes, such that the genetic manipulation of the characters by recombinant DNA technology requires a thorough understanding of the individual genes, their interactions in the expression of a particular quality characteristic, or the identification of the rate-limiting component of the characteristic. Quality factors that are determined by a single gene are more amenable to manipulation by genetic engineering and there are developing technologies through which the expression of individual genes can be either enhanced or inhibited, depending on the desired effect on malting quality. In this paper, the potential for engineering barley to enhance (1 → 3, 1 → 4)-β-glucanase activity is explored, together with the biochemical, genetic and physiological information that necessarily underpins genetic engineering technology.