Malting revisited: Germination of barley (Hordeum vulgare L.) is inhibited by both oxygen deficiency and high carbon dioxide concentrations

During malting, barley (Hordeum vulgare L.) seeds are germinated to promote the mobilisation of storage compounds. Germination is strongly influenced by O₂ and CO₂; however, any distinction between the particular effects is missing. Since, in this study, the ambient O₂ concentration was maintained when high CO₂ concentrations were applied, for the first time the impacts of CO₂ and of O₂ deficiency could be distinguished unambiguously.Germination was inhibited by both O₂ deficiency and high CO₂ (80%) concentrations, documented by the lack of any growth of coleoptiles and any increase of α-amylase and β-glucanase activity. In contrast, the related impacts of O₂ starvation and high CO₂ on fermentation differ strongly, demonstrated by quite different patterns of ethanol emission. Additionally, the stress metabolism - monitored by the means of GABA accumulation - was also differently impacted. The elucidation of the underlying, so far unknown, mechanisms will provide novel opportunities to improve malting.