Protein mobilization and malting-specific proteinase expression during barley germination

Malting is a process of controlled germination and early seedling growth. With appropriate control of grain moisture, environmental conditions, germination time, and kilning conditions, maltsters produce malt with the composition and enzymatic activity needed for brewing. In this study we compared protein mobilization in a widely grown malting barley variety germinated under controlled malting regimens and in a laboratory incubator not optimized for malting. Analysis of malts produced under three regimes showed differences in nitrogen mobilization and expression profiles of some proteinase genes. Many transcript probes changed in abundance during malting, with transcripts from the commercial malting and micromalting series trending similarly. Fewer transcripts showed differential expression between the laboratory germination series and the malting series that corresponded to protein mobilization differentials. Expression differentials that matched protein mobilization differences were seen for previously identified germination proteinases as well as those not previously linked to seed germination. These expression differentials suggest that several proteinases may serve previously unrecognized functions in protein mobilization during germination and early seed growth. Similarity of malting quality results and gene expression profiles in the two malting environments suggest that barley germination in an optimized micromalter is a suitable model system for barley germination in a commercial malting process.