Assessment of Enzymatic Endosperm Modification of Malting Barley Using Individual Grain Analyses

摘要

Enzymatic modification of the endosperm of malting barley is a main feature of the malting process. Uneven enzymatic modification of the endosperm (heterogeneity) can cause brewhouse problems. Although there is a general correlation between endosperm modification, beta-glucan breakdown and endo-beta-glucanase development, it is based on average results from sample analyses and may conceal heterogeneity. The primary aim of this work was to use individual grain analyses to investigate factors that control endosperm modification and beta-glucan breakdown. In terms of beta-glucan breakdown and physical modification, the barley variety Chariot malted faster than Decanter. However, both varieties showed similar distribution of endo-beta-glucanase in individual grains during malting. Further work on individual grains showed that the correlation between beta-glucan breakdown and endo-beta-glucanase activity was not significant. Surprisingly beta-glucan breakdown did not always correlate with the physical modification of the endosperm. Both these findings suggest that sample analyses of beta-glucan levels and malt beta-glucanase activities are not reliable indicators of the degrees of which malt samples are modified during malting. Since the distribution of beta-glucan in individual grains of the unmalted barley varieties was similar, the total beta-glucan levels of the original barley did not determine the rate at which beta-glucan was broken-down during malting. Although protein studies are at a preliminary stage, the rate of protein breakdown was not correlated with the rate at which beta-glucan was broken down in the malting grain. It is possible that the physico-chemical properties of endosperm storage proteins may limit the rate of beta-glucan breakdown during malting.