In Vivo Modeling of β-Glucan Degradation in Contrasting Barley (Hordeum vulgare L.) Genotypes

Abstract

An important determinative of malt quality is the malt beta-glucan content, which in turn depends on the initial barley beta-glucan content as well as the beta-glucan depolymerization by beta-glucanase (EC 3.2.1.73) during malting. Another enzyme, named beta-glucan solubilase, has been suggested to act prior to beta-glucanase; its existence, however, has not been unequivocally proven. We monitored changes in beta-glucan levels and in the development of beta-glucan-degrading enzymes during malting of five lots of contrasting barley genotypes. Two models of in vivo kinetics for beta-glucan degradation were then compared as follows: (i) a biphasic model based on the sequential action of beta-glucan solubilase and beta-glucanase and (ii) a monophasic model assuming that all beta-glucans are depolymerized by beta-glucanase without the previous intervention of another enzyme. Confirmatory regression analysis was used to test the fit of the models to the observed data. Our results show that beta-glucan degradation is mostly monophasic, although some enzyme other than beta-glucanase seems to be required for the early solubilization of a small fraction of insoluble beta-glucans (on average, 7% of total beta-glucans). Furthermore, the genotype-dependent kinetic rate constant (indicating beta-glucan degradability), in addition to beta-glucanase activity, is suggested to play a major role in malting quality.