Temporal Analyses of Barley Malting Stages Using Shotgun Proteomics

Malt derived from barley malting is an essential raw material for beer brewing. In this study, we performed the first dynamic proteome survey during barley malting using a gel-free proteomics approach. This entailed in-solution tryptic digestion of precipitated proteins and analysis of peptides by nanoliquid chromatography coupled with tandem mass spectrometry. A total of 1418 proteins were identified from the five malting stages: Steep, 1, 3, 5 days after germination, and end of Kiln. About 900 proteins identified in this analysis were uncharacterized or predicted proteins. Integrating information from Uniprot90, Uniprot50, Pfam, Interpro databases and gene ontologies from EnsemblPlants, 796 of the predicted and uncharacterized proteins were provided functional annotations. Nearly 63% of the identified proteins were present during all the five time points suggesting a coordinated activation of major metabolic pathways during malting. GO enrichment analysis showed over-representation of proteins associated with translation, carbohydrate metabolism, and stress response. Analysis of variance of the spectral counts of proteins present in all the five malting stages identified 205 proteins with significant differences in their abundance. Proteins associated with carbohydrate metabolism especially enzyme activity regulation provide novel targets for malting barley breeding and for predicting malting quality.