Submitted to: Journal of the American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2014
Publication Date: 5/8/2015
Citation: Vinje, M.A., Duke, S.H., Henson, C.A. 2015. A comparison of factors involved in starch degradation in barley germination under laboratory and malting conditions. Journal of American Society of Brewing Chemists. 73(2):195-205.
Interpretive Summary: Studies on germination and malting have been conducted for years without a consistent germination protocol. Two common barley germination treatments were compared to determine how each procedure effects sugar accumulation and composition and enzyme accumulation, degradation, and activity. The amount of time the barley grain is exposed to water is the most important step for consistency between the two treatments. This study fills a critical knowledge gap for malting and germination researchers and identifies the most important step for consistency between different germination treatments.
Technical Abstract: Grains of the malting barley cultivar Legacy were laboratory germinated (LG) or micromalted (MM) and sampled daily from 0 to 5 days after imbibition/steeping. Alpha-amylase and beta-amylase activities and protein levels along with starch, osmolyte concentration (OC), and sugar (glucose, sucrose, fructose, maltose, maltotriose, maltotetraose, maltopentaose, maltohexaose, and maltoheptaose) concentrations were determined. MM grains had a larger increase in alpha-amylase activity earlier in germination than LG grains. Additionally, MM grains had higher activity at every germination stage. Two beta-amylase isoforms were detected in LG and MM grains. In LG grains, the higher molecular weight (MW) isoform was the predominant isoform early in germination and as germination proceeded was degraded to the lower MW isoform. In MM grains, the lower MW isoform was the predominant form and increased as germination proceeded. Beta-amylase activity remained constant throughout both LG and MM germination procedures. However, LG grain beta-amylase underwent more proteolytic processing than MM grains. Maltose, maltotriose, maltotetraose, maltopentaose, maltohexaose, total sugars, and OC all accumulated one day later in LG grains. Differences in steeping/imbibition time appear to explain the delay in sugar and OC accumulation.